Leiorhynchoidea, Cloud, 1944

Sun, Yuanlin & Baliński, Andrzej, 2011, Silicified Mississippian brachiopods from Muhua, southern China: Rhynchonellides, athyridides, spiriferides, spiriferinides, and terebratulides, Acta Palaeontologica Polonica 56 (4), pp. 793-842 : 809

Leiorhynchoidea ? sp.

Fig. 10 .

Material.—One almost complete shell, 2 incomplete dorsal and 1 incomplete ventral valves, all from sample MH2. Eight very small fragments of single dorsal valves and shells from sample M2−8 and 10 fragments of dorsal valves from sample MH1 may be also attributed to this species.

Remarks.—The two recovered dorsal valves from the sample MH2 attain approximately 12 and 18 mm in length, respectively. The valves are convex, widely oval in outline, posteriorly with a very shallow, barely perceptible median excavation, which anteriorly changes to gentle fold. Exterior of both valves is smooth in the posterior 8 mm, anteriorly with extremely delicate, simple rounded costae. On larger and better preserved valve ( Fig. 10B ) there are 4 costae in the fold, 2 parietal costae, and at least 7 almost indistinguishable costae on the partially preserved flank. Interior of both valves shows septalium supported by a thin median septum, the latter reaches much less than a half of the valve length.

Probably to this species can be referred a slightly damaged young shell, as well as a fragment of a ventral valve, both from the same sample as the two dorsal valves described above. The shell ( Fig. 10D ) is 12.2 mm long, 12.8 mm wide, 5.1 mm thick, broadly oval in outline, lenticular, and equibiconvex in lateral profile. Anterior region of both valves shows a very feeble, almost imperceptible costation and presence of a very shallow sulcus on the ventral valve. The single broken ventral valve ( Fig. 10C ) shows also traces of costation as well as a presence of dental plates in its interior.

The described material is very fragmentary and the single shell at our disposal is too immature making the taxonomic determination of this form rather difficult. It bears some general resemblance to the Early Carboniferous–Late Permian genus Leiorhynchoidea . Our single complete shell shows some external similarity to Leiorhynchoidea carbonifera (Girty, 1911) described from the Chesterian of Idaho ( Butts 2007). Other specimens from Muhua show also evident similarity to L. carbonifera from the Heath Formation (Mississippian) of Montana, USA (see Easton 1962). Paucity of the present material, however, does not allow for a more detailed determination.

Figures

Fig. 10. Pugnacoid brachiopod Leiorhynchoidea? sp. from the Tornaisian Muhua Formation, southern China. A, B. Two isolated dorsal valves, PKUM02−0422 (A) and PKUM02−0423 (B), in exterior (A1, B1) and interior (A2, B2) views. C. Incomplete ventral valve, PKUM02−0424, in exterior (C1) and interior (C2) views. D. Almost complete shell, PKUM02− 0425, in dorsal view. Sample MH2.