Carinonautilus is a genus of extinct, Middle Cretaceous nautilid with a very involute, compressed shell in which the whorl section is higher than wide, umbilicus is small and shallow, or flanks converge on a narrow venter that has a rounded keel. A furrow on either side marks the ventro-lateral shoulder. The genus was erected by Spengler in 1910 on the basis of the holotype, found in Middle Cretaceous strata from India.