Cyclostomiceratidae is a family of Early Ordovician, (Cassinian),

ellesmerocerid The Ellesmerocerida is an order of primitive cephalopods belonging to the subclass Nautiloidea with a widespread distribution that lived during the Late Cambrian and Ordovician. Morphology The Ellesmerocerida are characterized by shells that ar ...

cephalopods characterized by short, essentially straight shells, a fairly rapidly expanding phragmocone and a ventral siphuncle in which septal necks are almost non-existent and connecting rings are thick and layered. As typical of the Ellesmerocerida, chambers are short, septa close spaced.

Genera

Five genera are recognized; '' Cyclostomiceras'', '' Eocyclostomiceras'', '' Microstomiceras'', '' Paracyclostomiceras'', and '' Pictetoceras''. ''Cyclostomiceras'' and ''Paracyclostomiceras'' were described in Flower (1964). :''Cyclostomiceras'' Hyatt 1900, found in the Fort Cassin Limestone of Champlain Valley, the Smithville Formation of Arkansas, and the Arneg of Chile, has a straight shell with a fairly rapidly expanding early portion, slightly depressed cross section. :''Paracyclostomiceras'' Cicioni 1953 is a slightly more slender cyclostomicerid from Argentina with an oblique aperture and slight ventral and dorsal lobes. ''Microstomiceras'' and ''Pictetoceras'' come from the Middle Ordovician Hälludden cliff section, Oland Island, Sweden, associated with such as '' Paldoceras''.

References

* Rousseau H Flower, 1964. Memoir 12. The Nautiloid Order Ellesmericerida (Cephalopoda). State Bureau of Mines and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico.
Cyclostomiceratidae
in Fossilworks Gateway {{Taxonbar, from=Q24883126 Prehistoric nautiloid families Ordovician animals Early Ordovician first appearances Early Ordovician extinctions Ellesmerocerida