Cycloceras is an extinct nautiloid cephalopod genus from the Carboniferous

Carboniferous

The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...

 of Western Europe, (Ireland and Scotland) of unknown affinity with the orthocerida (Sweet 1964 in)

Taxonomy

Cycloceras was named by McCoy (1844 and assigned to the Michelinoceratida

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

 by Flower (1962)and to the Orthocerida

Orthocerida

Orthocerida is an order of extinct nautiloid cephalopods also known as the Michelinocerda that lived from the Early Ordovician possibly to the Late Triassic . A fossil found in the Caucasus suggests they may even have survived until the Early Cretaceous...

by Sweet in Teichert et al. (1964);
Cycloceras is possibly a member of the Cycloceratidae and may be synomyous with Perigrammoceras Foerste

Morphology

The type species of Cycloceras, C. annularis, is based in an internal mold of a body chamber on which the position of the siphuncle is indiscernible (Sweet 1964,) Species referred to Cycloceras are annulated, subcylindrical orthocones with no longitudinal ornamentation . Fig 186, p K258 Teichert et al. (1964) shows Cycloceras as narrow, gently expanding, annulated othocone with a narrow subcentral siphuncle. Annuli (circular transverse bands or costae) are thick and close spaced giving a corregated appearance.