Aipoceratidae Hyatt 1884

Family Aipoceratidae Hyatt, 1884 Fig. 38 Diagnosis Family of the superfamily Aipoceratoidea with a gyroconic conch. Whorl profile usually laterally compressed. Included genera Asymptoceras Ryckholt, 1852 (Tournaisian to Serpukhovian; 6 species). Aipoceras Hyatt, 1884 (Tournaisian to Viséan; 7 species). Oncodoceras Hyatt, 1893 (Tournaisian; 3 species). Librovitschiceras Shimansky, 1957 (Moscovian; 1 species). Barskoceras Leonova & Shchedukhin, 2020 (Asselian or Sakmarian; 1 species). Remarks Of the genera of the family Aipoceratidae, only the two genera Aipoceras and Asymptoceras can be considered well known (e.g., Foord 1900; Miller & Furnish 1939). They show a continuous evolution in the degree of coiling, ending in the genera Acanthonautilus Foord, 1896 and Solenochilus Meek & Worthen, 1870. At the same time there is a continuous evolution towards a more depressed whorl profile. Librovitschiceras appears as a foreign item in the list of genera; this is due to the very different conch morphology with a wide umbilicus and low coiling rate (Fig. 38). The genus has been placed in the family Aipoceratidae because of the marginal ventral position of the siphuncle (Shimansky 1957, 1962, 1967, 1979; Kummel 1964), while Dzik (1984: 173) placed the genus in the Tainoceratidae with question mark. Kummel (1964) did not accept the validity of Librovitschiceras and synonymised the genus with Knightoceras, while Furnish & Glenister (in Kummel 1964, in the same Treatise volume) listed it among the superfamily Aipocerataceae. This controversy cannot be resolved at present.