Clinoceras

Systematic Paleontology Order: Orthocerida Family: Clinoceratidae Genus: Clinoceras

Clinoceras is an orthocerid nautiloid included in the Clinoceratidae from the middle Ordovician of northern Europe. Shells are elongate, subfusiform cyrtocones, the dorsal side straight or slightly concave, the vental side more distinctly convex, bulging slightly outward. The anterior part of the body chamber is constricted but then expands to the aperture. The surface is marked with sinuous growth lines that reveal ventral and lateral sinuses. The siphuncle is dorsal of the center, segments slightly expanded ventrally, generally straight dorsally, and apparently empty.

European Clinoceras differs Whiteavesites and Whitfieldoceras found in North America in that its shells are curved differently dorsally and ventrally, body chambers contract then expand, and siphuncle segments are dorso-ventrally asymmetrical. Shells of Whiteavesites and Whitfieldoceras are more symmetrical, their body chambers simply narrow to the aperture and their siphuncles expand more evenly into the chambers.

References: Walter C. Sweet, 1964. Nautiloidea - Orthocerida Treatise on Invertebrate Paleontology, Part K.