''Oonoceras'' is an extinct genus of fossil cephalopods included in the

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

order

Oncocerida The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian (early Carboniferous; one possible member is known from the Early Permian), in which the connecting rings are t ...

and the family Oncoceratidae from the Middle Ordovician to Middle Silurian of North America and Europe, arbitrarily included in the

Slender Oncoceratidae {{Taxobox , name = Slender Oncoceratidae , fossil_range = M Ord- U Sil , image = Oocerina plebeia.JPG , image_caption = ''Oonocerina plebeia'', Barrande from Slivenec, Prague, (Czech Republic) at the National Museum (Prague) , regnum = Ani ...

. Shells of this genus are generally slender, gradually expanding, exograstric cyrtocones with an ovoid cross section more narrowly rounded ventrally than dorsally as in (e.g.) ''

Bassleroceras ''Bassleroceras'' is an elongate upwardly curved, exogastric, genus with the venter on the under side more sharply rounded than the dorsum on the upper. The siphuncle is ventral, composed of thick-walled tubular segments in which connection ring ...

''. Curvature is generally greater than that in ''

Oocerina ''Oocerina'' is an extinct genus of nautiloid cephalopods that lived during the Late Silurian of Europe, Russia, and North America. ''Oocerina'', included in the oncoerid family Oncoceratidae and arbitrarily within the Slender Oncoceratidae, i ...

'' but less than that of '' Richardonoceras'' or '' Dunleithoceras''. The siphuncle of ''Oonoceras'' is cyrtochoanitic. Septal necks flare outwardly and unlike ''Oocerina'', are empty. Segments are either slightly or broadly expanded into the chambers.

References

* Walter C. Sweet, 1964. Natiloidea -Oncocerida. Treatise on Invertebrate Paleontology, Part K. Geological Society of America. * Dinosaurs to Dodos: An Encyclopedia of Extinct Animals by Don Lessem and Jan Sovak Prehistoric cephalopod genera Nautiloids Silurian animals of Europe Paleozoic life of the Northwest Territories Paleozoic life of Quebec {{silurian-animal-stub