Subfamily Trigonoceratinae Hyatt, 1884

Fig. 11

Diagnosis

Subfamily of the family Trigonoceratidae with cyrtoconic to evolute or subevolute conch. Whorl overlap small if present. Whorl profile ranging from triangular to depressed oval. Venter flat or rounded. Sculpture in the early species with longitudinal, equidistant ridges throughout ontogeny; advanced species with reduction of spiral ridge number. Suture line with broadly rounded lobes and saddles.

Included genera

Trigonoceras M‘Coy, 1844 (Tournaisian to Viséan; 3 species).

Discites M‘Coy, 1844 [non Schlotheim, 1813, nec De Haan, 1825; synonym of Discitoceras]. Nautiloceras d’Orbigny, 1849 (Tournaisian; 1 species).

Triboloceras Hyatt, 1884 (Tournaisian to Viséan; 11 species).

Discitoceras Hyatt, 1884 (Tournaisian; 4 species).

Rineceras Hyatt, 1893 (Tournaisian to Viséan; 17 species).

Rhineceras Hyatt, 1900 [synonym of Rineceras].

Apogonoceras Ruzhencev & Shimansky, 1954 (Artinskian; 1 species)?

Pararineceras Turner, 1954 [synonym of Rineceras].

Stroborineceras Korn & Bockwinkel, 2022 (Tournaisian to Viséan; 4 species).

Remarks

The cardinal character of the representatives of the subfamily Trigonoceratidae seems to be the slightly depressed oval whorl profile in the early ontogenetic stage and the approximately equidistantly arranged spiral ridges, which are equally developed on the venter as well as on the flanks and dorsum.

The general conch shape is very variable, ranging from cyrtoconic (Trigonoceras) to gyroconic (Triboloceras) and advolute (some species of Triboloceras and Rineceras) to evolute (most species of Rineceras). Almost all species have a more or less triangular or trapezoidal whorl profile.