Bisatoceras sp.

Dernov, Vitaly, 2022, Late Bashkirian Ammonoids From The Mospyne Formation Of The Donets Basin, Ukraine, Fossil Imprint 78 (2), pp. 489-512 : 504-505

Bisatoceras sp.

Text-fig. 12a–e

M a t e r i a l. Two poorly preserved specimens from stratigraphic level 5b of the Mospyne Formation.

D e s c r i p t i o n. Specimen IGSU-4/500 is a sideritic specimen with 16.8 mm conch diameter ( Text-fig. 12a–c ). The conch is thickly dicoidal (ww/dm = 0.57) with very narrow umbilicus (uw/dm = 0.10) and moderate coiling rate (WER = 1.80) and weakly depressed whorls (ww/wh = 1.13). The venter is narrow and convex. The flanks are broad and almost flattened; they slightly converge onto the ventrolateral shoulder. The umbilical margin is narrowly rounded and almost rectangular. The conch ornamentation is not preserved.

The conch surface of specimen IGSU-7/500a is covered with frequent and clearly visible growth lines. These form a wide, shallow external sinus and a low projection on the midflank and a wide, shallow sinus on the umbilical part of the flank. On the midflank, the growth lines are spaced about 0.15 to 0.20 mm apart.

R e m a r k s. Bisatoceras sp. is very similar in the form of conch and surface ornamentation to the species Bisatoceras kotti NASSICHUK, 1975 , but the umbilicus in B. kotti is closed from 6.2–28.0 mm diameter and very narrow in Bisatoceras sp. (uw/dm = 0.10 at conch diameter 16.8 mm).

O c c u r r e n c e. Late Bashkirian, Mospyne Formation; Donets Basin ( Ukraine).

Figures

Text-fig. 12. Ammonoids from the Mospyne Formation. a–e: Bisatoceras sp., dorsal view (a), lateral view (b, d), ventral view (c), surface ornamentation on the flank of specimen IGSU-7/500a (e); a–c – specimen IGSU-7/500, d, e – specimen IGSU-7/500a. f:?Owenoceras sp., lateral view; specimen IGSU-4/1367. Scale bars 2 mm (e) and 5 mm (a–d, f).