Genus Cyrtorizoceras Hyatt, 1900

Type species

Cyrtoceras minneapolis Clarke, 1897, from Minneapolis, Minnesota, USA, Platteville Formation, Black River Group, Sandbian; by original designation.

Diagnosis

Compressed cyrtocones; dorsal and ventral profiles diverging constantly adorally; sides converging slightly over mature body chamber; aperture with deep hyponomic sinus; nearly smooth or ornamented with transverse costae; siphuncle subventral, slender; segments slightly expanded, probably empty. (Adopted from Sweet 1964b.)