''Centroonoceras'' is a middle

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

cyrtoconic

nautiloid Nautiloids are a group of cephalopods (Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and species rich, with over 2,500 recorded species. Th ...

cephalopod, otherwise similar to the orthoconic '' Sactorthoceras'' and also included in the Sactorthoceratidae. It was named by Kobayashi, 1934, and has been found in Korea and in New York state in the eastern U.S. ''Centroonoceras'' is characterized by a smooth, gently expanding shell with a moderate but definite curvature and circular cross section. Septa are close spaced. The siphuncle is subcentral, as in ''Sactorthoceras''. Segments are subfusiform; generally straighter on the dorsal side and more expanded on the ventral side. No cameral or endosiphuncle deposits are known.

References

* Walter C Sweet 1964. Nautiloidea-Orthocerida;

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

, Part K. Geol. Soc. of America and Univ. Kansas Press. Prehistoric nautiloid genera Paleozoic life of Newfoundland and Labrador {{paleo-cephalopod-stub