Isorthoceras wahlenbergi Niko, 2008

Diagnosis.—Large species of Isorthoceras with circular shell cross section, weak endogastric curvature, smooth shell surface, and two constrictions in body chamber; maximum diameter of body chamber attains 31 mm; siphuncle near central in position shifting slightly with ontogeny from a slightly supracentral to a more central position; segments pyriform to fusiform in shape with weakly developed parietal endosiphuncular deposits.