The concept of the Carboniferous nautiloid Brachycycloceras normale Miller, Dunbar and Condra, 1933, is emended on the basis of new material from the Desmoinesian to Missourian sequences in Oklahoma. Because the species represents the type of Brachycycloceras and the family Brachycycloceratidae is monogeneric, this emendation requires modification of both the generic and familial diagnoses. This cephalopod genus has a longiconic conch with an annulated immature shell with a slight endogastric curvature, a rapidly inflated, straight, mature conch without annulations, and a siphuncle in a supracentral position. Contrary to earlier interpretations, new evidence from yet undescribed specimens shows that the living orientation of the convex side of the conch was dorsal. These discoveries suggest that assignment of the Brachycycloceratidae to the order Orthocerida is questionable.
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