Curtoceras
Introduction '''''Curtoceras''''' is a genus in the tarphycerid family Trocholitidae of mollusks found widespread in the late Early and Middle Ordovician of North America and northern Europe. ''Curtoceras'' has a shell that is gradually expanded, with half the fully mature body chamber divergent from the preceding volution. Whorl sections are near equidimensional with the inner margin (dorsum) moderately impressed. The surface may be smooth or weakly ribbed. The siphuncle is ventral in the initial chamber and becomes dorsal after one volution. With the exception of the dorsal siphuncle, ''Curtoceras'' is somewhat similar to the tarphyceratid ''Campbelloceras''
See also *List of nautiloids
References *Furnish, W.M. and Glenister, Brian F 1964; Nautiloidea -Tarphycerida, in Treatise on Invertebrate Paleontology, Part K, Nautiloidea; Geological Society of America and University of Kansas press.