Rhiphaeoceratidae Ruzhencev & Shimansky 1954

Family Rhiphaeoceratidae Ruzhencev & Shimansky, 1954 Diagnosis Family of the superfamily Pleuronautiloidea with a small, slender first whorl. Whorl profile weakly depressed, elliptical or trapezoidal. Venter broad and weakly convex, flanks convex or slightly flattened and umbilical margin broadly rounded or absent. Sculpture with short ribs on the flank. Suture line with a low external saddle, sometimes with a shallow external lobe, a very shallow lateral and a rather deep funnel-shaped internal lobe; without annular process (after Ruzhencev & Shimansky 1954). Included genera Rhiphaeoceras Ruzhencev & Shimansky, 1954 (Permian); Pararhiphaeoceras Ruzhencev & Shimansky, 1954 (Permian); Sholakoceras Ruzhencev & Shimansky, 1954 (Permian); Rhiphaeonautilus Ruzhencev & Shimansky, 1954 (Permian); Eximioceras Shchedukhin, 2022 (Permian); Alibashinautilus gen. nov. (Permian). Remarks The family Rhiphaeoceratidae can be distinguished from other Permian nautiloids by their suture line with its rather deep internal lobe. The only exceptions are the representatives of the family Aktubonautilidae, but these differ in having a much larger juvenile conch.