Gorbyoceras Shimizu et Obata, 1935

Diagnosis. Slender, circular or slightly compressed orthocones with symmetrically curved septa and straight transverse sutures. Sutures parallel to the annulations in each groove of the annulations. Annulations with fine transverse ornament, or growth lines. Annulations more distinctive in adult growth stages. Distinctive irregularly spaced longitudinal ridges that may form nodes at the ridges of the annulations. Siphuncle subcentral, expanded in early growth stages, with short cyrtochoanitic septal necks, nearly tubular in later growth stages, with suborthochoanitic septal necks. Endosiphuncular and cameral deposits not known.