Orthoceros Fossil Necklace. Comes on Faux Suede Necklace. Pendant Approx. 0.55x2.25" #OrthPend3 Orthoceros: An ancient mollusc that lived more than 400 million years ago in the Triasic Age. The name means straight horn. Orthoceras is a genus of extinct nautiloid cephalopod. It could be likened to an ancient form of squid with a shell. This genus is sometimes called Orthoceratites. Orthoceras fossils have a global distribution occurring in marine rock especially limestone. These are slender, elongate shells with the middle of the body chamber transversely constricted & a subcentral orthochoanitic siphuncle. The surface is ornamented by a network of fine patterning.