Diagnosis. Gorbyoceras with slightly cyrtoconic adult body chamber, shell slightly compressed, and relatively large adult size of more than 40 mm in cross section. Slightly irregularly spaced annulations, approximately three at the distance equal to the diameter. Approximately 35 irregularly spaced longitudinal ridges around the entire circumference of the shell. Approximately 15 growth lines between two successive ridges of annulations. Sutures straight, nearly transverse, one suture at each groove of the annulations. Siphuncle eccentric in juvenile, subcentral in more adult growth stages, septal perforation approximately one tenth of the diameter of the shell.