Turnoceras
Introduction '''''Turnoceras''''' is a genus of Devonian cephalopods belonging to the oncocerid family Nothoceratidae. Its shell is broadly expanding and exogastrically curved such that the flattened dorsum is on longitudinally concave side. Aperture unconstricted with no hyponomic sinus for the water jet funnel. siphuncle along the outer, ventral, side, with radial, plate-like actinosiphonate deposits occupying the interior. ''Conostichoceras'' is similar externally, but has a siphuncle with a trapezoidal aspect to its siphuncle segments. ''Perimecoceras'' has similar concave siphuncle segments but is tubular in form.
References * Sweet, W.C. 1964; Nautiloidea -Oncocerida;  Treatise on Invertebrate Paleontology, Part K ; Geological Society of America and University of Kansas press; Teichert and Moore (eds). *   Turnoceras-Paleodb*  Sepkoski Cephalopod Genera