Color. Dark body sections dark brown and without metallic reflections, and head mainly light reddish brown.
Head. Minimum distance between inner edges of eyes 1.3 times as long as maximum eye height (Fig. C28.4, black arrows), distance between inner edges of antennal sockets about 2.0 times the distance between inner edge of eye and outer edge of socket (Fig. C28.4, white arrows). Distance between inner edges of lateral ocelli 0.7 times as long as distance between outer edge of lateral ocellus and nearest edge of eye (Fig. C28.5). Head with setae sharp at apex. Gena rounded behind eye, without ridge, and densely pitted (Fig. C28.6). Antenna with 13–15 flagellomeres, the flagellomeres round or almost round in cross section, and middle flagellomeres about 3.0 times as long as high.
Thorax. Metatibia with two apical spurs. Fore wing angularly rounded at apex, with vein 2r–m joined to cell 3M, with cell 1Rs2 long (2r–m and 3r–m slightly or very clearly shorter than veins Rs2 and M above and below), with cell 3R1 3.5 times as wide as long, with vein 2r-rs joining stigma near middle, with stigma gradually attenuated even after junction with vein 2r-rs (Fig. B1.70), with vein 1cu–a joining vein Cu about mid way between veins 1m–cu and M, without vein Cu1, with vein 2A extending near posterior edge of fore wing for 0.3 times cell length (Fig. C28.7), and with vein 3A stump-like (Fig. C28.7). Hind wing with hamuli present mainly apically and basally (length of basal hamuli section 0.4–1.0 times as long as apical section) from junction of veins R1 and C (as in Fig. B1.11 and Fig. C28.8), and with cell 1A closed.
Abdomen. Female. Tergum 9 with median basin about as long as wide and convex, without setae and pits, and sharply outlined anteriorly with short and slightly divergent ridges. Cornus about 1.7 times as long as median basin length, very narrow, and clearly constricted at middle (Fig. B1.74); cercus present and disc-like. Sheath. Basal section about 0.45 times as long as apical section, and length about 0.9 times as long as fore wing length; teeth on dorsal surface of apical section present in apical 0.25, and each tooth with a small sharp apical spine (Fig. C28.10).
Male with terga 1–8 and sterna 2–9 densely pubescent (Fig. C28.9).
Smith (1978), Taeger and Blank (2011) and Taeger et al. (2010) listed two species from eastern Asia, X. matsumurae (Rohwer, 1910) from eastern Russia, China, Japan, and Korea, and X. praelongus Maa, 1949, from China.
Semenov–Tian–Shanskij (1921) included only his new species, X. mysta, in his new genus Xoanon, but questionably considered X. mysta as a possible synonym of Sirex matsumurae Rohwer, 1910, because he was unable to see Rohwer’s type. Xoanon mysta was described from 1 male and 1 female from “insula Sachalin” and “Vladivostok”. We have seen many specimens of Xoanon from Vladivostok and they match Rohwer’s type perfectly. Xoanon mysta is almost certainly Rohwer’s species. We agree with Takeuchi (1938: 191) that Xoanon mysta Semenov, 1921 is a synonym of X. matsumurae (Rohwer, 1920).
We studied 20 specimens of both sexes of X. matsumurae, including the holotype, and two specimens for molecular studies (Fig. E2.1). All specimens studied are in CNC, NSMT, and USNM.