1	Hypomera and epipleura dark brown; apical part of median lobe less than 3.0 times as narrow as basal part	2
–	Hypomera and epipleura yellowish brown to brown; apical part of median lobe (Figs 50–52) more than 3.0 times as narrow as basal part	Gyrinus pullatus
2	Median part of mesoventrite (Fig. 23) with deep pit and large groove; median lobe (Figs 44–46) slightly shorter than paramere, apical margin rounded	Gyrinus gestroi
–	Median part of mesoventrite (Fig. 26) with shallow pit and vertical plica; median lobe (Figs 47–49) distinctly shorter than paramere, apical margin broadly rounded	Gyrinus japonicus