Trigonoceratidae Hyatt 1884

Family Trigonoceratidae Hyatt, 1884 Diagnosis Family of the superfamily Trigonoceratoidea with cyrtoconic to subevolute conch with small whorl overlap if present; large or moderately large umbilical foramen. Whorl profile in the adult stage commonly ranging from triangular to depressed oval, rarely compressed oval or polygonal. Whorl profile usually depressed oval in the early juvenile stage. Ornament with longitudinal ridges or lines, rarely transverse ribs; sometimes the conch is smooth. Position of the siphuncle closer to the centre than to the ventral side. Suture line with broadly rounded shallow lobes and low saddles. Included subfamilies Trigonoceratinae Hyatt, 1884 (Early Carboniferous to Early Permian; 7 genera, 38 species). Chouteauoceratinae subfam. nov. (Early Carboniferous to? Early Permian; 3 genera, 5 species). Vestinautilinae subfam. nov. (Early Carboniferous; 3 genera, 29 species). Remarks Flower & Kummel (1950: 615) combined the families Triboloceratidae, Trigonoceratidae and Rineceratidae of Hyatt and gave priority to the first of these. Following the idea of Shimansky (1962), the family Trigonoceratidae is divided into several subfamilies here, which differ in the following morphological characteristics: Trigonoceratinae. – Whorl profile triangular, sculpture with very coarse longitudinal ridges (Fig. 11). Chouteauoceratinae subfam. nov. – Whorl profile compressed oval, sculpture with numerous longitudinal ridges of the same strength (Fig. 12). Vestinautilinae subfam. nov. – Whorl profile rounded trigonal or rounded trapezoidal, sculpture with a few coarse longitudinal ridges, usually of different strength (Fig. 13).