What is "diademoceras"

Diademoceras is a nautiloid cephalopod from the middle Ordovician of North America, named by Rousseau Flower,1945. The genus is a tainoceratacean included in the nautilid family Rutoceratidae.

The shell of Diademoceras is gyroconic, of no more than two whorls, coiled such that whorls do not touch. Whorls are broad, section depressed, sides converge ventrally meeting at a well developed keel. Ornamentation consists of a series of spines on either side as well as transverse straie which form a well developed hyponomic sinus (for the funnel) on the venter. Sutures are straight across the venter, but form a broad shallow lobe on the dorsum. The siphuncle is close to the venter, composed of straight and empty segments, i.e. orthochoanitic.