Spyroceras is a Devonian genus of orthocerid cephalopod recorded from Europe and North America.Characters (from Sweet 1964): Annulated orthocones with straight transverse sutures, transverse or slightly oblique surface annulations, and faintly cyrtoconic apices. Surface variously ornamented, longitudinal lirae conspicuous from earliest stage. Siphuncle central or slightly ventral; siphuncle orthochoanitic with forward-growing endosiphuncular annuli; in mature segments, […]