Rhithrogena amica Traver, 1935: 373

Figs. 1 – 36

Nymph (in alcohol with well-developed or dark wingpads). Body length: 9.00 – 12.50 mm (Mn = 10.67±1.28 SD; Md = 10.87; n=5). Description based on male nymph except where noted.

Head. Colour Pattern: Overall background colour chestnut brown with some areas anterior to compound eyes tinted with maroon (Fig. 1). Lateral edges of head capsule to outer margins of compound eyes dark greyish-brown. Pale narrow line between lateral ocelli and along anterior margins of compound eyes (Fig. 1). Pale narrow line widens where it meets lateral margin of head capsule. Posterolateral edges of head capsule brown. Ecdysial suture connects to faint pale spots anterior to bases of antennae. Vertex of head with two small median pale spots posterior to lateral ocelli and adjacent to inner edges of compound eyes (Fig. 1). Shape: Head capsule broadly oval with slight deviation of outer edges adjacent to posterior corners of compound eyes, posterolateral edges straight to hind margin such that it appears slightly indented adjacent to outer edges of compound eyes. Width of head slightly more than 2x length. Anterior margin with slight median emargination where labrum articulates with head capsule. Mouthparts completely concealed beneath margins of head capsule, except for posterior part of labrum. Compound Eyes: Compound eyes of male nymph large and somewhat teardrop-shaped, when viewed dorsally outer margins either reach outer margins of head capsule or extend slightly beyond them (Fig. 1). Anterior and posterior edges of compound eyes converge toward midline of head, but inner edges of compound eyes do not meet being separated by gap about width of one lateral ocellus. Female nymphs compound eyes smaller and separated by gap greater than twice that of male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Fig. 1. Pale spots occur over all ocelli with spots over lateral ocelli about 2x as large as spot over median ocellus. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow line anterior to compound eyes. Each ocellus with broad black, C-shaped base visible beneath cuticle (Fig. 1). Antennae: Basal membrane of antennal socket pale, but edge of socket ringed with dark brown. Scape, pedicel, and basal two-thirds of flagellum yellow-brown. Apical one-third of flagellum pale. Terminal 10 annuli of flagellum with distinctive dark brown mark on outer edge of each annulus. Antennal length about equal to midline length of head capsule or slightly longer.

Mouthparts. Labrum: Labrum somewhat semicircular (i.e., subtending ~120° of arc) with lateral margins smoothly curving to rounded posterior corners (Fig. 2). Anterior margin with shallow median emargination that has large and small rigid spines along its ventral edge (Fig. 3). Anterior median emargination with group of 5 – 6 large, rigid spines on either side of middle of ventral edge and 6 – 7 small, rigid spines occurring across middle of median emargination (Fig. 3). Dorsal surface of labrum with scattered long, hair-like setae with longest setae on posterior part of dorsal surface and setae becoming progressively shorter towards anterior margin. Ventral surface of labrum with two opposed patches of setae near anterior margin. Ventral lateral edges of labrum with dense row of long, hair-like setae that become shorter and less dense towards groups of large rigid spines at outer edges of median emargination. Ventral lateral edges of labrum with 5 – 6 small, stout spine-like setae in gaps between long marginal setae and large rigid spines at edges of median emargination. Maxillae: Left maxilla as in Fig. 4. Galea-lacinia with 10 – 11 pectinate crown setae, with what appears to be maximum of 10 teeth on largest crown setae (Fig. 5). Smallest lateral crown seta appears to have about eight teeth and medial-most crown seta has about five teeth (on this seta teeth are difficult to count because it is often pressed against apical canine of galea-lacinia). Submedial row of about 38 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 4). Near apex of submedial row of long setae, 1 – 2 long biserrate setae occasionally occur set back from main row of setae. Often at base of submedial row of long biserrate setae are small groups of 2 – 3 setae that are not aligned with main part of submedial row. Inner edge of galea-lacinia with dense rows of setae, with ventral row of inner edge setae only about one-quarter as long as dorsal row of setae. In addition, at base of double row of inner edge setae is basal row of about nine very long, simple setae. Maxillary palp as in Fig. 4 appearing 2-segmented. Inner edge of apical segment of palp straight to slightly concave near tip (Fig. 4). Concave edge usually with row of about 20 small setae set back from edge. Apical segment of palp with distinctive longitudinal sclerotized band and diffuse brown vertical band (vertical brown band can fade on some specimens). Most of ventral surface of apical segment of palp covered with stout mono-pectinate setae (Fig. 6) with maximum of about eight sharp teeth. Outermost edge of apical segment with dense row of large, simple setae with downward curved tips (Fig. 7). Interspersed in field of large mono-pectinate setae and large simple setae are more delicate mono-pectinate setae with finer and more numerous teeth compared to larger mono-pectinate forms. Hypopharynx: Lingua somewhat variable appearing pear-shaped with broad base on some specimens (Fig. 8a) and more rectangular with apex not distinctly narrowed as in pear-shaped form on other specimens (Fig. 8b). Superlinguae with broadly rounded outer and anterior edges. Fine hair-like setae restricted to anterior edges of superlinguae. Outer basal edges of superlinguae as in Fig. 8a, tapering to base of hypopharynx. Mandibles. Right mandible (Fig. 9a, ventral view): Anterior margin between edge of molars and prostheca straight with row of fine hair-like setae becoming progressively longer toward base of prostheca (Fig. 9b). Dense tuft of setae at innermost edge of molar surface. Molars composed of rows of variously shaped conical teeth, molar surface terminates in single large round apical tooth (Fig. 9b). Adjacent to terminal apical tooth are several long, hair-like setae (Fig. 10). Prostheca composed of row of about six long, thick finely biserrate setae arising next to base of inner incisor. Incisors as in Fig. 11. Outer incisor length about 2.3x width, smaller sized teeth along outer edge mostly homonomous from apex almost to base where last 12 – 13 teeth become thinner and sharper than others (Fig. 11). Larger sized inner teeth fewer than outer row teeth, with 10 teeth along inner edge up to apical complex (Fig. 12). Apical complex composed of three teeth, one terminal tooth flanked by one upper tooth and one lower tooth, all teeth subequal in size. Basal part of outer incisor with comb of about 28 long, fine teeth. Most teeth of basal comb forked at tip with depth of fork less than one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 13). Leading edge of inner incisor with row of about 16 long, hair-like setae below upper edge of large irregular teeth. Upper edge of inner incisor with row of 12 – 13 large coarse teeth that gradually merge with trailing edge row of fine comb-like teeth (Fig. 13). Outer edge of mandible below incisors and inner edge below molars without long setae. Left mandible (Fig. 14, ventral view): Anterior margin between molars and base of prostheca straight with uniform row of short, fine hair-like setae (Fig. 14). Uppermost part of molar surface transitions to row of fine, hair-like setae via series of multi-toothed transparent molars. Majority of molar surface as in Fig. 14, rows of short rounded conical teeth end in series of long, somewhat flattened and transparent brush teeth. No distinct apical molar tooth, but several long apical setae present. No evidence of large single molar tooth set-back from last row of molar teeth on ventral side of molar surface, but three similar large teeth are present in middle of last row of molar teeth, which are different from remainder of row. Prostheca composed of row of about 11 long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 15). Incisors as in Fig. 16. Outer incisor length about 2.4x width, smaller sized teeth of outer edge mostly homonomous from apex to near junction with posterior comb, where last 10 – 11 teeth become thinner and sharper. Larger sized inner teeth fewer with 13 teeth along inner edge up to apical complex (Fig. 17), basal three teeth becoming progressively smaller and sharper towards end of row. Apical complex composed of three teeth similar to those of outer incisor of right mandible. Base of outer incisor with comb of about 30 long, fine teeth, most teeth forked near tip with depth of fork from tip less than one-quarter length of each tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 15). Leading edge of inner incisor with row of about 10 hair-like setae below upper edge of large irregular setae. Upper edge of inner incisor with large coarse teeth that become progressively thinner and eventually merge with row of fine comb-like teeth (Fig. 15). Outer edge of left mandible below incisors and inner edge below molars bare without long setae. Labium: Labium as in Fig. 18. Dorsal surface of glossae with long, hair-like setae on inner apical surface and row of similar hair-like setae that extends from apical area to base of glossae (Fig. 19). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and beyond large spine-like setae from ventral surface (Fig. 19). Ventral surface of paraglossae with rows of short, stout spine-like setae. Lobes of glossae distinctly diverging from midline of labium such that inner edges form V-shaped gap (Fig. 19), distance between tips of glossae about 3.82x width of base, measured corner to corner. Labial palps appearing 2 segmented. Apical segment of palps with distinct brush of pectinate setae on ventral surface and at tip of palp. Ventral surface of apical segment of palps with row of long hair-like setae with curved tips. Dorsal surface of apical segment of palps with array of long curved bifurcate setae. 

Thorax. Pronotum: Overall shape broadly rectangular with rounded lateral margins (Fig. 1). Anterior margin straight, but posterior margin slightly convex on either side of body midline. Posterior lateral edges of pronotum appear fused with mesonotum forming straight connection despite pale boundary line between them. Posterior half of pronotum slightly raised on either side of body midline forming pair of low rounded humps. Lateral margin of pronotum semitransparent and tinted brown. Majority of pronotum similar to head capsule in colour (Fig. 1). Middle of pronotum brown with distinctive patterning. Lateral areas with pale marks consisting of lateral inverted U-shaped marks each with one median pale streak, which connects to curving pale band that extends toward midline of pronotum where it eventually meets an outwardly slanting pale dash (Fig. 1). Pale markings on pronotum seem consistent between male and female nymphs. Mesonotum: Overall colour similar to head and pronotum. Lightly sclerotized areas of mesonotum pale, more heavily sclerotized regions dark brown producing somewhat mottled appearance. On last instar nymphs medial longitudinal pale stripe along medial longitudinal suture (MLs) becomes more pronounced and dark brown areas of adult anatomy are clearly visible through mesonotal cuticle. Lateral margins of mesonotum gradually taper from bases of forewingpads to junction with pronotum, but usually do not appear greatly indented. Most of scutellum (SL) between forewingpads not darker than surrounding surface of mesonotum, but edges of apical medial notch shaded brown (Fig. 20a). Metanotum: Overall colour similar to mesonotum, in preserved specimens no obvious dark or distinctive colour features present. Pleural Region: Membranous area of pleural region anterior to forecoxae with dark brown smudge. Membranous areas of pleural regions anterior to mid and hind coxae with only faint traces of dark brown. Coxal sclerites of all legs with edges flared upward. 

Abdomen. Tergites: Background colour of all tergites yellow-brown with slight orange tint (Fig. 20a). Anterior and lateral edges of all tergites dark brown. Tergites II – V with two pairs of small pale submedian spots, one pair located directly on anterior margin spanning midline of each tergite, often spots obscured by edge of preceding segment, and one pair near middle of each tergite (Fig. 20a). Tergites VI – IX with one pair of pale submedian spots. Tergite X with one pair of submedian streaks that extend from anterior margin to middle of tergite (Fig. 20a). Pale spots on tergites II – IX may fade completely on last instar nymphs. Lateral margins of tergites II – VII with pale, somewhat triangular indentations marked by dark brown smudge around upper edge. In addition, pale triangular indentations may have one small pale secondary spot near posterior edge. Tergites VIII – IX appear to lack lateral indentations and markings as described above, but tergite VIII has one lateral pale spot and tergite IX has one lateral pale streak that extends length of lateral margin. Posterolateral edges of tergite IX flare outward away from lateral margin of tergite X (these are more pronounced on female nymphs). Most tergites have scattered hair-like setae, but no other obvious cuticular features. Tergite Spinules and Posterolateral Projections: Posterior margin of all tergites with distinctive row of spinules (Fig. 21). Spinules near midline of tergites alternate with shorter and often thinner spinules (Fig. 21). This pattern becomes less consistent laterally, where groups of relatively similar thick spinules occur without alternating with smaller or thinner spinules. Microspinules often occur above bases of spinules near midline of posterior margin, but gradually become less evident laterally. Posterolateral projections short and rounded on tergites I – VI, minute and acute on tergites VII – VIII and short and somewhat rounded on tergite IX (Fig. 20b). Small brown sclerous lobe-like structure associated with posterior margin of tergites VII – IX between end of row of spinules and posterolateral projection. Sclerous lobe-like structure on tergite IX large and completely fused with posterior margin producing distinct bulge adjacent to posterolateral projection (on male nymphs bulge on tergite IX more noticeable because it seems to be larger than on female nymphs and incorporated into edge of segment adjacent to developing male forceps). On tergite VIII sclerous lobe-like structure smaller than on tergite IX, but also fused to posterior margin adjacent to posterolateral projections. On tergite VII sclerous lobe-like structure small, elongate and only weakly fused to posterior margin (small size and proximity to edge of posterior margins make this structure on tergite VII difficult to observe). Sternites: Background colour yellow-brown slightly lighter than tergites, sternites II – VII each with one pair of small median pale spots below one pair of pale dashes with tips converging toward anterior margin (Fig. 20b). Sternite I with anterior flanges that have distinctly pointed corners. Sternites II – IX with transverse crease near posterior margin, each appearing as thin brown line (Fig. 20b). 

Legs. Forelegs: Overall background colour medium to light brown to light brown on all segments. Forefemora length about 3.4x width with pale median spot resembling an elongated fleur-de-lis with its apex oriented toward joint with foretibiae and reaching well past midpoint of forefemora (Fig. 22). Middle of pale fleur-de-lis spot with dark brown, somewhat rectangular median mark. Smaller pale upper lobe of fleur-de-lis spot more distinct than lower lobe, but both always present. Basal part of fleur-de-lis occasionally enlarged to form large pale spot adjacent to base of forefemora (Fig. 22). Surface of forefemora around pale fleur-de-lis spot darker than background colour of leg segment. Dorsal and ventral edges of forefemora dark brown along base of rows of marginal setae. Apex of forefemora with dark brown adjacent to joint with foretibiae. Ventral edge of forefemora adjacent to joint with foretrochanter dark brown and articulation almost black. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges. Although many setae of dorsal edge row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edges of variable width and length; some seem similar to elongate flags. Dorsal edge row of setae of relatively uniform length, except for few shorter setae at either end of row (Fig. 23). Dorsal surface of forefemora with field of short, rounded setae as in Fig. 24. Larger setae over middle of surface with distinctive dark brown bases, smaller flattened setae often lack brown bases. Ventral edges of forefemora with scattered, spine-like setae with blunt tips (Fig. 25), spine-like setae interspersed with fine, hair-like setae. Faint greyish-black mark within groove along ventral edge of forefemora adjacent to joint with foretibiae (foretibiae completely cover this mark when folded in against forefemora). Foretibiae: Length about 0.9x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint dark brown with colour extending entire length of tibiopatellar suture (Fig. 26). Median and apical areas of foretibiae uniform light brown, but apical edge of joint with foretarsi dark brown (Fig. 26). Ventral edge of foretibiae with scattered stout setae with rounded tips, setae most numerous near joint with foretarsi. Ventral edge of joint with foretarsi surrounded by scattered hair-like setae and one large monopectinate seta. Dorsal edge of foretibiae with longitudinal row of small hair-like setae extending from joint with forefemora to apex. Embedded in row of hair-like setae are 1 – 2 stout, flattened setae near joint with foretarsi. Foretarsi: Length about 0.3x length of foretibiae. Foretarsi slightly darker brown than foretibiae with base and apical areas slightly darker than middle, but colour difference is subtle and foretarsi of preserved specimens do not appear banded. Longitudinal row of small, hair-like setae of foretibiae continues along outer edge of foretarsi and three evenly spaced large, paddle-like setae embedded in this row (Fig. 27, and as in Fig. 267). Scattered hair-like setae occur along other surfaces of foretarsi, but are most densely clustered at apex adjacent to joint with foreclaw. Foreclaws: Foreclaws as in Fig. 28a, with pale base and elongate, sharp brown tip. One basal tooth and up to five preapical denticles present (Fig. 28b). Denticles decrease in size from distal-most to basal-most position, outer three denticles distinctly larger than inner two denticles (Fig. 28b). Outer apical portion of claw about one-quarter total length of claw. Middle and Hind Legs: Colour: colour patterns and arrangement of setae similar to that of forelegs (Fig. 29). There is some variation in appearance of pale fleur-de-lis spot on mid and hind femora with tip of fleur-de-lis spot extending further toward apex of femora compared to forelegs (Fig. 30); pale base of fleur-de-lis spot on mid-femora constricted, but still obviously connected to middle portion of pale spot; and on hind-femora pale basal area may be completely separated by an area of brown from pale mid region of fleur-de-lis spot. Apex of fleur-de-lis spot often thinner on mid- and hind-femora than on forelegs. Bristle-like setae along dorsal edges of mid- and hind-femora shorter and more widely spaced than on forefemora (Fig. 31). Structure and appearance of mid and hind tibiae, tarsi, and claws generally similar to that of forelegs; however, there are some differences. Apices of mid and hind tibiae with about eight large, curved setae extending over joint with tarsi. Mid claws similar to foreclaws, but hind claws different. Apex of hind claws appears more slender than foreclaws and appears to have only three denticles (two large and one minute) as in Fig. 32.

Abdominal Gills. Colour and Position: Gills mostly transparent, but with faint traces of brown in proximal half of each gill. Basal half of gill filaments light brown (sometimes with faint yellow or greenish tint), tips usually pale. Thickened area of gills adjacent to base of filaments brown. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edges (i.e., inner edge) of gill 1 do not quite reach ventral midline. Abdominal gills 2 – 6 positioned laterally with anterior edge of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Fig. 20b). Gill 1: Abdominal gill 1 as in Fig. 33a, anterior corner where straight inner margin meets dorsal edge broadly rounded. Outer margin with incisions forming ruffled edge, depth of incisions usually less than width of each division – thus edge appears to have small ruffles. Incisions along ruffled edge become shallower posteriorly and cease at outer corner where ruffled edge meets posterior margin of gill. Posterior margin of gill 1 broadly rounded. Plica of dorsal surface as in Fig. 33b, broadly rounded spanning more than half of length of anterior portion of gill. About two-thirds of gill thickened and somewhat opaque, edge of thickened zone appears as longitudinal line where transition to thinner and more transparent ruffled edge occurs (Fig. 33a). Cluster of filaments at gill base composed of about 18 filaments that appear to originate from tracheal base without subsequent branching (Fig. 33a). Area of gill adjacent to gill base with short, sclerotized rib. Gill 2: Abdominal gill 2 as in Fig. 34. Overall shape of gill 2 broadly oval with partially ruffled posterior margin similar to that on gill 1. Dorsal margin of gill 2 straight from base to rounded apical margin (Fig. 34). Width of gill 2 about 0.9x length. Tuft of filaments as in Fig. 34, tuft composed of more than 20 filaments that appear to mostly arise individually at major tracheal branch with minimal secondary branching. Filaments only extend to about midpoint of gill 2. Lower portion of gill 2 supported by transparent L-shaped sclerotized rib (Fig. 34), lower part of L-rib slightly curved. Base of upper portion of gill 2 supported by short, straight, brown sclerotized rib. Both internal gill supports seem to lack surface setae. Gill 5: Abdominal gill 5 as in Fig. 35, shape broadly oval with width little more than 0.5x length. Ventral portion of posterior margin of gill 5 with few ruffles as in gill 2. Dorsal margin of gill 5 smoothly curved to posterior margin (Fig. 35). Tuft of filaments at base of gill 5 as in Fig. 35, similar in number and structure to gill 2. Lower portion of gill 5 supported by transparent L-shaped sclerotized rib (Fig. 35), lower part of L-shaped rib less curved compared to gill 2. Base of upper portion of gill 5 supported by short straight brown rib similar to gill 2. Gill 7: Abdominal gill 7 as in Figs. 36a,b, with membranous dorsal margin folded toward midline of gill and fused with transparent rib and short, brown basal rib resulting in upper part of gill 7 fitting curvature of side of abdomen. Width of gill 7 only slightly more than 0.5x length. Posterior margin of gill 7 with 4 – 5 ruffles and with marginal setae similar to preceding gills. Dorsal margin of gill 7 usually appressed to edge of abdominal segment VIII and posterior portion of gill extending beneath body to about ventral midline of abdomen. Tuft of filaments at gill base reduced in size and number compared to preceding gills. Transparent support for lower portion of gill 7 present and slightly curved. Base of gill 7 supported by short brown rib as on preceding gills. 

Caudal Filaments. Colour and Structure: Three subequal caudal filaments, length about 1.2x length of abdomen. Basal one-quarter of caudal filaments uniform yellow-brown, similar to abdominal tergites, but colour gradually fades to pale yellow or white at tips. All but apical annuli with uniform short spines along posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 36 (as counted from base). Fine hair-like setae begin sparse, with only 2 – 3 per annulus, but rapidly increase to about six per annulus. Terminal 16 annuli lack marginal hair-like setae, but may have occasional short spines at margins of some annuli.

Diagnosis Rhithrogena amica. Nymph: Nymphs of R. amica can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) relatively large body size of near final instar nymphs (9.00 – 12.50 mm; Mn=10.67 (n=5); Md= 10.87 (n=5)), the smallest black wingpad specimen studied was from Maine (9.00 mm), but all other specimens from Tennessee were larger than 10.00 mm, (2) femora with mostly symmetrical pale median fleur-de-lis spot with its apex directed toward tibia and its tip reaching well past middle of femora and small dark median mark in center of pale fleur-de-lis spot (Fig. 30), (3) presence of faint greyish-black mark within groove along inner edge of femora adjacent to joint with tibiae, (4) abdominal gill 1 shaped as in Figs. 33a,b with broadly rounded plica, apical bulge of plica extending almost to base of outer ruffled edge, (5) abdominal gills 2 – 6 without a dorsal lobe, (6) the lower part of abdominal gills 2 – 6 with distinctive L-shaped transparent sclerous rib (Fig. 34) with the lower arm of the L-shaped rib distinctly curved on gill 2, but becoming progressively straighter on succeeding gills, (7) abdominal gill 7 with most of the upper portion of the gill pressed around edge of tergite VIII and dorsal edge fused with surface of the gill near basal short sclerous rib, (8) crown of maxillae with 10 – 11 large pectinate setae (Fig. 5), (9) glossae of labium separated by a broad V-shaped gap (Fig. 19), and (10) lingua of hypopharynx usually rectangular, but on some specimens can appear pear-shaped. See Appendix 3 for comparative list of R. amica diagnostic characters and those of other northeast species. 

Taxonomic Discussion. Currently there are no detailed descriptions or figures of the nymph of R. amica. Although the type series of R. amica contained reared specimens and nymphal exuviae of some specimens were slide mounted for study, Traver chose not to include the nymph in the species original description. Later Traver (1937) reported R. amica from North Carolina and attempted to rear it, but apparently had difficulty obtaining intact nymphal exuviae for study. Detailed comparative study of specimens from the type series and nymphs collected from sites in Maine and Tennessee has shown that nymphs have several distinctive morphological features that distinguish them from the nymphs of the other known northeastern species of Rhithrogena. Further, the current keys by Traver (1935) and Morse et al. (2017) which separate nymphs based mostly on body size are incomplete and body size in near final instar nymphs is shown here to be variable across the geographic range of R. amica, thus body size alone seems to be a problematic diagnostic character. 

Distribution. Rhithrogena amica was described by Traver (1935) based on specimens collected from two small streams east of the campus of Cornell University in central New York. Later Traver (1937) showed R. amica to be distributed much further south to streams in western North Carolina and the mountains of eastern Tennessee. Rhithrogena amica is now known to be an uncommon, but broadly distributed species along the Appalachian highlands (Fig. 332) and adjacent areas from northeastern Mississippi (McCafferty 2009) and northern Alabama (Kondratieff and Harris 1986) to southwestern Maine (new record herein). The account of R. amica from southern Quebec (DeLude 1992) can’t be verified, but the species range could likely include some areas in Quebec south of the Gulf of St. Lawrence. Suitable cool, clean streams occur across the interior of the Gaspé region of Quebec where other species of Rhithrogena are known to occur. 

All previous records of R. amica reported from Connecticut (Burian and Bednarik 1994) and Maine (Burian and Gibbs 1991) were based on determinations made using incomplete keys and descriptions and are now known to be referable to other species of Rhithrogena. Most recently Meyers et al. (2011) added new records to the known distribution in New York. Attempts to recollect R. amica near its type locality in New York and at historic sites in western Massachusetts (McCafferty 2009) were unsuccessful. No evidence of any Rhithrogena species was detected at either location suggesting that R. amica may be locally extirpated at these sites. The northeastern distribution of R. amica is given in Appendix 2.

Life History and Ecology. Rhithrogena amica data from New York, North Carolina, and Tennessee indicate that emergence usually occurs from early to late May (about May 10 – 27). Black wingpad nymphs were collected in Tennessee on May 2 and in New York on June 9 suggesting that these may be the limits of early and late emergence times. Throughout its range R. amica appears to be univoltine. 

Based on field observations at sites in New York and Tennessee where R. amica were collected for this study, R. amica seems to be associated with 1st – 3rd order streams with channels dominated by complex rocky substrates (most particles in the range of small to large cobble); swift permanent flow; seasonally cool water temperatures (i.e., max. 20° – 23°C); and stable channels that do not seem to be highly mobile from year to year within their average annual flood elevation (i.e., they don’t appear to meander over the course of annual peak flows). Remote inspection of the R. amica site in southwestern Maine via Google Earth® images showed that site had similar morphometry to sites in northern New York on the North Branch of the Saranac River where R. amica was collected most recently.

In contrast to sites where R. amica is now known to occur, the sites in central New York (Slaterville Creek, Slaterville, NY) and western Massachusetts (Amethyst Brook, Amherst and Pelham, MA) where the species was historically recorded are quite different. Both sites exhibit evidence of flooding events that produced extremely high flows sufficient to scour channel substrates and cause much lateral movement of the main channel. Large mixed cobble substrates were uncommon and most of the channel at both sites was composed of smaller substrates ranging from small gravel to small cobble. There was also much evidence of bank erosion and the collapse of large trees into the channel. The channels at both sites were wider and, in many places, shallower than at the best R. amica site on the North Branch of the Saranac River in northern New York. Although water temperatures taken at Slaterville Creek and Amythest Brook were <20°C when searches were conducted for R. amica, it is expected that the wider channels allowing more sun exposure combined with the shallower depth of the water would result in maximum temperatures exceeding the range associated with known R. amica habitats. Based on these observations it seems that changes in land use in the areas where R. amica was historically recorded that adversely affect runoff patterns and processes may be important in explaining why this species no longer seems to be present at these sites.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Type Material Examined. Holotype: USA: New York: Tompkins Co., Ellis Hollow [42.438718°/-076.374510°, elev. 379 m, small stream off Ringwood Rd., Town of Ellis – formerly known as Ellis Hollow], J.R. Traver, 16 May 1933, 1♂(+Nex) [CUIC]; Allotype: same, 16 May 1933, 1♀(+Nex) [CUIC]; Paratypes: same, 14 May 1933, 2♂,1♀ [CUIC]; same, 16 May 1933, 1♂(+Nex), 1♀(+Nex) [CUIC]; same, Slaterville [42.391713°/-076.367179°, elev. 318 m, coordinates of Sixmile Creek in Slaterville], J.R. Traver, 21 May 1932, 1♂(+Nex) [CUIC]; same, 24 May 1932, 1♂,3♀ [CUIC]; same, 23 – 25 May 1932, 2♂,1♀ [CUIC]; same, Slaterville, W.F. Preserve [no coordinates estimate – “W.F. Preserve” possible stands for Wild Flower Preserve – location uncertain, perhaps part of area now known as “600 Preserve”], 20 May 1932, 2♂,2♀ [CUIC]; same, Ringwood Creek [42.438718°/-076.374510°, elev. 379 m, small stream off Ringwood Rd., Town of Ellis – formerly known as Ellis Hollow], J.R. Traver, 12 May 1933, 2♂,1♀ [CUIC]; same, 20 May 1933, 2♂,4♀ [CUIC];

Other Material Studied. USA: Maine: Oxford Co., West Branch of Magalloway River, at washed out bridge on Rump Hill Rd. (site 32) [45.25531°/-071.0341337°], elev. 573 m, M. Seibenmann, 28 May 2008, 1N♂ [NEL]; New York: Franklin Co., North Branch of Saranac River, upstr. of bridge on Thatcherville Rd. off Rt. 26 [44.539979°/-074.051845°], elev. 465 m, S.K. Burian and L. Myers, 25 May 2017, 1♂ [NEL]; same, [44.54015°/-074.05208°], elev. 465 m, Sk. Burian, 28 May 2020, 1♂,1♀ [NEL]; Tompkins Co., Slaterville [42.391713°/-076.367179°, elev. 318 m, coordinates of Sixmile Creek in Slaterville], J.R. Traver, 15 May 1932, 1N♀ [CUIC]; same, 3 May 1931, 1♂(+Nex) [CUIC]; same, 20 May 1932, 1♂, 1N♂, [CUIC]; same, Trout Brook [no coordinate estimate – location uncertain, possibly a stream at 600 Preserve area], J.R. Traver, 16 April 1931, N(on slide) [CUIC]; same, Ringwood Creek [42.438718°/-076.374510°, elev. 379 m, small stream off Ringwood Rd., Town of Ellis – formerly known as Ellis Hollow], J.R. Traver, 15 May 1933, 4S♂,3♀ [CUIC]; same, 9 May 1933, 1N♀, 3♂(+Nex), 2♀(+Nex) [CUIC]; North Carolina: Avery Co., nr. Banner Elk [36.163239°/-081.871521°, elev. 1129 m, coordinates for Town of Banner Elk], J.R. Traver, 3 June 1936, 2N♂, 2N♀ (on slides) [CUIC]; same 8 June 1936, 2♂ [CUIC]; same, 25 May 1936, 1N♀ [CUIC]; same, Heaton [36.171992°/-081.942583°, elev. 923 m, coordinates for Curtis Creek in Town of Heaton], J.R. Traver, 3 June 1936, 1♂, 1N♀ (on slide) [CUIC]; same, 2 June 1936, 2♀ [CUIC]; same, Watauga Co., Valle Crucis [36.209375°/-081.778512°, elev. 816 m coordinates for Town of Valle Crucis], J.R. Traver, 2 June 1936, 1♀ [CUIC]; same, 6 June 1936, 1♂ [CUIC]; same, 9 June 1936, 1N♂ [CUIC]; same, 25 May 1936, 1♀, 1N♀ (on slide) [CUIC]; Tennessee: Cocke Co., Twentymile Creek, Great Smoky Mountian National Park [35.467088°/-083.876705°, elev. 401 m, coordinates at ranger station next to Twentymile Creek], J.G. Needham, 3 April 1934, 9N♂, 7N♀ [CUIC]; same, Big Creek, dnstr. of confluence with Rattlesnake Branch (creek), 11.3 km SE of Del Rio, off County Road 107 (nr. Round Mtn. Rec. Area) [35.83245°/-082.960717°], elev. 858 m, S.K. Burian, 2 May 1982, 1N♂, 3N♀ [NEL].

Rhithrogena anomala McDunnough, 1928: 239

Figs. 37 – 78

Nymph (in alcohol with well-developed or dark wingpads). Body length: 6.75 – 9.75 mm (Mn = 7.73±1.25 SD; Md = 7.50; n=17). Description based on male nymph except where noted. 

Head. Colour Pattern: Overall background colour brown (close to NCG# 22B – Raw Umber dark hue) with some areas anterior to compound eyes lighter brown (Fig. 37). Anterior lateral edges of head capsule shaded with greyish-brown, especially on either side of pale narrow line connecting lateral ocelli to outer margin of head capsule (Fig. 37). Pale narrow line occurs between ocelli and along anterior margins of compound eyes. Pale narrow line usually joins pale diagonal spot before gradually widening to lateral margin of head capsule (Fig. 37). Pale diagonal spots anterior to compound eyes point inward toward bases of antennae and vary from thin, faint marks similar to connecting pale line of ecdysial suture to broad distinct, oblong pale spots. Two head capsule colour morphs occur, brown and bicolour. Brown-morph has anterior half of head capsule solid brown with scattered darker brown freckles along anterior margin, except for small spots near bases of antennae and pair of minute pale spots anterior to median ocellus (Fig. 37). Bicolour-morph has large pale-yellow spot that occupies most of area between compound eyes extending from anterior margin posteriorly to just beyond Y-junction of ecdysial suture, 2 small pale spots anterior to antennal bases occur as noted above and lateral areas of head capsule dark brown (Fig. 38). Posterolateral corners of head capsule adjacent to outer corners of compound eyes pale on both colour morphs. Both colour morphs have pair of small pale spots on vertex between compound eyes, as well as an irregular cluster of four small, pale spots. Vertex pale spots vary between male and female nymphs. On male nymphs, paired pale spots not connected across ecdysial suture, or if connected only weakly so by small pale line. On female nymphs paired pale spots usually connected to median ecdysial suture via pale line. In addition, male nymphs have compact cluster of four irregular pale, spots on vertex. On female nymphs cluster of spots somewhat different with anteriormost pair of spots in cluster on vertex distinct or at best only weakly connected to larger oblong posterior pair of pale spots. Shape: Head capsule broadly oval with symmetrically rounded outer margins that show minimal deviation where transition occurs near posterior corners of compound eyes, hence not appearing distinctly indented (Fig. 37). Width of head capsule about 1.6x length. Anterior margin of head capsule with slight median emargination where labrum articulates with head capsule. Except for posterior edge of labrum, all mouthparts concealed beneath edges of head capsule. Posterior margin essentially straight on near last instar nymphs. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped, when viewed dorsally, outer margins of compound eyes either just reach outer margins of head capsule or in last instar nymphs extend slightly beyond them (Fig. 38). Although anterior and posterior margins of compound eyes converge toward midline of head, on some males both margins transition to broadly rounded inner corner and except in final instar nymphs compound eyes separated by gap about width of one lateral ocellus. Female compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Fig. 37) and gap between eyes more than 2x as wide as on male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Figs. 37, 38. Pale spots present over all ocelli, with spots over lateral ocelli slightly larger than over median ocellus (on female nymphs all spots over ocelli about equal in size). Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle. Antennae: Basal membrane of antennal socket pale and edge of socket dark brown (Fig. 37). Scape and pedicel brown, but flagellum much paler brown on intermediate instar nymphs. On near final instar nymphs most of flagellum brown similar to scape and pedicel, but apical part of flagellum pale, almost colourless. Antennae length about equal to midline length of head capsule or slightly longer.

Mouthparts. Labrum: Labrum somewhat semi-circular shaped (i.e., segment of circle subtending ~140° of arc) with outer edges smoothly merging with rounded posterior corners (Fig. 39). Anterior margin without shallow median emargination, appearing almost straight at midpoint and with large and small rigid spines mostly along ventral edge. Area of anterior median emargination with group of 9 – 10 large rigid spines on either side of ventral edge, medially either no distinct spines or scattered irregular small, rigid spines (Fig. 40). Posterior half of dorsal surface of labrum with field of long, hair-like setae with bases relatively widely separated (Fig. 41). Middle and anterior portion of dorsal surface of labrum with relatively few, short hair-like setae. Lateral edges of dorsal surface each with small group of short, hair-like setae and one long, distinctive hair-like seta (Fig. 39). Ventral lateral edges of labrum with row of long, hair-like setae that are longest at posterior corners and become shorter and progressively less dense near area of rigid spines of anterior margin (Fig. 42), and with 6 – 7 small, stout spine-like setae in gaps between long marginal setae and large rigid spines at edges of median emargination. Maxillae: Left maxillae as in Fig. 43. Galea-lacinia with nine pectinate crown setae, with what appears to be a maximum of 10 teeth on largest crown setae (Fig. 44). Smallest lateral crown seta appears to have about eight teeth and medial-most crown seta has five long teeth pressed against base of long canine of galea-lacinia. Submedial row of about 34 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 43). Near apex of submedial row of setae one long, biserrate seta occurs set back from main row of long setae. Often at base of submedial row of setae are small groups of 2 – 3 short setae that are not aligned with the submedial row. Inner edge of galea-lacinia with dense double row of long, simple setae, setae of ventral row only about one-third length of setae of dorsal row. In addition, at base of double row of inner edge setae is basal row of about nine very long, simple setae. Maxillary palp as in Fig. 43, appearing two-segmented. Inner edge of apical segment slightly concave near tip with row of evenly spaces hair-like setae (Fig. 43). Apical segment of maxillary palp with distinctive longitudinal sclerotized band, but no dark vertical or diagonal band near tip. Most of ventral surface of apical segment of maxillary palp covered with short monopectinate setae (Fig. 45) with 6 – 8 sharp teeth on most large setae present in middle and apical parts of total array. Outermost edge of apical segment with dense row of large, simple setae with downward curved tips (Fig. 45). Interspersed between large monopectinate setae and large simple setae are 2 – 3 rows of smaller monopectinate setae with much finer and more numerous teeth than occur on large monopectinate forms. Hypopharynx: Lingua shaped like stemless brandy-glass, i.e., with broad base and rounded sides that taper to narrower top with straight apical edge (Fig. 46). V-shaped fold of dorsal surface visible through ventral surface of lingua. Superlinguae as in Fig. 47, with indented bases and broadly rounded anterior edges. Long, hair-like setae occur along anterior and lateral margins of superlinguae (Fig. 47). Mandibles. Right mandible (Fig. 48a, ventral view): Anterior margin between edge of molars and prostheca slightly concave with short setae appressed to edge closest to molars (Fig. 48a). Tuft of sharp bristles at innermost edge of molar surface. Molars composed of rows of teeth that vary from sharp, conical forms at ventral edge to rounded, knob-like forms along dorsal edge (Fig. 49). Apical teeth of molar surface different from others being thin, sharp, and closely spaced. Molar surface terminates with one large distinctive rounded tooth (Fig. 49). Adjacent to apex of molars are about six long, simple setae. Prostheca composed of one row of about nine long, thick finely biserrate setae adjacent to base of inner incisor. Incisors as in Figs. 50. Outer incisor length about 2.7x width, smaller teeth on outer edge homonomous from apex to base, basalmost teeth slightly smaller (Fig. 50). Larger inner edge teeth fewer, with seven distinct teeth up to apical complex (Fig. 51). Apical complex of outer incisor composed of three subequal teeth, one each from outer and inner rows and one terminal tooth. At base of apical complex appears to be an additional small (perhaps vestigial) basal tooth that seems fused with base of complex (Fig. 50). Basal part of outer incisor with comb of about 29 fine teeth, most teeth forked near tip with depth of fork about one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 50). Leading edge of inner incisor with about six long setae in row below large tridentate apical tooth. Upper edge of inner incisor with row of about 12 large coarse teeth that gradually merge into trailing edge row of fine comb-like teeth (Fig. 50). Outer edge of mandible below incisors with only one hair-like seta, inner edge below molars without long setae (Fig. 48a). Left Mandible (Fig. 52a, ventral view): Anterior margin between molars and base of prostheca with slightly raised median area and short appressed setae near spines before edge of molars (Fig. 52b). Remainder of anterior margin leading up to prostheca slightly concave and appears to have at least some short, appressed setae. Upper edge of molar surface with multidentate edge that transitions to individual spines that extend on to anterior margin (Fig. 52b). Majority of molar surface as in Fig. 53, where rows of short, rounded teeth terminate in series of about 13 long, somewhat flattened, and transparent brush teeth. No distinct apical tooth present, but 6 – 7 long, hair-like setae occur below apical cluster of teeth. Middle of first ventral row of molar teeth with one large brown molar tooth. Prostheca composed of row of about eight finely biserrate setae, three basal setae larger and thicker than outer five (Fig. 54). Incisors as in Fig. 54. Outer incisor length about 2.8x width, smaller teeth of outer edge homonomous from apex to about midpoint of row with remaining teeth becoming thinner and sharper to junction with posterior comb. Larger inner teeth fewer, with about nine similar sized teeth and one small basal tooth up to the apical complex (Fig. 55). Apical complex of outer incisor composed of three subequal teeth, one each from outer and inner rows and one terminal tooth (Fig. 55). Basal part of outer incisor with comb of about 34 fine teeth, most teeth forked near tip with depth of fork about one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 54). Leading edge of inner incisor with row of about nine long, thin setae below large upper edge tooth. Upper edge of inner incisor with row of about 16 large coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of incisor (Fig. 54). Labium: Labium as in Fig. 56. Dorsal surface of glossae with long, hair-like setae on inner apical halves and an irregular row of short setae that extends from apex to base of glossae (Fig. 57). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface (Fig. 58). Ventral surface of glossae mostly bare, except for one large subapical seta and few small scattered hair-like setae. Upper half of ventral surface of paraglossae with area of large spine-like setae with some large spine-like setae at anterior edge extending more than half length of long, hair-like setae from dorsal surface. Glossae diverging from midline of labium such that inner edges form moderate V-shaped gap (Fig. 56), distance between tips of glossae about 2.6x width of base of gap [Note: “moderate” here means less distinctly diverging compared to what is observed in R. amica, Fig. 19]. Labial palps two-segmented (Fig. 56). Apical segment of palp with distinct array of pectinate brush setae on ventral surface and apical brush of simple setae. In addition, ventral surface also has row of long setae with curved tips along outer edge. Dorsal surface of apical segment with array of long curved bifurcate setae.

Thorax. Pronotum: Overall shape broadly rectangular with rounded lateral margins, anterior edges of lateral margins slightly straighter than posterior edges (Fig. 59). Anterior margin straight, but posterior margin distinctly convex on either side of body midline (Fig. 59). Posterior lateral edges appear fused with mesonotum forming straight connection despite pale boundary line between them (Fig. 59). Posterior half of pronotum slightly raised on either side of body midline forming pair of low humps (most noticeable on near final instar nymphs). Rounded outer edges of lateral margins shaded with dark brown, longitudinal pale band separates darker edge from contrasting patterns of medial portion of pronotum. Dark brown colour of pronotum similar to background colour of head capsule. Middle and lateral areas with distinctive pattern of pale marks as in Figs. 59, 60, consisting of lateral inverted U-shaped marks with one pale median streak. Inner edge of inverted U-shaped mark ends in small pale spot that connects to larger curved pale spot, which extends to midline of pronotum where it curves toward anterior margin (Fig. 60). Anterior margin with small, paired triangular pale spots. Anterior lateral corners of pronotum each with large pale spot. Pronotal pattern consistent on female nymphs, but among both sexes extent of pale marks vs. surrounding brown areas is variable. On some specimens large curved pale spots merge with pale areas of anterior margin resulting in greatly reduced areas of brown shading as in Fig. 60. Mesonotum: Overall background colour similar to darker brown areas of pronotum, but colour generally lighter compared to that of head capsule. Anterior margin shaded dark brown, colour darker than most other parts of mesonotum (Fig. 60). Lightly sclerotized areas of mesonotum pale, more heavily sclerotized regions dark brown producing somewhat mottled appearance with dark curved lines around bases of forewingpads (Fig. 60). Lateral margins of mesonotum from bases of forewingpads to outer edges of pronotum mostly straight or slightly tapering to junction with edge of pronotum, but not appearing distinctly indented. Area of SL between forewingpads shaded with dark brown as well as medial notch at apex of SL. MLs pale and pale stripe broadened over area of medioscutum (MS), occasionally flanked by two small pale spots. Metanotum: Metanotum mostly pale with some light brown shading similar to mesonotum. On some specimens dark brown occurs along posterior margin of metanotum and along bases of hind wingpads. Pleural Region: Membranous area of pleural region anterior and posterior to each coxa with dark greyish-brown smudge. Dark smudge more extensive in membranous area above forecoxae compared to mid and hind coxae. Coxal sclerites with surface enlarged and flared upward. Pro- and mesocoxal sclerites with short, flared edges compared to those of larger metacoxal sclerites.

Abdomen. Tergites: Background colour of all tergites of preserved specimens yellow-brown (Figs. 61a,b), but colour of live nymphs closer to Raw Sienna (NCG# 136). Anterior and lateral areas shaded slightly darker brown on preserved specimens, but on live nymphs these areas are more distinctively tinted with Raw Umber (NCG# 223). Tergites II – IX with one pair of small, pale submedian spots near middle of each tergite (Fig. 62). Anterior margins of tergites II – VIII with one pair of thin pale submedian dashes, pale dashes become fainter on tergites VII and VIII compared to other tergites. Anteriormost edge of abdominal tergites with thin dark brown line. Tergite X with pair of pale submedian streaks that extend from anterior margin to middle of tergite (Fig. 62). Lateral margins of tergites II – VII with pale, somewhat triangular indentations marked by dark brown smudge around upper edge of each indentation. In addition, separate small pale spot occurs between posterior edge of pale triangular marks and posterolateral projections [Note: Although small pale spot is consistent in its occurrence on both male and female nymphs, it is difficult to observe on lighter coloured specimens]. Tergites VIII and IX appear to lack lateral indentations, but do have lateral pale spots surrounded by dark brown shading. On tergite IX anterior pale oval spots merge with pale longitudinal streaks making them appear L-shaped (Figs. 61b, 62). Posterolateral corners of tergite IX not flared outward and do not extend much beyond anterior margin of tergite X. Posterior intersegmental membranes of abdominal tergites I – VIII often with dark greyish-brown shading appearing as dark band across posterior edge of tergites (dark shading can be faint on some preserved specimens). Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 63). Spinules near midline of tergites generally alternate with one or two short spinules between larger and longer spinules (Fig. 63). This alternating pattern becomes less consistent laterally where spinules gradually all become similar in size and have slightly curved tips. Microspinules occasionally occur among bases of larger spinules, originating slightly before marginal row and continue to occur to outer edges of spinule fringe. Posterolateral projections short and rounded on tergites I – VII (Fig. 64). Tergites VIII and IX have rounded posterolateral corners. Small brown sclerous lobe-like area associated with posterior margin of tergites VIII and IX between end of row of spinules and posterolateral projection. Sclerous patch on tergite IX slightly larger than on tergite VIII. Sternites: Abdominal sternites pale yellow-brown, sternites VII – IX slightly darker than preceding sternites (Fig. 64). Sternite I with anterior flanges tinted darker than rest of surface, outer corners of flanges vary from pointed to slightly rounded. Sternites II – VIII with transverse crease near posterior margin that appears as thin brown line (Fig. 64).

Legs. Forelegs: Overall background colour brown to light brown, darker shading on some parts of femora and other leg segments (Fig. 37, 38). Forefemora length about 2.4x width. Dorsal surface of forefemora brown to light brown, darker shading around some pale areas (Fig. 65), with pale median spot shaped like an asymmetrical fleur-de-lis (i.e., fleur-de-lis with only upper lobe well developed, lower lobe diffuse broadly rounded pale spot) with its tip pointed toward apex (Fig. 37, 38, S.1). Upper lobe of pale fleur-de-lis spot usually separated from dorsal margin and fringe of long setae by brown band, but sometimes edge of upper lobe extends almost to bases of long setae. Middle of pale median fleur-de-lis spot with dark brown vertical mark, sometimes extending completely across widest part of pale area (Fig. 37, 38, S1). On some specimens dark median mark can be compact and even slightly crescent-shaped or subtriangular (Fig. 37). Basal area of pale fleur-de-lis often broadened to base of forefemora. Surface of forefemora around pale fleur-de-lis usually slightly darker brown, even more so along ventral edge of forefemora. Apical portion of forefemora mostly pale, except for dark brown edge at joint with foretibiae and brown spot on ventral apical corner (Fig. 37, 65). Dorsal surface of forefemora, below marginal fringe of long, hair-like setae, with thin pale longitudinal streak that connects to pale upper lobe of fleur-de-lis spot and to pale apical area. Dorsal and ventral edges of forefemora dark brown along rows of marginal setae. Ventral edge adjacent to joint with trochanter dark brown. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges. Although many long setae of dorsal edge row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edges of variable width and length; some seem similar to elongate flags. Dorsal row of long setae of uniform length, except for few shorter setae at beginning of row near base of forefemora (Fig. 66). Dorsal surface of forefemora with field of short, flattened setae as in Fig. 67. Flattened setae over middle of dorsal surface with distinctive dark brown bases. Flattened setae vary in shape from ones with almost parallel sides to those that are distinctly paddle-shaped (Fig. 67). Ventral edges of forefemora with combination of scattered spine-like setae with blunt tips and flattened setae similar to those on dorsal surface, as well as small, scattered hair-like setae. Distinct greyish-black mark within groove along ventral edge of forefemora adjacent to joint with foretibiae (foretibiae completely cover this mark when folded against forefemora). Foretibiae: Length of foretibiae about 0.9x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint with dark brown band (Fig. 37). Middle of foretibiae slightly darker brown compared to base, this contrast with pale apical band gives foretibiae weakly banded appearance. Tibiopatellar suture region with two short, stout setae similar to those on dorsal surface of forefemora. Ventral edge of foretibiae with 2 – 3 short, stout setae with rounded tips. Edge of tibio-tarsal joint with two large monopectinate setae and one large paddle-shaped seta. Dorsal edge of foretibiae with longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae (Fig. 68, as in Fig. 271). No large paddle-shaped setae occur in longitudinal row of hair-like setae. Foretarsi: Length of foretarsi about 0.5x length of foretibiae. Background colour similar to foretibiae, but with base and apical areas darker brown than middle producing banded appearance, band most distinct on live specimens (Fig. 37,38). Longitudinal row of hair-like setae on foretibiae continues along edge of foretarsi and embedded in row setae is one paddle-shaped seta. Scattered hair-like setae occur along other parts of foretarsi, but do not appear clustered in any one location. Foreclaws: Foreclaws as in Fig. 69, with pale base and elongate sharp, brown tip. One basal tooth and five preapical denticles present. Distal three denticles large and subequal in size, basal two denticles smaller and thinner. Outer apical portion of foreclaw slightly more than one-third its total length. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Fig. 61a). There is some variation in appearance of pale median fleur-de-lis spot on femora with small upper lobe sometimes elongated into pale streak. Also, longitudinal pale streak connecting upper lobe of fleur-de-lis spot to pale spot at apex of femora variable, ranging from thin faint line to distinctive pale stripe. Medial dark mark in center of pale fleur-de-lis spot varies from vertical dark brown smudge to more distinctive and compact subtriangular or crescent-shaped mark (Fig. 61a, 70). Basal portion of pale median fleur-de-lis spot on mid legs similar to forelegs, but on hind legs base often with distinct constriction of pale area making basal part pale area appear somewhat hourglass shaped. Structure and appearance of mid and hind tibiae, tarsi, and tarsal claws generally similar to that of forelegs (Fig. 71), however there are some differences. Large paddle-shaped and rounded setae more numerous along dorsal surface and ventral edge of mid and hind femora compared to forelegs. Ventral edge of mid and hind tibiae have more short, stout setae with rounded tips and dorsal row of hair-like setae has three large paddle-shaped setae embedded in row. Apex of mid and hind tibiae with two large, thick curved setae and small cluster of long hair-like setae. Mid and hind tarsi with one paddle-shaped seta embedded in lateral longitudinal row of hair-like setae (Fig. 72). Mid and hind claws similar in shape and dentition to those of forelegs, but brown apical region appears to be slightly thicker near tip than on forelegs (Fig. 73).

Abdominal Gills. Colour and Position: Gills mostly transparent, but with some brown shading in proximal dorsal half of all gills (Fig. 61b), except gill 1. Base of gill filaments pale yellow or cream coloured, individual filaments brown (on live nymphs tips of individual filaments can appear pale yellow or colourless). Thickened area of gills adjacent to base of filaments dark brown. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) of gill 1 either does not meet opposite gill 1 or meets opposite gill 1 at rounded posterior corner of straight part of inner margin (Fig. 64). Abdominal gills 2 – 6 positioned laterally with anterior edge of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Fig. 64). Gill 1: Abdominal gill 1 as in Fig. 74, anterior corner where straight inner margin meets dorsal edge broadly rounded. Outer margin with incisions forming ruffled edge. Depth of incisions usually greater than width of each division, thus edge appears to have large ruffles (Fig. 74). Divisions of ruffled edge become shallower posteriorly and cease at corner where outer edge meets posterior margin of gill. Posterior margin of gill 1 varies from almost straight to broadly rounded. Plica of dorsal surface as in Fig. 75, broadly rounded spanning most of anterior portion of gill. About half of gill somewhat thickened and slightly opaque. Edge of thickened zone of gill appears as longitudinal line where transition to thinner and more transparent ruffled edge occurs (Fig. 74). Cluster of filaments at gill articulation composed of about 10 filaments that appear to originate from one tracheal base without subsequent branching (Fig. 74). Short, sclerotized support present at base of gill. Gill 2: Abdominal gill 2 as in Fig. 76. Overall shape of gill 2 broadly oval with slightly ruffled posterior margin with fine hair-like setae. Dorsal margin of gill 2 from upper edge of pigmented basal strip to rounded outer apical edge more or less straight (Fig. 76) lacking any lobe-like projection. Width of gill 2 about 0.8x length. Tuft of filaments as in Fig. 76, composed of about 20 filaments that appear to mostly arise from two major tracheal branches at base of gill and lack secondary branching. Filaments extend to or slightly beyond midpoint of gill 2. Lower portion of gill 2 supported by transparent L-shaped sclerotized rib (Fig. 76). Base of upper portion of gill 2 supported by short, straight sclerotized rib that is pigmented brown. Both internal gill supports seem to lack surface setae. Gill 4: Abdominal gill 4 as in Fig. 77, shape broadly oval slightly longer than wide. Ventral portion of posterior margin slightly ruffled as in gill 2. Dorsal margin of gill 4 also similar to gill 2 lacking any distinct projection or lobe. Lower portion of gill 4 supported by transparent L-shaped sclerotized rib (Fig. 77). Base of upper portion of gill 4 supported by rib similar in form and colour to that of gill 2. Tuft of filaments at base of gill 4 similar to gill 2. Gill 7: Abdominal gill 7 as in Fig. 78a, with membranous dorsal margin only slightly folded against side of tergite and not fused to surface near medial brown sclerotized rib. Thus, majority of gill 7 extends beneath abdomen as more or less free flattened structure without complex folding of dorsal margin (Fig. 78b). Ventral margin of gill 7 with few small ruffles that don’t extend around posterior of gill. Tuft of filaments at gill base reduced to about eight, which appear to arise independently from basal tracheal branch. Length of filaments shorter than on preceding gills. Transparent support for lower portion of gill 7 extends length of gill and is slightly curved. Base of upper portion of gill 7 supported by short, brown sclerotized rib similar to preceding gills. 

Caudal Filaments. Colour and Structure: Three subequal caudal filaments, about 1.3x length of abdomen. On preserved specimens caudal filaments uniform pale brown, but on live specimens caudal filaments greyish-brown and slightly darker at row of small spines at posterior edges of annuli. All annuli (except for apical annuli) with row of short spines on posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 30 (as counted from base). Fine hair-like setae begin with only 2 – 3 per annulus, but rapidly increase to maximum of about six per annulus. Terminal 8 – 10 annuli lack marginal setae, but may have an occasional small marginal spine.

Diagnosis Rhithrogena anomala. Nymph: Nymphs of R. anomala can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) medium to large body size of near final instar nymphs (6.70 – 9.70 mm; Mn=7.73 (n=17); Md= 7.50 (n=17)), the largest near final instar nymphs were all from Connecticut and overlapped the body size range for R. amica, the smallest near final instar specimens were all from northern New York, (2) femora with an asymmetrical pale median fleur-de-lis spot, lower lobe of fleur-de-lis is usually indistinct and merges with a pale band along the ventral margin of femora, apex of fleur-de-lis directed toward tibia and its tip reaching well past middle of femora, and small dark median mark (which can appear subtriangular or crescent-shaped) completely contained within center of pale fleur-de-lis spot (Fig. 37, 38, 70, S.1), (3) presence of distinct greyish-black mark within groove along ventral edge of femora adjacent to joint with tibiae, (4) abdominal gill 1 as in Fig. 75, plica broadly rounded, without a distinct apical bulge and edge of plica does not reach to base of outer ruffled edge, (5) abdominal gills 2 – 6 without a dorsal lobe, (6) lower part of abdominal gills 2 – 6 with distinctive L-shaped transparent sclerous rib with mostly straight upper and lower arms forming a near 90° angle (Fig. 76), on gill 2 the corner of the “L” may be exaggerated as a slight bulge, (7) abdominal gill 7 with dorsal margin only slightly folded against tergite VIII and not fused with surface of gill near basal short sclerous rib, sclerous L-shaped rib not apparent on gill 7, (8) crown of maxillae with nine large pectinate setae (Fig. 44), (9) glossae of labium separated by a moderate V-shaped gap (Fig. 56), (10) lingua of hypopharynx rectangular with wide base resembling a stemless brandy glass, (11) molars of right mandible not in line with anterior margin and outer incisor with seven distinct teeth on inner edge up to the apical complex of three teeth, and (12) labrum distinctly semicircular (Fig. 39) with anterior margin subtending an arc of ~140° from corner to corner. See Appendix 3 for comparative list of R. anomala diagnostic characters and those of other northeast species.

Taxonomic Discussion. Before this study, there have been no detailed descriptions or figures of the nymph of R. anomala. Although mentioned briefly by Traver (1933a) in the description of R. fasciata and again in her monograph on mayflies of the Heptageniidae (Traver 1933b) only a few scant details of the imago were added to what was previously known. The lack of earlier details was later redressed by Traver (1935) in her much more extensive redescription of the male imago. Because this species was not included in any key to nymphs detection of this species required male imagos. However, as part of an all-taxa biodiversity survey of Great Smoky Mountain National Park, TN some specimens were collected, barcoded, and sequences deposited in the Barcode of Life Data System (Ratnasingham and Hebert 2007). Although this barcode information may provide an additional taxonomic resource for future studies, these specimens were not examined as part of this study.

Distribution. Rhithrogena anomala was originally described by McDunnough (1928) from two male imagos collected from each of two sites in southern Quebec, Canada. Both sites were within 24 km of the international border north of Vermont, USA. Traver (1935) later reported studying R. anomala from two sites in New York and since then it has irregularly been reported from Alabama (Harris et al. 1996), Connecticut (Burian and Bednarik 1994), Massachusetts (McCafferty 2009), New York (Meyers et al. 2011), Virginia (Kondratieff and Voshell 1983), and New Brunswick (Jacobus and McCafferty 2001b). The distribution somewhat parallels that of R. amica following the Appalachian Highlands (Fig. 333), but R. anomala seems to occur over a wider range of channel widths, elevations, and water temperatures compared to R. amica. Although R. anomala has yet to be recorded from Maine or New Hampshire, it is likely present as there are many streams in these states similar to those in New York and Connecticut where sustaining populations are known. A new record is reported herein for Vermont. The northeastern distribution of R. anomala is given in Appendix 2.

Life History and Ecology. Rhithrogena anomala and R. amica co-occur in the North Branch of the Saranac River, New York indicating that nymphs of both species likely have similar habitat requirements and ecological tolerances. Basic habitat conditions that have already been summarized for R. amica can be applied to R. anomala. Water temperatures at the North Branch of the Saranac River site when R. anomala nymphs were collected for rearing ranged from 13.5° C (May 25, 2017) to 22.5° C (May 27, 2020). However, in Connecticut at the Salmon River site where R. anomala were obtained for rearing the water temperature was 15.7°C (May 20, 2014), which falls within the range for values obtained in New York within the same seasonal time period. Although this represents only a few widely spaced measurements, it does suggest what the critical thermal limit may be for near final instar nymphs before emergence. Streams that may be suitable in other habitat parameters, but are either colder than the minimum or warmer than the maximum values at this seasonal period may be unsuitable for sustaining populations of R. anomala. Finally, searches made in the Amherst, Massachusetts area where historic records of R. anomala occur (McCafferty 2009) failed to locate any evidence of this species (or any Rhithrogena species). It is possible that R. anomala may be lost from this area for the same reasons discussed previously for the absence of R. amica.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Material Examined. USA: Connecticut: New London Co., Salmon River, riffle upstr. of bridge on Rt. 16, Colchester [41.552686°/-073.449123°], elev. 24 m, S.K. Burian, 20 May 2014, 1♂(+Nex), 2♀(+Nex), 4N♂, 3N♀ [NEL]; Litchfield Co., Blackberry River, dnstr. of Rt. 44 bridge [42.024436°/-073.341503°], elev. 198 m, S.K. Burian, 8 June 1997, 1N♀ [NEL]; Toland Co., Fenton River, sample site s-4, G-123 [41.824874°/-072.236075°, elev. 99 m, estimated to be s-shaped bend in channel ~150 m upstr. from pump house nr. UConn campus], P.J. Dodds, 28 May 1977, 4N♂, 3N♀ [NEL]; Massachusetts: Franklin Co., tributary to West Branch North River, Colrain [42.704131°/-072.782871°, elev. 276 m], no collector on label, 17 Nov 1994, 1N♂, 1N♀ [NEL]; New York: Franklin Co., North Branch Saranac River, 50 m upstr. of bridge on Thacherville Rd., off Rt. 26 [44.539979°/-074.051845°], elev. 465 m, S.K. Burian, 25 May 2017, 1♂(+Nex), 7N♂, 6N♀ [NEL]; same [44.54015°/-074.05208°], elev. 465 m, S.K. Burian, 27 May 2020, 1♂(+Nex), 15N♂, 16N♀ [NEL]; same, 28 May 2020, 2♂(+Nex), 1♀(+Nex) [NEL]: Vermont: Bennington Co., Batten Kill (River), Arlington, at Camping On Batten Kill Campground, Rt. 7a [43.086459°/-073.148884°], elev. 197 m, S.K. Burian, 19 June 1999, 1N♀ [NEL].

Rhithrogena brunneotincta McDunnough, 1933: 280

Figs. 79 – 128

Nymph (in alcohol with well-developed or dark wingpads). Body length: 8.50 – 13.10 mm (Mn = 10.82±1.09 SD; Md = 11.25; n=15). Description based on male nymph except where noted.

Head. Colour Pattern: Overall background colour light cinnamon brown (close to NCG# 123A – Cinnamon) with some darker areas around bases of antennae and along midline extending to anterior margin of head capsule (Fig. 79). Lateral margins of head capsule somewhat lighter brown compared to anterior margin. On some live nymphs, colour of head capsule variable, medial area on some individuals ranges from dark brown to dark greyish-brown and lateral areas transparent, on other individuals medial area dark brown (close to NCG# 223 – Raw Umber) and lateral areas light greyish-brown. Pale areas of head capsule can appear translucent such that concealed outer edges of maxillary palps may be visible through edges of head capsule. Pale narrow line between lateral ocelli and along anterior margins of compound eyes (Fig. 79). Pale narrow line widens where it meets lateral margin of head capsule into diffuse triangular spot (Fig. 79). Vertex of head of male nymphs usually with one small, faint spot close to inner margin of each compound eye and anterior to small cluster of faint irregular brown marks. Vertex of head of female nymphs often entirely brown similar to rest of head capsule (except for pale ecdysial suture), occasionally on some specimens one pair of small, pale spots occur straddling ecdysial suture. Shape: Head capsule broadly oval with symmetrically rounded lateral margins (Fig. 79). Posterior corners do not appear angulate or distinctly indented adjacent to compound eyes (Figs. 79). Width of head capsule about 1.7x length. Anterior margin with slight median emargination where labrum articulates with head capsule. When head capsule viewed dorsally curvature of anterior margin obscures median emargination. In addition, labrum almost always flexed downward and hidden by anterior margin of head capsule. Mouthparts completely concealed beneath edges of head capsule. Posterior margin of head capsule usually straight on near final instar nymphs, with only slight indentation at ecdysial suture on some specimens. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped and when viewed dorsally outer margins reach, but do not extend beyond outer margins of head capsule (Fig. 79). Anterior and posterior margins of compound eyes converge toward midline of head transitioning to broadly rounded inner corner (Fig. 79). Compound eyes separated by gap about 2x width of lateral ocellus. Female compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Fig. 80) and gap between eyes more than 2x width of lateral ocellus. Compound eyes of male nymphs large, but collectively occupy less than half of head capsule posterior to antennae. Compound eyes of female nymphs much smaller than males and cover proportionately less of posterior half of head capsule compared to males. Ocelli: Median and lateral ocelli as in Fig. 79. Pale spots present over all ocelli, with all pale spots about same size. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle (Fig. 79). On some specimens, black colour associated with bases of ocelli fades extensively. In addition, on some specimens slightly darker brown spot occurs anterior to lateral ocelli and these specimens may also have pair of dark brown marks on anterior lateral edges of median ocellus that form part of base of fleur-de-lis pattern that extends to bases of antennae. Antennae: Basal membrane of antennal socket pale and edge of socket slightly darker brown than surrounding cuticle (Fig. 80). Scape and pedicel dark brown similar to surface of head capsule and darker than pigmented portion of flagellum. Flagellum light brown (Fig. 81), but membrane between annuli pale giving flagellum banded appearance. Apical 5 – 8 annuli with dark brown spot on inner edge of each annulus (Fig. 81). Antennae length equal to about midline length of head capsule.

Mouthparts. Labrum: Labrum as in Fig. 82, with medial area of anterior margin essentially straight and lateral areas of anterior margin curving to meet short and nearly straight lateral margins. Essentially straight lateral margins of labrum meet posterior corners at about 80° angle (Fig. 82). Anterior margin of labrum lacks shallow median emargination, but has about six large rigid spines extending beyond edge, spines originate as ridges on dorsal surface (Fig. 83), ridges and spines may be worn down on late instar nymphs or individuals about to moult. Central area of dorsal surface of labrum medium brown with pale areas laterally. Posterior half of dorsal surface of labrum with field of short, hair-like setae that transitions to row of about 20 long, hair-like setae across middle of labrum. Anterior to row of 20 long setae are two solitary long setae, one on each side of labrum near lateral edge of anterior margin (Fig. 84). Scattered small hair-like setae occur across anteriormost part of dorsal surface of labrum. Ventral lateral margins of labrum with many (> 20) long, setae in irregularly spaced rows with setae decreasing in length from outermost to innermost position (Fig. 85). Ventral lateral edges of labrum with 6 – 7 stout setae with finely biserrate tips in gaps between long marginal setae and large rigid medial spines. Maxillae: Left maxillae as in Fig. 86. Galea-lacinia with 10 pectinate crown setae, with what appears to be maximum of 10 teeth on largest mid-crown setae (Fig. 87a). Apical crown setae appear to have about half number of teeth of largest mid-crown setae. Smallest posterior crown setae have 8 – 9 teeth. Galea-lacinia with large canine with rounded tip. Submedial row of about 50 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 87b). Near apex of submedial row of setae one long, biserrate seta occurs set back from main row of long setae. Cluster of about 14 short, simple setae at base of submedial row of setae and cluster not aligned with submedial row. Inner edge of galea-lacinia with dense double row of long, simple setae, setae of ventral row only about one-third length of setae of dorsal row (Fig. 86). In addition, at base of double row of inner edge setae is basal row of about 14 long, simple setae with tips extending well beyond setae of main portion of row (Fig. 86). Maxillary palp as in Fig. 86, appearing two-segmented. Inner edge of apical segment of maxillary palp near tip almost straight with row of about 12 evenly spaced blade-like setae (Fig. 88). Apical segment of maxillary palp with distinctive curved longitudinal sclerotized band close to inner edge and faint vertical diagonal brown band near apex of segment (Fig. 86, 88). Most of ventral surface of apical segment of maxillary palp covered with short, stout monopectinate setae (Fig. 88) with 6 – 8 sharp teeth on most large forms across basal and middle parts of array. Outermost edge of apical segment with dense rows of large, simple setae with downward curved tips (Fig. 89). Between field of large monopectinate setae and outer large simple setae are about six rows of more delicate and smaller monopectinate setae with much finer and more numerous teeth than on large monopectinate forms. Hypopharynx: Lingua somewhat rectangular with sides slightly convex near base (Fig. 90). Apical margin of lingua appearing mostly flat with dense brush of fine setae. Superlinguae as in Fig. 90 with outer edges only slightly indented near bases and with broadly rounded anterior and lateral edges. Apical and lateral margins of superlinguae with many long, hair-like setae. Mandibles. Right mandible (Fig. 91a, ventral view): Anterior margin between molars and prostheca straight with continuous row of short, hair-like setae along edge ending in row of about seven larger hair-like setae at base of prostheca (Fig. 92). Molar surface distinctly depressed relative to position of anterior margin. Molars composed of rows of teeth that vary from small sharp, conical forms at ventral edge to large somewhat cylindrical forms with rounded or flattened or peg-like tops along dorsal edge (Fig. 93). Apical molar teeth of ventral edge differ from others being thin, sharp, and closely spaced. Apex of molar surface appears to lack large terminal tooth, but adjacent to apex of molars are about 12 long setae (Fig. 91a). Prostheca composed of one row of about 8 long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 94a). Incisors as in Fig. 94a. Outer incisor length about 2.7x width, teeth along outer edge vary along edge. Large saw-like teeth occur from apex to about middle of outer edge where teeth become smaller and less hook-shaped. Teeth near base of outer edge gradually become straighter and thinner appearing more comb-like (Fig. 94a). Larger inner edge teeth fewer, with only eight distinct teeth plus one flat subapical tooth and small basal tooth (Fig. 94b). Flat blade-like subapical tooth occurs between apical complex and first large tooth of inner edge, flat subapical tooth does not project away from edge as do other inner edge teeth (Fig. 95). Also, starting at 3rd tooth of inner edge there appears to be an undulating basal ridge paralleling teeth 3 – 8. Apical complex of outer incisor appears to be composed of only two teeth, an outer edge tooth and medial tooth (Fig. 95). Basal part of outer incisor with comb of about 33 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 94a). Leading edge of inner incisor with row of 8 – 9 long hair-like setae below large jagged teeth of upper edge. Upper edge of inner incisor with row of about 12 large coarse teeth that gradually merge into trailing edge row of fine comb-like teeth (Fig. 94a). Outer edge of mandible below incisors with fringe of 8 – 9 long hair-like setae, inner edge below molars without long setae (Fig. 91b). Left Mandible (Figs. 96, 97, ventral view): Anterior margin between molars and base of prostheca essentially straight with short area lacking setae adjacent to molars, otherwise continuous row of short hair-like setae present up to base of prostheca (Fig. 98a). Upper edge of molar surface with small row of spine-like setae that transition into row of large molar teeth with multidentate tips (Fig. 98b). Majority of molar surface with rows of short, rounded or conical teeth each terminating with somewhat flattened brush-like tip on upper part of molar surface (Fig. 99a) or short multidentate tooth on lower part of molar surface (Fig. 99b). About 19 rows of molar teeth are present, but only upper 12 – 13 rows terminate with flattened, transparent brush-like teeth. No distinct apical tooth present, but 7 – 8 long, hair-like setae occur below apical cluster of short molar teeth. One large brown conical molar tooth (because of wear apex can appear rounded) occurs set back from middle of first ventral row of molar teeth among field of short bristle-like setae (Fig. 100). Prostheca composed of row of about six finely biserrate setae that gradually increase in length up to base of inner incisor (Fig. 101). Incisors as in Fig. 101. Outer incisor length about 2.6x width, arrangement and size of teeth of outer edge and posterior comb similar to those on outer incisor of right mandible. Larger sized inner edge teeth also similar in number and structure to that on right mandible, including occurrence of undulating basal ridge. Apical complex of outer incisor composed of two teeth as on right mandible (Fig. 102). Basal part of outer incisor with comb of about 30 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter (or less) length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 101). Leading edge of inner incisor with row of 6 – 7 long, thin setae below large apical tooth of upper edge. Upper edge with row of 13 – 14 large, coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of incisor. Outer edge of mandible below incisors with fringe of 5 – 6 long, hair-like setae (Fig. 96). Inner edge of mandible below molars without fringe of long, hair-like setae (Fig. 97). Labium: Labium as in Fig. 103. Dorsal surface of glossae with long, hair-like setae on inner apical surface and row of similar hair-like setae along upper half of inner margin. Dorsal surface of glossae with fan-shaped apical patch of setae that transitions to narrow band of setae that extends diagonally across dorsal surface almost to base of glossae (Fig. 104). Long apical setae of glossae have curved tips and finely biserrate edges and extend well above apex of glossae. Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and large spine-like setae from ventral surface (Fig. 104). Ventral surface of glossae mostly bare, except for one large subapical seta. Upper half of ventral surface of paraglossae with large spine-like setae with some large spine-like setae at anterior edge extending about half length of long, hair-like setae from dorsal surface. Glossae somewhat subtriangular in shape with rounded apices, slightly concave outer edges, and oriented about parallel to midline of labium. Inner edges of glossae also parallel with midline of labium usually forming narrow U-shaped gap (Fig. 103). One specimen studied had moderate U-shaped gap that may have resulted from preservation in Kahle’s kill-fix solution used instead of ethanol. Labial palps two-segmented. Apical segment with distinct array of pectinate brush setae on ventral surface and apical brush of simple setae. Ventral surface of apical segment of labial palps with row of long, thin setae with curved tips along outer edge. Dorsal surface of apical segment of labial palps with array of pectinate brush-like setae.

Thorax. Pronotum: Overall shape broadly rectangular with rounded lateral margins (Fig. 105). Anterior corners of lateral margin gradually curve to meet anterior margin, but posterior corners of lateral margin meet posterior margin at almost 90° angle on some specimens (Fig. 105). Thus, abrupt transition at posterior corners of pronotum makes it appear slightly wider close to posterior margin. Anterior margin essentially straight, but posterior margin slightly convex on either side of body midline (Fig. 105). Posterior lateral edges appear fused with mesonotum despite pale boundary line between them (Fig. 105). Posterior half of pronotum slightly raised on either side of midline forming pair of low humps (most noticeable on near final instar nymphs). Lateral edges at widest part of pronotum light brown, colour extends short distance inward from edge (Fig. 105). Anterolateral corners with large pale spot that connects to pale transverse band near anterior margin, which extends about halfway across anterior margin. On some specimens, small lateral pale spots separated from transverse pale band by area of dark brown. Small lateral pale spots absent on specimens with mostly brown pronotum. Posterior of pronotum with paired humps has most extensive brown shading and usually distinctive pattern of pale curved lines that meet at midline forming symmetrical mirror images (Fig. 106). Pronotal patterning seems consistent on both male and female nymphs. Mesonotum: Overall background colour brown, similar to pronotum, but with some lighter areas on MS and at bases of forewingpads. Anterior margin distinctly dark brown with colour extending into MS as paired lobes and about halfway along MLs (Fig. 107). Lateral edges of mesonotum, forewingpads, and bases of forewingpads dark brown (Fig. 107). Less well sclerotized areas of MS and submedioscutum (SMS) pale cream coloured or white. On live nymphs pale areas can appear tinted with grey or greyish-green. Forewingpads mostly light brown or cream coloured with only costa and basal costal cross veins dark brown, all other developing wing veins indistinct (even on final instar nymphs). Anterior lateral corners of mesonotum with pale triangular spots near points of fusion with pronotum. SL of mesonotum mostly pale cream coloured with brown along outer edges of medial notch. Pale streak of MLs relatively narrow over length of MS. Metanotum: Colour mostly pale cream coloured lacking darker brown markings as occur on mesonotum (live nymphs same as preserved in this respect). Light brown entirely restricted to small area at base of hind wingpads (colour only visible if hind wingpads are lifted). Pleural Region: Membranous area of pleural region anterior and posterior to pleural sclerites of all legs pale without dark brown smudge.

Abdomen. Tergites: Background colour of all tergites of preserved specimens yellow-brown, but colour of live nymphs closer to dusky brown (close to NCG# 19). Abdominal tergites I –VI mostly uniform yellow-brown (Fig. 107) with little evidence of darker colour along anterior or posterior margins, occasionally on tergites II and III traces of darker pigment occur along posterior margins. On live nymphs tergites I –VI mostly brown to greyish-brown with distinctive dark brown posterior margins. On preserved specimens tergites V and VI with brown shading reduced and variable as in Fig. 107, colour patterns of tergites V and VI also variable among sexes with no apparent consistency. Colour of tergites V and VI can range from being almost completely pale yellow to cream coloured with brown shading restricted to anterior, posterior, and lateral margins to half being brown and half pale to some combination of variably restricted brown spots against pale cream-coloured background (Fig. 108). On some specimens, large brown triangular mark occurs on tergites V and VI with base of triangle along anterior margin and apex reaching posterior margin. Abdominal tergites I – IV and VII – IX shaded with brown and usually lack paired pale spots, but occasionally small faint paired pale spots can occur medially near posterior margin. In addition, slightly larger pale spots can occasionally occur near posterior margin of tergites VI – IX. On tergite X paired pale streaks usually extend from anterior to posterior margin. Lateral margins of tergites II – VII with small somewhat triangular indentations, each marked with pale triangular spot with posterior edge of pale spot shaded dark brown. On tergites V and VI lateral colour features can connect to larger pale spot that can extend to posterior margin or merge with dorsally oriented pale area on these tergites. Tergites VIII and IX appear to lack pale lateral indentations, but do have faint pale spots and lateral streaks that extends from anterior corners to posterior margins above posterolateral projections. Posterior intersegmental membranes of tergites I – IX lack dark pigmentation. Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 109). Spinules near midline of tergites essentially straight and generally alternate with thinner and slightly shorter spinules between thicker and larger spinules (Fig. 109). Alternating pattern of spinules mostly maintained across edge with occasionally two thinner spinules occurring together between thicker spinules. Spinules at midline are straight, but those lateral to midline are curved slanting toward midline. On each tergite row of marginal spinules abruptly ends without gradual reduction in spinule length. No microspinules occur among bases of large primary spinules. Posterolateral projections short and pointed or at best weakly pointed on tergites I – VII (Fig. 110). Posterolateral projections of tergites VIII and IX sharply pointed, but not elongated and only those on tergite IX flare outward slightly. In addition, posterolateral projections of tergite IX extend to about midpoint of tergite X. Small brown sclerous lobe-like area associated with posterior margin of tergites VII – IX occurs between end of row of spinules and posterolateral projection. Small sclerous structure on tergites VII – IX appears to be weakly fused to posterior margins of respective tergites. Small sclerous structures on tergites IX larger than same structure on tergite VIII. Small sclerous structure on tergite VII often more oval than others. Sternites: Background colour of abdominal sternites of most preserved specimens pale yellow or cream coloured with dark lateral margins (Fig. 110). Sternites II –VII with dark brown along lateral margins, thin dark edge can be quite faint on some preserved specimens. On live or freshly preserved specimens this dark edge is much more distinctive. Median area of sternites II – VIII pale and appears to lack spots or diagonal streak. Sternite I with anterior flanges short, not projecting much beyond anterior margin and outer corners rounded and shaded brown, which contrasts with mostly pale median area of sternite (Fig. 110). Inner corners of anterior flanges of Sternite I sharply pointed. Sternites II – VIII with thin transverse crease near posterior margins, crease not marked with colour and is difficult to observe directly (often most noticeable because of reflected highlights that occur on either side of indentation in cuticle). On some specimens, faint brown line spanning width of each sternite occurs near posterior margin. On some specimens, small light brown spot present near posterior lateral corners of sternites II – VIII. Median area of sternites I and VIII not raised, but flanked by slight longitudinal creases that sometimes can make median areas appear to be raised. Sternite IX usually darker yellow-brown compared to other sternites, especially on late instar nymphs. Except for colour variations noted for sternite IX, there appears to be little difference in colouration of other sternites between male and female nymphs.

Legs. Forelegs: Overall background colour light brown to yellow-brown with some darker brown shading on some parts of femora and other leg segments, especially adjacent to joints (Fig. 111). Forefemora length about 2.5x width. On live or freshly preserved specimens light brown background colour tinted with medium grey, thus overall darker shaded areas are more distinctive than in preserved specimens, also some pale areas can appear almost white on live specimens. Dorsal surface of forefemora medium yellow ocher (close to NCG#123C), with slightly darker shading around pale median spot (Fig. 111). Forefemora with large pale oval median spot that extends over about two-thirds of dorsal surface of forefemora (Fig. 111, 112). Often above pale median spot is separate thin pale streak that runs along base of dorsal fringe of long setae (Fig. 112). On live or freshly preserved specimens, area of pale median spot can appear opaque yellow-brown and surrounding colour of dorsal surface of forefemora appears shaded with greyish-brown in contrast to yellow ocher of preserved specimens. No medial dark mark present in pale median spot of forefemora (Fig. 112). Apical portion of forefemora beyond brown margin of pale median spot mostly pale, except for dark brown adjacent to joint with foretibiae. Dorsal and ventral edges of forefemora slightly darker brown along rows of marginal setae. Dorsal edge of forefemora with 1 row of long setae with variously expanded transparent tips and edges (Fig. 112). Although many long setae of dorsal edge row seem to have sharp tips, several seem to have sharp tip associated with broad transparent flattened edge of variable width and length; some seem similar to elongate flags. Dorsal edge row of setae of uniform length, except for one or two short setae near apex of forefemora. Scattered short, stout setae below middle of dorsal edge row of long setae. Dorsal surface of forefemora with field of short, flattened setae as in Fig. 113. Field of flattened setae mostly concentrated over middle of pale median spot and have distinctive dark brown bases. Most flattened setae are 2x as long as wide with parallel sides and rounded tips (Fig. 113). Surface of forefemora ventral to pale median spot dominated by longer and more attenuated flattened setae. Along ventral edge of forefemora flattened setae form closely spaced irregular row together with scattered spine- and hair-like setae (Fig. 114). Groove along ventral edge of forefemora pale without dark shading adjacent to joint with foretibiae (foretibiae completely cover this area when folded against forefemora). Foretibiae: Length of foretibiae about 1.0x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint and along tibiopatellar region shaded with dark brown. On live specimens, intensity of brown colour on foretibiae much greater. Overall foretibiae mostly uniform light brown, with slightly darker brown shading at joint with foretarsi (Fig. 115). Ventral edge of foretibiae with about eight widely separated stout spine-like setae. Ventral apical edge of tibio-tarsal joint with two large monopectinate setae and cluster of 3 – 4 paddle-shaped setae. Dorsal edge of foretibiae with longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae. Foretibiae with eight paddle-shaped setae distributed along dorsal row of small hair-like setae. Lateral to major dorsal edge row of hair-like setae is sparse secondary row of scattered small hair-like setae extending from base to apex of foretibiae. Foretarsi: Length of foretarsi about 0.3x length of foretibiae. Background colour similar to foretibiae (including lack of any distinct pale areas), but apical edge adjacent to claw shaded slightly darker brown. Major dorsal edge row of hair-like setae on foretibiae continues along dorsal edge of foretarsi with two paddle-shaped setae embedded in row near apex of foretarsi (Fig. 116 as in Fig. 171a). In addition, small apical cluster of hair-like setae occurs between last paddle-shaped seta and edge below joint with foreclaws. Foreclaws: Foreclaws as in Fig. 117, with medium brown base and dark brown elongate tip. Length of tip of foreclaw only slightly more than 2x length of largest subapical denticle. One basal tooth and two preapical denticles present that gradually become thicker and longer toward claw tip (Fig. 117). In addition to preapical denticles on dorsal side of foreclaws are at least two hair-like setae that curve upward from claw edge, but as many as seven evenly spaced small hair-like setae may be present. Outer apical portion of foreclaws slightly more than one-third their total length. [Special Note Regarding Foretrochanter: Foretrochanter with only small cluster of small spine-like setae on ventral edge.]. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Fig. 111, 118a). There is some variation in appearance of pale median spot, which is more elongate than on forefemora and usually appears more connected to pale dorsal streak below row of long marginal setae. (Fig. 118a). In addition, pale apical area on femora is larger than on forelegs. Flattened setae with brown bases on mid and hind femora often more numerous across lower part of pale median spot, basal pale spot, and surrounding darker brown margin compared to forefemora. Ventral edge setae of mid and hind femora are also more numerous than on forefemora. Mid and Hind Trochanters: Mid and hind trochanters with distinctive row of large, spine-like setae along ventral edge (Fig. 118b). Structure and appearance of mid and hind tibiae, tarsi, and tarsal claws generally similar to that of forelegs (Fig. 111, 119), however there are some differences. Large paddle-shaped setae and large spine-like setae are more numerous along longitudinal row of hair-like setae on mid and hind tibiae. Apex of mid and hind tibiae with 6 – 7 large spine-like setae organized into small clusters with 2 – 3 setae distributed along apical edge (Fig.120a). No large pectinate setae occur as on forelegs. Mid and hind tarsi with two evenly spaced large paddle-shaped setae in lateral longitudinal row of hair-like setae. Apical edge of mid and hind tarsi with clusters of hair-like setae as occurs on forelegs. Mid and hind claws similar in shape, size, and proportion to those of forelegs, but with three subapical denticles and five small hair-like setae on dorsal surface opposite position of subapical denticles (Fig. 120b). 

Abdominal Gills. Colour and Position: Gills mostly transparent, but with some light brown shading along sclerotized dorsal margin, median sclerous ribs, and basal half of gills 2 – 7. Brown shading on basal portion of gills 2 – 6 can be more extensive on some specimens. On live or freshly preserved specimens posterior part of gills 2 – 7 may be tinted pale yellow – this colour fades completely after initial preservation. On gill 1 brown shading restricted to straight inner margin anterior to gill base (Fig. 121). Base and lower portion of gill filaments green, tips of gill filaments shaded yellowish-green. On live nymphs, green colour much more intense and filaments tinted brownish-green near base with overall green colour extending to tips of filaments. Tracheae faintly stained on gills 2 – 5, tracheae present but indistinct on gills 6 and 7. Gill tracheols have consistent branching pattern with secondary tracheols branching from main tracheae toward dorsal margin of gills. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) of gill 1 meets, but does not overlap dorsal margin of gill 1 from opposite side of abdomen (Fig. 110), only rounded anterior corner of inner edge overlaps same part of opposite gill 1. Abdominal gills 2 – 6 positioned laterally with anterior third of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Fig. 110). Abdominal gills 3 – 6 with anterior margin near base becoming progressively more concave towards gill 7. Gill 1: Abdominal gill 1 as in Fig. 122, anterior corner rounded where straight inner margin meets dorsal edge, but only slightly protruding. Outer margin with incisions forming ruffled edge. Depth of incisions relatively consistent along entire edge, but usually less than width of each division (Fig. 122). Major divisions of ruffled edge may have smaller secondary indentations making edge appear complex. Ruffled edge extends about halfway around posterior margin of gill 1 and has small hair-like setae along entire length of edge. Plica of dorsal surface as in Fig. 123, appearing as thickened raised edge with series of 6 – 7 widely spaced small, pointed projections. On some specimens, two or three projections may be distinctly larger than others along edge of Plica (Figs. 124a,b). Curvature of plica edge without distinct apex and thus does not noticeably point toward base of ruffled edge, but is distinctly raised above gill surface (Fig. 124b). Inner two-thirds of gill thicker and more opaque than outer ruffled edge. Cluster of about 18 filaments at gill base that appear to originate from two or three major divisions of main tracheal branch (Fig. 122). Short, sclerotized rib present adjacent to gill base. Tracheae of gill extremely faint. Gill 2: Abdominal gill 2 as in Fig. 125a. Overall shape of gill broadly oval (irregularly shaped ventral margin interrupts overall oval shape), posterior margin with deep incisions producing distinct ruffled edge as occurs on gill 1. Small hair-like setae are present along entire posterior margin. Ruffled edge of gill 2 with occasional secondary divisions similar to those on gill 1. Width of gill 2 about 0.9x length. Dorsal margin without distinct lobe. Dorsal margin from base of filaments to posterior ruffled edge essentially straight (Fig. 125a). Dorsal half of gill 2 shaded light brown with colour darkest along short basal sclerous rib, median sclerous rib, and along edge adjacent to tuft of filaments at gill base. Tracheae faint on gill 2, only slight traces of greyish-green colour remain on most specimens studied. Tracheae of gill 2 exhibit distinct branching pattern with larger tracheols extending upwards toward dorsal margin from central tracheae. Tuft of filaments as in Fig. 125a, composed of about 35 long filaments and basal group of about seven short filaments that appear to arise from two or three tracheal branches at base of gill. Filaments of gill 2 extend to or slightly beyond midpoint of gill and base of tuft of filaments seems to originate from shallow depression on ventral surface of gill. Lower portion of gill 2 supported by distinctive thick median sclerotized rib, usually shaded yellow-brown (Fig. 125b). In addition, smaller basal sclerotized rib extends from gill base and forms upper edge of pigmented region of gill, which extends to thick median rib. Neither small basal rib nor thick median rib appears to have surface setae, but smaller setae occur on surface of gill between these structures. Gill 4: Abdominal gill 4 as in Fig. 126, shape broadly oval without dorsal lobe. Width of gill 4 about 0.7x length. Colour of gill and tracheae as in gill 2. Ventral portion of posterior margin of gill 4 with ruffles as in gill 2, but restricted to smaller area of posterior margin (Fig. 126). Small hair-like setae present along posterior margin. Dorsal margin of gill 4 concave adjacent to gill base (Fig. 126). Lower portion of gill 4 with thick median sclerotized rib, usually shaded yellow-brown as in gill 2 (Fig. 126). Base of upper portion of gill 4 supported by short, sclerotized rib similar in form and colour to that on gill 2. Surface of thick median rib of gill 4 appears to lack setae, as on gill 2, but scattered small setae present on surface of gill between short basal rib and thick median rib. Tuft of filaments (i.e., >20) at base of gill 4 as in Fig. 126, similar in length and arrangement to those on gill 2. Gill 6: Abdominal gill 6 as in Fig. 127, shape somewhat triangular, different from preceding gills 2 – 5. Thick ventral sclerotized median rib similar to those on gills 2 – 5, but reduced in size. Except for its unusual shape, overall shape basic structural features of gill 6 similar to those described for gill 4. Gill 7: Abdominal gill 7 as in Fig. 128, with dorsal margin folded back on itself and apparently fused to surface of gill near basal sclerotized rib. Gill 7 lacks dorsal lobe. Folded dorsal margin of gill 7 allows part of ventral surface to partially wrap around edge of abdominal tergite IX and simultaneously allows ruffled edge to extend beneath abdomen to meet opposite gill 7 (Fig. 110). Ventral posterior margin with about eight incisions forming short ruffled edge (Fig. 128), occasionally small secondary divisions also present. Tracheae of gill 7 are indistinct, but brown shading occurs over central and basal parts of gill (Fig. 128). Small hair-like setae scattered along ruffled edge of gill 7. Tuft of filaments at gill base shorter and with fewer filaments (~18) compared to preceding gills, but otherwise similar in colour and structure. Ventral sclerotized features not developed as on preceding gills, thick median sclerotized rib absent.

Caudal Filaments. Colour and Structure: Caudal filaments subequal in length and together are about 1.6x length of abdomen. On preserved specimens, caudal filaments uniform light brown to almost cream coloured. On live nymphs, caudal filaments usually uniform medium to dark brown. Row of short spines on posterior margins all annuli, except for apical annuli of median terminal filaments. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 40 (as counted from base). Fine hair-like setae begin with only 2 – 3 per annulus, but rapidly increase to maximum of 8 – 9 per annulus. Terminal six annuli usually lack marginal setae, but occasionally individual marginal setae occur on some annuli.

Diagnosis Rhithrogena brunneotincta Nymph: Nymphs of R. brunneotincta can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) Large body size of near final instar nymphs (8.50 – 13.10 mm; Mn=10.82 (n=15); Md= 11.25 (n=15)), only 1 female nymph from Maine was observed reaching a body length greater than 11.50 mm suggesting that the one larger specimen may be atypical for the species, (2) femora with large pale oval median spot without a dark median mark (Figs. 111, 112), field of large flattened setae extend across most of pale median spot and surrounding brown area of femora (Fig. 113), (3) abdominal gill 1 shaped as in Fig. 122, plica broadly curved with a thickened edge raised above dorsal surface of the gill and with a series of 6 – 7 small pointed projections (some appearing tooth-like), on some specimens two or three projections may be distinctly larger than others (Fig. 123), posterior edge of plica also slightly raised above the surface of the gill, outer ruffled edge with many moderately sized ruffles, (4) abdominal gills 2 – 6 without a dorsal lobe (Fig. 121), and dorsal one-third to one-half of gills shaded light yellow-brown with colour darkest along the dorsal margins and the short sclerotized ribs near base of gills, (5) tracheae of abdominal gills 2 – 7 indistinct with only faint traces of greyish-green colour on some gills and tracheae exhibit distinctive branching pattern with tracheols extending upward towards dorsal margin from central tracheae, (6) abdominal gills 2 – 6 with the lower part of gills with distinctive thick, median sclerotized rib with only a few small hair-like setae scattered across gill surface, ventral view of gills 2 – 6 shows thick median sclerotized ribs on gills in alignment along the length of abdomen as a discontinuous row of gill supports (Figs. 110), (7) posterior margins of gills 2 – 6 with many small shallow incisions forming ruffles with a gradual reduction in number of ruffles from gill 3 – 6, on gill 6 only about half of posterior margin has ruffles, (8) abdominal gill 6 sub-triangular in shape, (9) crown of maxillae with 10 large pectinate setae, (10) apical segment of maxillary palp with faint diagonal brown vertical band near tip (occasionally absent on some preserved specimens), (11) submedial row of about 50 setae long biserrate setae below crown of galea-lacinia (Figs. 87b), (12) glossae of labium almost parallel to midline of labium forming a narrow U-shaped gap (Fig. 103), (13) outer incisor of right mandible length about 2.7x width and with eight distinct teeth on inner edge up to apical complex and secondary undulating basal ridge present starting at the 3rd large tooth and parallels bases of teeth 3 – 8, (14) outer edge of both mandibles with fringe of 8 – 9 long, hair-like setae, (15) labrum shape as in Fig. 82 with nearly straight lateral edges, (16) abdominal tergites V and VI with brown shading reduced and variable producing different light and dark shaded areas as in Figs. 107, 108, which vary between sexes with no apparent consistency, (17) majority of spinules on posterior margins of abdominal tergites distinctly slanted toward body midline (Fig. 109), and (18) forewingpads distinctly triangular in shape with little evidence of developing wing veins, outer and inner edges of forewingpads usually dark brown (Fig. 107). See Appendix 3 for comparative list of R. brunneotincta diagnostic characters and those of other northeast species.

Taxonomic Discussion. Compared to other Nearctic species of Rhithrogena there have been few taxonomic treatments of R. brunneotincta. McDunnough (1933) and Traver (1935) provide the only detailed taxonomic discussions of the adults of R. brunneotincta and among these treatments Traver (1935) noted that she was never able to study any specimens directly. Both authors commented on the morphology of the male imago, specifically the genitalia, with regards to the western Nearctic species R. robusta. McDunnough (1933) provided a detailed figure of the male genitalia that was essentially duplicated by Traver (1935). Although there are similarities between the genitalia of R. brunneotincta and R. robusta, other distinctive wing and body characters of R. brunneotincta provide strong evidence that it is indeed a different species. The nymph of R. brunneotincta is described herein for the first time and allows comparison with the nymph of its presumed sister species R. robusta. First, the nymph of R. brunneotincta seems slightly smaller than that of R. robusta with the mean length of late instar nymphs 11.25 mm (n=15), only one specimen was greater than 12.00 mm, which is in the body size range of R. robusta nymphs. Second, colour of the body, legs, gills, and colour patterns of abdominal tergites of R. brunneotincta nymphs have much more contrasting and distinctive abdominal colour patterns compared to those of R. robusta. Live nymphs of R. brunneotincta have strongly contrasting light and dark marks on abdominal tergites V and VI, greenish-grey gill filaments, dark brown shading over the central part of the head capsule and anterior margin and central part of MS of the thorax. Legs are more lightly pigmented, as well as lateral areas of the head capsule (which can appear almost transparent on some specimens). In both species all femora lack a median dark mark in pale median spot. Preserved specimens of R. brunneotincta have more uniform colouration of the head capsule and thorax, also the developing forewingpads can appear opaque whitish with distinct brown edges. Pale areas are also more visible on the mesonotum adjacent to the bases of the forewings. Colour of abdominal tergites can become even more distinctive on some live specimens and gill filaments have greatly subdued greenish colour. Caudal filaments of preserved specimens lose most of their life colour, with cerci becoming similar to the median terminal filament, whereas on live specimens, cerci are distinctly darker brown. In addition, the legs and head capsule also lose their semi-transparent quality after preservation. With regards to mouthparts and body diagnostic characters described herein for R. brunneotincta, the labrum of R. robusta is more semicircular in shape with slightly convex anterior lateral edges that transition to broadly rounded posterior corners; the maxillae of R. robusta are similar in most respects to those of R. brunneotincta; the glossae of the labium of R. robusta are subtriangular with more distinctive truncated apices and slightly sinuous outer margins compared to R. brunneotincta and the gap between glossae of R. robusta is V-shaped compared to the narrow U-shaped gap in R. brunneotincta. The outer incisor of the right mandible of R. robusta has 9 – 10 large teeth on its inner edge compared to eight teeth in R. brunneotincta. Abdominal gill 1 of R. robusta has the plica composed of broad curved and thickened edge with small, sharp projections along the anterior portion of the edge and a posterior section with a distinct bulge without small projections. This is in contrast to R. brunneotincta which has small, sharp projections along the anterior portion of the plica, but no posterior bulge or small projections.

In addition to the morphological features that appear to be shared with the nymph of R. robusta, the nymph of R. brunneotincta appears to share some features with some European species in the Rhithrogena alpestris species group (Bauernfeind 1995, Baurenfeind and Soldan 2012, and Studemann et al. 1992). At least two European species (R. allobrogica Sowa and DeGrange, 1987 and R. beskidensis Alba-Tercedor and Sowa, 1987) appear to have morphologically similar labra and abdominal gill 1 lacking a plica with a distinct anterior bulge. Although it is not possible to do more at this time than point out these apparent similarities, it is hoped that anyone taking on future phylogenetic studies of Rhithrogena will include taxa from both continents for a more comprehensive analysis of the group.

Distribution. Rhithrogena brunneotincta has the second smallest range of any of the northeastern species of Rhithrogena (Fig. 334). The type series used by McDunnough (1933) to describe R. brunneotincta came from a single location in the center of the Gaspé Peninsula, Quebec. However, there was one additional specimen studied by McDunnough (1933) from northern New Hampshire that was apparently collected 22 years before the type series that McDunnough concluded was R. brunneotincta, but not designated as among the types. Thus, the area encompassing the Gaspé of Quebec and the mountains of northern New Hampshire represented the known range at that time. Subsequent studies in Maine (Burian and Gibbs 1991) reported R. brunneotincta from several sites in western and central Maine. In addition, Chandler et al. (2006) reported R. brunneotincta from additional sites in northern New Hampshire. It is possible that the range of R. brunneotincta is larger than current records indicate because habitats similar to those in Maine, New Hampshire, and Quebec where R. brunneotincta occurs are present in adjacent areas of New Brunswick, New York, and Vermont where the species has yet to be detected. The northeastern distribution of R. brunneotincta is given in Appendix 2.

Life History and Ecology. Rhithrogena brunneotincta is always associated with clean, 1st – 2nd order high gradient streams with perennially cool-cold water temperatures, medium to large cobble substrates (without extensive moss or attached filamentous algae), and swift currents (~0.5 m/s or greater). In Maine R. brunneotincta was only found in such streams at higher elevations of the central and western Moosehead Plateau and northwest tributaries of the St. John River (Burian and Gibbs 1991). Site elevations where R. brunneotincta was recorded ranged from 219 – 658 m asl. The lowest elevation sites were in tributaries of the St. John River in far northwestern Maine close to the international border. The highest elevation sites were in the upper reaches of the SBrCR near Sugarloaf Mountain in western Maine. In New Hampshire it was likewise only found in similar habitats in the mountainous northern tier of the state (Chandler et al. 2006). Although no water quality measurements were made at the SBrCR sites in 1984 and 1985 when nymphs of were collected, on 21 May 1986 at about the same site on the SBrCR the following data was recorded: Water Temperature = 11.0 °C; pH = 7.10; Specific Conductance = 48.0 µS. Substrate at these sites was predominantly medium cobble (128.0 – 256.0 mm), large cobble (256.0 – 512.0 mm), and scattered boulders with lesser amounts of small cobble (64.0 – 128.0 mm) and various sized gravel towards the edges of the channel. Dissolved oxygen was not measured, but prevailing conditions (land use within 1 km of site was mostly undisturbed mixed deciduous and coniferous forest) indicated it likely was at or close to equilibrium value of about 10.0 ppm pursuant to water temperature and elevation, which ranged from 399 – 650 m asl. 

Rhithrogena brunneotincta is univoltine throughout its range and appears to have a relatively short emergence period based on the brief presence of last instar nymphs in samples collected in early June and collections of adults in mid-June. However, there is some evidence that in perennially cold habitats emergence may be delayed until early July. Among the type series of R. brunneotincta were some adults that were recorded from the perennially cold central Gaspé region from the first week in July. Further, the new observation (reported herein) of the late emergence of Rhithrogena impersonata from this same area of the Gaspé tends to support the hypothesis that prolonged colder regional water temperatures produces later emergence times. The life history of R. brunneotincta has not been studied, but understanding the environmental and biotic variables that affect its survival, developmental, and dispersal may be important in predicting how this species might respond to changes in its sensitive high gradient stream habitats as a result of climate change or local anthropogenic disturbances.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Material Studied. Canada: Quebec: La Haute-Gaspésie [Mt. Albert]: St. Anne River, dnstr. of bridge on dirt road just off Rt. 229 nr 90 km marker N of Mt. Lyall, collected from under rocks in middle of river [48.8701°/-066.0998°], elev. 318 m, J. Moisan – De Serres, 21 Aug 2020, 4N (instars too small to determine sex) [NEL]; USA: Maine: Aroostook Co., Chimenticook Stream, upstr. from confl. with St. John River [47.046683°/ -069.330119°, elev. 218 m], T. Mingo, D.L. Courtemanch, & K.E. Gibbs, 22 – 25 Sept 1977, 1N♂, 4N♀ [NEL]; same, Campbell Brook [47.081027°/-069.141907°, elev. 219 m], T. Mingo, D.L. Courtemanch, & K.E. Gibbs, 23 Sept 1977, 4N♂, 3N♀ [NEL]; same, Little Hafey Brook, site 13 [47.261110°/-069.195513°, elev. 291 m], no collector given, 22 – 25 Sept 1977, 2N♂, 4N♀ [NEL]; Franklin Co., Carrabassett River (SBrCR), nr entrance to Sugarloaf Ski area, Rt. 16, site F20 [45.0801044°/-070.313262°], elev. 390 m, S.K. Burian, 20 Oct 1984, 1N♂, 5N♀ [NEL]; Carrabassett River (SBrCR), at Appalachian Trail crossing [45.038459°/-070.342896°], elev. 658 m, S.K. Burian, 20 Oct 1984, 1N♂ [NEL]; same, un-named trib. to Carrabassett R. (SBrCR) nr. entrance to Sugarloaf Ski Area, site F18 [45.081085°/-070.319434°], elev. 399 m, S.K. Burian, 13 June 1985, 1♂ [NEL]; same, Carrabassett R. (SBrCR) at pump-house, site F21, Sugarloaf Ski Area [45.063326°/-070.338534°], elev. 492 m, S.K. Burian, 16 June 1985, 1♂(+Nex) [NEL]; same, small stream (trib. to Carrabassett R. (SBrCR)) nr. E-mountain Rd., site F19, Sugarloaf Ski Area [45.066635°/-070.311649°], elev. 531 m, S.K. Burian, 16 June 1985, 1S♂ [NEL]; Piscataquis Co., Katahdin Stream, Katahdin Stream Campground, Baxter State Park [45.887361°/-068.999174°, elev. 328 m], T. Mingo, 23 May 1979, 1N♂, 1N♀ [NEL]; same, 4 May 1980, 1N♂, 1N♀ [NEL]; same, Nesowadnehunk Stream at bridge to Kidney Pond, Baxter State Park [45.900720°/-069.039157°, elev. 324 m], T. Mingo, 23 May 1979, 1N♀ [NEL]; same, Little Nesowadnehunk Stream, Baxter State Park [45.978608°/-068.074251°, elev. 401 m], T. Mingo, 14 June 1979, 1N♂ [NEL]; same, Abol Stream, about three quarters of way up hill, Baxter State Park [45.861243°/-068.957961°, elev. 347 m], T. Mingo, 27 Oct 1979, 1N♂, 1N♀ [NEL]; same, Abol Stream, at top of hill [45.874245°/-068.964895°, elev. 396 m], T. Mingo, 21 Oct 1979, 1N♂, 1N♀ [NEL]; same, 25 Mar 1980, 3N♂ [NEL]; same, 2 Apr 1980, 4N♂ [NEL]; New Hampshire: Coos Co., Mill Creek (main branch), 5.6 km S of Stark [44.565430°/-071.399977°, elev. 481 m ], E. Wolff, J. Lemire, & D.C. Chandler, 22 Aug 2006, 6N♀ [NEL]

Rhithrogena gaspeensis McDunnough, 1933: 279

Nymph (Unknown).

Diagnosis Rhithrogena gaspeensis Nymph: Not possible at this time. 

Taxonomic Discussion. What is known about the taxonomy of R. gaspeensis is restricted to discussion of the male and female imagos of the type series (McDunnough, 1933). Based on the structure of the male genitalia McDunnough (1933) places this species in the doddsi-morrisoni group, which was later redescribed by Traver (1933) as the brunnea group. Currently, R. gaspeensis is the only known member of this group that occurs east of the Rocky Mountains. Although Edmunds (1952) postulated that nymphs of western species of Rhithrogena of the brunnea group may have similar gill morphologies, recent work by Newell and Schenck (2010) on the nymph of R. virilis McDunnough (1934) shows this not to be true. Thus, it is currently not possible to speculate on what the nymph of R. gaspeensis may be like. 

Distribution. Rhithrogena gaspeensis was originally described by McDunnough (1933) from the central mountainous region of the Gaspé peninsula, Quebec. The exact location is uncertain and was simply described by McDunnough (1933) as being near the headwaters of the Caspedia River, Mt. Lyall at an elevation of 1500 ft (~457 m). The specimens described by McDunnough (1933) were collected as part of the Dominion Entomological Branch insect survey of the Gaspé. Unfortunately, there seems to be no surviving records of the exact locations of field sites of the Dominion Entomological Branch’s survey. The number of male and female individuals in the type series that were collected over a period of three consecutive days suggest that the sampling site was at (or near) a stream where emergence was occurring and not at a more remote site away from the water. This is based on the observation of rare solitary occurrences of other northeastern Rhithrogena species away from probable emergence sites in Maine (likely dispersing individuals). No swarms of northeastern Rhithrogena species have ever been observed inland away from any potential emergence site. Currently R. gaspeensis has not been reported from any other location and is one of the few narrow endemic mayflies within the region (Appendix 2). 

Life History and Ecology. Unknown; however, based on the dates from the type series and scant details of the type locality given by McDunnough (1933) it is possible to make a few deductions. First, the dates that adults were collected (August 8-10) are the latest for any species of Rhithrogena currently known from northeastern North America. The late emergence period suggests that any eggs laid at a time of declining water and air temperatures would likely delay hatching until the following spring. That would give early instar nymphs the greatest chance to avoid the rigors of winter, which are frequently severe in the central Gaspé region. Moreover, delayed hatching would avoid competition with nymphs of other species of Rhithrogena (e.g., R. brunneotincta) that likely already hatched. Because seasonal water temperatures in the small streams of the central Gaspé are historically cold, upon hatching growth of R. gaspeensis nymphs would be expected to be slow perhaps requiring the entire summer leading into a late summer or early fall emergence time.

Second, because the collection site was described as near the headwaters of the Caspedia River on the slopes of Mt. Lyall it is possible to examine the current basic structure of these streams using Google Earth Images. In general, the small streams at an elevation of ~457 m of this region appear to be <10m wide, relatively shaded, and have moderate to steep slopes with complex mineral substrates. Structure of the surrounding forests suggests a large CPOM annual input supporting a largely heterotrophic stream community. Flow rates seem to be moderate to high throughout the warmer months of the year. Although it is possible that R. gaspeensis could also occur in the larger main channel area of the Caspedia River currently there are no records to support this. Since the type series was collected in 1933 there has been increased commercial and recreational use of the forests of the central Gaspé region and it is not known to what extent these activities have affected the Caspedia River watershed regarding the occurrence or survival of R. gaspeensis.

Rhithrogena impersonata (McDunnough, 1925: 191)

Figs. 129 – 179

Heptagenia impersonata McDunnough, 1925 (original description)

Rhithrogena impersonata McDunnough 1925 (McDunnough 1926: 195)

Rhithrogena sanguinea Ide, 1954 (Flowers and Hilsenhoff 1975: 211)

Nymph (in alcohol with well-developed or dark wingpads). Body length: 5.60 – 9.50 mm (Mn = 7.42±1.24 SD; Md = 7.62; n=17). Description based on male nymph except where noted.

Head. Colour Pattern: Overall background colour ranging from medium brown to slightly darker brown (darker colour close to NCG# 23 – Raw Umber) (Fig. 129). Area between compound eyes and along anterior and lateral margins of head capsule shaded dark brown. Dark grey shading evident along tracheae beneath cuticle from antennal bases to anterior margin of head capsule. Pale narrow line between lateral ocelli and along anterior margins of compound eyes (Fig. 129). Pale narrow line only slightly wider where it meets lateral margin of head capsule. Anterior half of head capsule uniform brown, lacking any distinct pale markings (Fig. 129). Vertex of head male nymphs usually with one small, faint spot close to inner margin of each compound eye. However on female nymphs, vertex between compound eyes usually entirely brown (except for pale ecdysial suture), occasionally one pair of small, faint pale spots straddle ecdysial suture (Figs. 130 a,b). Shape: Head capsule broadly oval with symmetrically curved anterior and lateral margins with minimal deviation at posterior corners near edges of compound eyes, thus not appearing to be distinctly indented at this point (Figs. 129). Width of head capsule about 1.7x length. Anterior margin with slight median emargination where labrum articulates with head capsule. When head capsule viewed dorsally, curvature of anterior margin can obscure median emargination making it appear absent. Further, from dorsal perspective anterior margin of some specimens appears to vary from smoothly curved to straight where labrum articulates with head capsule. Mouthparts completely concealed beneath edges of head capsule. Posterior margin of head capsule essentially straight on near last instar nymphs. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped, when viewed dorsally outer margins reach, but do not extend beyond outer margins of head capsule (Fig. 129). Anterior and posterior margins of compound eyes converge toward midline of head transitioning to broadly rounded inner corner (Fig. 129). Compound eyes separated by gap about width of one lateral ocellus. Female nymphs compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Figs. 130a, b) and gap between eyes more than 2x as wide as on male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Figs. 129, 130a,b. Pale spots present over all ocelli, with spots over lateral ocelli slightly larger than over median ocellus. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle (Fig. 129). Antennae: Basal membrane of antennal socket pale and edge of socket slightly darker brown than surrounding cuticle (Fig. 131). Scape and pedicel dark brown similar to surface of head capsule and often darker than pigmented portion of flagellum. Proximal 12 – 13 annuli of flagellum vary from light brown to same colour as scape and pedicel (Fig. 131). Apical 8 – 10 annuli of flagellum colourless or pale cream coloured. Antennae length about 1.3x midline length of head capsule.

Mouthparts. Labrum: Labrum somewhat trapezoidal, not distinctly semicircular with sides of anterior margin varying from straight to slightly convex before merging with rounded posterior corners (Fig. 132). Anterior margin of labrum with shallow median emargination, on some specimens this feature is so subtle it can appear to be absent. Anterior median emargination with group of 4 – 5 small, rigid spines on either side of ventral edge (Fig. 133). Only tips of small rigid spines visible from dorsal perspective. Dorsal surface of labrum medium brown with slightly lighter areas laterally. Posterior half of dorsal surface with field of long, hair-like setae with bases relatively widely separated and with small patches of short, hair-like setae tending to be grouped toward middle of labrum. Middle and anterior portion of dorsal surface with few relatively long hair-like setae, but medially one pair of larger, slightly thicker, setae close to center of median emargination. Group of 2 – 3 widely separated setae (similar to medial pair) occur near each lateral margin. Ventral lateral margins of labrum with many (> 20) long, setae in four irregularly spaced rows with setae decreasing in length from outermost to innermost position (Fig. 134). Shortest ventral margin setae stop at transition point where straight (or slightly convex) lateral margins meet anterior margin (i.e., point before where small rigid spines begin). Ventral lateral edges of labrum with 2 – 6 small, spine-like setae in gaps between long marginal setae and small rigid spines at edges of median emargination. Maxillae: Left maxillae as in Fig. 135. Galea-lacinia with nine pectinate crown setae, with what appears to be maximum of 12 teeth on largest mid-crown setae (Fig. 136) and one vestigial seta lacking teeth. Apical crown seta appears to have half number of teeth of largest mid-crown setae. Submedial row of about 39 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 135). Near apex of submedial row of setae one long, biserrate seta occurs set back from main row of long setae. Often at base of main submedial row of setae are small groups of 2 – 3 shorter setae that are not aligned with the submedial row. Inner edge of galea-lacinia with dense double row of long, simple setae, setae of ventral row only about one-third length of setae of dorsal row (Fig. 135). In addition, at base of double row of inner edge setae is basal row of 9 – 10 long, simple setae with tips extending well beyond those of main portion of inner edge row. Maxillary palp as in Fig. 137, appearing two-segmented. Inner edge of apical segment near tip straight with 11 – 12 small, short, somewhat flattened setae with pointed tips widely spaced along edge (Fig. 138). Apical segment of maxillary palp with distinctive longitudinal sclerotized band and broad, light brown vertical band near apex of segment (Fig. 137). Most of ventral surface of apical segment of maxillary palp covered with short, stout monopectinate setae (Fig. 138) with 3 – 4 sharp teeth on most large forms across middle of array of setae. Some setae near apex of array of monopectinate setae have six or more teeth that are longer and thinner than those in middle of array. Outermost edge of apical segment with 5 – 6 rows of large, simple setae with downward curved tips. Dorsal surface of apical segment with scattered long, hair-like setae. Hypopharynx: Lingua mostly rectangular, but base slightly wider than apex such that sides appear to taper slightly toward curved apical margin (Fig. 139). Apical margin of lingua appears slightly arched with field of short setae uniformly distributed across surface. Superlinguae as in Fig. 140 with outer edges not greatly expanded and nearly straight. Bases of superlinguae gradually tapering to base of hypopharynx. Apical margins of superlinguae smoothly rounded to inner margins and with long, hair-like setae as in Fig. 140. Mandibles. Right mandible (Fig. 141a, ventral view): Anterior margin between molars and prostheca straight with continuous row of short, hair-like setae (Fig. 142). Molar surface only slightly depressed relative to position of anterior margin, mostly in line with anterior margin (Fig. 142). Molars composed of rows of teeth that vary from sharp, conical forms at ventral edge to large cylindrical forms with rounded, tops along dorsal edge (Fig. 143a). Apical teeth of ventral edge differ from others being thin, sharp, and closely spaced. Molar surface terminates with one large, sharp outwardly pointing tooth (Fig. 143b). Adjacent to apex of molars are 9 – 10 long, simple setae that are thicker than typical hair-like setae. Prostheca composed of one row of 6 – 7 long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 142). Incisors as in Fig. 144. Outer incisor length about 3.0x width, smaller sized teeth on outer edge homonomous from apex to base where basal teeth become thinner and sharper. Larger sized inner teeth fewer, with eight distinct teeth up to apical complex teeth. Apical three inner edge teeth (excluding apical complex) each with small tubercle near base (Fig. 145). Apical complex of outer incisor composed of two smaller lateral teeth and one large medial tooth not fused into single unit. Basal part of outer incisor with comb of about 27 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Figs. 144, 146). Leading edge of inner incisor with about six long setae in row below large, jagged teeth of upper edge. Upper edge of inner incisor with row of about nine large coarse teeth that gradually merge into trailing edge row of fine comb-like teeth (Fig. 146). Outer edge of mandible below incisors with fringe of many long, hair-like setae, often obscured by detrital debris on mandible (Fig. 141b), inner edge below molars without long setae. Left Mandible (Fig. 147, ventral view): Anterior margin between molars and base of prostheca essentially straight with row of short, hair-like setae beginning near middle of margin and extending up to prostheca (Fig. 148). Anterior margin adjacent to molars bare. Upper edge of molar surface with large multidentate first tooth that transitions to smaller multidentate teeth of outer row of upper molar surface. Majority of molar surface as in Fig. 149, where about 10 rows of short, rounded or conical teeth each terminate with somewhat flattened brush-like teeth on upper part of molar surface or short multidentate teeth on lower part of molar surface. No distinct apical tooth present, but 5 – 6 long, hair-like setae occur below apical cluster of short molar teeth. One large brown conical molar tooth occurs set back from middle of first ventral row of molar teeth (Fig. 150). Prostheca composed of row of 9 – 10 finely biserrate setae that gradually increase in length up to base of inner incisor (Fig. 151). Incisors as in Fig. 151. Outer incisor length about 3.0x width, smaller sized teeth of outer edge homonomous from apex to final 5 – 6 teeth of row with remaining teeth becoming thinner and sharper to junction with posterior comb. Outer edge homonomous teeth appear to have small tubercle at base of each tooth giving appearance of secondary row of teeth. Larger sized inner teeth fewer, with nine distinct large teeth and one smaller basal tooth (Fig. 152). Teeth of inner edge lack small basal tubercles. Apical complex of outer incisor composed of two smaller lateral teeth and one larger terminal tooth not fused (Fig. 152). Basal part of outer incisor with comb of about 28 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter length of entire tooth (Fig. 151). Inner incisor scoop-shaped with toothed upper edge (Fig. 151). Leading edge of inner incisor with row of 7 – 8 long, thin setae below large elongate tooth of upper edge. Upper edge with row of about nine large, coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of inner incisor (Fig. 153). Outer edge of mandible below incisors with fringe of many long, hair-like setae, often obscured by detrital debris on mandible (Fig. 147), inner edge below molars without long setae. Labium: Labium as in Fig. 154. Dorsal surface of glossae with long, hair-like setae on inner apical surface and row of similar hair-like setae that extends from apical area to base of glossae (Fig. 155). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and beyond large spine-like setae from ventral surface (Fig. 155). Ventral surface of glossae mostly bare, except for one large subapical seta. Ventral surface of paraglossae with area of large spine-like setae with some large spine-like setae at anterior edge of paraglossae extending about half length of long, hair-like setae from dorsal surface (Fig. 156). Glossae diverging slightly from midline of labium such that inner edges form relatively wide V-shaped gap (Fig. 156), Base of gap between glossae with continuous curving edges (i.e., no distinct corners) and uppermost part of inner edge of each glossa diverging outward more than lower part of each edge making V-shaped gap more pronounced (Fig. 156). Labial palps two-segmented. Apical segment of labial palps with distinct array of pectinate brush setae on ventral surface and apical brush of simple setae. Ventral surface of apical segment with row of long, thin setae with curved tips along outer edge. Dorsal surface of apical segment with array of long curved bifurcate setae.

Thorax. Pronotum: Overall shape somewhat tetragonal with greatest width at middle of lateral margins (Fig. 157). Anterior margin essentially straight, but posterior margin slightly convex on either side of body midline (Fig. 157). Posterior lateral edges appear fused with mesonotum despite pale boundary line between them (Fig. 157). Posterior half of pronotum slightly raised on either side of midline forming pair of low humps (most noticeable on near final instar nymphs). Lateral edges of widest part of pronotum uniform brown similar to majority of pronotum. Anterolateral corners pale with pale areas extending along anterior margin almost to midline of pronotum (Fig. 157). Middle of pronotum brown without distinctive patterning. Lateral areas of pronotum with faint pale inverted U-shaped mark with short slanting pale mark in center of pale U-shaped mark (Fig. 157). Lateral pale pattern of pronotum often appears incomplete or absent on some specimens with well-developed forewingpads. On pronotum of live nymphs some aspects of pattern of pale marks more distinctive. Pronotal patterning seems consistent on female nymphs. Mesonotum: Overall background colour similar to pronotum. Anterior margin shaded slightly dark brown, especially along concave portion following curvature of pronotum (Figs. 158, 159). Small, dark brown spot present where inner edge of forewingpads meet mesonotum and MLs pale with stripe of uniform width (Fig. 158). Outer and inner edges of forewingpads slightly darker brown, as well as portion of MS parallel to body midline and notched medial apex of SL (Fig. 158). Lightly sclerotized areas pale compared to thicker areas of cuticle. Lateral margins of mesonotum from base of forewingpads to outer edges of pronotum slightly curved inward, but not distinctly indented. Metanotum: Mostly pale with brown shading similar to mesonotum along anterior margin. Dark brown occurs lateral to bases of hind wingpads and on flared edge of hind coxae. Pleural Region: Membranous area of pleural region posterior to forecoxae with only faint traces of grey smudge. Membranous areas of pleural region anterior and posterior to meso and metacoxae appear mostly pale.

Abdomen. Tergites: Background colour of all tergites of preserved specimens ranges from cinnamon (close to NCG# 123A) to light yellow-brown (Figs. 159, 160). On live or freshly preserved specimens background colour of tergites is darker brown (close to NCG# 123 Raw Umber), especially on lateral areas. Tergites of male nymphs are slightly darker brown compared to female nymphs (Fig. 159). Nymphs of sanguinea-form have slightly reddish tint to brown background colour of tergites. Surface of tergites above lateral margins slightly darker brown compared to medial dorsal surface of tergites. On some nymphs faint pale median longitudinal stripe present on tergites V – IX, stripe most noticeable on near final instar nymphs. Tergites II – IX with one pair of small, pale submedian spots. On some nymphs second pair of pale spots occurs on anterior margin of tergites II – VII, thus these tergites appear to have two pair of pale submedian spots. On tergite X paired pale submedian streaks replace paired submedian spots as occur on other tergites (Figs. 159, 160). On some specimens paired streaks on tergite X can be diffuse, thus almost appearing absent. Also, on some specimens paired pale submedian spots on tergites VII and VIII can be elongated into dashes oriented parallel to body midline. Lateral margins of tergites II – VIII with somewhat triangular indentations. On tergites II – VII indentations marked with dark brown (Fig. 161), but dark shading absent on tergite VIII. On live or freshly preserved nymphs triangular indentations appear pale, contrasting with darker lateral areas of tergites. Lateral areas of tergites II – VIII usually with small dark brown spot adjacent to base of posterolateral projections. Anterolateral margins of tergites usually uniform brown, but occasionally slightly darker brown dash occurs on tergites II – IV. Lateral areas of tergites IX – X lack dark contrasting colour, as occurs on preceding tergites. Posterolateral corners of tergite IX do not flare outward and short projections do not extend much beyond anterior margin of tergite X. Posterior intersegmental membranes of tergites I – IX lack dark pigmentation. Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 162). Spinules all of similar size and do not alternate across width of row. Microspinules occur among bases of many, but not all spinules. Posterolateral projections short and weakly pointed or blunt on tergites I – VII (Fig. 163a). Tergites VIII and IX have short, blunt, posterolateral projections and tergite X lacks these structures. Small brown sclerous lobe-like area associated with posterior margin of tergites VII – IX occurring between end of row of spinules and posterolateral projection. Small sclerous structure on tergites VII – IX appears to be weakly fused to posterior margins of respective tergites. Small sclerous structures on tergites IX larger than on tergite VIII. Small sclerous structure on tergite VII does not seem to be fused with posterior margin of tergite VII. Sternites: Abdominal sternites medium to light brown, but on sanguinea-form nymphs sternites yellow-brown. Sternites VII – IX usually darker brown compared to other sternites (Fig. 163a). Sternite I with anterior flanges transparent light brown, outer corners of flanges sharply pointed. Sternites II – VII with pair of pale diagonal submedian dashes margined with brown that is slightly darker than background colour (Fig. 163a). Anterior margin of sternite VIII often with pale band that does not extend to edges of sternite, occasionally on sternite IX more restricted version of this pale band occurs along anterior margin (Figs. 163a,b). Further, on sternite IX brown shading restricted to anterior margin often darker and more distinctive than any similar shading that may occur on other sternites. Center of sternite I occasionally with pale medial pattern that can appear as an inverted triangle flanked by pair of small pale spots. Lateral areas of sternites I – VIII with paired longitudinal indentations that extend almost to posterior margin of sternites. Longitudinal indentations usually appear as thin pale lines sometimes margined with brown and flanking paired diagonal dashes, on some specimens dashes slightly darker than background colour, but on others can be slightly lighter than background colour (Fig. 163a,b). Sternite IX on both male and female nymphs with similar brown shading. On red tinted sanguinea-form nymphs abdominal sternites can be quite uniform in colour and longitudinal indentations and medial dashes, although present, are usually indistinct lacking dark brown pigment to highlight edges.

Legs. Forelegs: Overall background colour light brown to light greyish-brown with slightly darker shading on some parts of femora and other leg segments, especially adjacent to joints (Fig. 164). Forefemora length about 2.5x width. Dorsal surface of forefemora medium brown with dark brown shading around pale oval median spot (Fig. 164, 165). In addition to pale oval median spot, separate thin pale streak along base of dorsal fringe of long setae (Fig. 165). Middle of pale oval spot with oval or somewhat teardrop-shaped dark brown median mark, usually entirely within pale oval median spot (Fig. 164, 165). If dark median mark is teardrop-shaped, its apex points toward apex of forefemora. On red tinted sanguinea-form nymphs dark median mark usually absent, usually replaced by longitudinal red streak. Apical portion of forefemora beyond dark brown border of pale oval median spot mostly pale (Fig. 164). Dorsal and ventral edges of forefemora slightly darker brown along rows of marginal setae. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges. Although many long setae of dorsal edge row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edges of variable width and length; some seem similar to elongate flags. Dorsal row of setae of uniform length, except for one or two setae near apex of forefemora (Fig. 165). Row of irregularly spaced short, hair-like setae below middle of dorsal edge row of long marginal setae. Dorsal surface of forefemora with field of short, flattened setae as in Fig. 166. Flattened setae over middle of dorsal surface with distinctive dark brown bases. Flattened setae relatively uniform in shape, almost all with parallel sides without noticeably constricted bases (i.e., not distinctly paddle-shaped) (Fig. 166). Ventral edge of forefemora with relatively few large, spine-like setae or narrow flattened forms similar to those with parallel-sides as noted above. Groove along ventral edge of forefemora pale without dark shading adjacent to joint with foretibiae (foretibiae completely cover this area when folded against forefemora). Foretibiae: Length of foretibiae about 0.97x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint shaded with dark brown (Figs. 164, 165). Foretibiae mostly uniform light brown. Ventral edge of foretibiae with about five widely separated stout setae, some with parallel sides and broad rounded tips and others with tapering sides and pointed tips. Ventral apical edge of tibio-tarsal joint with one large monopectinate seta and one large parallel-sided seta. Dorsal edge of foretibiae with longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae. Lateral to dorsal edge of foretibia sparse longitudinal row of scattered small hair-like setae extending from base to apex of foretibiae. Dorsal longitudinal row of hair-like setae with three large, paddle-shaped setae (Fig. 167). Foretarsi: Length of foretarsi about 0.3x length of foretibiae. Background colour similar to foretibiae and also lacks any distinct pale areas (Fig. 164). On live specimens dark brown shading at base of foretarsi along joints with foretibiae is more distinctive than on preserved specimens. Longitudinal row of hair-like setae on foretibiae continues along dorsal edge of foretarsi with one paddle-shaped seta embedded in row (Fig. 168). In addition, scattered hair-like setae occur along other edges of foretarsi and along apical margin below foreclaws. Foreclaws: Foreclaws as in Fig. 169, with light brown base and dark brown elongate sharp, tip. One basal tooth and three preapical denticles present that gradually become thicker and longer toward claw tip (Fig. 169). Outer apical portion of foreclaws slightly more than one-quarter their total length. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Figs. 164, 170). There is some variation in appearance of pale oval median spot, which is more elongate than on forefemora and dark median mark is also elongated (Fig. 164). On hind femora dark median mark becomes dark streak (Fig. 170) and on some specimens, thin pale streak along dorsal row of long marginal setae may be connected to upper edge of pale oval median spot. On sanguinea-form nymphs mid and hind femora similar to above except dark median mark usually absent or replaced by elongate reddish-brown streak. Short, flattened setae on mid and hind femora often more numerous across lower part of pale oval median spot and surrounding dark brown margin compared to forefemora. Structure and appearance of mid and hind tibiae, tarsi, and tarsal claws generally similar to that of forelegs (Fig. 164), however there are some differences. Large paddle-shaped setae that occur on foretibiae are replaced by 11 large parallel-sided setae with rounded tips (Fig. 171a). Ventral edge of mid and hind tibiae with more large, tapered setae with pointed tips. Ventral apex of mid and hind tibiae with group of large stout setae with sharp tips (Fig. 171b), mid tibiae with 4 – 5 and hind tibiae with 6 – 7 setae respectively. Dorsal apex of mid and hind tibiae with 1 – 2 large parallel-sided setae with rounded tips and scattered hair-like setae. Mid and hind tarsi with one large paddle-shaped seta embedded in lateral longitudinal row of hair-like setae (Fig. 172). Mid and hind claws similar in shape, size, and proportion to those of forelegs, but subapical denticles reduced to two (Fig. 173).

Abdominal Gills. Colour and Position: Gills mostly transparent. All gills (except gill 1) have distinct yellow-brown shading in proximal dorsal half following darkly stained tracheae (Fig. 174). On gill 1 brown shading restricted to straight inner margin anterior to gill base (Fig. 175a). Gill filaments pigmented from base to tips faint greyish-green, on live nymphs, filaments more green (Figs. 174, 175b). Dorsal margins of gills adjacent to base of filaments sclerotized and shaded brown (Fig. 175b). Tracheae darkly stained and gills have consistent pattern of distinct secondary tracheols branching from main tracheae toward dorsal margin as in Figs. 175b. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) of gill 1 does not meet or overlap dorsal margin of gill 1 from opposite side of body (Fig. 163a). Abdominal gills 2 – 6 positioned laterally with anterior half of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Figs. 163a, 174). Gill 1: Abdominal gill 1 as in Fig. 175a, anterior corner where straight inner margin meets dorsal edge rounded, but only slightly protruding. Outer margin with incisions forming ruffled edge. Depth of incisions usually less than width of each division (Fig. 175a) and outer margin has several relatively similar sized ruffles. Ruffles tend to become more irregular along posterior margin. Posterior margin of gill 1 broadly rounded with ruffles extending to inner edge. Plica of dorsal surface as in Fig. 176, appearing as thickened, rounded edge (usually opaque white). Curved edge of plica extends only about halfway to base of ruffled edge and raised slightly above gill surface (Fig. 161, 176). On sanguinea-form nymphs, plica appears as curved red line distinct against lighter red tinted background colour of gill. Inner two-thirds of gill 1 thicker and more opaque than outer ruffled edge. Cluster of filaments at gill base composed of 10 – 12 filaments that appear to originate from one tracheal base without subsequent branching (Fig. 175b). Short, sclerotized rib present adjacent to gill base. Tracheae in posterior portion of gill 1 stained dark and dorsal surface of gill over dark tracheae with field of many short, bristle-like setae (Fig. 175b). Gill 2: Abdominal gill 2 as in Fig. 177. Overall shape of gill 2 broadly oval, posterior margin with shallow incisions forming short, ruffled edge. Width of gill 2 about 0.75x length (width measured from base of dorsal lobe). Dorsal margin of gill 2 with distinct rounded lobe that is about as high as wide and has apical area of short, hair-like setae (Fig. 177). On some specimens tip of dorsal lobe can fold over its base obscuring its full size and shape. Dorsal margin of gill 2 from gill base to edge of dorsal lobe slightly convex. Dorsal and medial areas of gill 2 shaded light brown, darkest along dorsal margin and adjacent to tuft of filaments (Fig. 177). Tracheae stained dark and exhibit distinct branching pattern with larger secondary tracheols extending upwards toward dorsal margin from central tracheae (Fig. 177). Tuft of filaments as in Fig. 177, composed of about 21 filaments that appear to mostly arise from one major tracheal branch at base of gill and lack secondary branching. Filaments extend to or slightly beyond midpoint of gill 2. Lower portion of gill 2 supported by curved transparent sclerotized rib that has faint traces of brown shading (Fig. 177). Base of upper portion of gill 2 supported by short, straight transparent sclerotized rib. Both internal gill supports seem to mostly lack surface setae, but on some specimens short setae occasionally present along ventral rib. Gill 5: Abdominal gill 5 as in Fig. 178, shape somewhat oval with dorsal lobe. Width of gill 5 about 0.60x length (width measured from base of dorsal lobe). Colour of gill 5 and tracheae as in gill 2. Ventral portion of posterior margin of gill 5 lacks ruffles unlike gill 2. Dorsal margin of gill 5 similar to gill 2 including presence of dorsal lobe and dense strip of small, hair-like setae at apex of lobe (Fig. 178). Width of base of dorsal lobe about twice its height and several dark stained tracheols extend into base of lobe. On some specimens tip of dorsal lobe folds over its base obscuring its full size and shape. Lower portion of gill 5 supported by transparent slightly curved sclerotized rib that is straighter than on gill 2 (Fig. 178). Base of upper portion of gill 5 supported by short, sclerotized rib similar in form and colour to that on gill 2. Tuft of filaments at base of gill 5 similar to gill 2. Gill 7: Abdominal gill 7 as in Fig. 179, with dorsal portion folded against sides of tergites VIII and IX and apparently fused to surface of gill near basal sclerotized rib. Gill 7 lacks distinctive dorsal lobe present on gills 2 – 6. Majority of gill 7 lamella extends beneath abdomen as more or less free flattened structure. Apical margin of gill 7 meets, but does not overlap that of opposite gill 7 beneath body. Ventral posterior margin either smoothly rounded or with 2 shallow incisions (Fig. 179). Distinct dark tracheae and brown shading of gills 2 – 6 absent on gill 7. However, on sanguinea-form nymphs gill 7 is stained red. Tuft of filaments at gill base reduced compared to preceding gills, but otherwise similar in colour and structure. Transparent support for lower half of gill 7 seems to merge with medial sclerotized rib. Base of medial sclerotized rib with traces of brown similar to preceding gills. 

Caudal Filaments. Colour and Structure: Median terminal filament slightly longer than cerci and together length of caudal filaments about 1.47x length of abdomen. On preserved specimens, caudal filaments pale cream coloured to light brown. On live nymphs caudal filaments usually pale white to cream coloured. All annuli (except for apical annuli) with row of short spines on posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 27 (counting from base). Fine hair-like setae begin with only 2 – 3 per annulus, but rapidly increase to maximum of 5 – 6 per annulus. Terminal 9 – 10 annuli lack marginal setae, but may have occasional small, spines at margins of annuli.

Diagnosis Rhithrogena impersonata Nymph: Nymphs of R. impersonata can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) medium to large body size of near final instar nymphs (7.40 – 9.50 mm; Mn=7.37 (n=16); Md= 7.50 (n=16)), the largest specimens observed were two final instar nymphs (male and female) from New York, if these specimens are excluded (perhaps outliers) the maximum body length recorded was 8.70 mm, thus mean and median body size values are believed to be of greater diagnostic value across the range of this species, (2) femora medium brown with pale oval median spot and dark oval or teardrop-shaped median mark that does not extend to or beyond the upper and lower edges of pale oval median spot (Figs. 164, 165), on sanguinea-form nymphs dark median mark usually absent or replaced by red tinted streak, mid and hind femora similar in most respects to forefemora with some differences in elongation of both pale and dark markings, (3) abdominal gill 1 shaped as in Fig. 175a, plica broadly rounded (Fig. 176) and slightly raised above dorsal surface of gill with edge not reaching the base of ruffled edge, on sanguinea-form nymphs, plica is tinted red, (4) tracheae of posterior portion of gill 1 stained dark and dorsal surface above dark tracheae with field of short, bristle-like setae, (5) abdominal gills 2 – 6 with a dorsal lobe that is about as high as long (most distinctive on anterior gills) with apical strip of short hair-like setae (Figs. 174, 177), (6) dorsal half of gills shaded yellow-brown with colour darkest along dorsal margin, (7) tracheae of gills 2 – 6 stained dark and exhibit distinctive branching pattern with larger secondary tracheols branching upward towards dorsal margin from central tracheae (Fig. 177), (8) abdominal gills 2 – 6 with the lower part supported by moderately curved (i.e., intermediate between full crescent and straight shape) transparent, sclerous rib (Fig. 177, 178), (9) abdominal gill 7 basic shape an elongated oval with dorsal edge only slightly folded against and tergites VIII and IX and apparently fused with surface of gill near short basal sclerous rib, (10) abdominal gill 7 without dorsal lobe, as occurs on gills 2 – 6, (11) crown of maxillae with nine large pectinate setae and what appears to be a 10th vestigial seta at inner end of row of large pectinate setae, (12) apical segment of maxillary palp with distinct brown vertical band (Fig. 137), (13) glossae of labium distinctly diverging from midline of labium forming a V-shaped gap (Figs. 155, 156) with the upper inner edge of each glossa angled outward making the top of the V-shaped gap seem wider relative to its base,  (14) lingua of hypopharynx rectangular with straight sides that are only slightly convex near base, (15) outer incisor of right mandible length about 3.0x width and with eight distinct teeth on inner edge, apical three teeth below apical complex each with small tubercle near base, (16) outer edge of both mandibles with fringe of several long, hair-like setae that extend half of the length of the outer edge, and (17) pronotum tetragonal in shape. See Appendix 3 for comparative list of R. impersonata diagnostic characters and those of other northeast species.

Taxonomic Discussion. The taxonomy of R. impersonata has been discussed more by previous authors than for any other species of the northeastern Rhithrogena. Following the original description of R. impersonata by McDunnough (1925) various comments and taxonomic details of the male imago were presented by McDunnough (1926) and Traver (1933b). Later Traver (1935) redescribed the male imago and further commented on differences in the male genitalia with regards to remarks made earlier by McDunnough (1925, 1926). Ide (1954) provided a detailed comparative analysis of the nymph of R. impersonata and that of a new species (R. sanguinea). Leonard and Leonard (1962) briefly redescribed the male imago and nymphs of R. impersonata and R. sanguinea based on specimens from Michigan and provided a full habitus figure of the sanguinea-form nymph. Flowers and Hilsenhoff (1975) studied R. impersonata in Wisconsin and provided a key to nymphs of Rhithrogena that included R. impersonata with new figures of the femora and abdominal gill 3. They also comparatively discussed the taxonomic status of R. impersonata and R. sanguinea, concluding that R. sanguinea was a new subjective junior synonym of R. impersonata. Based on observations made as part of this study, it can be said that throughout the northeast there are no known populations of R. impersonata that lack sanguinea-form individuals. 

Distribution. Rhithrogena impersonata was originally described by McDunnough (1925) in the genus Heptagenia based on male imagos collected in the vicinity of Montreal, Quebec, Canada. The species was later transferred to Rhithrogena by McDunnough (1926). Rhithrogena impersonata is principally northeastern in its distribution (Fig. 335) with the majority of records extending from the Canadian Maritime Provinces in the east across southern Quebec and Ontario (Randolph and McCafferty 1998), south to northern New England and New York, USA (Burian and Gibbs 1991, Chandler et al. 2006, Myers et al. 2008, Myers et al. 2011) and finally reaching its western extent in northern Michigan and Wisconsin (Flowers and Hilsenhoff 1975, Randolph and McCafferty 1998, and Klubertanz 2016). There are also a few rare (possibly disjunct) occurrences in both Kentucky (McCafferty et al. 2010) and eastern Oklahoma (McCafferty et al. 1997). Ide (1954) presents a plausible hypothesis for these rare occurrences with regards to glacial rivers that existed at the time the Laurentide ice sheet was retreating. The northeastern distribution of R. impersonata is given in Appendix 2.

Life History and Ecology. Rhithrogena impersonata is almost always associated with clean, 1st – 3rd order streams with perennially cool water temperatures, small to medium cobble substrates (without extensive moss or attached filamentous algae), and swift currents (~0.5 m/s). In Maine R. impersonata was only found in such streams at higher elevations on the Moosehead Plateau in the western part of the state (Burian and Gibbs 1991). In New Hampshire it was likewise only found in similar habitats in the mountainous northern tier of the state (Chandler et al. 2006). Ide (1954) describes the stream habitat in southern Ontario where R. impersonata occurs with regards to local geology and recent geological history involving glaciation. Water quality measurements were recorded in Maine at sites F6 and F8 on the South Branch of the Carrabassett River (SBrCR) where nymphs were collected. Data recorded on 21 May 1986 (F6) and 12 July 1986 (F8) is as follows: Water Temperature = 11.0 °C (F6), 17.0 °C (F8); pH = 7.15 (F6), 7.20 (F8); and Specific Conductance = 32.50 µS (F6), 50.0 µS (F8). The water depth at the sampling points ranged from 0.34 m (F6) – 0.18 m (F8); current velocity at 0.6x depth 0.62 m/s (F6), 0.35 m/s (F8). Substrate at these sites was predominantly small cobble (64.0 – 128.0 mm) and various sized gravel with lesser amounts of medium cobble (128.0 – 256.0 mm), large cobble (256.0 – 512.0 mm), and scattered boulders. Dissolved oxygen was not measured, but prevailing conditions (land use within 1 km of site was mostly undisturbed mixed deciduous and coniferous forest) indicated it likely was at or close to equilibrium value of about 10.0 ppm pursuant to water temperature and site elevation, which ranged from 273 m (F6) – 228 m (F8). 

Rhithrogena impersonata is univoltine throughout its range, but the time to completion of development seems to be variably associated with differences in water temperature. This is evident from emergence dates from some higher elevation and colder streams compared to what occurs throughout most of its range. For example, in Maine most populations seem to be able to complete development and emerge by the second week of June (at elevations <300m), but at one site near Baxter State Park at an elevation of about 417 m adults were collected the first week of July. The latest record of an adult was obtained on 21 August 2020 from a river in the perennially cold central Gaspé Peninsula of Quebec at an elevation of about 318 m. The nature and extent of these apparent phenological differences has not been studied, but understanding the range of developmental responses of R. impersonata may be important in predicting how this species might respond to habitat changes related to climate change throughout its range.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Material Studied. Canada: New Brunswick: Northumberland Co., Catamaran Brook (emergence trap) upstr. of road, Middle-reach sampling area [46.856842°/-066.189625°], elev. 156 m, M. Dobrin, 5 July 1994, 1♂ [NEL]; Quebec: La Haute-Gaspésie [Mt. Albert]: St. Anne River, dnstr. of bridge on dirt road just off Rt. 229 nr 90 km marker N of Mt. Lyall, collected resting on rock [48.8701°/-066.0998°], elev. 318 m, J. Moisan – De Serres, 21 Aug 2020, 1♂ [NEL]; USA: Maine: Franklin Co., Carrabassett R. (SBrCR) at Appalachian Trail crossing [45.038459°/-070.342896°], elev. 658 m, S.K. Burian, 20 Oct 1984, 1N♂, 3N♀ [NEL]; same, small stream (trib. to Carrabassett R. (SBrCR)) nr. E-mountain Rd., site F19, Sugarloaf Ski Area [45.066635°/-070.311649°], elev. 531 m, S.K. Burian, 17 June 1985, 1♂ [NEL]; same, Carrabassett R. (SBrCR) at outlet of Caribou Pond [45.009552°/-070.356041°], elev. 834 m, S.K. Burian, 11 June 1985, 1♂ [NEL]; same, Carrabassett R. (SBrCR) at pump-house, site F21, Sugarloaf Ski Area [45.063326°/-070.338534°], elev. 492 m, S.K. Burian, 23 May 1985, 1N♂, 3N♀ [NEL]; same, 17 June 1985, 1♂ [NEL]; same, Carrabassett R. (SBrCR) nr. entrance to Sugarloaf Ski Area, Rt. 16, site F20 [45.0801044°/-070.313262°], elev. 390 m, S.K. Burian, 27 June 1985, 1N♀ [NEL]; same, un-named trib. to Carrabassett R. (SBrCR) nr. entrance to Sugarloaf Ski Area, site F18 [45.081085°/-070.319434°], elev. 399 m, S.K. Burian, 15 June 1985, 4N♀ [NEL]; same, Carrabassett R. (SBrCR) behind Fenderson’s camp, site F6 [45.091297°/-070.223354°], elev. 273 m, S.K. Burian, 21 May 1986, 1N♀ [NEL]; same, Carrabassett R. (SBrCR) , pool/run habitat behind rest area off Rt. 16, site F7 [45.047140°/-070.194812°], elev.229 m, S.K. Burian, 20 June 1986, 1♂ [NEL]; Piscataquis Co., Nesowadnehunk River below outlet of Nesowadnehunk Lake, Baxter State Park [46.019392°/-069.069846°, elev. 417 m], T. Mingo, 7 July 1979, 1♂ [NEL]; same, Nash Stream, Coplin Plantation, ~ 200 m east of Rt. 16 [45.106719°/-070.477981°, elev. 390 m], M. Siebenmann, 7 June 2008, 1N♂ [NEL]; New Hampshire: Coos Co., Mill Brook, 0.5 km S of Stark, nr. Hwy. 110 [44.596329°/-071.409412°, elev. 305 m], E. Wolff, J. Lemire, & D. Chandler, 13 June 2006, 1N♀ [NEL]; New York: Franklin Co., North Branch Saranac R., 20 m upstr. of bridge on Thatcherville Rd. off CR. 26 [44.539700°/-074.051656°], elev. 460 m, S.K. Burian, 25 May 2017, 1♂(+Nex), 1S♂(+Nex), 1♀(+Nex), 1♂, 1N♂, 3N♀ [NEL]; same, 90 m upstr. of metal grate bridge on Thatcherville Rd., off CR. 26 [44.54015°/-074.05208°], elev. 465 m, S.K. Burian, 27 May 2020, 2S♂(+Nex), 1S♀(+Nex), 1N♂, 3N♀ [NEL]; same, 28 May 2020, 1♀(+Nex), 2S♀(+Nex) [NEL].

Rhithrogena jejuna Eaton, 1885: 252 s.s.

Figs. 180 – 227

Baetis fusca Walker, 1853 (Homonym of Baetis fusca Burmeister, 1839: 800)

Heptagenia fusca (Walker, 1853) (Homonym new combination, Eaton 1871: 138)

Rhithrogena fusca (Walker, 1853) (Homonym new combination, renamed and placed in genus Rhithrogena, Eaton 1885: 252 original description)

Epeorus undulatus Banks 1924: 425 (original description)

Heptagenia undulata (Banks, 1924) (recombined by McDunnough 1925: 191)

Rhithrogena undulata (Banks, 1924) (recombined by McDunnough 1926: 195); Traver 1935: 383; Spieth 1940: 334; Flowers and Hilsenhoff 1975: 212; Dance 1979: 71; Larson and Colbo 1983: 620; Klubertanz 2016: 218. NEW SYNONYM

Nymph (in alcohol with well-developed or dark wingpads). Body length: 6.20 – 10.40 mm (Mn = 8.00±1.42 SD; Md = 7.77; n=12). Description based on male nymph except where noted. Most recent specimens available for study were collected from Maine in 1986, hence nymphs preserved in ethanol have undergone variable levels of fading regarding colour and colour patterns. Descriptions of colour given here should be used cautiously because live or freshly preserved material could differ in some aspects of these characters. 

Head. Colour Pattern: Overall background colour medium brown, slightly darker posterior to antennal sockets and between compound eyes (colour close to NCG# 39 – Cinnamon) (Fig. 180). Pale narrow line between lateral ocelli and along anterior margins of compound eyes (Figs. 181 a,b). Pale narrow line does not widen where it contacts lateral margin of head capsule. Anterior half of head capsule uniformly shaded brown lacking distinct pale markings (Figs. 181 a,b). Diffuse dark brown spots next to pale areas over lateral ocelli. Vertex of head capsule entirely brown except for pale ecdysial suture and two small slightly darker brown spots on opposite sides of ecdysial suture. Shape: Head capsule broadly oval, but some female nymphs may be slightly less so with lateral margins angled more to produce a sub-trapezoidal shape in later instars (Fig. 181a). Width of head capsule about 1.7x length. Anterior margin with slight median emargination where labrum articulates with head capsule. Curvature of anterior margin of head capsule can obscure median emargination making it appear absent when viewed from dorsal perspective. Also anterior margin appears to vary from straight to slightly curved across area of labrum when viewed from dorsal perspective (Figs. 181 a,b). Mouthparts usually completely concealed beneath outer edges of head capsule, only on last instar nymphs can edges of maxillary palps protrude beyond lateral margins. Posterior margin of head capsule seems to vary between male and female nymphs. On male nymphs posterior margin of head capsule is slightly to moderately concave, but on female nymphs it is essentially straight. Differences in shape of posterior margin of head capsule appear greatest on last instar nymphs. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped, when viewed dorsally. Outer margins of compound eyes reach, but do not extend beyond, outer margins of head capsule (Fig. 182). Anterior and posterior margins of compound eyes converge toward midline of head transitioning to broadly rounded inner corner. Compound eyes of male separated by gap slightly greater than width of one lateral ocellus. Female nymphs’ compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Fig. 181a) and gap between eyes more than 2x as wide as on male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Fig. 181a. Pale spots present over all ocelli, with spots over lateral ocelli slightly larger than over median ocellus. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle (Fig. 181a). Antennae: Basal membrane of antennal socket pale and edge of socket slightly darker brown than surrounding cuticle (Figs. 181a,b). Scape and pedicel brown, slightly darker than rest of head capsule, but distinctly darker than pigmented portion of flagellum. Proximal 12 – 13 annuli of flagellum light brown. Apical 12 – 14 annuli of flagellum pale grey to cream coloured. Antennae length about 1.3x midline length of head capsule.

Mouthparts. Labrum: Labrum somewhat sub-trapezoidal shaped with outer edges straight to slightly convex merging with rounded posterior corners (Fig. 183). Anterior margin of labrum with slight median emargination. Group of 4 – 5 small rigid spines occur on either side of ventral edge of median emargination (Fig. 184) and only tips of small rigid spines usually visible from dorsal perspective. Posterior half of dorsal surface of labrum with field of long, hair-like setae with bases widely separated. Middle and anterior portion of dorsal surface with few, relatively long hair-like setae, but one pair of long, slightly thicker setae occur near center of median emargination (Fig. 183). Group of 2 – 3 setae similar in form to medial pair occur near each lateral margin. Ventral lateral margins of labrum with many (>20) long, setae in 3 – 4 irregularly spaced rows with setae decreasing in length and becoming less dense near small rigid spines of anterior median emargination (Fig. 185). Rows of ventral edge setae stop just beyond halfway point of lateral margins. Ventral lateral edges of labrum with 5 – 6 small, spine-like setae in gaps between long marginal setae and small rigid spines at edges of median. Maxillae: Left maxillae as in Fig. 186. Galea-lacinia with eight pectinate crown setae, with what appears to be maximum of 12 – 13 teeth on largest crown setae (Fig. 187). No vestigial crown setae present. Apical crown seta appears to have about four large teeth, which are much thicker than those on mid-row crown setae. Submedial row of about 35 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 186). Near apex of submedial row one long, biserrate seta occurs set back from main row of long setae. Often at base of main submedial row of setae are small groups of 2 – 3 shorter setae that are not aligned with submedial row. Inner edge of galea-lacinia with dense double row of long, simple setae, setae of ventral row only about one-third to one-half length of setae of dorsal row (Fig. 186). In addition, at base of double row of inner edge setae is basal row of 9 – 10 long, simple setae with tips extending well beyond those of main portion of inner edge row (Fig. 186). Maxillary palp as in Fig. 188, appearing two-segmented. Inner edge of apical segment of maxillary palp near tip straight with row of about 16 short, somewhat curved setae with pointed tips (Fig. 188). Apical segment of maxillary palp with distinctive longitudinal sclerotized band and diffuse broad light brown vertical band near tip (Fig. 188). Most of ventral surface of apical segment of maxillary palp covered with short monopectinate setae (Fig. 189) with 3 – 4 sharp teeth across basal and middle portions of the array of setae, increasing to 7 – 8 teeth at apex of segment. Teeth of setae at apex of segment longer and thinner than those of other areas. Outermost edge of apical segment of maxillary palp with 5 – 6 rows of large, simple setae with downward curved tips (Fig. 189). Dorsal surface of apical segment with scattered long, hair-like setae. Hypopharynx: Lingua mostly rectangular, but sides can vary from straight to slightly convex near midpoint of edge (Fig. 190). Apical margin varies from straight to slightly arched with field of short setae uniformly distributed across surface. Superlinguae as in Fig. 191 with outer edges not greatly expanded and nearly straight. Bases of superlinguae gradually tapering to base of hypopharynx. Apical margin of superlinguae smoothly rounded to inner margin and with long, hair-like setae (Fig. 191). Mandibles. Right mandible (Fig. 192a, ventral view): Anterior margin between molars and prostheca straight with continuous row of short, hair-like setae along entire edge (Fig. 193). Tuft of sharp bristles at innermost edge of molar surface. Molars composed of rows of teeth that vary from sharp, conical forms at ventral edge of molar surface to rounded, knob-like forms along dorsal edge (Fig. 194a). Molar surface terminates with one outwardly pointing tooth (Fig. 194b). Adjacent to apex of molars are 9 – 10 long, simple setae that are thicker than typical hair-like setae. Prostheca composed of one row of about eight long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 193). Incisors as in Figs. 195a,b. Outer incisor length about 2.1x width, smaller sized teeth on outer edge homonomous from apex to base where basal teeth become thinner and sharper. Larger sized inner teeth fewer, with seven distinct teeth up to apical complex (Fig. 196). Apical complex of outer incisor composed of only two teeth, one each from outer and inner rows. Basal part of outer incisor with comb of 27 – 28 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter to one-third length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 195b). Leading edge of inner incisor with 10 – 11 long setae in row below large tridentate apical tooth. Upper edge of inner incisor with row of about nine large coarse (occasionally jagged) teeth that gradually merge into trailing edge row of fine comb-like teeth (Fig. 195b). Outer edge of mandible below incisors with fringe of many long, hair-like setae (Fig. 192b), which can be obscured by detrital debris on mandible. Inner edge of mandible below molars without fringe of long setae, occasionally one hair-like seta occurs on edge well below molar surface. Left Mandible (Fig. 197a, ventral view): Anterior margin between molars and base of prostheca essentially straight with row of short, hair-like setae beginning near middle of margin and extending to prostheca (Fig. 198). Occasionally, three long, hair-like setae occur near end of row of short setae before prostheca. Anterior margin adjacent to molars without setae. Upper edge of molar surface with multidentate first tooth (can appear as tuft) that transitions to clearly defined individual multidentate teeth of upper molar surface (Fig. 199a). Majority of molar surface as in Fig. 199b, where rows of short, rounded teeth transition to ridges ending with flattened brush-like teeth. No distinct apical tooth present, but 4 – 5 long, hair-like setae occur below apical cluster of molar teeth. First ventral row of molar teeth with one large brown conical molar tooth set back from middle of row (Fig. 200). Prostheca composed of row of about 11 finely biserrate setae that gradually increase in length up to base of inner incisor (Fig. 201). Incisors as in Fig. 202. Outer incisor length about 2.3x width, smaller sized teeth of outer edge homonomous from apex to last 5 – 6 teeth of row with remaining teeth becoming thinner and sharper to junction with posterior comb. Larger sized inner teeth fewer, with seven distinct teeth and one small basal tooth. Apical complex of outer incisor composed of only two teeth, one each from outer and inner rows that are fused to produce bifid structure (Fig. 202). Basal part of outer incisor with comb of 26 – 28 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter to one-third length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 203). Leading edge of inner incisor with row of 7 – 8 long, thin setae below large elongate tooth of upper edge. Upper edge of inner incisor with row of about nine large coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of inner incisor (Fig. 203). Labium: Labium as in Fig. 204. Dorsal surface of glossae with long, hair-like setae on inner apical surface and band of similar hair-like setae that extends from apical area to base of glossae (Fig. 205). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and beyond large spine-like setae from ventral surface (Fig. 205). Ventral surface of glossae mostly bare, except for one large subapical seta. Ventral surface of paraglossae with area of large spine-like setae with some large spines at anterior edge of paraglossae extending about half length of long, hair-like setae from dorsal surface. Glossae diverging slightly from midline of labium such that inner edges form relatively narrow U-shaped gap (Fig. 204, 205), distance across base of gap (corner to corner distance) between glossae about 0.3x width of top of gap with top distance measured across tips of glossae. Labial palps two-segmented. Ventral surface of apical segment of labial palp with distinct array of pectinate brush setae that extend to tip of segment and with small cluster of simple setae below tip. Outer edge of ventral surface of apical segment with row of long, thin setae with curved tips. Dorsal surface of apical segment with array of long curved bifurcate setae.

Thorax. Pronotum: Overall shape somewhat tetragonal with greatest width near middle of lateral margins, but lateral margins smoothly curved (Fig. 206a). Anterior margin mostly straight, but posterior margin convex on either side of body midline. Posterior lateral edges appear fused with mesonotum despite pale boundary line between them. Posterior half of pronotum slightly raised on either side of midline forming pair of low humps. Lateral edges of widest part of pronotum brown, similar to majority of pronotum (Figs. 206a, 207). Anterolateral corners pale and each connected to pale longitudinal band that extends from anterior to posterior margin. Lateral areas of pronotum with faint diagonal pale spot within which is an elongate, dark brown spot (Fig. 206b). Middle of pronotum brown without distinctive patterning. Anterior margin with narrow transverse pale area on either side of pale median stripe (Figs. 206a, 207). Small dark brown spots occur at outer edges of pale transverse areas. On extensively faded specimens most patterning is obscured and only pale edge of developing subimaginal pronotum is visible through nymphal cuticle. From available specimens pronotal patterning seems consistent on both male and female nymphs. Mesonotum: Overall background colour similar to pronotum (Fig. 207). Anterior margin slightly darker brown compared to most other parts of mesonotum and concave following opposite curvature of pronotum. Small, dark brown spot posterior to base of each forewingpad and MLs with distinctive pale stripe (Fig. 206b). Outer and inner edges of forewingpads slightly darker brown, as well as portion of MS parallel to body midline and notched apex of SL (Fig. 206b). Lightly sclerotized areas pale compared to thicker areas of cuticle. Lateral margins of mesonotum from bases of forewingpads to outer edge of pronotum smoothly curved inward, but not distinctly indented. Metanotum: Mostly pale with some brown shading as base of hind wingpads and along anterior margin. Dark brown occurs on some specimens above bases of hind coxae. Pleural Region: Membranous areas of pleural region above pleural sclerites of all coxae shaded with dark brown (almost black on some specimens) smudge. Coxal sclerite of all legs with outer edge shaded with brown. Meso- and metacoxal sclerites enlarged and flared upward compared to forecoxal sclerites.

Abdomen. Tergites: Background colour of all tergites of preserved specimens from Maine ranged from brown (close to Raw Umber NCG# 123) to light Cinnamon brown (NCG# 123A) (Figs. 208a,b). Older preserved specimens from Wisconsin were light yellow-brown (Fig. 207). Male and female nymphs seem similar in base background colour of tergites. Overall tergites seem to have uniform colour without median spots or stripes. Sides of tergites above lateral margins slightly deeper shade of brown or yellow-brown. Lateral margins of tergites II – VIII with somewhat triangular indentations marked with dark brown on tergites II – VII, but dark outline shading absent on tergite VIII. Lateral areas of tergites II – VIII usually with small faint brown spot between triangular indentations and base of posterolateral projections. Anterior margin of tergites uniformly shaded brown. Lateral areas of tergites IX – X lack dark contrasting colour, as occurs on preceding tergites. Posterolateral corners of tergite IX do not flare outward and short posterolateral projections do not extend much beyond anterior margin of tergite X. Posterior intersegmental membranes of tergites I – IX lack dark pigmentation. Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 209). Spinules all of similar size and do not alternate across width of row. Microspinules occasionally occur among bases of larger spinules, originating slightly before major row and continue to occur to outer edges of spinule fringe. Posterolateral projections short and weakly pointed or blunt on tergites I – VII (Fig. 210). Tergites VIII and IX have extremely short, blunt, posterolateral projections and tergite X lacks these structures. Small brown sclerous lobe-like area associated with posterior margin of tergites VII – IX between end of row of spinules and posterolateral projections. Small sclerous structure on tergites VII – IX appears to be weakly fused to posterior margins of respective tergites. Small sclerous structures on tergites VIII – IX similar in size, but larger than on tergite VII. Small sclerous structure on tergite VII does not seem to be fused with posterior margin of tergite VII. Sternites: Abdominal sternites light brown to cream coloured with sternites VII – IX usually darker brown (intensity of brown shading gradually increases from VII to IX) (Figs. 210, 211). Sternite I with transparent anterior flanges light yellow-brown and sharply pointed corners on male nymphs, but more rounded corners on female nymphs. Sternites II – VIII with pair of pale, diagonal submedian dashes margined with brown near anterior margin of sternites (Figs. 210, 211). Brown shading around diagonal dashes fades almost completely on older ethanol preserved specimens leaving only traces of pale dashes. Sternites II – IX with anterior transverse brown bands interrupted medially where anterior edges of brown diagonal dashes merge with brown bands (Figs. 210, 211). Lateral margins of sternites VII – IX with more pronounced longitudinal brown marks. Anterior lateral corners of sternite IX with small group of pale spots. Pale spot also occurs at each posterior lateral corner of sternite IX, adjacent to base of forceps on male nymphs and at corners of genital plate on female nymphs. 

Legs. Forelegs: Overall background colour light brown with darker shading on some parts of femora and other leg segments, especially adjacent to joints (Figs. 212a,b). Forefemora length about 2.6x width. Dorsal surface of forefemora light brown with dark brown shading around pale oval median spot (Figs. 212a,b). Forefemora with pale oval median spot and somewhat teardrop-shaped dark brown median mark entirely within pale oval median spot (Figs. 212a,b). If dark median mark is teardrop-shaped its apex points toward apex of forefemora. Dorsal and ventral edges of forefemora slightly darker brown along rows of marginal setae. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges. Although many long setae of dorsal edge row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edges of variable width and length; some seem similar to elongate flags (Fig.213). Dorsal edge row of setae of uniform length except for 4 – 5 adjacent to apex of forefemora. Row of irregularly spaced short, hair-like setae below middle of dorsal edge row of long marginal setae. Dorsal surface of forefemora with field of short, flattened setae as in Figs. 212a, 213. Flattened setae over middle of dorsal surface with distinctive dark brown bases. Flattened setae with uniform shape, almost all with slightly curved sides and slight constriction near base giving producing slight paddle-shape (Fig. 213). Some flattened setae near ventral edge of field of setae more distinctly parallel-sided. Ventral edge of forefemora with relatively few large, spine-like setae or narrow flattened forms similar to those of dorsal surface with parallel-sides. Groove along ventral edge of forefemora pale with only faint light brown shading adjacent to joint with foretibiae (foretibiae completely cover this area when folded against forefemora). Foretibiae: Length of foretibiae about 1.0x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint shaded with dark brown (Fig. 212a). Foretibiae uniform light brown without apical or basal pale areas. Ventral edge of foretibiae with about five widely separated short, setae appearing to be somewhat flattened with tapered sides and narrowed tips. Edge of tibio-tarsal joint with one large monopectinate seta and 2 – 3 large parallel-sided setae set back from edge of joint. Dorsal edge of foretibiae with dense longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae. Lateral to dorsal edge of foretibia sparse longitudinal row of scattered small hair-like setae extending from base to apex of foretibiae. Nine large, paddle-shaped setae occur within dorsal longitudinal row of hair-like setae (Fig. 215 as in Fig. 171a). Foretarsi: Length of foretarsi about 0.4x length of foretibiae. Background colour similar to foretibiae and also lacks distinct pale areas. Longitudinal row of hair-like setae on foretibiae continues along dorsal edge of foretarsi with four paddle-shaped setae embedded in row (Fig. 216). Scattered hair-like setae occur along other parts of foretarsi and along apical margins below foreclaws. Foreclaws: Foreclaws as in Fig. 217, with pale base and elongate sharp, brown tip. Foreclaw with one basal tooth and three preapical denticles that gradually become thicker and longer toward claw tip (Fig. 217). Outer apical portion of foreclaws slightly more than one-third their total length. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Fig. 212b). Pale median spot on mid and hind femora more elongate than on forefemora (Fig. 218) and dark median mark becomes an elongated oval on mid femora, but variability on hind femora ranges from one dark streak to two narrowly connected dark oval marks. Dorsal edge of mid and hind femora uniform brown lacking pale streak as on forefemora, but diffuse pale spot does occur adjacent to joint with tibiae. Mid and hind femora with short, flattened setae (Fig. 219) more numerous across lower part of pale median spot and surrounding dark brown border compared to forefemora. Structure and appearance of mid and hind tibiae, tarsi, and claws generally similar to that of forelegs, however there are some differences. Hind tibiae have 16 large parallel-sided setae embedded in dorsal longitudinal row of hair-like setae. Ventral edge of mid and hind tibiae with more flattened setae with tapered sides (some appear spine-like) than on forelegs. Dorsal apex of mid and hind tibiae with 1 – 2 large parallel-sided setae with rounded tips and scattered hair-like setae. In addition, one large, curved seta usually occurs adjacent to large parallel-sided setae at apex of mid and hind tibiae (Fig. 220). Mid and hind tarsi with two paddle-shaped setae embedded in lateral longitudinal row of hair-like setae. Mid and hind claws similar in shape, size, and dentition to those of forelegs (Fig. 221).

Abdominal Gills. Colour and Position: Gills mostly transparent, but with some yellow-brown shading near gill bases and along base of dorsal margins, except for gill 1. On gill 1 brown shading restricted to straight inner margin anterior to gill base (Fig. 222). Gill filaments similar in colour to gill, but bases of some filaments with traces of greyish-green pigment. Tracheae transparent on all specimens available for study with only faint traces of dark pigment and all gills have consistent pattern of distinct secondary tracheols branching from main tracheae toward dorsal margin of gills. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) meets, but does not overlap edge of gill 1 from opposite side of body (Fig. 210). Abdominal gills 2 – 6 positioned laterally with anterior one-third to one-half of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Figs. 210, 213). Gill 1: Abdominal gill 1 as in Fig. 222, anterior corner where straight inner margin meets dorsal edge rounded, but only slightly protruding. Outer margin with incisions forming ruffled edge. Depth of incisions variable, but usually less than width of each division (Fig. 222). In addition, what appears to be variable arrangement of wide and narrow ruffles occurs on some specimens. Ruffles tend to become more regular posteriorly. Posterior margin broadly rounded with ruffles extending to straight inner edge. Plica of dorsal surface as in Fig. 224a, broadly rounded and semicircular extending from near gill base to about halfway to base of ruffled edge and raised slightly above gill surface. Plica most visible as white curved line when viewed ventrally through gill or laterally directly below hind trochanter (Fig. 224b). Inner two-thirds of gill 1 slightly opaque compared to outer ruffled edge. Cluster of 10 – 11 filaments at gill base that appear to originate from one tracheal branch. Short sclerotized support present adjacent to base of gill 1. Tracheae of gill 1 transparent on preserved specimens. Gill 2: Abdominal gill 2 as in Fig. 225. Overall shape of gill 2 broadly oval, posterior margin usually with one shallow incision, but no ruffle edge as on gill 1. Width of gill 2 (measured from base of dorsal lobe) about 0.75x length. Dorsal and medial areas of gill 2 shaded light brown, darkest along dorsal margin and adjacent to tuft of filaments (Fig. 225). Tracheae mostly transparent except for trace of dark pigment near gill base. Tracheols exhibit distinctive branching pattern with larger secondary tracheols extending upwards toward dorsal margin from central tracheae (Fig. 225). Dorsal margin of gill 2 with distinctive thumb-shaped lobe with short, hair-like setae along entire edge of lobe. Length of thumb-shaped lobe about 1.9x width (Fig. 225). Thumb-shaped lobe usually erect, but on some specimens, lobe top folds over obscuring its full size and shape [Note: on specimens where gills seem to have been lost and subsequently regenerated replacement gills seem to lack dorsal lobe and most of basal tuft of filaments]. Sclerotized edge of dorsal margin of gill 2 straight to base of dorsal thumb-shaped lobe. Tuft of filaments as in Fig. 225, composed of 10 – 12 filaments that appear to arise from one major tracheal branch at base of gill base and lack secondary branching. Filaments extend to or slightly beyond midpoint of gill 2. Lower portion of gill 2 supported by curved transparent sclerotized rib that has faint traces of brown shading (Fig. 225). Base of upper portion of gill 2 supported by short, straight transparent sclerotized rib. Both internal gill supports seem to lack surface setae. Gill 4: Abdominal gill 4 as in Fig. 226, shape mostly oval, but straight ventral margin and tapering sides near gill base can make some gills appear almost tear-drop shaped. Width of gill 4 (measured from base of dorsal lobe) about 0.6x length. Colour of gill 4 and gill tracheae as in gill 2. Posterior margin of gill 4 with one shallow incision as on gill 2. Dorsal margin of gill 4 with distinctive thumb-shaped lobe as on gill 2, but apex of lobe with only few short, hair-like setae. Length of thumb-shaped lobe about 1.6x width (because lobe has broad tip, narrow middle, and wider base measurements of overall lobe length:width ratio determined by average of values obtained by measuring widths all three positions). Thumb-shaped lobe usually erect, but can be folded over as described for gill 2. Dorsal margin of gill 4 straight to base of thumb-shaped lobe. Lower portion of gill 4 supported by shallow curved transparent sclerotized rib (Fig. 226) that is not as deeply curved as occurs on gill 2. Base of gill 4 with short, sclerotized rib with traces of brown shading. Tuft of filaments at base of gill 4 similar to gill 2. Gill 7: Abdominal gill 7 as in Fig. 227, with dorsal portion folded against sides of tergites VIII and IX and apparently fused to surface of gill near basal sclerotized rib. Gill 7 lacks distinctive dorsal thumb-shaped lobe present on gills 2 – 6 and only apical area and inner third of gill 7 extends beneath body with remainder extending laterally and overlapping margin of gill 6 (Fig. 210). Beneath abdomen apex of gill 7 meets or overlaps that of opposite gill 7 (Fig. 210). Ventral posterior margin of gill 7 either smooth or occasionally scalloped along outer edge (Fig. 227). Tuft of filaments at base of gill 7 reduced compared to preceding gills, but otherwise similar in colour and structure. Transparent support for lower half of gill 7 seems to merge with basal sclerotized rib. Short basal sclerotized rib with traces of brown similar to preceding gills.

Caudal Filaments. Colour and Structure: Median terminal filament broken on all specimens available for study, however on specimens with more than three-quarters of this filament intact diameter of filament at point of break was about equal to intact cerci at this point. Hence it is presumed to be about equal to cerci in length and thus subequal caudal filaments. On preserved specimens, caudal filaments uniform pale cream coloured with edges of annuli slightly darker brown. All annuli (except for apical annuli) with row of short spines on posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 29 (as counted from base). Fine hair-like setae begin with 1 – 2 per annulus, but rapidly increase to maximum of 4 – 5 per annulus. Terminal 10 annuli of cerci lack marginal setae.

Diagnosis Rhithrogena jejuna Eaton s.s. Nymph: Nymphs of R. jejuna can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) medium to large body size of near final instar nymphs (6.20 – 10.40 mm; Mn=8.00 (n=12); Md= 7.77 (n=12)), the largest specimens exceeding 10.00 mm were female nymphs from Wisconsin, if these two large bodied specimens are excluded (perhaps as outliers) the maximum body length recorded was 8.90 mm, thus mean and median body size values are believed to be of greater diagnostic value across the range of this species, (2) femora usually with pale oval median spot and dark median mark that does not extend beyond middle of pale oval median spot (Figs. 212a,b), dark median mark may be somewhat elongated on some specimens with apex directed toward apex of femora, also femora have an apical pale area adjacent to dark brown edge near joint with tibiae, (3) abdominal gill 1 shaped as in Fig. 222, plica broadly rounded (almost semicircular), thickened, and (Figs. 224a,b) slightly raised above surrounding surface of gill, plica edge extends only about halfway to base of ruffled edge, (4) abdominal gills 2 – 6 with a dorsal thumb-shaped lobe that is distinctly longer than wide (Fig. 224b, 225), on gill 2 the dorsal thumb-shaped lobe length is about 1.9x width and has an apical row of minute hair-like setae, on succeeding gills some variability occurs in the length:width relationship of the thumb-shaped lobe, therefore it is recommended to evaluate this character on anterior gills if possible, (5) Tracheae and tracheols of gills 2 – 6 not darkly pigmented and gills with only faint yellow-brown shading near gill base, (6) lower part of abdominal gills 2 – 6 with distinctive curved (almost crescent shaped) transparent sclerous rib (Fig. 225), (7) abdominal gill 7 an elongated oval with dorsal edge only slightly folded against tergites VIII and IX and appearing to be fused with surface of gill near short basal sclerous rib, (8) abdominal gill 7 without dorsal lobe as occurs on gills 2 – 6, (9) crown of maxillae with 8 large pectinate setae (Fig. 187), (10) glossae of labium separated by a narrow U-shaped gap (Fig. 204) with inner edge of each glossa relatively straight, only curving outward near apex, (11) lingua of hypopharynx rectangular with straight apical edge and sides only slightly convex, (12) outer incisors of right mandible length about 2.1x width and with seven distinct teeth on inner edge up to apical complex of two fused teeth, (13) outer edge of both mandibles with fringe of several long, hair-like setae that extend about half of the length of the outer edges, and (14) labrum shaped as in Fig. 183, somewhat sub-trapezoidal with anterior edge on either side of midline straight or only slightly convex before merging with rounded posterior corners. See Appendix 3 for comparative list of R. jejuna diagnostic characters and those of other northeast species.

Taxonomic Discussion. The history and taxonomic status of R. jejuna Eaton s.s. is complicated and interwoven with the taxonomic status of two other species. Walker (1853) first described the species known today as R. jejuna Eaton s.s. under the name Baetis fusca from specimens collected from the historic Canadian site “St. Martin’s Falls, Albany River, Hudson Bay” (Ontario). Eaton (1871) reviewed Baetis fusca, Walker and transferred the species to the genus Heptagenia under the name Heptagenia fusca (Walker) and published the first illustration of the genitalia of the male imago. Eaton (1885) later reviewed H. fusca and noted that because the original name (Baetis fusca) was previously occupied, and therefore unavailable, he proposed a new name for this species in the genus Rhithrogena, hence Rhithrogena jejuna, and referenced his previous illustration of the male genitalia. After this point Eaton’s concept of R. jejuna became confused. It seems that several events that happened between 1909 and 1975, both individually and collectively resulted in: (1) the failure to recognize a critical new synonym; (2) the failure to recognize a new species of Rhithrogena; and (3) the subsequent misidentification of R. jejuna for about 112 years.

Chronologically, the first problem arose when C.P. Alexander collected a male imago of Rhithrogena from Gloversville, New York, determined it to be R. jejuna and deposited it in the collection of the Museum of Comparative Zoology (MCZ), Harvard University. This specimen has now been carefully studied and determined to be misidentified (see description of new species, below). However, the result of this error made before 1924, wouldn’t affect later taxonomic decisions for almost 20 years. In the meantime, several other events happened between 1924 and 1933 that would serve to compound this initial taxonomic mistake. First, general comments about R. jejuna made by McDunnough (1924, 1925, and 1926) provided the impression that the species concept (as published by Eaton, 1885) was well understood. Second, Traver (1933b) later discussed the systematics of the species group that included R. jejuna, but she did not provide any new taxonomic details thereby reinforcing the notion that the species concept was not in doubt. Finally, between these events Banks (1924) published the description of an apparently new species of Rhithrogena from New Mexico, USA and named it Epeorus undulatus. McDunnough (1925) discussed its status and first placed it in Heptagenia under the name H. undulata and later in Rhithrogena as R. undulata (McDunnough 1926). Comparative study of samples of adults of R. undulata from across its Nearctic range and study of reared specimens from Wisconsin and two of the syntypes now indicate R. undulata (Banks, 1924) to be a subjective junior synonym of R. jejuna Eaton s.s. The possibility of this synonymy was first presented by Spieth (1940) in a review of the North American species of Francis Walker. Spieth’s comments concerning possible synonymy were based on his study of a new slide-mount of the male genitalia of the holotype of R. jejuna, but even though it seems that Spieth had sufficient evidence to designate a synonym, he didn’t, suggesting instead that further study was needed. Careful study of new high resolution digital images of the slide-mount studied by Spieth, as well as of the pinned type specimens of R. jejuna Eaton s.s. and adult specimens of what has been known as R. undulata from Montana, Wisconsin, and Labrador show that R. jejuna and R. undulata are indeed the same species. However, from 1924 to 1935 the validity of R. undulata was unchallenged and in 1935 Traver published redescriptions of the male imagos of both R. jejuna and R. undulata with more detail than was previously given, as well as figures of the male genitalia. The redescription and new figure of the male genitalia by Traver (1935), of what she called R. jejuna, were based on the misidentified specimen of R. jejuna collected by C.P. Alexander and deposited in the MCZ (and described as a new species, below). Lines of evidence supporting the conclusion that this was the specimen studied by Traver (1935) are: (1) Traver’s statement in her 1935 redescription that she had only seen one specimen of this species and it was from the MCZ, and (2) multiple high resolution digital images of the MCZ specimen matched the description given by Traver (1935) and the slide-mount of its genitalia matched exactly the line drawing figure (Fig. 102 in Traver, 1935) accompanying the description. Congruence of the slide-mount and published figure were assessed by overlaying a photocopy of Traver’s figure on the digital image of the slide-mounted genitalia. Unfortunately for Traver, and everyone else who used Traver’s key, this specimen was not R. jejuna, but an unrecognized new species of Rhithrogena (to be named later herein). This is the point where the original concept of R. jejuna was lost and replaced by that of this unrecognized new species. 

The last major taxonomic work that not only cemented this error, but also provided data necessary to unraveling it was by Flowers and Hilsenhoff (1975). Flowers and Hilsenhoff (1975) reported on the Heptageniidae of Wisconsin largely based on the work of R.W. Flowers (1975) who reared many heptageniid species to associate nymphs with adults and study their life histories. Flowers and Hilsenhoff (1975) included new keys to both nymphs and adults of Rhithrogena and for the first-time new details of the nymphs of what they believed to be R. jejuna and R. undulata. It is likely that because they obtained reared adults that matched the descriptions given by Traver (1935) for R. jejuna and R. undulata that they believed they had indeed successfully associated nymphs and adults of both species. Widespread use of the keys by Traver (1935) and Flowers and Hilsenhoff (1975) firmly fixed the apparent species concepts for both species, but unintentionally resulted in many misidentifications. Now with the understanding that R. undulata is actually a junior synonym of R. jejuna all records of R. undulata are now referable to R. jejuna and all records of R. jejuna Eaton since 1935 that were based on identifications made pursuant to Traver’s 1935 redescription of the male imago must be referable to the new unrecognized species of Rhithrogena (to be named herein).

Despite the inclusion of the nymph of R. undulata (now jr. syn. R. jejuna) in the key published by Flowers and Hislsenhoff (1975), currently there are no detailed descriptions or figures of the nymph of R. jejuna. Flowers and Hilsenhoff (1975) described and figured what they determined to be diagnostic characters relevant to Wisconsin species of Rhithrogena, but for R. undulata they referred back to Edmunds (1952) for a more complete description of the nymph. Unfortunately, Edmunds (1952) did not actually describe the nymph of R. undulata, but defaulted to his description of R. doddsi McDunnough, 1926 (now a jr. synonym of R. hageni Eaton, 1885) indicating specimens he believed to be R. undulata to be virtually identical to those of R. doddsi. In fact, Edmunds (1952) never was able to rear R. undulata and made several critical errors in deductive logic supporting his conclusion that these unassociated nymphs were actually R. undulata. Thus, it is uncertain whether the nymphs Edmunds (1952) thought were R. undulata were actually of that species or another species. Jensen (1966) also referred to Edmunds (1952) regarding the apparent description of the nymph of R. undulata. 

In the eastern half of the range of R. jejuna identifying unassociated nymphs is possible because there are no known Rhithrogena species with the same combination of distinctive morphological characters as described here for R. jejuna, with possible exception of R. gaspeensis, which is unknown in the nymphal stage. The problem of the unknown nymph of R. gaspeensis is greatly reduced for two reasons: (1) it seems to be a narrow endemic restricted to a few streams in the core of the Gaspé Peninsula of southern Quebec and (2) no specimens of R. gaspeensis have been reported since the type series of adults was obtained in 1933. Current efforts to recollect R. gaspeensis by Canadian workers have been unsuccessful suggesting that it could be extinct. However, a different problem identifying nymphs of R. jejuna occurs in the western half of its range. In western North America Edmunds (1952) suggested that perhaps R. morrisoni (Banks, 1924) and R. futilis McDunnough, 1934 had nymphs with gill morphologies that may be similar to that of R. doddsi (which is now a syn. of R. hageni) because they were all members of the brunnea species group. If they do, this poses a problem in recognizing nymphs of R. jejuna in the west where these other species occur. However, with the association of the nymph and adult of R. virilis (Newell and Scheneck 2010), it seems that nymphal gill morphologies are not consistent within the brunnea species group. So, perhaps if these other species lack gills similar to R. jejuna nymphs maybe they could be separated using these characters. Therefore, until all the nymphs of western Rhithrogena are associated and described, caution is advised in making species determinations of unassociated nymphs. In addition, because of this problem it is recommended that all previous western records of R. undulata (now recognized as R. jejuna) that were based on unassociated nymphs should be considered tentative.

Distribution. Rhithrogena jejuna was originally described based on two adult specimens collected at the historic, and until now somewhat enigmatic, site in Canada known as “St. Martin’s Falls, Albany River, Hudson Bay.” Although the Albany River is clearly in Ontario, the exact location on the river has been uncertain until Handfield and Handfield (2020) provided a detailed review of the history of the fur trading station known as “St. (for station) Martin’s Falls.” Although Handfield and Handfield (2020) provided much needed clarity about this location, their final coordinates are extremely conservative and do not allow for acceptable geo-referencing on the Albany River. Using two distance estimates of the location of the fur trading station at Martin’s Falls from historic accounts given by Handfield and Handfield (2020) and Barnston (1841) and Google Earth® images of rapids (i.e., falls) along the Albany River it is estimated that this site was at or near 51.533259/-086.512276. These coordinates were the result of the intersection of distance estimates from known fixed starting points and an area of rapids – hence a type of 3-point corroboration. Rhithrogena jejuna has the largest geographic range of any Nearctic Rhithrogena (Fig. 336). All records of R. jejuna before 1935 are believed to be of adults determined using Eaton’s (1885) concept of the species and therefore considered valid. Because R. undulata is designated a junior synonym of R. jejuna, all records of adults of R. undulata reported across North America and nymphs reported from Wisconsin east to Atlantic Canada represent previously unrecorded geographic data points for R. jejuna. Thus, considering all records now assignable to R. jejuna, the geographic range in Canada extends from Newfoundland-Island (Dance 1979, Larson and Colbo 1983) to Newfoundland-Labrador, across central Canada to British Columbia (Walley 1927) and north to the Yukon and Northwest Territories (McCafferty and Randolph 1998, Giberson and Burian 2017). In the United States, Randolph and McCafferty (1998) summarized previously published records for R. jejuna (reported as R. undulata) from northern Wisconsin and Michigan, and Klubertanz (2016) provides new records for northern Wisconsin. New records are reported here for western and central Maine. Although there are no published accounts of R. jejuna from Minnesota or the Dakotas, the species is broadly distributed across states of the intermountain west (McCafferty et al. 2012), which extends from Montana and Idaho, south to parts of New Mexico, and west into Nevada. Although there are records of nymphs and adults of R. jejuna (reported as R. undulata) west of the Rocky Mountains, only previous adult records of the R. undulata are accepted as valid records of R. jejuna at this time. Meyer and McCafferty (2007a, 2007b, and 2008a) list adult records for Washington, Oregon, and California. Finally, with regards to U.S. records there is an anomalous figure that appears in Burks (1953) monograph on the mayflies of Illinois that is at least noteworthy. On page 153 figures 324B and 324C illustrate what Burks refers to as abdominal gills 5 and 7, respectively, of Rhithrogena presumably from Illinois. The gill illustrated in figure 324B has the unmistakable dorsal thumb-shaped lobe of gills of R. jejuna and figure 324C of gill 7 is similar to that of R. jejuna. The rendering of the basal tuft of filaments is anomalous and possibly a mistake of the illustrator because no known North American species of Rhithrogena has filaments that appear this way. Burks (1953) noted that only one species of Rhithrogena (R. pellucida – now a syn. of R. manifesta) occurred in Illinois, but the gill figures are not those of that species – so where did the gills used for these figures come from? If they came from a specimen from Illinois, it would mean that R. jejuna occurred in Illinois at that time and thus indicates an undocumented part of the species range. However, it is also possible that the gills may have come from somewhere else and thus do not provide any new distributional information for Illinois. Collectively all Canadian and United States records indicate a full transcontinental range that extends from far northern Canada to the southwestern United States and essentially coast to coast. The northeastern distribution of R. jejuna is given in Appendix 2.

Life History and Ecology. Detailed observations of habitat and environmental conditions associated with positively identified nymphs of R. jejuna (i.e., those previously determined as R. undulata from eastern parts of the range) are few. Dance (1979) and Larson and Colbo (1983) provide some information on preferred substrate type and general flow conditions where nymphs were collected in Newfoundland-Island. They emphasized the requirement of large, fairly smooth cobble and small boulders in swift currents and channels greater than 5 m wide. Flowers and Hilsenhoff (1975) describe this species as being tolerant of higher levels of silt that can occur in some sandstone rivers of northern Wisconsin. Assuming some of Edmunds (1952) specimens were in fact R. jejuna (reported as R. undulata), he noted their occurrence in medium to large rivers at an elevation between 1584 – 2194 m. McCafferty et al. (2012) commented on the occurrence of this species in large and silted rivers of the intermountain western United States. In Maine, nymphs were collected at two sites on the SBrCR and one site in Baxter State Park where the channel widths exceeded 5 m and medium to large cobble substrate was abundant in swift flows in the permanently wetted channels. Water quality data recorded at one site on the SBrCR on 20 May 1986 (two days before the collection record at that site) were: Water temperature = 11.5 °C; pH = 7.15; and Specific Conductance = 34.0 µS. The water depth at the sampling point was 0.54 m; current velocity at 0.6x depth 0.45 m/s; and channel width >10 m. No habitat data was available for specimens collected in Baxter State Park. Yanoviak and McCafferty (1996) provide physical and chemical data for sites in northern Michigan where nymphs R. jejuna (reported as R. undulata) were collected. The physical habitat conditions they reported were similar to those observed in Maine on the SBrCR. Among the chemical data reported by Yanoviak and McCafferty (1996) for northern Michigan, Ca2+ and SO42- for the Huron River, which had the greatest number of nymphs collected, were among the lowest values listed for all sites they studied.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Type Material Examined. Holotype of Rhithrogena jejuna: Canada: Ontario: St. Martin’s Falls, Albany River [51.53329°/-086.512276°, elev. 184 m estimated site of Martin Falls fur trading station], G. Branston, 15 May – 1st week of July 1840* [year estimated based on comments given by collector (Branston 1841)], 1♂ [NHMUK011247868 (https://data.nhm.ac.uk/object/9b4cbe19-8399-41bb-bd1f-8d757a9e7d66)] with genitalia on slide [NHM]; Lectoallotype: Canada: same, 1♀ [NHMUK011247867(https://data.nhm.ac.uk/object/fb095336-bcc3-425c-91e5-df467ff0a6c4)] [NHM]. Original NHM Accession code on the back of original labels of both the Holotype and Lectoallotype was 44-17, indicating the 17th accession made in 1844. Syntypes of Rhithrogena undulata (Banks): USA: New Mexico, Jemez Mts. (verbatim from label, but in original description location given as “Jemez Springs”), J. Woodgate? (no collector specifically listed on label, but John Woodgate is indicated in the original description), 25 May yr?. 1♂ [MCZ-ENT00014919 (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:14919), 1♂ MCZ-ENT00803706 (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:803706)]. 

Other Material Studied. Canada: Newfoundland – Labrador: Menihek, ~1.9 km E of railroad stop at edge of Ashuanipi River (dnstr. Menihek Hydroelectric Dam) at Labrador Adventure Fishing Camp, site # 2003-1, sample #12.4.3 [54.489031°/-066.600431°], elev. 471 m , R.J. Pupedis, 11 July 2003, 1♂ [YPMIC]; USA: Maine: Franklin Co., Carrabassett River (SBrCR), below entrance to Sugarloaf Ski Area at Rt. 16, Site F20 [45.079940°/-070.312878°], elev. 390 m, S.K. Burian, 20 Oct 1984, 1N♀ [NEL]; same, Carrabassett River (SBrCR) SE of rest area on Rt. 16 (at ford), Site F9 [45.041082°/-070.188990°], elev. 225 m, S.K. Burian, 22 May 1986, 1N♀ [NEL]; Pistcataquis Co., Nesowadnehunk Stream, where Tote Rd. crosses stream, Baxter State Park [45.900653°/-069.039364°], elev. 324m, A.C. Graham, 30 June 1982, 2N♂ [SWRC]; Montana: Madison Co., Madison River, Ennis [45.342646°/-111.724836°, elev. 1508 m, boat ramp area Ennis], W.G. Downs, 8 July 1981, 10♂,1♀ [NEL]; same, O’Dell Creek, Ennis [45.342856°/-111.714937°, elev. 1505 m, where creek crosses Rt. 287], W.G. Downs, 7 July 1981, 9♂ [NEL]; Powell Co., Danaher Creek, Bob Marshall Wilderness Area [no coordinates – location uncertain], W.G. Downs, 6 July 1978, 1N♀ [NEL]; Wisconsin (Note – all Wisconsin material below previously determined as R. undulata (Banks), is herein determined as R. jejuna Eaton s.s.): Bayflield Co., Pine Creek [46.549822°/-091.61614°, elev. 204 m, estimated dnstr. of bridge on old US Hwy. 2], no collector on label (R.W. Flowers?), 18 April 1974, 2N♂, 1N♀ [WIRC]; same, 30 May 1974, 1♂ (+Nex – note emerged 3 June 1974) [WIRC]; same, Pine Creek, site# 3, Ashland [46.549822°/-091.61614°, elev. 204 m, estimated as dnstr. of bridge on old US Hwy. 2], no collector on label (R.W. Flowers?), 8 June 1979, 1N♂, 1N♀ [WIRC]; same, North Fork Fish Creek, site# 1, Ashland [46.54015°/-091.062177°, elev. 206 m, estimated ~112 m upstr. of bridge on old US Hwy 2], no collector on label (R.W. Flowers?), 6 Oct 1979, 1N♂ [WIRC]; same, 8 June 1979, 2N♂ [WIRC]; same, East Fork Cranberry River [46.788504°/-091.273188°, elev. 207 m, estimated at riffle ~90 m dnstr. of Touve Rd. nr. intersection with Cranberry River Rd., Clover], no collector on label (R.W. Flowers?), 25 May 1970, 1N♀ [WIRC]; same, 7 July 1970, 1♂ [WIRC].

Rhithrogena manifesta Eaton, 1885: 253

Figs. 228 – 280

Siphlonurus debilis (Eaton, 1871: 130 new combination)

Rhithrogenia manifesta (Eaton, 1885 renamed and placed in genus Rhithrogena, Eaton 1885: 253

Heptagenia manifesta (Eaton, 1885) (recombined by McDunnough 1924: 117,119)

Rhithrogena manifesta (Eaton, 1885) (recombined by McDunnough 1926: 195)

Rhithrogena pellucida Daggy, 1945 (Jacobus and McCafferty 2002)

Nymph (in alcohol with well-developed or dark wingpads). Body length: 5.00 – 7.00 mm (Mn = 6.08±0.65 SD; Md = 6.00; n=19). Description based on male nymph except where noted.

Head. Colour Pattern: Overall background colour ranging from medium brown to slightly darker brown (colour close to NCG# 123A – Cinnamon) from bases of antennae to anterior margin of head capsule (Fig. 228a). Lateral margins of head capsule somewhat lighter yellow-brown (close to NCG# 123 – Yellow Ocher). On live nymphs head capsule more extensively dark brown and more transparent, area from lateral margins to compound eyes tinged with greyish-brown. On larger nymphs of both sexes tracheae below cuticle of head capsule outlined in dark brown and most visible in center of head (Fig. 228b). Small dark brown speckles may also occur over and around area of head capsule where dark tracheae occur (Fig. 228b). Pale narrow line between lateral ocelli and along anterior margin of compound eyes (Figs. 228a,b). Pale narrow line slightly wider where it meets lateral margin of head capsule. On male nymphs, pale narrow line broadens adjacent to anterior edge of compound eyes forming short, elongate pale spots before narrowing again near lateral margin of head capsule (Fig. 228a). Female nymphs lack elongate pale spots adjacent to compound eyes. Anterior half of head capsule uniform brown, lacking any distinct pale markings (Fig. 228b). Vertex of head of male nymphs usually with one small, faint spot close to inner margin of each compound eye. However, on female nymphs, vertex between compound eyes usually entirely brown (except for pale ecdysial suture), occasionally one pair of small, faint pale spots occur close to each other, straddling ecdysial suture. Shape: Head capsule broadly oval in both sexes (Figs. 228a,b), but on male nymphs with well-developed wingpads posterior lateral edges adjacent to compound eyes can be quite straight where they meet posterior margin, producing somewhat angulate appearance to this part of head capsule. Although male head capsule can appear angulate it does not appear distinctly indented adjacent to compound eyes (Fig. 228a). Width of head capsule about 1.8x length. Anterior margin smoothly curved with slight median emargination where labrum articulates with head capsule (Figs. 228a,b). When head capsule viewed dorsally curvature of anterior margin can obscure median emargination, making it appear absent. Mouthparts completely concealed beneath edges of head capsule. Posterior margin of head capsule concave on most nymphs. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped and when viewed dorsally outer margins reach, but do not extend beyond, outer margins of head capsule (Fig. 228a). Anterior and posterior margins of compound eyes converge toward midline of head transitioning to broadly rounded inner corner (Fig. 228a). Male compound eyes separated by gap slightly wider than width of one lateral ocellus. Female compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Fig. 228b) and gap between eyes more than 2x as wide as on male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Figs. 228a,b. Pale spots present over all ocelli, with spots over lateral ocelli slightly larger than over median ocellus. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle (Figs. 228a,b). Antennae: Basal membrane of antennal socket pale and edge of socket slightly darker brown than surrounding cuticle (Figs. 228a,b). Scape and pedicel dark brown similar to surface of head capsule and often darker than pigmented portion of flagellum. Proximal 13 – 14 annuli of flagellum vary from light brown to same colour as scape and pedicel. Apical 8 – 10 annuli of flagellum colourless or cream coloured. Antennae length about 1.2x midline length of head capsule.

Mouthparts. Labrum: Labrum somewhat trapezoidal, not distinctly semicircular with sides of anterior margin varying from straight to slightly convex before merging with rounded posterior corners (Fig. 229). Anterior margin almost straight with only slight median emargination, on some specimens this feature is so subtle it can appear absent. Anterior median emargination without flanking groups of large rigid spines, but groups of 3 – 5 irregular small to minute tubercles usually occur on either side of ventral edge of median emargination and several slightly larger tubercles can occur across middle of median emargination (Fig. 230). None of these projections are visible dorsally. Dorsal surface of labrum medium brown with slightly lighter areas laterally. Posterior half of dorsal surface of labrum with field of long, hair-like setae with bases relatively widely separated. Embedded in field of long, hair-like setae is an irregular row of about eight short, thick bristle-like setae with rounded tips (Fig. 231). Middle of dorsal surface with 6 – 8 relatively long and slightly thicker hair-like setae. Medially one pair of long setae, that are thicker than hair-like setae, set close to center of anterior median emargination (Fig. 229). Group of two long setae similar in form to medial pair of long setae occur near each lateral margin. Ventral lateral margins of labrum with many (> 20) long, setae in about four irregularly spaced rows with setae decreasing in length toward anterior margin (Fig. 232). Longest at posterior corners of labrum. Innermost row of ventral edge setae directed medially toward brush of short setae flanking ventral midline of labrum. Shortest ventral margin setae stop at point where straight (or slightly convex) lateral margins meet anterior margin (i.e., point before where small irregular tubercles begin). Ventral lateral edges of labrum occasionally with 4 – 6 small, stout spine-like setae in gaps between long marginal setae and small irregular tubercles at edges of median emargination. Maxillae: Left maxillae as in Fig. 233. Galea-lacinia with eight pectinate crown setae, with what appears to be maximum of 7 – 8 teeth on largest mid-crown setae (Fig. 234). Apical crown seta appears to have about half number of teeth compared to largest mid-crown setae. Submedial row of about 24 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 233). Near apex of submedial row one long, biserrate seta occurs set back from main row of long setae. At base of main submedial row of setae is one short bristle-like seta separated by gap from submedial row of setae. Inner edge of galea-lacinia with dense double row of long, simple setae with setae of ventral row only about one-third length of setae of dorsal row (Fig. 233). In addition, at base of double row of inner edge setae is basal row of 14 – 15 long, simple setae with tips extending well beyond those of main portion of inner edge row (Fig. 233). Maxillary palp as in Fig. 235, appearing two-segmented. Inner edge of apical segment of maxillary palp slightly concave with row of about 24 short setae with downward curved tips hanging over edge of palp and another 12 larger and straighter setae recessed back from edge (Fig. 235). Apical segment of maxillary palp with distinctive longitudinal sclerotized band, but no vertical band near apex (Figs. 233, 235). Most of ventral surface of apical segment of maxillary palp covered with short, stout monopectinate setae (Fig. 236) with 5 – 6 sharp teeth on most large forms across basal and middle portions of array of setae. Setae near apex of array of monopectinate setae have seven or more teeth that are longer and thinner compared to setae in middle of array. Outermost edge of apical segment with about four rows of large, simple setae with downward curved tips (Fig. 236). Dorsal surface of apical segment with numerous short, thick setae and long, hair-like setae with tips that extend well beyond edge of rows of curved ventral edge setae. Hypopharynx: Lingua broad and somewhat rectangular, but sides convex near base such that shape approximates that of stemless brandy glass (Fig. 237). Apical margin of lingua concave with dense brush of fine setae and medial projecting point. Superlinguae as in Fig. 238 with outer edges nearly straight. Bases of superlinguae distinctly indented below straight outer margin and are relatively broad where they meet base of hypopharynx. Apical margins of superlinguae smoothly rounded to inner margin and with long, hair-like setae (Fig. 238). Ventral surface lingua with broad, rectangular hole where hypopharynx attaches to base of labium (Fig. 239). Mandibles. Right mandible (Fig. 240, ventral view): Anterior margin between molars and prostheca straight with continuous row of short, hair-like setae ending in row of about seven larger hair-like setae at prostheca (Figs. 241a,b). Molar surface distinctly depressed relative to position of anterior margin (Fig. 240). Molars composed of rows of teeth that vary from sharp, conical forms at ventral edge to large cylindrical forms with rounded, tops along dorsal edge (Fig. 242). Apical teeth of ventral edge differ from others being thin, sharp, and closely spaced. Molar surface terminates with one large, outwardly pointing sharp tooth (Fig. 243). Adjacent to apex of molars are 7 – 8 long, simple setae that are thicker than typical hair-like setae. Prostheca composed of one row of about six long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 244). Incisors as in Figs. 244. Outer incisor length about 2.4x width, smaller sized teeth on outer edge homonomous from apex to base where basal teeth become thinner and sharper. Larger sized inner teeth fewer, with seven distinct teeth (Fig. 245a). First six inner teeth with small basal tubercle (Fig. 245b), last tooth may have one or two basal tubercles. Apical complex of outer incisor composed of one medial tooth divided at tip with small basal tubercle flanked by first outer and inner teeth respectively (Fig 245b). Basal part of outer incisor with comb of about 23 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 244). Leading edge of inner incisor with 3 – 4 small hair-like setae in row below large upper edge tooth. Upper edge of inner incisor with row of about 10 large coarse teeth (none appear to have jagged edges) that gradually merge into trailing edge row of fine comb-like teeth (Fig. 244). Outer edge of mandible below incisors without fringe of long, hair-like setae, inner edge below molars also without long setae. Left Mandible (Fig. 246, ventral view): Anterior margin between molars and base of prostheca essentially straight except for small, raised area near molars, raised area with small tooth-like spines pointing toward molars. (Fig. 247). Remainder of anterior margin with continuous row of small hair-like setae merging into area of prostheca where hair-like setae become longer and more numerous (Fig. 247). Upper edge of molar surface with what appears to be closely positioned (possibly fused) group of 3 – 4 flattened multidentate teeth that become progressively larger up to transition with slender and distinctly separate individual multidentate teeth of upper molar surface (Fig. 247). Majority of molar surface as in Fig. 248, where rows of short, rounded or conical teeth each terminate with somewhat flattened brush-like tooth on upper part of molar surface or short multidentate tooth on lower part of molar surface. No distinct apical tooth present, but 5 – 6 long, hair-like setae occur below apical cluster of short molar teeth. First ventral row of molar teeth with one large brown conical molar tooth in middle of row (Fig. 249). Prostheca composed of row of about nine finely biserrate setae that gradually increase in length up to base of inner incisor (Fig. 250). Incisors as in Fig. 251. Outer incisor length about 2.3x width, smaller sized teeth of outer edge homonomous from apex to final 5 – 6 teeth of row with remaining teeth becoming thinner and sharper to junction with posterior comb. Larger sized inner teeth fewer, with seven large teeth and one smaller basal tooth (Fig. 252). Except for small basal tooth, all large inner edge teeth have small basal tubercle. Apical complex of outer incisor composed of two small lateral teeth and one small terminal tooth (Fig. 251). Basal part of outer incisor with comb of about 25 fine teeth, most teeth forked near tip with depth of fork from tip about one-quarter (or less) length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 251). Leading edge of inner incisor with row of 7 – 8 long, thin setae below large elongate tooth of upper edge. Upper edge with row of about 14 large, coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of incisor (Fig. 251). Outer edge of mandible below incisors without fringe of long, hair-like setae. Inner edge below molars also without fringe of long, hair-like setae. Labium: Labium as in Fig. 253. Dorsal surface of glossae with long, hair-like setae on inner apical surface and row of similar hair-like setae extending from apex to about one-quarter distance to base of glossae where long setae transitions to single row of about nine short, stout sharp setae with curved tips (Fig. 254). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and beyond large spine-like setae from ventral surface. Ventral surface of glossae mostly bare, except for one large subapical seta. Ventral surface of paraglossae with area of large spine-like setae occupying upper half of each paraglossa (Fig. 255). Some anterior ventral edge spine-like setae long, extending above edge about half length of long setae from dorsal surface (Fig. 255). Glossae somewhat subtriangular in shape with lower part of inner edges almost perpendicular with base of gap (Fig. 253) and upper part of inner edges distinctly diverging from midline of labium. On most specimens this produces relatively wide U-shaped gap between glossae (Fig. 253). Labial palps two-segmented. Apical segment of palps with distinct array of pectinate brush setae on ventral surface and brush of simple setae at tip. Ventral surface of apical segment with row of long, thin setae with curved tips along outer edge. Dorsal surface of apical segment with array of long curved bifurcate setae.

Thorax. Pronotum: Overall shape somewhat tetragonal with greatest width at middle of lateral margins (Fig. 256). Anterior margin essentially straight, but posterior margin slightly convex on either side of body midline (Fig. 256). Appearance of lateral margins somewhat variable form early to late instars, with pronounced apex of curve appearing most acute on early instars and less acute, more rounded on later instars. Posterior lateral edges appear fused with mesonotum despite pale boundary line between them (Fig. 257). Posterior half of pronotum slightly raised on either side of midline forming pair of low humps. Lateral edges of widest part of pronotum uniform brown similar to majority of pronotum. Anterolateral corners with large pale spot that connects to curved pale transverse band that extends posteriorly along lower edge of lateral margin, but does not reach edge of pronotum (Fig. 256, 257). Pale band along anterior margin extends from each anterolateral pale spot toward midline, but does not connect at midline. Middle of pronotum brown without distinctive pattern. On live nymphs, pronotum usually more extensively shaded dark brown compared to preserved specimens. Thin dark lines of tracheae visible below cuticle across pronotum of most specimens. Lateral areas of pronotum with faint pale inverted U-shaped mark with short slanting pale mark in center of pale U-shaped mark (Fig. 256). Lateral inverted U-shaped pattern often appears incomplete with only anteriormost part of pattern clearly visible, medial pale mark and posterior part of inverted U-shape extremely faint (Fig. 256). Pronotal patterning seems consistent on both male and female nymphs. Mesonotum: Overall background colour similar to pronotum. Anterior margin shaded slightly darker brown, especially along concave portion following curvature of pronotum (Figs. 258a,b). Small, dark brown area where inner edge of forewingpad meets mesonotum and MLs pale with stripe of uniform width (Figs. 258a,b). However, pale stripe along MLs slightly wider on male black wingpad nymphs compared to female black wingpad nymphs. Outer and inner edges of forewingpads dark brown, as well as portion of MS parallel to body midline and notched apex of SL (Fig. 258a). Small pale spot present on some nymphs at base of forewingpads closes to body midline. Lightly sclerotized areas pale compared to thicker areas of cuticle. Lateral margins of mesonotum from base of forewingpads to outer edge of pronotum slightly curved inward, on some specimens this edge appears almost straight. On live nymphs, overall colouration of brown shading of mesonotum much darker compared to preserved specimens, darker shading of live nymphs makes pale spots and other lighter coloured areas more distinctive. Metanotum: Light brown laterally, generally similar to background colour of mesonotum. Metanotum pale medially and in areas along lateral margin near base of hind wingpads. Dark brown shading occurs along ventral edge of metapleural sclerites and on flared surface of hind coxae. Pleural Region: Membranous area of pleural region anterior to mesocoxae with small dark brown (almost black) smudge (Fig. 257). Posterior edge of mesopleuron occasionally with 1 – 2 small isolated dark brown spots. Metacoxal sclerites with surface enlarged and flared upward. Pro- and mesocoxal sclerites with short flared edges.

Abdomen. Tergites: Background colour of tergites of preserved specimens yellow ocher (close to NCG# 123C) tinged with cinnamon (close to NCG# 123A) (Figs. 258a,b). On live or freshly preserved specimens background colour of tergites much more extensively shaded with dark brown. Tergites of male nymphs with well-developed or black wingpads dark brown (close to NCG# 223 – Raw Umber), with darker colour dominant over lighter background colour on tergites I – VII. In general, male nymphs seem to have slightly darker shade of brown across tergites compared to female nymphs. Two colour morphs of tergites VIII – X occur in some populations: (1) Pale-form with most of tergites VIII and IX pale and with wide paired parallel pale stripes on tergite X, which are broadly connected across its anterior margin by pale band (Fig. 258a); and (2) Brown-form with all or almost all of tergites VIII – X brown, lacking distinct pale areas as on pale-form, but with small paired pale submedian spots on tergites VIII and IX, as well as either faint or more distinct narrow paired pale stripes on tergite X (Fig. 258b). On both colour morphs, tergites II – VII have paired pale submedian spots. On live or freshly preserved specimens, small paired submedian spots are much more distinctive and on tergites V - VII there are faint traces of pale median stripe that broadens where it contacts posterior margin. On live pale-form nymphs, faint brown shading on anterior and lateral areas of tergites VIII and IX fades extensively upon preservation in ethanol, but colour of tergite X does not seem to change after preservation. Lateral margins of tergites II – VIII (on both colour morphs) with triangular indentations marked with pale triangular spot, anterior edge of pale spot more noticeable on tergites with slightly darker brown shading. Lateral areas of tergites lack brown spots or marks between pale triangular spot and posterolateral projections. Anterolateral margin (of both colour morphs) usually uniform brown, but occasionally with narrow pale band directly adjacent to dark brown edge. Lateral areas of tergites IX – X lack contrasting pale triangular marks. Posterolateral corners of tergite IX do not flare outward and short posterolateral projections do not extend much beyond anterior margin of tergite X. Posterior intersegmental membranes (of both colour morphs) of tergites I – IX lack dark pigmentation. Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 259). Spinules somewhat variable across posterior margins of tergites with medial section of large spinules alternating with shorter and thinner spinules and lateral section with large relatively uniform spinules that don’t alternate (Fig. 259). Microspinules occur among bases of many, but not all large spinules. Posterolateral projections short and weakly pointed or blunt on tergites I – VII (Fig. 260). Tergites VIII and IX have short, blunt, posterolateral projections and tergite X lacks these structures. Small brown sclerous lobe-like area associated with posterior margin of tergites VII – IX occurring between end of row of spinules and posterolateral projection. Small sclerous structure on tergites VII – IX appears weakly fused to posterior margins of respective tergites. Small sclerous structures on tergites IX larger than same structure on tergite VIII. Sternites: Background colour of abdominal sternites of preserved specimens pale yellow or cream coloured. Median area of sternites II – VIII medium brown with pair of pale diagonal submedian dashes and pair of small, faint submedian dots (Fig. 261a). Pale diagonal dashes and dots most distinctive on sternites V – VIII, much less obvious on sternites II – IV. On male nymphs, median area of sternite IX somewhat variable, ranging from mostly pale yellow or cream coloured to light brown. On female nymphs, sternite IX mostly medium brown as on preceding sternites. Sternite I with anterior flanges shaded medium brown, which contrasts with mostly pale median area of sternite. Outer corners of anterior flanges of sternite I broadly rounded (Fig. 261a). Sternites II – VII with thin brown line spanning width of median brown shaded area of each sternite near posterior margin (Fig. 261b). Lateral areas of sternites II – VIII pale contrasting with brown median area and dark brown outermost edges of lateral margins (Fig. 261b). Median brown areas of sternites II – VIII slightly raised compared to lateral areas. Median area of sternites I and IX not raised. Except for colour variations noted for sternite IX, there appears to be little difference in colouration of other sternites between male and female nymphs.

Legs. Forelegs: Overall background colour pale yellow or cream coloured over shaded with yellow ocher (close to NCG# 123C) and dark brown on some parts of femora and other leg segments, especially adjacent to joints (Fig. 262a). Forefemora length about 2.4x width. On live or freshly preserved specimens, pale background colour of some areas shaded with medium greyish-brown, making darker shaded areas more distinctive than on preserved specimens. Also, some pale areas on live or freshly preserved specimens can appear almost white. Dorsal surface of forefemora of pale-form nymphs medium yellow ocher (close to NCG#123C), with slightly darker shading around pale median spot (Fig. 262a). Alternate brown-form nymphs have much more brown shading on femora and much reduced pale median spot (Fig. 262b). Forefemora typical of pale-form nymphs with spear-point shaped pale oval median spot that is variably separated from or weakly connected to pale spot near base of forefemora (Fig. 263). Above spear-point shaped pale median spot often there is separate thin pale streak along base of dorsal fringe of long setae (Figs. 262a, 263). On live or freshly preserved specimens, dorsal surface of forefemora appears shaded with greyish-brown in contrast to yellow ocher of preserved specimens. Middle of spear-point shaped pale oval median spot with vertical dark brown median mark (on live specimens this mark often appears reddish-brown contrasting with greyish-brown colour of surrounding surface) that sometimes extends beyond upper and lower edges of pale median spot (Figs. 262a, 263). Apical portion of forefemora beyond shaded edge of pale median spot with 1 – 2 pale spots (Fig. 262a). Dorsal and ventral edges of forefemora slightly darker brown along rows of marginal setae compared to background colour. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges. Although many long setae of dorsal row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edge of variable width and length, some seem similar to elongate flags. Dorsal row of setae of uniform length, except for 1 – 2 setae near apex of forefemora. Row of irregularly spaced short, hair-like setae below middle of dorsal edge row of long marginal setae. Dorsal surface of forefemora with field of short, flattened setae as in Fig. 264. Field of flattened setae over middle of dorsal surface with distinctive dark brown bases. Field of flattened setae composed of two types, parallel-sided and paddle-shaped (Fig. 264). Parallel-sided forms lacked constriction at base and were more numerous than paddle-shaped forms, which had distinct basal constriction. Smaller paddle-shaped setae appear to be mostly restricted to apical portion of field of flattened setae. Ventral edge of forefemora with relatively few large, spine-like setae and scattered hair-like setae. Groove along ventral edge of forefemora pale without dark shading adjacent to joint with foretibiae (foretibiae completely cover this area when folded against forefemora). Foretrochanter: Foretrochanter with irregular row of 8 – 9 large, flat, parallel sided setae above joint with forefemora. Foretibiae: Length of foretibiae about 0.9x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint dark brown (Figs. 262a, 263). Foretibiae mostly uniform light brown. Ventral edge of foretibiae with about five widely separated stout setae, all with tapered sides and narrow rounded tips. Ventral apical edge of tibio-tarsal joint with two large monopectinate setae (Fig. 265), one large monopectinate seta with closely spaced, short, stout, teeth and other large monopectinate seta with widely spaced long, thin, teeth. Dorsal edge of foretibiae with longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae (Fig. 266). Lateral to dorsal edge sparse longitudinal row of scattered small hair-like setae extending from base to apex of foretibiae. Apex of dorsal longitudinal row of hair-like setae with one large, paddle-shaped seta. Foretarsi: Length of foretarsi about 0.3x length of foretibiae. Background colour similar to foretibiae and also lacks distinct pale areas, but basal area usually slightly darker than rest of segment (Figs. 262a, 263). Longitudinal row of hair-like setae on foretibiae continues along dorsal edge of foretarsi with two paddle-shaped setae embedded in row of setae (Fig. 267). In addition, scattered hair-like setae also occur on other parts of foretarsi and on apical margin below foreclaws. Foreclaws: Foreclaws as in Fig. 268, with basal area pale and dark brown elongate sharp, tip. Foreclaw with one basal tooth and usually four preapical denticles (one specimen studied had five preapical denticles) that gradually become thicker and longer toward claw tip (Fig. 268). Outer apical portion of foreclaws slightly more than one-third their total length. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Figs. 262a,b). There is some variation in appearance of pale median spot, which is more elongate than on forefemora with more attenuated connection to basal pale spot. In addition, dark median mark is also elongated on mid and hind femora or may fade out completely on hind femora. Thin pale streak along dorsal edge row of long marginal setae often reduced small pale line on mid and hind femora on some specimens (Fig. 262a). Short, flattened setae on mid and hind femora often more numerous across lower part of pale median spot, basal pale spot, and surrounding dark brown margin compared to forefemora. Fewer small, paddle-shaped setae present in field of flattened setae compared to forefemora. Mid and Hind Trochanter: Dorsal edge of mid and hind trochanters with irregular row of about 10 large, flat, parallel sided setae above joint with femora. Structure and appearance of mid and hind tibiae, tarsi, and tarsal claws generally similar to that of forelegs (Fig. 269), however there are some differences. Mid and hind tibiae have at least one large paddle-shaped seta embedded in dorsal longitudinal row of hair-like setae and about nine large spine-like setae occur along ventral edge of tibiae. Ventral apex of mid tibiae with one large spine-like seta and hind tibiae usually with two large spine-like setae (Fig. 270). Small hair-like setae also present at apex of mid and hind tibiae, but no large, flattened setae present. Mid and hind tarsi without large paddle-shaped setae (Fig. 271). Mid and hind claws similar in shape, size, and proportion to those of forelegs, but dark apical area more curved than on foreclaws (Fig. 272).

Abdominal Gills. Colour and Position: Gills mostly transparent, all gills (except gill 1) have distinct yellow-brown shading in proximal dorsal half following gill tracheae (Fig. 273). On live or freshly preserved specimen’s posterior part of gills 2 – 7 also pale yellow, but colour fades completely after initial preservation. On gill 1, brown shading restricted to straight inner margin anterior to gill base (Fig. 274). Gill filaments pigmented from base to tips, faint greyish-green (on live nymphs, filaments more green). Dorsal margins of gills adjacent to base of filaments sclerotized and shaded brown (Fig. 273). Tracheae faintly stained on gills 2 – 5, tracheae indistinct on gills 6 and 7. On gill 2 tracheae most distinct and have consistent branching pattern of secondary tracheols from main tracheae toward dorsal margin of gill. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) of gill 1 meets or slightly overlaps dorsal margin of gill 1 from opposite side of abdomen (Fig. 274). Abdominal gills 2 – 6 positioned laterally with anterior half of each gill overlapped by preceding gill forming almost continuous disc around perimeter of abdomen (Figs. 258a, 261a). Gill 1: Abdominal gill 1 as in Fig. 274, anterior corner where straight inner margin meets dorsal edge rounded, but only slightly protruding. Outer margin with incisions forming ruffled edge. Depth of incisions variable, but usually less than width of each division (Fig. 274) and outer margin has relatively few, but similar sized ruffles. Anterior ruffles of outer margin often slightly narrower compared to posterior ruffles. Secondary shallow incisions can occur between deep primary incisions on some specimens. Ruffles become irregular in size along posterior margin. Posterior margin of gill 1 varies from somewhat rounded to nearly straight with ruffles extending to straight inner edge. Plica of dorsal surface as in Fig. 275, apex rounded with wide triangular base that is lightly sclerotized and shaded light yellow-brown. Apex of plica extends almost to base of ruffled edge and raised above gill surface (Fig. 276). Inner two-thirds of gill 1 thicker and more opaque than outer ruffled edge. Cluster of filaments at base of gill 1 composed of 8 – 10 filaments that appear to originate from one trachea without subsequent branching (Fig. 275). Short, sclerotized rib present adjacent to gill base. Tracheae in posterior portion of gill faintly stained with dark pigment and faint traces of tracheae extend anteriorly into plica. Gill 2: Abdominal gill 2 as in Fig. 277a. Overall shape of gill 2 broadly oval, posterior margin with one shallow incision, otherwise no ruffles. Width of gill 2 about 0.8x length. Dorsal margin without distinct lobe. Dorsal margin convex and appears to lack small hair-like setae. Dorsal half of gill 2 shaded light brown with colour darkest along short, sclerotized rib and dorsal margin adjacent to tuft of filaments (Figs. 273, 274). Tracheae stained grey-green and exhibit distinct dendritic branching pattern with 2 large tracheols extending upwards toward dorsal margin from central tracheae (Fig. 277b). Tuft of filaments as in Figs. 277a,b, composed of 18 – 20 filaments that appear to mostly arise from one major tracheal branch at gill base. Gill filaments extend beyond midpoint of gill 2 and base of tuft of filaments seems to lie in shallow depression on surface of gill between dark brown sclerotized rib and dorsal margin. Lower portion of gill 2 supported by distinctive L-shaped transparent sclerotized rib (Fig. 277a,b) that is acutely angled (~70°). Basal portion of L-shaped rib lies next to broad oblong lightly sclerotized area that is usually shaded light brown or yellow-brown. Colouration of oblong sclerotized area fades completely after extended preservation in ethanol. L-shaped rib and lightly sclerotized oblong structures are most distinctive ventral features of gill 2 (Fig. 278). Base of upper portion of gill 2 supported by short, straight transparent sclerotized rib, usually shaded dark brown. Both internal gill supports seem to lack surface setae, but short hair-like setae occasionally occur along ventral edge of gill. Proximalmost part of ventral edge of gill 2 terminates in distinctive rounded lobe (Figs. 277a,b). Gill 5: Abdominal gill 5 as in Fig. 279, shape broadly oval without dorsal lobe. Width of gill 5 about 0.7x length. Colour of gill 5 and tracheae as in gill 2. Ventral portion of posterior margin lacks ruffles as in gill 2, but one shallow incision occurs toward middle of posterior margin. Dorsal margin of gill 5 similar to gill 2. Lower portion of gill 5 supported by transparent L-shaped sclerotized rib as in gill 2 (Fig. 279). Base of upper portion of gill 5 supported by short, sclerotized rib similar in form and colour to that on gill 2. Scattered short hair-like setae occur along ventral portion of posterior margin of gill 5. Tuft of filaments at base of gill 5 similar in length, number, and arrangement to gill 2 (Fig. 279). Proximalmost part of ventral edge of gill 5 terminates in distinctive rounded lobe as in gill 2 (Fig. 279). Gill 7: Abdominal gill 7 as in Fig. 280, with dorsal portion folded against side of tergite VIII and sometimes anterior lateral corner of tergite IX and apparently fused to surface of gill near basal sclerotized rib. Gill 7 lacks dorsal lobe and majority of gill extends beneath abdomen as more or less free flattened structure (Fig. 278). Apex of gill 7 meets or overlaps apex of opposite gill 7 beneath body (Figs. 261b, 278). Ventral posterior margin of gill 7 with 2 – 3 shallow incisions forming short, ruffled edge (Fig. 280). Distinct dark tracheae and brown shading of gills 2 – 6 much reduced and restricted to base of gill 7 and anterior margin adjacent to filaments. Tuft of filaments at base of gill 7 shorter and with fewer filaments compared to preceding gills, but otherwise similar in colour and structure. Transparent L-shaped support for lower half of gill 7 (as on gills 2 – 6) seems to be incorporated into folded edge of gill that lies against tergites.

Caudal Filaments. Colour and Structure: Median terminal filament slightly longer than cerci and together length of caudal filaments about 1.4x length of abdomen. On preserved specimens, caudal filaments pale cream coloured to light brown. On live nymphs caudal filaments usually light greyish-brown. Most annuli with row of short spines on posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 20 (as counted from base). Fine hair-like setae begin with only 2 – 3 per annulus, but rapidly increase to maximum of 8 – 9 per annulus. Terminal 20 annuli of median terminal filament and terminal 14 – 15 annuli of cerci lack marginal setae. Terminal five annuli of median terminal filament and cerci also lack short spines.

Diagnosis Rhithrogena manifesta Nymph: Nymphs of R. manifesta can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) small to medium body size of near final instar nymphs (5.00 – 7.00 mm; Mn=6.08 (n=19); Md= 6.00 (n=19)), only one female nymph from Maine was observed reaching a body length of 7.00 mm suggesting the one larger specimen may be atypical for the species, thus mean and median body size values are believed to be of greater diagnostic value across the range of this species, (2) femora with small pale median spot, often shaped like a spear-point (Figs. 262a, 263) that is often weakly connected to small pale spot at base of femora and with a vertical dark brown mark in center of pale spear-shaped median spot, vertical brown mark reaching to or beyond upper and lower edges of pale median spot on some specimens, (3) abdominal gill 1 shaped as in Fig. 274, plica triangular-shaped with rounded apex (Fig. 275), anterior edge of base of plica much larger than posterior edge and usually shaded light yellow (on specimens from Colorado anterior edge of plica slightly concave), (4) tracheae of posterior portion of gill 1 faintly stained with dark pigment and faint traces of tracheae can be seen extending into base of plica, (5) abdominal gills 2 – 6 without a dorsal lobe (Figs. 273, 277a, 279) and dorsal half of gills shaded light brown with colour darkest along dorsal margin and short sclerotized rib near base of gills, (6) tracheae of abdominal gills 2 – 6 stained greyish-green and exhibit distinctive dendritic branching pattern from two large tracheols within gills that extend upward towards the dorsal margin from a central trachea (Fig. 277b), (7) abdominal gills 2 – 6 with the lower part of gills supported by L-shaped sclerous rib that is acutely angled at ~70° (Figs. 277a, 278, 279), (8) proximal part of ventral edge of gills 2 – 6 terminates in a distinctive rounded lobe (Figs. 277a, 279), (9) abdominal gill 7 shaped as an elongated oval with dorsal edge folded against tergite VIII and anterior corner of tergite IX and dorsal edge apparently fused with surface of gill near basal sclerous rib and L-shaped sclerous support incorporated into folded upper portion of gill, (10) crown of maxillae with eight large pectinate setae, (11) apical segment of maxillary palp without brown vertical band, (12) submedial row of about 24 long biserrate setae, below crown of galea-lacinia (Fig. 233), (13) glossae of labium with relatively broad U-shaped gap (Fig. 253), (14) lingua of hypopharynx with sides distinctly convex near base approximating the shape of a stemless brandy glass (Fig. 237), (15) outer incisors of right mandible length about 2.4x width and with seven large teeth on inner edge up to apical complex, last preapical tooth below apical complex may have 1 – 2 small tubercles near base, (16) outer edge of both mandibles without fringe of long, hair-like setae, (17) labrum shape somewhat of a flattened trapezoid, not distinctly semicircular, and (18) abdominal tergites VIII and IX usually with broad pale area across much of dorsal surface [the most common pale-form nymph] (Fig. 258a), however tergites VIII and IX can be uniform brown similar to preceding tergites [much less common brown-form nymph] (Fig. 258b), and both colour morphs can co-occur in a population. See Appendix 3 for comparative list of R. manifesta diagnostic characters and those of other northeast species.

Taxonomic Discussion. Rhithrogena manifesta has a complicated taxonomic history. The details surrounding its reinstatement were presented by Jacobus and McCafferty (2002) and included the designation of R. pellucida as a subjective junior synonym of R. manifesta. Although initially described by Eaton (1885) from Illinois it wasn’t until Daggy (1945) provided details of the nymph (under the name R. pellucida) concerning colouration of the body and legs noting the variation in the characteristic pale areas of abdominal tergites VIII and IX, as well as the distinctive markings on the femora, that it was possible to reliably recognize nymphs of this species. However, Daggy (1945) did not provide any details of mouthparts, gills, or other salient anatomical features. Leonard and Leonard (1962) provided a brief description of the nymph using specimens from Michigan, but again focused mostly on colour patterns. Flowers and Hilsenhoff (1975) included the nymph in their key to Wisconsin species (under the name of R. pellucida). Comparative details presented by Flowers and Hilsenhoff (1975) concerning gill morphology and colouration of the femora allowed the species to be easily identified among Wisconsin species of Rhithrogena. In addition, Flowers and Hilsenhoff (1975) noted that the characteristic pale area of abdominal tergites VIII and IX tended to fade after preservation and that a somewhat similar pale area on some abdominal tergites also appeared on some of the nymphs they determined as R. jejuna (herein recognized as a new species). Among the key characters presented by Flowers and Hilsenhoff (1975) for nymphs of R. manifesta (under the name of R. pellucida), the lack of a central dark mark within the pale median spot of the femora was of primary importance in separating this species from what they called R. jejuna. This key characteristic together with the lack of a dark central mark on their Figure 3I suggests that they believed it was absent throughout the species. This is perplexing, because Daggy (1945) specifically noted the presence of a brown median mark on the femora of R. pellucida in his original description based on specimens from Minnesota. Study of reared specimens from Maine and nymphs from New Hampshire have shown that a brown median mark within the pale oval median spot on the femora to be a consistent character. However, these marks on the femora tend to fade after preservation; moreover, dark median marks can vary in intensity among live individuals with some having faint marks even before preservation. Dark median marks even vary from forelegs to mid and hind legs with those on mid and hind legs often being much less distinctive or absent on some specimens. Perhaps the somewhat variable nature of this character explains the discrepancy between the description given by Daggy (1945) and the key character in Flowers and Hilsenhoff (1975). On live specimens, dark median marks on the femora have a reddish-brown tint and are quite distinctive within the pale oval median spot, which is further emphasized by the slightly darker greyish-brown shading surrounding it. Finally, Durfee and Kondratieff (1994) discuss the taxonomic features of R. manifesta (under the name of R. pellucida) with regards to other species of Rhithrogena from Colorado and draw attention to a new gill character (L-shaped sclerous rib) not mentioned in previous accounts of this species.

Distribution. Rhithrogena manifesta is mostly distributed east of the Rocky Mountains (Fig. 337). The species was initially described from material collected in Illinois (Eaton 1885), but has subsequently been reported in the U.S. from Illinois, Indiana, Iowa, Maine, Michigan, Minnesota, New Hampshire, and Wisconsin (Daggy 1945, Burian and Gibbs 1991, Klubertanz 1995, 2016, Randolph and McCafferty 1998, Jacobus and McCafferty 2002, and Chandler et al. 2006). In the southeastern United States R. manifesta has been reported from Alabama, Arkansas, Missouri, South Carolina, Tennessee, and Virginia (Sarver and Kondratieff 1997, McCafferty et al. 2010). Records of R. manifesta from the western United States are restricted to North Dakota (Guenther and McCafferty 2005) and Colorado (Durfee and Kondratieff 1994). In Canada R. manifesta has been reported from Manitoba, New Brunswick, Ontario, and Quebec (McCafferty and Randolph 1998, Jacobus and McCafferty 2002). The northeastern distribution of R. manifesta is given in Appendix 2.

Life History and Ecology. Rhithrogena manifesta is almost always associated with clean, 3rd order or larger streams and rivers with small to medium cobble substrates (without extensive moss or attached filamentous algae), and swift currents (~0.5 m/s). Most specimens reared for this study were collected from the lower section of the Narraguagus River, a coastal river in far northeastern Maine. Near final instar and black wingpad nymphs were collected from shallow, swift chutes with small to medium gravel and small cobble at the edges of the main channel and from broad swift, deep riffles at mid-channel. Thus, nymphs appeared to be broadly distributed across the width of the channel wherever microhabitat requirements were met. Water temperature when near final instar nymphs were collected on 8 August 2018 ranged from 28.0 – 29.1°C between sites separated by a distance of 10.6 km. In general, water quality of the Narraguagus River is considered quite high as it is a spawning river for Atlantic Salmon. On 21 June 2011 at the Little Falls Field Station site (Cherryfield, ME) the following data was recorded: Water temperature = 19.9°C, pH = 6.84, and Specific Conductance = 25 µS (Dissolved oxygen was not measured, but prevailing conditions (land use within 1 km of site was mostly undisturbed deciduous and coniferous forest) indicated it likely was at or close to equilibrium value of about 9.0 ppm pursuant to water temperature and site elevation (27 m above sea level). Within larger river habitats of the northeast R. manifesta appears to have the highest thermal tolerance of all Rhithrogena species, with nymphs completing their development in water 15 – 17°C warmer than that known for any other northeastern species of Rhithrogena. Additional evidence of high thermal tolerance of R. manifesta is provided by McShaffrey and McCafferty (1998), who reported maintaining mature nymphs in laboratory observation chambers for extended periods at water temperatures of 20 – 25° C.

Rhithrogena manifesta seems to be univoltine throughout its range, but there have been no detailed studies of its life history. Considering the species’ broad geographic range and its high thermal tolerance it would seem that changes in its occurrence could be used to monitor large scale changes in the thermal conditions of mid to lower sections of drainage networks if a detailed understanding of its life history were available. More specifically, because of this species’ high thermal tolerance it could possibly act as an upper thermal threshold indicator species useful in detecting and/or monitoring the critical upper thermal limit in habitats where it occurs.

Material Studied (Details of all repetitive site records listed in Appendix 1)

Material Studied. USA: Colorado: Jackson Co., North Platte River, Verner SWA (State Wildlife Area) 7 mi. (11.67 km) SW of Walden [40.695784°/-106.41487°, elev. 2437 m], B. Kondratieff & R. Durfee, 19 Aug 1993, 2♂(+Nex), 1♀(+Nex), 1S♂, 2S♀(+Nex), 1N♂, 1N♀ [CSU]; Maine: Washington Co., Narraguagus River, “Barrens” (area behind Deblois airport off Rt. 193) [44.713647°/-068.006516°, elev. 30 m], T. Mingo, 6 June 1974, 1N♂, 1N♀ [NEL]; same, Narraguagus River, Little Falls Field Station (National Marine Fisheries Site) off Rt. 193, N of Cherryfield [44.653061°/-067.957068°], elev. 21 m, S.K. Burian, 12 Aug 2009, 1♂(+Nex), 1S♂(+Nex), 2N♂, 1N♀ [NEL]; same, 21 June, 2011, 1N♂, 1N♀ [NEL]; same, 30 July 2014, 4N♀ [NEL]; same, 14 Aug 2014, 1N♂, 3N♀ [NEL]; same, 8 Aug 2018, 1N♂, 2N♀ [NEL]; same, Narraguagus River, west side of channel at picnic area off River Rd., Cherryfield [44.603687°/-067.925977°], elev. 3 m, S.K. Burian, 12 Aug 2009, 1♂ [NEL]; same, 5 July 2014, 1N♀ [NEL]; same, 30 July 2014, 2N♂ [NEL].

Rhithrogena serpenglena sp. n.

Figs. 281 – 331

Rhithrogena jejuna (sensu Traver 1935: 380 [male imago], Fig. 102: 378 male genitalia; sensu Flowers and Hilsenhoff 1975: 211 [nymph], Fig. 1A: 203 male genitalia, Fig. 3A: 205 nymph gill 3, Fig. 3G: 205 nymph forefemur).

Type Material: Holotype and Paratype designated in Material Studied Section.

Etymology: The species name is a descriptive name formed from the Latin noun serpens (snake) and Greek noun glena (pupil of the eye) and stands in apposition. The name describes the appearance of the vertical dark mark over the pale oval spot on the femora of nymphs, which resembles the eye of a snake.

Nymph (in alcohol with well-developed or dark wingpads). Body length: 7.60 – 10.60 mm (Mn = 8.95±1.26 SD; Md = 9.25; n=16). Description based on male nymph except where noted.

Head. Colour Pattern: Overall background colour brownish-yellow (colour close to NCG# 24 – Buff) (Fig. 281). Anterior and lateral edges of head capsule tinted with grey, especially along edges of pale narrow line connecting lateral ocelli (Fig. 281). Pale narrow line between lateral ocelli and along anterior margins of compound eyes, line merges with edge of faint oblong spots posterior to antennal bases. Pale narrow line gradually widens where it meets lateral margin of head capsule. On some specimens, one pale spot occurs anterior to base of antenna. Anterior margin often with short dark brown medial dash along midline where labrum articulates with head capsule. Posterolateral edges of head capsule adjacent to outer corners of compound eyes pale. Vertex of head between compound eyes with pair of small pale spots, often spots more distinct on females. On male nymphs, small pale spots can be elongated and close to ecdysial suture. In addition, small groups of 2 – 4 irregular brown spots can occur on vertex. Shape: Head capsule broadly oval with symmetrical anterior and lateral margins with minimal deviation at posterior corners near compound eyes, thus not appearing to be distinctly indented at this point (Fig. 281). Width of head capsule about 1.5x length. Anterior margin with slight median emargination where labrum articulates with head capsule. When head capsule viewed dorsally, curvature of anterior margin can obscure median emargination making it appear absent. Except for outer edges of maxillary palps, mouthparts completely concealed beneath edges of head capsule. Posterior margin of head capsule essentially straight on late instar nymphs. Compound Eyes: Compound eyes of male nymphs large and somewhat tear-drop shaped, when viewed dorsally outer margins reach to, or extend slightly beyond, outer margins of head capsule (Fig. 281). Anterior and posterior margins of compound eyes converge toward midline of head transitioning to broadly rounded inner corners (Fig.281). Compound eyes separated by gap slightly greater than width of one lateral ocellus. On female nymphs, compound eyes smaller, less tear-drop shaped than on males, with anterior and posterior margins meeting at about 90° angle (Fig. 282) and gap between eyes more than 2x as wide as on male nymphs. Compound eyes of male nymphs occupy most of posterior half of head capsule, on female nymphs much less so. Ocelli: Median and lateral ocelli as in Figs. 281, 282. Pale spots present over all ocelli, with spots over lateral ocelli slightly larger than over median ocellus. Pale lateral Y-arms of ecdysial suture merge into pale spots of lateral ocelli, which connect to pale narrow lines anterior to compound eyes. Each ocellus with broad black C-shaped base visible beneath cuticle (Figs. 281, 282). Antennae: Basal membrane of antennal socket pale and edge of socket dark brown (Fig. 281). Scape and pedicel dark brown, similar to surface of head capsule. Proximal two-thirds of flagellum light brown. Apical 6 – 7 annuli of flagellum colourless or pale cream coloured. Antennae length about 1.3x midline length of head capsule.

Mouthparts. Labrum: Labrum somewhat semicircular shaped (i.e., segment of circle subtending ~100° of arc), curved lateral margins merge with rounded posterior corners (Fig. 283). Anterior margin with shallow median emargination. Anterior median emargination with groups of 3 – 4 small, rigid spines on either side of ventral edge (Fig. 284). In addition, center of ventral edge of emargination may have an irregular rough tooth-like projection. Small rigid spines usually not visible from dorsal perspective. Anterior dorsal surface of labrum medium brown with lighter areas laterally. Posterior part of dorsal surface dark brown with field of short, hair-like setae with bases widely separated (Fig. 283). Middle and anterior portion of dorsal surface with few relatively long hair-like setae, but medially one pair of large setae occurs close to median emargination (Fig. 285). Group of 2 – 3 widely spaced setae, similar in form to medial pair of long setae, occur near each lateral margin. Ventral lateral edges of labrum with 17 – 18 long, setae with setae decreasing in length toward anterior margin (Fig. 286). Adjacent to row of long ventral edge setae, 15 – 18 shorter setae occur in an irregular row and decrease in length as described for long setae. Ventral anterior edges of labrum with 6 – 7 small, stout spine-like setae in gaps between long marginal setae and small rigid spines at edges of median emargination (Fig. 284). Maxillae: Left maxillae as in Fig. 287. Galea-lacinia with eight pectinate crown setae, with what appears to be a maximum of eight teeth on all but apical three crown setae (Fig. 288), which each appear to have five teeth. No vestigial crown seta present. Submedial row of 33 – 34 long setae with finely biserrate edges present below crown of galea-lacinia (Fig. 289). Near apex of submedial row of setae, one long and biserrate seta occurs set back from main row of long setae. Often at base of submedial row of setae, small groups of 2 – 3 shorter setae occur that are not aligned with the submedial row. Inner edge of galea-lacinia with dense double row of long, simple setae; setae of ventral row only about one-third length of setae of dorsal row (Fig. 289). In addition, at base of double row of inner edge setae is basal row of 9 – 10 long, simple setae with tips extending well beyond those of main portion of inner edge row (Fig. 289). Maxillary palp as in Fig. 290, appearing two-segmented. Inner edge of apical segment slightly concave with 8 – 10 small, simple setae widely spaced along edge. Apical segment of maxillary palp with distinctive longitudinal sclerotized band and distinct narrow, brown vertical band near tip (Fig. 290). Most of ventral surface of apical segment of maxillary palp covered with short, stout monopectinate setae (Fig. 291) with 4 – 5 sharp teeth on most large forms across middle of array of setae. Some setae near apex of array of monopectinate setae have eight or more longer and thinner teeth than those in middle of array. Outermost edge of apical segment with about five rows of large, simple setae with downward curved tips (Fig. 291). Dorsal surface of apical segment with scattered long, hair-like setae. Hypopharynx: Lingua rectangular with essentially straight apical edge and roughly parallel sides (Fig. 292). Setae of apical margin short and appear to be uniformly distributed across surface. Superlinguae as in Fig. 293 with nearly straight outer edges not greatly expanded. Bases of superlinguae gradually tapering to base of hypopharynx. Apical margins of superlinguae with distinct notch and long, hair-like setae (Fig. 293). Mandibles. Right mandible (Fig. 294a, ventral view): Anterior margin straight near molars, but slightly concave near prostheca and with continuous row of short, hair-like setae (Fig. 295). Molar surface distinctly depressed relative to position of anterior margin. Molars composed of rows of teeth that vary from sharp, conical forms at ventral edge to large cylindrical forms with rounded, tops along dorsal edge (Fig. 296). Apical teeth of ventral edge thin, sharp, and closely spaced. Molar surface terminates with one large, outwardly pointing tooth (Fig. 297). Adjacent to apex of molars are about eight long, simple setae thicker than typical hair-like setae. Prostheca composed of one row of about seven long, thick finely biserrate setae adjacent to base of inner incisor (Fig. 298a). Incisors as in Figs. 298a. Outer incisor length about 3.0x width, smaller sized teeth on outer edge homonomous from apex to base where basal teeth become thinner and sharper. Larger sized inner teeth fewer, with seven distinct teeth each with small tubercle near tip making teeth appear bifid up to apical complex (Fig. 298b). Apical complex of outer incisor composed of two smaller lateral teeth, one large medial tooth apparently fused into one tricuspid unit. Basal part of outer incisor with comb of about 24 fine teeth, most teeth forked near tip with depth of fork from tip about one-eighth length of entire tooth (Fig. 299). Inner incisor scoop-shaped with toothed upper edge (Fig. 299). Leading edge of inner incisor with about four long setae in row below large apical tooth. Upper edge of inner incisor with row of about seven large coarse teeth that gradually merge into trailing edge row of fine comb-like teeth (Fig. 299). Outer edge of mandible below incisors with fringe of many (usually > 20) long, hair-like setae (Fig. 294b, often obscured by detritus on mandible). Inner edge of mandible below molars without long setae. Left Mandible (Fig. 300a, ventral view): Anterior margin between molars and base of prostheca essentially straight with row of short, hair-like setae beginning near middle of margin and extending up to prostheca (Fig. 301). Anterior margin adjacent to molars bare. Upper edge of molar surface with large multidentate first tooth that transitions to smaller multidentate teeth of outer row of upper molar surface (Fig. 301). Majority of molar surface as in Fig. 302, where about 10 rows of short, rounded or conical teeth each terminate with somewhat flattened brush-like teeth. Outer three teeth adjacent to apex short and not brush-like. No distinct apical tooth present, but 3 – 4 long, hair-like setae occur below apical cluster of short molar teeth. First ventral row of molar teeth with one large brown conical tooth set back from middle of row (Fig. 303). Prostheca composed of row of about 10 finely biserrate setae that gradually increase in length up to base of inner incisor (Fig. 301). Incisors as in Figs. 301, 304. Outer incisor length about 2.9x width, smaller sized teeth of outer edge homonomous from apex to final 3 – 4 teeth of row with remaining teeth becoming thinner and sharper to junction with posterior comb (Fig. 304). Larger sized inner teeth fewer, with seven distinct teeth and one smaller basal tooth. Large teeth of inner edge each with small tubercle near tip making them appear bifid (Fig. 305). Apical complex of outer incisor composed of two small lateral teeth and one large terminal tooth fused into one tricuspid structure (Fig. 304). On some specimens, lower tooth of apical complex much smaller than upper tooth making apical complex appear bicuspid-like. Basal part of outer incisor with comb of about 25 fine teeth, most teeth forked near tip with depth of fork from tip about one-eighth length of entire tooth. Inner incisor scoop-shaped with toothed upper edge (Fig. 301). Leading edge of inner incisor with row of about four long, thin setae below large tooth of upper edge. Upper edge with row of about eight large, coarse teeth that become progressively thinner merging with row of fine comb-like teeth on trailing edge of inner incisor (Fig. 301). Outer edge of mandible below incisors with fringe of many (usually >20) long, hair-like setae (Fig. 300b, setae often obscured by detritus on mandible). Inner edge of mandible below molars without long setae. Labium: Labium as in Fig. 306. Dorsal surface of glossae with long, hair-like setae on inner apical surface and row of similar hair-like setae that extends from apical area to base of glossae (Fig. 307). Most of dorsal surface of paraglossae with dense patch of long, hair-like setae with curved tips that extend well above its surface and beyond large spine-like setae from ventral surface. Ventral surface of glossae mostly bare, except for one large subapical seta. Upper half of ventral surface of paraglossae with area of large spine-like setae, some large spine-like at anterior edge extending about half the length of long, hair-like setae from dorsal surface (Fig. 308). Upper part of inner edges of glossae diverging from midline of labium more than lower part of inner edges forming relatively wide U-shaped gap between glossae (Fig. 306). Labial palps two-segmented. Apical segment of palps with distinct array of pectinate brush setae on ventral surface and apical brush of simple setae. Ventral surface of apical segment of palps with row of long, thin setae with curved tips along outer edge. Dorsal surface of apical segment of palps with array of long curved bifurcate setae.

Thorax. Pronotum: Overall shape somewhat trapezoidal with greatest width near anterior margin (Fig. 309a). Anterior margin mostly straight, but posterior margin slightly convex on either side of body midline (Fig. 309a). Posterior lateral edges appear fused with mesonotum despite pale boundary line between them (Fig. 309b). Posterior half of pronotum slightly raised on either side of midline forming pair of low humps. Lateral edges of widest part of pronotum brown (Fig. 309b). Anterolateral pale spots adjacent to brown lateral edges (Fig. 309b). Pronotum with distinctive pattern (Fig. 309a), with short slanting dark bar in center of pale inverted U-shaped mark adjacent to elongate and reversed C-shaped mark that extends almost to midline of pronotum. On live nymphs slanting dark bar does not appear as it does on preserved specimens, instead it appears to have pale oblong core. Other pale marks of this pattern are more consistent between live and preserved specimens. Anterior margin of pronotum with paired dark brown dashes on either side of midline. Pronotal pattern seems consistent on female nymphs. Mesonotum: Overall background colour similar to pronotum in darker regions along anterior margin and at base of forewingpads, but generally lighter brown compared to head capsule. Anterior margin shaded with dark brown along concave portion of edge (Fig. 310). Small, dark brown spot posterior to base of each forewingpad producing mottled effect (Fig. 310), and MLs pale with stripe of uniform width. Outer and inner edges of forewingpads slightly darker brown, as well as portion of MS parallel to body midline and notched apex of SL (Fig. 310). Lightly sclerotized areas pale compared to thicker areas of cuticle. Lateral margins of mesonotum from base of forewingpads to outer edge of pronotum almost straight. Metanotum: Mostly pale with brown shading similar to mesonotum along anterior margin. Dark brown shading occurs lateral to bases of hind wingpads and above hind coxae. Pleural Region: Membranous area of pleural region posterior to forecoxae with black smudge. Black smudge also present on membranous area anterior and posterior to mesocoxae (Fig. 311). 

Abdomen. Tergites: Background colour of tergites of preserved specimens yellow-brown, on some specimens tergites VI – X slightly darker brown than tergites I – V (Figs. 310, 312). On live or freshly preserved specimens, background colour is uniform medium brown. Sides of tergites above lateral margins slightly darker brown. Tergites II – IX with one pair of small submedian spots near middle of each tergite, spots range from pale yellow on posterior tergites to nearly same as background colour on anterior tergites (where spots are similar to background colour, they have slightly darker edges). Anterior margins of tergites II – VIII brown and lack pale dashes or spots. On tergite X paired pale submedian streaks replace paired submedian spots as occur on other tergites (Fig. 310). Lateral margins of tergites II – VIII with somewhat triangular or oval indentations. On tergites II – VII lateral indentations marked with dark brown (Fig. 312), but dark shading absent on tergite VIII. On live or freshly preserved nymphs, triangular marks appear pale, contrasting with dark lateral areas of tergites. Lateral areas of tergites II – VIII usually with small dark brown spot adjacent to base of posterolateral projections. Anterolateral corners of tergites II – VIII with short dark brown dash along anterior margin. Lateral areas of tergites IX – X lack dark contrasting colours, as occurs on preceding tergites. Posterolateral projections of tergite IX not flared outward and do not extend much beyond anterior margin of tergite X. Posterior intersegmental membranes of tergites I – IX with band of dark greyish-brown pigmentation along posterior margin of tergites (Fig. 312; on some specimens, dark colour may be obscured by overlap of adjacent tergites). Tergite Spinules and Posterolateral Projections: Posterior margin of all abdominal tergites with distinct row of spinules (Fig. 313). Spinules all similar in size and do not alternate across width of row. Microspinules occur among bases of spinules, originating slightly before bases of spinules and occur to outer edges of spinule row. Posterolateral projections short and weakly pointed or blunt on tergites I – VII (Fig. 314). Tergites VIII and IX have short, blunt, posterolateral projections and tergite X lacks these structures. Small brown sclerous lobe-like structure associated with posterior margin of tergites VII – IX occurring between end of row of spinules and posterolateral projection. Small sclerous structures on tergites VII – IX appear to be weakly fused to posterior margins of respective tergites. Small sclerous structure on tergites IX larger than on tergites VII and VIII. Small sclerous structure on tergite VII does not seem to be fused with posterior margin of tergite. Sternites: Abdominal sternites range from pale yellow-brown to light brown on some specimens. Sternites VII – IX usually with extensive dark brown shading along anterior margins (Fig. 314). Sternite I with anterior flanges transparent light brown, outer corners of flanges vary from weakly pointed to rounded (Fig. 314). Sternites I – VIII with pair of small, pale submedian spots near anterior margin, flanked by pair of faint brown diagonal dashes and pale lateral transverse streaks margined with brown (Figs. 314, 315). Anterior margin male sternite IX with dark brown median mark and dark brown shading at bases of developing forceps. Female sternite IX similar in colour to preceding sternites.

Legs. Forelegs: Overall background colour yellow-brown to light greyish-brown with slightly darker shading on some parts of femora and other leg segments, especially adjacent to joints (Fig. 316a). Forefemora length about 2.8x width (forefemora of mid instar nymphs can be wider compared to its length than late instar nymphs, hence length only about 2.5x width). Dorsal surface of forefemora light brown with dark brown shading around pale oval median spot (Fig. 316a). Forefemora with pale oval median spot with upper edge connected to pale streak along base of dorsal fringe of long setae. Middle of pale oval median spot with vertical, occasionally teardrop-shaped, dark brown median mark that extends completely across middle of pale oval median spot (Figs. 316a, 317). On some specimens, vertical dark median mark can appear connected to small dark area along ventral edge row of setae by diffuse lighter brown band. In addition, vertical dark median mark can appear crescent shaped on some specimens (Fig. 316b). Apical portion of forefemora beyond dark brown border of pale oval median spot mostly pale (Figs. 316a, 317). Dorsal and ventral edges of forefemora slightly darker brown along rows of marginal setae. Edge of forefemora adjacent to joint with trochanter dark brown. Dorsal edge of forefemora with one row of long setae with variously expanded transparent tips and edges (Fig. 317). Although many long setae of dorsal edge row seem to have sharp tips, several seem to have sharp tips associated with broad transparent flattened edges of variable widths and lengths; some seem similar to elongate flags. Dorsal row of setae of uniform length, except for 1 – 2 setae near apex of row. Row of irregularly spaced short, hair-like setae below middle of dorsal row of long marginal setae. Dorsal surface of forefemora with field of short, flattened setae as in Fig. 318. Flattened setae over middle of dorsal surface with distinctive dark brown bases. Flattened setae relatively uniform in shape, almost all with parallel sides without noticeably constricted bases (i.e., not distinctly paddle-shaped). Ventral edge of forefemora with relatively few large, spine-like setae or narrow flattened forms similar to those with parallel-sides, as noted above. Groove along ventral edge of forefemora pale with only faint light greyish shading adjacent to joint with foretibiae or completely lacks colour (foretibiae completely cover this area when folded against forefemora). Foretibiae: Length of foretibiae about 0.9x length of forefemora. Basal part of foretibiae adjacent to tibio-femoral joint shaded with dark brown (Figs. 316a, 317). Apex of foretibiae pale at joint with foretarsi. Middle of foretibiae either uniform light brown (Fig. 316a) appearing unbanded or may be slightly darker than rest of segment appearing weakly banded (Fig. 317). Ventral margin of foretibiae with 6 – 7 scattered stout setae, some with rounded tips and others with pointed tips. Ventral apical edge of tibio-tarsal joint with two large monopectinate setae and on opposite side of joint one large, flattened seta (Fig. 319). Dorsal edge of foretibiae with dense longitudinal row of small hair-like setae extending from tibio-femoral joint to apex of foretibiae. Sparse longitudinal row of scattered small hair-like setae occur from base to apex of foretibiae lateral to dorsal edge. No large, paddle-shaped setae occur within dense dorsal longitudinal row of hair-like setae. Foretarsi: Length of foretarsi about 0.4x length of foretibiae. Background colour similar to foretibiae, but brown colour slightly darker across middle of segment producing appearance of faint brown band (Figs. 316a, 317). Longitudinal row of hair-like setae on foretibiae continues along dorsal edge of foretarsi with one paddle-shaped seta embedded in row. In addition, scattered hair-like setae occur along other edges of foretarsi and 2 – 3 long, hair-like setae on apical margin below foreclaws. Foreclaws: Foreclaws as in Fig. 320, with pale base and elongate sharp, brown tip. Foreclaw with one basal tooth and three preapical denticles that gradually become thicker and longer toward claw tip (Fig. 320). Outer apical portion of foreclaws slightly less than one-third their total length. Middle and Hind Legs: Colour: colour patterns, and arrangement of setae similar to that of forelegs (Fig. 316a). There is some variation in appearance of pale oval median spot, which is slightly smaller than on forefemora and upper edge is often more broadly connected to pale elongate area adjacent to dorsal edge row of long marginal setae (Figs. 316a, 321). Vertical dark median mark often smaller and restricted to limits of pale oval median spot; on some specimens, dark median mark can become less teardrop-shaped than on forelegs. Short, flattened setae on mid and hind femora often more numerous across lower part of pale oval median spot and surrounding dark brown border compared to forefemora. Structure and appearance of mid and hind tibiae, tarsi, and claws generally similar to that of forelegs (Fig. 316a), however there are some differences. Both larger paddle-shaped and smaller parallel-sided setae with rounded tips present in dorsal longitudinal row of hair-like setae on mid and hind tibiae compared to foretibiae. Ventral apex of mid and hind tibiae with group of 6 – 7 large stout setae with sharp tips, 1 – 2 isolated large, curved setae, 1 – 2 paddle-shaped setae, and dense patch of short hair-like setae. Mid and hind tarsi with two paddle-shaped setae embedded in lateral longitudinal row of hair-like setae (Fig. 322 as in Fig 267). Mid and hind claws similar in shape, size, and dentition to those of forelegs (Fig. 323).

Abdominal Gills. Colour and Position: Gills mostly transparent, but with some yellow-brown shading near gill bases and along base of dorsal margins, except for gill 1 (Fig. 310). On gill 1 brown shading restricted to straight inner margin anterior to gill base (Fig. 324). Gill filaments pigmented from base to tips faint greyish-green; on live nymphs, filaments more green. Dorsal margins of gills adjacent to base of filaments sclerotized and shaded brown. Tracheae transparent on all specimens available for study with only faint traces of pigment and all gills have consistent pattern of distinct secondary tracheols branching from main tracheae toward dorsal margins of gills as in Figs. 327. Expanded anterior portion of gill 1 extends under body to ventral midline. Functional dorsal edge (i.e., inner margin) of gill 1 meets or extensively overlaps dorsal margin of gill 1 from opposite side of body (Fig. 314). Abdominal gills 2 – 6 positioned laterally with anterior half of each gill overlapped by preceding gill, forming almost continuous disc around perimeter of abdomen (Fig. 315). Gill 1: Abdominal gill 1 as in Fig. 324, anterior corner where straight inner margin meets dorsal edge rounded. Outer margin with incisions forming ruffled edge. Depth of incisions variable, but usually less than width of each division and outer margin appears to have few wide ruffles (Fig. 324). Ruffles tend to become shallow posteriorly and cease at corner of posterior margin. Posterior margin broadly rounded with slight indentation at innermost point that mimics incisions of ruffled edge. Plica of dorsal surface as in Fig. 325a, acutely pointed with wide triangular base lightly sclerotized and shaded brown on mid to late instars (plica of early instar nymphs appears same colour as rest of gill surface — usually opaque white). Tip of plica extends about halfway to base of ruffled edge and slightly raised above gill surface (Fig. 325b). Except for slightly thicker region of gill within base of plica, most of gill 1 appears to be about same thickness. Cluster of filaments at gill base composed of 14 – 15 filaments that appear to originate from one tracheal base without subsequent branching (Fig. 326). Short, sclerotized support present adjacent to gill base. All tracheae of gill 1 transparent. Gill 2: Abdominal gill 2 as in Fig. 327. Overall shape of gill 2 broadly oval, with smooth posterior margin, no ruffled edge. Width of gill 2 about 0.7x length. Dorsal margin of gill 2 from pigmented basal strip to rounded apical edge straight to slightly convex and lacks any lobe-like projection (Fig. 328). A short strip of small, hair-like setae occurs just before apex of dorsal margin of gill 2, with setae extending around curvature of edge (Fig. 328). Dorsal and medial areas of gill 2 shaded light brown, darkest along dorsal margin and adjacent to tuft of filaments. Tracheae mostly transparent, except for traces of dark pigment near gill base. Tracheols of gill 2 seem to exhibit dendritic branching pattern with larger secondary tracheols extending in various directions from central tracheae (Fig. 328). Tuft of filaments as in Fig. 327, composed of about 20 filaments that appear to mostly arise from one major tracheal branch at base of gill 2 and lack secondary branching. Filaments extend to, or slightly beyond, midpoint of gill 2. Lower portion of gill 2 supported by curved transparent sclerotized rib that has faint traces of brown colour (Fig. 328). Base of upper portion of gill 2 supported by short, straight transparent sclerotized rib shaded with light brown. Both internal gill supports seem to lack surface setae. Gill 5: Abdominal gill 5 as in Fig. 329, shape broadly oval. Width of gill 5 about 0.7x length. Colour of gill 5 and tracheae as in gill 2. Ventral portion of posterior margin of gill 5 lacks ruffles similar to gill 2. Dorsal margin of gill 5 also similar to gill 2 including presence of strip of small, hair-like setae about halfway along margin (Fig. 330). Lower portion of gill 5 lamella supported by transparent curved sclerotized rib that is straighter than on gill 2 (Fig. 330). Base of upper portion of gill 5 supported by short, sclerotized rib similar in form and colour to that on gill 2. Tuft of filaments at base of gill 5 similar to gill 2 (Fig. 329). Gill 7: Abdominal gill 7 as in Fig. 331, with dorsal edge folded against sides of tergites VIII and IX, but not fused to gill surface. Thus, majority of gill 7 extends beneath abdomen as more or less free flattened structure. Apical margin of gill 7 meets and overlaps that of opposite gill 7 beneath body (Fig. 315). Ventral posterior margin with 2 – 3 shallow incisions (Fig. 331). Tuft of filaments at gill base reduced compared to preceding gills, but otherwise similar in colour and structure. Transparent support for lower half of gill 7 seems to merge with medial sclerotized rib. Base of medial sclerotized rib of gill 7 with traces of brown similar to preceding gills. 

Caudal Filaments. Colour and Structure: Median terminal filament slightly longer than cerci and together length of caudal filaments about 2.1x length of abdomen. On preserved specimens, caudal filaments pale white to cream coloured. All annuli (except for apical annuli) with short spines on posterior margins. Fine hair-like setae present along inner edges of cerci and sides of median terminal filament starting at about annulus 38 (as counted from base). Fine hair-like setae begin with only 2 – 3 per annulus, but rapidly increase to maximum of 6 per annulus. Terminal 15 – 18 annuli, lack marginal setae, but may have occasional small, spines at margins of some annuli.

Diagnosis Rhithrogena serpenglena sp. n. Nymph: Nymphs of R. serpenglena can be separated from those of other northeastern North American species of Rhithrogena by the following characters: (1) medium to large body size of near final instar nymphs (7.60 – 10.60 mm; Mn=8.95 (n=16); Md= 9.25 (n=16)), because largest specimens fall well within the body size range for R. amica, mean and median body size values are of greater diagnostic value across the range of this species, (2) femora with large, pale oval median spot and large, teardrop-shaped dark median mark that extends to or beyond the upper and lower edges of pale oval median spot (Figs. 316a, 317), on mid and hind femora of some specimens dark median mark may be curved or crescent-shaped, (3) abdominal gill 1 shaped as in Fig. 324, plica acutely pointed with lightly sclerotized triangular base (Fig. 325a), and plica projects upward from the dorsal surface of gill, (4) abdominal gills 2 – 6 without a dorsal lobe and lower part of gills with transparent, slightly curved rib that is most distinctive on anterior gills (Fig. 328), dorsal edge of gills 2 – 6 with strip of many small, hair-like setae that extend to posterior margin of gills, (5) tracheae of abdominal gills 2 – 6 not darkly pigmented and gills with faint yellow-brown shading near base and along dorsal margin, (6) abdominal gill 7 an elongated oval with dorsal edge only slightly folded against tergites VIII and IX, dorsal edge not fused with gill surface, (7) crown of maxillae with eight large pectinate setae, (8) apical segment of maxillary palp with distinct narrow brown vertical band (Figs. 287, 288), (9) glossae of labium diverging from midline of labium forming a broad U-shaped gap (Fig. 306), (10) lingua of hypopharynx rectangular with straight apical edge and sides only slightly convex, (11) outer incisors of right mandible length about 3.0x width, inner edge with seven large teeth and each tooth with a small tubercle near the tip making teeth appear bifid (Figs. 298b, 305), apical complex of three fused teeth forming a tricuspid unit, (12) outer edge of both mandibles with fringe of many (> 20) long, hair-like setae (Figs. 294b, 300b). See Appendix 3 for comparative list of R. serpenglena sp. n. diagnostic characters and those of other northeast species.

Taxonomic Discussion. The history and taxonomic status of R. serpengelna sp. n. is part of the complex series of events described herein for R. jejuna Eaton s.s. (please see that discussion for details). Among all of the events described earlier in the discussion of R. jejuna, the failure to recognize this species as distinct from R. jejuna first in the 1930’s (Traver 1935) and later in the 1970’s (Flowers and Hilsenhoff 1975) are perhaps the most important because they resulted in the true identity of R. jejuna being replaced by that of this species. These events have resulted in a long history of misidentifications leading up to the present day. To correct this problem this species is now named and types designated from specimens that were deposited in MCZ by C.P. Alexander (MCZ: ENT: 733352 [Holotype] (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:733352); MCZ: ENT: 733353 [Paratype] (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:733353) – note the Holotype specimen label lacks a year, but it is likely that the specimen was collected by C.P. Alexander while he was a student at Cornell University between 1909 and 1918 — see material studied for full specimen label details). The description and figure of the male genitalia given by Traver (1935, under the name R. jejuna) and photograph of the male genitalia presented by Flowers and Hilsenhoff (1975) provide adequate details of the male imago of R. serpenglena sp. n. However, the brief description of the nymph given by Flowers and Hilsenhoff (1975, under the name R. jejuna) and figures of the femur and an abdominal gill are insufficient for detailed comparison with nymphs of other species; thus a complete and comparative description is provided here with illustrations of mouth and body parts.

Distribution. Rhithrogena serpenglena sp. n. is one of the most broadly distributed Rhithrogena species in North America (Fig. 338). Based on analyses presented here, all records of R. jejuna that are known to be or can likely be ascribed to determinations made using the keys and associated descriptions given by Traver (1935) and Flowers and Hilsenhoff (1975) are applicable to R. serpenglena sp. n. Canadian records of R. jejuna listed by McCafferty and Randolph (1998) for New Brunswick and Nova Scotia; and Giberson and Burian (2017) for Northwest Territories are now referable to R. serpenglena sp. n. However, records of R. jejuna collected prior to 1935 from Alberta, British Columbia, Manitoba, and Saskatchewan are believed to be based on adults that were determined using the description given by Eaton (1885) and thus are not considered referable to the new species. In addition, records listed by McCafferty and Randolph (1998) for Newfoundland (i.e., Labrador) and Quebec are also of adults that are believed to have been determined using the original concept of R. jejuna and thus not referable to the new species. In the northeastern United States, records of R. serpenglena sp. n. have been published for Connecticut, Maine, New Hampshire, and New York (Burian and Gibbs 1991, Burian and Bednarik 1994, Chandler et al. 2006, Dodds 1978, and Meyers et al. 2008, Meyers et al. 2011 — under the formerly recognized concept of R. jejuna sensu Traver). New records presented here add Massachusetts to the list of New England states. Although there are no published accounts from Ohio, there are records for Indiana (McCafferty 2009). Most records from the upper Midwestern region are from Michigan and Wisconsin (Randolph and McCafferty 1998, Klubertanz 2016). Further west, this species has been reported from North Dakota (Guenter and McCafferty 2005), Iowa (McCafferty et al. 2003), and Oklahoma (McCafferty et al. 1997) and a new record is presented here for Minnesota. The northeastern distribution of R. serpenglena sp. n. is given in Appendix 2.

Life History and Ecology. Rhithrogena serpenglena sp. n. occurs in clean, 2nd – 4th order streams with perennially cool water temperatures, with small to medium cobble substrates (without extensive moss or attached filamentous algae), and swift currents (~0.5 m/s). If seasonal water levels fluctuate much in a stream system, nymphs seem to be restricted to parts of the channel that are permanently wetted during the lowest flow conditions of the year. Thus, if spring high flows fill a channel to a width of 30 m and summer base flow reduces the wetted channel to 10 m, nymphs will most often be found only in that same 10 m wide section of the channel even when flows fill the channel to its full 30 m width. Hence, there doesn’t seem to be much, if any lateral movement of nymphs during high flow periods. Currently, there are only a few detailed observations of habitat and environmental tolerances (Burian and Gibbs 1991). In Connecticut, R. serpenglena sp. n. nymphs were reared from the Fenton River (Thames River drainage). Water quality data recorded on 11 Mar 2016 were: Water temperature = 11.4 °C; pH = 7.17; and Specific Conductance = 117.0 µS. The water depth at the sampling point ranged from 0.35 – 0.40 m; current velocity at 0.6x depth = 0.51 m/s; and channel width = 10.5 m. Substrate at this site was predominantly small cobble (64.0 – 128.0 mm) with lesser amounts of medium cobble (128.0 – 256.0 mm) and large cobble (256.0 -512.0 mm). Dissolved oxygen was not measured, but prevailing conditions (land use within 1 km of site was protected deciduous forest) indicated it likely was at or close to equilibrium value of 10.5 ppm pursuant to water temperature and site elevation (110 m asl).

Material Studied (Details of all repetitive site records listed in Appendix 1)

Type Material Examined. Holotype: USA: New York: Fulton Co., Gloversville [43.053658°/-074.344377°, elev. 249 m, location in town of Gloversville uncertain], C.P. Alexander, 15 May year? (year collected estimated to be within period 1909 – 1918), 1♂ (genitalia on slide) [MCZ: ENT: 733352 (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:733352)]; Paratype: USA: New York: Fulton Co., Sport Island (location no longer exists as an “island”) [43.216583°/-074.182467°, elev. 239 m, coordinates of historic marker for “Sport Island” in Northville, NY], 12 June year?, C.P. Alexander, 1♂ [MCZ: ENT: 733353 (https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:733353)].

Other Material Studied. USA: Connecticut: Tolland Co., Fenton River, ~300 m S of bridge on Old Turnpike Rd., Mansfield [41.829885°/-072.240051°], elev. 113 m, S.K. Burian, 11 Mar 2016, 1♂(+Nex), 2N♂, 6N♀ [NEL]; same, Fenton River north of Gurleyville Rd., Mansfield [41.824204°/-072.235243°], elev. 100 m, S.K. Burian, 17 Apr 2014, 1♀(+Nex) [NEL]; same, Fenton River, sample s-2 G71 S of Liska Rd. nr Moose Meadow Rd., Willington [41.892831°/-072.231874°, elev. 159 m], P.J. Dodds, 25 April 1977, 1N♂, 1N♀ [NEL]; Maine: Somerset Co., Carrabassett River (SBrCR), 2.4 km W of North Anson, site S8 [44.862743°/-069.934039°], elev. 96 m, S.K. Burian, 22 May 1986, 1S♂ [NEL]; Washington Co., Narraguagus River, west side of channel nr picnic area on River Rd., Cherryfield [44.603687°/-067.925977°], elev. 3 m, S.K. Burian, 17 May 2005, 1N♂, 3N♀ [NEL]; Massachusetts: Berkshire Co., Cold River, riffle at entrance to Mohawk State Park, Savoy [42.641445°/-072.957387°, elev. 251 m], no collector given, 7 Nov 1994, 1N♀ [NEL]; same, Deerfield River, Florida (town of) [no coordinates estimated – location uncertain], no collector given, 9 Nov 1994, 3N (less than mid-instar) [NEL]; Franklin Co., Deerfield River, from shallow swift water at pull-off west of village of Zoar, Charlemont [42.655113°/-072.939631°, elev. 184 m], no collector given, 16 Nov 1994, 13N (less than mid-instar) [NEL]; same, 9 Nov 1994, 2N (less than mid-instar) [NEL]; Hampshire Co., Lower Joe Wright Brook, Audubon Sanctuary – Grave’s Farm, Williamsburg [42.398776°/-072.712779°], elev. 154 m, B. Colburn?, 7 Oct 1992, 2N (less than mid-instar) [NEL]; Minnesota: Lake Co., West Branch Splitrock River at Rt. 3 [47.241491°/-091.481233°], elev. 376 m, S.K. Burian, 29 May 1999, 1N♂ [NEL].