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.