''Eremoceras'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

in the

Ellesmeroceratidae The Ellesmeroceratidae constitute a family within the cephalopod order Ellesmerocerida. They lived from the Upper Cambrian to the Lower Ordovician. They are characterized by straight and endogastric shells, often laterally compressed, so the d ...

which lived during the Early

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 ...

, characterized by an orthoconic adult stage, similar to ''

Ellesmeroceras ''Ellesmeroceras'' is the type genus for the Ellesmeroceratidae, a family of primitive nautiloid cephalopods, that is characterized by its small, generally compressed, gradually expanded, orthoconic shell, found in Lower Ordovician marine sedime ...

'', but with the dorsal side of the adult living chamber somewhat convex, and a juvenile portion that is more gradually expanding and ventrally concave. The siphuncle is ventral, partitioned by diaphragms as typical for the family.

Siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

segments have short septal necks and thick connecting rings.

References

*Rousseu H Flower, 1964. The Nautiloid Order Ellesmeroceratida (Cephalopoda) New Mexico Bureau of Mines and Mineral Resources Memoir 12. {{Taxonbar, from=Q5385534 Ellesmerocerida