Thrincoceras Hyatt, 1893

Korn, Dieter, Miao, Luyi & Bockwinkel, Jürgen, 2022, The nautiloids from the Early Carboniferous Dalle à Merocanites of Timimoun, western Algeria, European Journal of Taxonomy 789, pp. 104-129 : 115

Genus Thrincoceras Hyatt, 1893

Type species

Thrincoceras depressum Hyatt, 1893 ; subsequent designation by Schmidt (1951).

Diagnosis

Genus of the family Trigonoceratidae with evolute conch; whorls slightly impressed or slightly detached; whorl profile nearly quadrate with flattened venter and narrowly rounded ventrolateral shoulder and umbilical margin. Ornament with fine growth lines and moderately coarse spiral lines. Suture line with shallow external and lateral lobes. Siphuncle small with subcentral position (after Kummel 1964; emended).

Included species

Thrincoceras depressum Hyatt, 1893 , Kentucky; Gyroceras Hibernicum Foord, 1891, Ireland; Thrincoceras Hyatti Foord, 1900 , Ireland; Thrincoceras kentuckiense Hyatt, 1893 , Kentucky; Thrincoceras devolvere sp. nov., Algeria.

Remarks

Several genera with a coarse spiral ornament and granulation on the spirals were introduced within the family Trigonoceratidae ; these show a rather continuous morphological variation:

Chouteauceras Miller & Garner, 1953 – whorls compressed, oval, separated by interspaces;

Rineceras Hyatt, 1893 – whorls depressed, oval or rounded triangular, separated by interspaces;

Pararineceras Turner, 1954 – whorls depressed, oval or rounded triangular to rounded-trapezoidal, touching or slightly embracing the preceding one;

Discitoceras Hyatt, 1884 – whorls depressed, subtrapezoidal with narrowly rounded venter, slightly embracing the preceding one;

Thrincoceras Hyatt, 1893 – whorls subquadrate in section and embracing the preceding one. However, one must bear in mind that Thrincoceras also developed an adult stage in which the whorl loses contact with the preceding one. The holotype of T. hyatti, for instance, uncoils at about 90 mm conch diameter ( Foord 1900; Histon 1999).

Stratigraphic range

Late Tournaisian to Late Carboniferous (?).