Branneroceras sp. B

Dernov, Vitaly, 2022, Late Bashkirian Ammonoids From The Mospyne Formation Of The Donets Basin, Ukraine, Fossil Imprint 78 (2), pp. 489-512 : 508

Branneroceras sp. B

Text-fig. 13v–z

2018 Branneroceras branneri ; Dernov, p. 11, pl. 5, fig. 4, pl. 6, fig. 4.

M a t e r i a l. Three specimens of small conch and several fragments of conch from stratigraphic level No. 5a of the Mospyne Formation.

D e s c r i p t i o n. Specimen IGSU-4/626 is an almost fully limonitized specimen with 13.7 mm diameter ( Text-fig. 13v, w ). The conch is discoidal (ww/dm = 0.46) with wide umbilicus (uw/dm = 0.50) and moderately depressed whorl profile (ww/wh = 1.85); the venter is broad and weakly convex; the ventrolateral shoulder is broadly rounded. The flanks are weakly convex and narrow, they slightly converge with the ventrolateral shoulder. The umbilical margin is narrowly rounded. The umbilical wall is weakly convex and at a 45º angle to the plane of symmetry of the conch. The surface of the conch is covered with weak elongated umbilical nodes and growth lines and well-developed lirae on the venter and ventrolateral shoulders. The growth lines form a shallow, broad sinus on the venter, a low projection on the ventrolateral shoulder and a broad shallow sinus on the flanks. On the umbilical margin, the growth lines are spaced about 0.15 to 0.20 mm apart. There are three or four lirae per mm on the ventrolateral shoulder. Three weak concavoconvex constrictions with a high ventrolateral projection and a very shallow ventral sinus are prominent on the whorl.

Specimen IGSU-4/3984а ( Text-fig. 13x, y ) is discoidal (ww/dm = 0.45) with a wide umbilicus (uw/dm = 0.53) and a moderately depressed whorl profile (ww/wh = 1.87) at 12.9 mm diameter. The venter is broad and weakly convex. The ventrolateral shoulder is broadly rounded. The flanks are narrow and weakly convex, they slightly converge onto the ventrolateral shoulder. The umbilical margin is narrowly rounded. The umbilical wall is weakly convex and at an angle of 45º to the plane of symmetry of the conch. The surface of the conch is covered with elongated umbilical nodes and growth lines; lirae on the venter and ventrolateral shoulders are not preserved. Three weak concavo-convex constrictions with a high ventrolateral projection and a very shallow ventral sinus are prominent on the whorl.

R e m a r k s. Branneroceras sp. B differs from Branneroceras branneri ( SMITH, 1896) in the weak constrictions, which are absent in Branneroceras branneri . Branneroceras sp. B is distinguished from B. hillsi Nassichuk by the less elongated umbilical nodes. Branneroceras sp. B differs from Branneroceras nicholasi Nassichuk in the more depressed whorl profile, less frequent constrictions and a wider umbilicus. Branneroceras sp. B differs from Branneroceras sp. A by the greater relief on the umbilical nodes and a more depressed whorl profile.

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

Figures

Text-fig. 13. Ammonoids Branneroceras sp. A (a–u) and Br. sp. B (v–z) from the Mospyne Formation. a–c: Specimen IGSU-4/315, dorsal view (a), lateral view (b), ventral view (c). d, e: Specimen IGSU-4/338, lateral view (d), ventral view (e). f: Specimen IGSU- 4/669, lateral view. g, h: Specimen IGSU-4/315a, lateral view (g), ventral view (h). i, j: Specimen IGSU-4/609, lateral view (i), ventral view (j). k, l: Specimen IGSU-4/350, lateral view (k), ventral view (l). m: Specimen IGSU-4/350a, lateral view. n, o: Specimen IGSU-4/725, lateral view (n), ventral view (o). p: Specimen IGSU-4/338a, lateral view of the juvenile conch. q: Fragment of the suture line of specimen IGSU-4/725 (at wh = 6 mm). r: Specimen IGSU-4/338, reticulate ornamentation of the ventrolateral shoulder of conch. s: Specimen IGSU-4/503, lateral view. t: Specimen IGSU-4/710a, lateral view. u: Specimen IGSU-4/5180, lateral view of early whorls. v, w: Specimen IGSU-4/626, lateral view (v), ventral view (w). x, y: Specimen IGSU-4/3984a, lateral view (x), ventral view (y). z: Specimen IGSU-4/626а, lateral view of early whorls. Scale bars 5 mm (p–r, u, z) and 10 mm (a–o, s, t, v–y).