The Naedyceras group comprises three similar and closely related openly coiled, gyroconic, genera within oncocerid family,

Brevicoceratidae The Brevicoceratidae is a family of oncocerids that contains genera characterized by exogastric (or rarely endogastric) gyrocones, brevicones, and torticones. that tend to develop vestigial actinosiphonate deposits and subtriangular transverse ...

: ''Naedyceras'', ''Gonionaedyceras'', and ''Gyronaedyceras''. ''Naedyceras'' was named by Hyatt in 1884; ''Gonionaedyceras'', and ''Gyronaedyceras'' by Flower in 1945. All three have open, gyroconic coiling, a subtriangular whorl section with a flattened dorsum. The

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 ...

in each is ventral with flared out, cyrochoanitic septal necks and internal, longitudinal blade-like actinosiphonate deposits. All three come from the

Middle Devonian In the geological timescale, the Middle Devonian epoch (from 393.3 ± 1.2 million years ago to 382.7 ± 1.6 million years ago) occurred during the Devonian period, after the end of the Emsian age. The Middle Devonian epoch is subdivided into two ...

of N Am, specifically New York, Ohio, and Wisconsin. Differences lie primarily in the symmetry of the whorl section and in the suture. ''Naedyceras'' is described as having a loosely coiled low-spired coiled dextral torticonoc. or trochoidal, shell with a flattened dorsum and subtriangular whorl section. The body chamber bulges slightly. The aperture in mature specimens is somewhat contracted. Sutures form slight lateral lobes, dorsal lobes, and broad ventral and umbilical saddles. Whorl section is symmetric. ''Gonionaedyceras'' has a strongly curved cyrtoconic shell with an asymmetric subtriangular whorl section. The inside, or dorsal, curvature is obliquely flattened and sides converge onto a narrow, ventral, outside curvature that bears a rounded to angular ridge. Sutures have dorsal and lateral lobes and umbilical and ventral saddles. Umbilical saddles are sharper on the left than on the right. Ventral saddles are rounded. ''Gyronaedyceras'' has a compressed gyroconic shell of about two volutions with an assymmetrical, subtraingular whorl section having a broadly rounded to subangular venter and flat dorsum. Sutures are essentially straight and transverse. Actinosiphonate structures are discretely developed. ''Naedyceras'', most especially, outwardly resembles ''

Stereotoceras ''Stereotoceras'' is a Middle and Upper Devonian genus in the oncocerid family Brevicoceratidae that formed a smooth, depressed, gyroconic shell with the dorsum much flatter that the venter. Sutures are straight ventrally but have dorsal lobes. ...

'', which in contrast has a depressed, wider than high, cross section and a beaded, nummuloidal siphuncle. ''

Oxygonioceras ''Oxygonioceras'' is a genus in the Oncocerid family, Brevicoceratidae, from the Middle Silurian of North America and Europe. ''Oxygonioceras'', named by Foeste, 1925, has a loosely coiled, dextrally torticonic shell with a rounded dorsum on t ...

'' is another loosely coiled brevicoceratid but in which the dorsum rounded rather than flat.

References

* Sweet W. C. (1964). Nautiloidea -Oncocerida;

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 ...

Part K, Mollusca 3, K277-K317 {{Taxonbar, from=Q16986168 Nautiloids