Schellwienella sp.

Sun, Yuanlin & Baliński, Andrzej, 2008, Silicified Mississippian brachiopods from Muhua, southern China: Lingulids, craniids, strophomenids, productids, orthotetids, and orthids, Acta Palaeontologica Polonica 53 (3), pp. 485-524 : 513-514

Schellwienella sp.

Fig. 21 .

Material.—Two fragmentary ventral valves, one complete and five fragmentary dorsal valves.

Description.—Single complete dorsal valve is transversely semi−oval in outline and nearly two−thirds as long as wide; hinge line straight, almost equal the greatest valve width; interarea short but distinct, triangular, and apsacline; chilidium thick, rather small. Cardinal process generally high, ventrally directed when valve is deep, or almost posteriorly directed in weakly convex valves ( Fig. 21C, D ); lobes well separated by deep sulcus and bear deep, divergent myophore slits. Socket ridges rather short, recurved, and ankylosed to the cardinal process. Dorsal adductor scars well marked in one thick−shelled valve ( Fig. 21D 2 ), laterally bounded by curved ridge and divided anteriorly by short and low median myophragm. Interior of ventral valve with short dental plates.

Ornamentation finely parvicostellate by intercalation.

Remarks.—Lack of more complete ventral valves in the studied material, which could be attributed to the same species as the four dorsal valves here described, precludes more precise identification. The single complete dorsal valve attains 32 mm in width and is quite deep, possibly representing gerontic stage. The cardinal process of the specimen is ventrally directed ( Fig. D 3), as compared to other valves in the collection in which it is posteriorly directed ( Fig. C 3). It seems that this feature depends on curvature of the valve: specimens with strongly convex posterior region of the valve have the cardinal process turned more ventrally. A single dorsal valve also shows several strong concentric growth lines which might have been induced by damage to the mantle epithelium by boring organisms ( Fig. 21D ).

Stratigraphic and geographic range.—This is rather rare species in the Muhua Formation. The studied specimens were found in samples D2(?), D4, MH2, M2/4, M2−8, and GB.

Figures

Fig. 21. Orthotetoid brachiopod Schellwienella sp. from the Muhua Formation. A. Slightly incomplete ventral valve, PKUM02−0314, in exterior (A1), interior (A2), posterior (A3), lateral (A4), and anterodorsal (A5) views. B. Slightly damaged dorsal valve, PKUM02−0315, in exterior (B1), interior (B2), posterior (B3), and enlarged dorsal (B4) views. C. Incomplete dorsal valve, PKUM02−0316, in exterior (C1), interior (C2), and lateral (C3) views. D. Dorsal valve, PKUM02−0317, in exterior (D1), interior (D2), posterior (D3), and lateral (D4) views. Samples M2/4 (A), M2−8 (B), and MH2 (C, D).

Fig. 2. Lithological sections of the Tournaisian Muhua Formation at five sampling sites around Gedongguan village and their locations near Muhua, Guizhou Province, China (modified after Dzik 1997).