Hypothyridina sp.

Baliński, Andrzej, 2006, Brachiopods and their response to the Early-Middle Frasnian biogeochemical perturbations on the South Polish carbonate shelf, Acta Palaeontologica Polonica 51 (4), pp. 647-678 : 662-663

Hypothyridina sp.

Fig. 7A, B .

Material.—Eleven complete shells and 14 fragments of shells and valves from Wietrznia Id−W (beds 4, 5, and 14) and Ie (beds 29–30, 50–51, 60, and 66) sections. Specimens partially to strongly decorticated, especially in their posterior region.

Description.—Shell medium sized to small for the genus, attaining up to about 16 mm in length, subpentagonal in outline, wider than long, strongly dorsibiconvex; lateral margins rounded, anterior margin truncated to very weakly arched, anterior commissure strongly uniplicate.

Ventral valve weakly convex with slightly concave flanks in anterior view; sulcus very weak, although wide, originating about 7 mm from the umbo, with slightly convex bottom; tongue long, distally almost straight to slightly arched, with subparallel sides.

Dorsal valve very deep with inflated umbonal region which, however, does not extend beyond ventral beak; flanks strongly curved, almost vertical; fold very low, with weakly convex top.

Costae low, flattened, and simple, starting at some distance from the umbonal regions, separated by very narrow furrows. There are about 9 median costae and 10–12 lateral ones.

Interior poorly known; dental plates can be identified on the internal shell moulds.

Remarks.—This small collection of strongly decorticated shells from Wietrznia quarry exhibit some futures characteristic for cosmopolitan genus Hypothyridina Buckman. In his revision of some hypothyridinids Sartenaer (2003) discussed the taxonomic problems of the genus and its allies. He concluded that the group urgently needs further studies especially because Hypothyridina is still inadequately known and became a catch−all name. Recently a few new hypothyridinid genera were described from different stratigraphic intervals, i.e., Glosshypothyridina Rzhonsnitskaya, 1978 from the upper Eifelian, Xiaobangdaia Wang, 1985 from the upper Famennian, and Tullypothyridina Sartenaer, 2003 from the upper Givetian.

Occurrence.—The species was recovered in Wietrznia Id−W and Wietrznia Ie sections; all occurrences represent Palmatolepis transitans conodont Zone.

Figures

Fig. 7. Rhynchonellid brachiopods from the Frasnian of Wietrznia and Dębnik. A, B. Hypothyridina sp., ZPAL Bp 60/28 (A) and GIUS 4−273 Wt/IM−4 (B), two complete shells from the middle Wietrznia Beds of Wietrznia Ie and Id−W, respectively, in dorsal (A1, B1), ventral (A2, B2), lateral (A3, B3), posterior (A4, B4), and anterior (A5, B5) views. C. Fitzroyella alata Biernat, 1969, GIUS 4−273 Wt/GR−1, complete shell from the middle Wietrznia Beds of Wietrznia Id−W. D, E. Fitzroyella sp. from the middle Wietrznia Beds of Wietrznia Id−W. D. Incomplete specimen GIUS 4−273 Wt/IM−7 in dorsal (D1) and ventral (D2) views. E. Complete shell GIUS 4−273 Wt/GR−2 in dorsal (E1), ventral (E2), lateral (E3), posterior (E4), and anterior (E5) views. F, G. Plionoptycherhynchus cracoviensis (Gürich, 1903) from the Nodular Limestone (Palmatolepis hassi Zone) of Dębnik. F. ZPAL Bp 60/17, fragment of a large shell in ventral view. G. ZPAL Bp 60/4, complete shell in dorsal (G1), ventral (G2), lateral (G3), posterior (G4), and anterior (G5) views. H. Phlogoiderhynchus polonicus (Roemer, 1866) from the middle Wietrznia Beds of Wietrznia Id−W, shell GIUS 4−273 Wt/IM−8 in dorsal (H1), ventral (H2), lateral (H3), posterior (H4), and anterior (H5) views.