Genus Isorthoceras Flower, 1962

Type species

Orthoceras sociale Hall in Miller, 1877, from the Elgin Member, Maquoketa Formation, latest Katian, Graf, Iowa, USA; 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-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. (Adopted from Flower 1962 and Frey 1995.)