Subvestinautilus

Subvestinautilus is a genus of evolute koninckioceratids, in the order Nautilida, with a depressed, trapezoidal whorl section. The venter is broadly rounded, ventrolateral shoulders sharply rounded, flanks flattened and converging toward a narrow rounded dorsum. In early growth stages a keel forms on the umbilical shoulder which becomes rounded or marked by a longitudal rib at maturity . The suture has a broadly rounded ventral lobe and a deeper lateral lobe.
"Subvestinautilus", named by Turner, 1954, has been found in the Lower Carboniferous of Ireland and the Isle of Man.