Genus Isorthoceras Flower, 1962

Type species

Orthoceras sociale Hall in Miller, 1877, from Graf, Iowa, USA, Elgin Member, Maquoketa Formation, latest Katian; by original designation.

Diagnosis

Orthoconic longicones with subcircular cross section and subdued ornamentation, smooth or with fine transverse and / or longitudinal lirae; siphuncle subcentral, with barrel-shaped early segments and subcylindrical later segments; septal necks suborthochoanitic to cyrtochoanitic; endosiphuncular annuli grow forward and backward, joining those of adjacent segments to form continuous parietal lining of uniform thickness throughout segments; mural to episeptal cameral deposits. (Compiled from Flower 1962 and Frey 1995.)