Genus Cyclostomiceras Hyatt, 1900

Type species

Gomphoceras cassinense Whitfield, 1886 from the Fort Cassin Formation (Floian) at Fort Cassin headland, Vermont, USA; by original designation.

Diagnosis

Gomphoceroid, breviconic orthocones with circular to depressed conch cross section; phragmocone expanding adorally rapidly; anterior half of mature body chamber slightly contracted. Sutures and growth lines straight and directly transverse; siphuncle small, rSD = 0.15, ventral in position but not marginal; septal necks orthochoanitic, connecting rings thick and layered (from King 1998).