Agastrioceras sp.

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

? Agastrioceras sp.

Text-fig. 11

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

D e s c r i p t i o n. Specimen IGSU-4/389 is a sideritic specimen with a 27.8 mm conch diameter. The conch is thinly discoidal (ww/dm = 0.42) with narrow umbilicus (uw/dm = 0.25) and high coiling rate (WER = 2.22). It has a weakly compressed whorl profile (ww/wh = 0.88). The venter is narrow, strongly convex and roof-like because of the presence of three thin ridges, of which the median one is less clearly visible than the two lateral ones. The flanks are broad and almost flattened; they are slightly convergent. The umbilical margin is narrowly rounded and almost rectangular. The surface of the conch is covered with frequent lamellae that form a deep, broad sinus on the flanks and a low projection on the venter. Three thin ridges are present on the venter.

R e m a r k s.? Agastrioceras sp. differs from Agastrioceras amaliae in the lamellae having less relief l and the absence of umbilical nodes. The conch form of? Agastrioceras sp. differs from the specimens of Agastrioceras supinum . Growth lines of Agastrioceras clathratum have a ventral sinus, but the growth lines of? Agastrioceras sp. have a low projection on the venter.? Agastrioceras sp. is differs from A. clathratum in the absence of umbilical nodes and from A. reifi by its thinly discoidal conch.

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

Figures

Text-fig. 11.?Agastrioceras sp., dorsal view (a), lateral view (b), ventral view (c); specimen IGSU-7/389. Scale bar 10 mm.