''Charactoceras'' is a tarphycerid genus

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

which lived during the

Late Ordovician The Late Ordovician is the third and final epoch of the Ordovician period, lasting million years and spanning from around 458.2 to 443.1 million years ago. The rocks associated with this epoch are referred to as the Upper Ordovician Series. At ...

. ''Charactoceras'' has a closely coiled, rapidly expanding evolute shell, dorsally impressed, with a flattened venter and rounded sides. Sutures are close spaced laterally, but with broad ventral and dorsal lobes. Hyponomic sinus is well developed. The siphuncle is cyrtochoanitic and empty, located between the center and venter; segments expanded slightly into the chambers. The genus '' Charactocerina'' from the Late Orovician is similar but has costae on the dorsolateral region of the shell. Both are included in the family Apsidoceratidae. Also somewhat similar to ''Charactoceras'' in external form are '' Uranoceras'' and '' Cumingsoceras'' from the Middle

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

, but both differ in detail.

References

* Walter C. Sweet, 1964. Nautiloidea- Barrandeocerida;

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 ...

. Geological Society of America and University of Kansas Press. {{Taxonbar, from=Q18346133 Prehistoric nautiloid genera Paleozoic life of Manitoba Paleozoic life of the Northwest Territories Paleozoic life of Nunavut Paleozoic life of Quebec