Cyrtocycloceras
Cyrtocycloceras is a genus of orthocerids from the Middle Silurian of Europe included in the Paraphragmitidae. The shell, or conch, of "Cyrtocycloceras" is a moderately expanding annulated exogastric cyrtocone, with curvature like that of a rocking chair rocker. Annulations, encircling ribs, are close spaced and transverse and the surface is transversely striated. "Calocyrtoceras" from the Middle Silurian of both Europe and North America is striated both transversely and longitudinally while "Gaspocyrtoceras" is striated only longitudinally. Moreover the annulations on "Calocyrtoceras" and "Gaspocyrtoceras" tend to be thicker and further apart than on "Cyrtocycloceras".