Key to Hemistola species of the Baikal region

1. Forewing antemedial line (usually present) rather long, convex, more or less parallel to postmedial transverse line and termen, terminates near 1/3 of costa (Fig. 17B). Male genitalia: stout sclerotized spine in base of valva comparatively long; posterior projections of sternite A8 usually rounded (Figs. 34A–34C). In female genitalia (Fig. 37E) lamella postvaginalis small, without distinct semicircular furrow.................................................... H. chrysoprasaria (Esper, 1795)

- Forewing antemedial line (often almost absent: Figs. 17A, 57D) markedly shorter than in H. chrysoprasaria, not convex, sharply curved inwards anteriorly, terminates closer to wing base, near ¼ of costa (Figs. 16D, 57C). Male genitalia: stout sclerotized spine in base of valva slightly shorter than in H. chrysoprasaria; posterior projections of sternite A8 tapered (Figs. 9A–G, 10 A–H, 34D–34F). In female genitalia (Figs. 37F, 37G) lamella postvaginalis considerably larger than in H. chrysoprasaria, with distinct semicircular furrow................................................ H. zimmermanni (Hedemann, 1879)