Spyroceras in matrix b.jpg
Spyroceras Cephalopod in Matrix
Chesterian Zone of the Bangor Limestone Formation in northern Alabama
Mississippian Period (ca 325,000,000 years old)
Spyroceras is a genus of pseudorthocerids from the Devonian of North America and Europe, defined by Hyatt in 1884. Pseudorthocerids are a kind of orthocertaoid, a taxonomic group within the Nautiloidea. Spyroceras had annulated orthocones with straight transverse sutures, transverse or slightly oblique surface annulations, and faintly cyrtoconic apeces Surface ornamentation varies but longitudinal lirae are conspicuous from earliest stage. The siphuncle was central or slightly offset ventrally, and composed of expanded segments typical of the Pseudorthocerida. Cameral and siphonal deposits developed later than in most pseudorthocerids and are thus confined to the apical portion of the phragmocone.