Stenacron
Figures: 26, 57, 64, 82, 96, 112, 171, 193, 241
In addition to the Heptageniinae characteristics, the following combination of characteristics will identify the genus:
Larval Diagnosis
Larvae of Stenacron are differentiated from all other Nearctic genera by having gill lamellae 1-6 with a submarginal anal rib and a pointed apex (Fig. 96).
Adult Diagnosis
The presence of a black spot joining two or three crossveins below the bullae of the forewings (Fig. 193) will differentiate adults of Stenacron from other Heptageniinae. The well-developed spines on the lateral margins of the base of the penes (Fig. 171) will differentiate males of Stenacron from all other Nearctic genera. Stenacron carolina (Banks) and S. candidum (Traver) may lack the lateral spines on the base of the penes. Maccdunnoa and Maccaffertium may have minute lateral spines, but their penes will be either subquadrate or 'L' shaped. The eggs of Stenacron are unique in having a large coiled thread around each pole (Fig. 112).
Distribution
Nearctic (Fig. 241).
