''Oncoceras'' is a genus of oncocerids, family Oncoceratidae from the middle and upper

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start ...

of North America and Europe. The shell, or conch, of ''Oncoceras'' is relatively short, a curved, compressed brevicone with a maximum width in the phragmocone just behind the body chamber, narrowing toward the aperture. The

siphuncle The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...

is small, necks recurved.

References

* Waltre C. Sweet, 1964. Nautiloidea-Oncocerida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America. Prehistoric nautiloid genera Ordovician cephalopods Middle Ordovician first appearances Late Ordovician extinctions Paleozoic life of the Northwest Territories Paleozoic life of Quebec {{paleo-nautiloidea-stub