{A conchological study shows that there are three valid nominal taxa in the Gyraulus subgenus Torquis: Gyraulus parvus, G. circumstriatus and G. huronensis. Gyraulus parvus is the most common and widespread species, but G. circumstriatus is also widely distributed in North America. Gyraulus huronensis is limited to the northern Michigan shores of Lakes Huron and Michigan. Diagnostic anatomical characters of the subgenus Torquis are the sigmoidly folded kidney with undulating margins, the prostate diverticula arranged in a single row, and the straight, uncoiled intestine. The anatomy of G. parvus and G. circumstriatus is very similar; G. huronensis differs in external pigmentation, in the direct connection of the prostate gland diverticula to the sperm duct, in the overall shape of the prostate gland, and in the number of prostate diverticula. The three species exhibit several differences in radular teeth. The chromosome numbers of Gyraulus parvus, G. circumstriatus and G. huronensis are n=36