Ulrichoceras is an extinct genus of cephalopod belonging to the subclass Nautiloidea, order Discosorida, and family Cyrtogomphoceratidae. It was named by Foerste in 1928, with the type species being U. beloitense.
Description The shell of Ulrichoceras is cyrtoconic (curved) and endogastric (curved such that the ventral side is concave), expanding fairly rapidly toward the middle of the body chamber and then contracting toward the aperture. The cross-section is slightly depressed and subtriangular, with the dorsal and ventrolateral sides strongly rounded. The sutures are faintly sinuate, describing broad lobes on the ventral side, and there is a broad hyponomic sinus on the venter. The siphuncle is located between the center and the venter, with short segments that are not strongly contracted at the septal foramen. The connecting rings are thickened and feature inflated bullettes.
Taxonomic significance Ulrichoceras is recognized as the basal cyrtogomphoceratid genus, considered the source for the rest of the Cyrtogomphoceratidae as well as for the Westonoceratidae. The Cyrtogomphoceratidae are endogastric, while the Westonoceratidae are exogastric (curved such that the ventral side is convex).
Stratigraphic range Ulrichoceras dates to the Middle Ordovician period, specifically from the Dapingian stage (beginning approximately 471.26 million years ago) through the Darriwilian stage (ending approximately 458.18 million years ago).
Geographic distribution Fossils of Ulrichoceras have been found in the United States, specifically in Wisconsin.
