Meekella beipeiensis Chen, 2005

Chen, Zhong-Qiang, Campi, Monica J., Shi, Guang R. & Kaiho, Kunio, 2005, Post-extinction brachiopod faunas from the Late Permian Wuchiapingian coal series of South China, Acta Palaeontologica Polonica 50 (2), pp. 343-363 : 350-352

Meekella beipeiensis Chen sp. nov.

Figs. 7D, E, 9 .

Holotype: NMV P309624 ( Fig. 7E), 5.4 mm wide, 5.1 mm long and 3.9 mm thick.

Type locality: Daijiagou section, Beipei, Chongqing City, South China.

Type horizon: 4 th member of the lower Lungtan Formation (early Wuchiapingian, Late Permian).

Derivation of the name: Named for the Beipei area, where the Daijiagou section is located.

of a dorsal internal mold NMV P309634. I. Meekella pusilloplicata Liao, 1980b , dorsal view of a dorsal internal mold NMV P309623. J. Magniderbyia sp. indet., ventral view of a ventral external mold NMV P309628. K. Chengxianoproductus cf. changxingensis Liao and Meng, 1986 , dorsal view of a dorsal external mold NMV P309626. A, from the 5 th member of the Lungtan Formation of Daijiagou. B, C, G, H, J, K, from the 1 st member of the Lungtan Formation of Daijiagou; D, E, from the 4 th member of the Lungtan Formation of Daijiagou; I, from the 3 rd member of the Lungtan Formation of Daijiagou; F, from the 5 th member of the Lungtan Formation of Chuanmu.

Material.—Of six studied specimens, NMV P309624–625 are figured and NMV P309627 is sectioned.

Diagnosis.—Large species for genus; elongate ovate to triangular in outline; ventral umbo moderately conical; dorsal median sulcus distinct, forming a lingual extension at anterior margin; external surfaces weakly plicate. The new species is distinguished from Meekella dorsisulcata Feng and Jiang, 1978 by its more anteriorly extended dorsal median sulcus and narrower, more rounded plicae, and from the Capitanian Me. zhejiangensis Liang, 1990 by its significantly lower ventral interarea.

Description.—Nearly biconvex in profile; shell width anterior to midvalve; extremities round. Ventral beak normally twisted slightly and deformed by cicatrix of attachment; interarea moderately high, concave to slightly flattened; pseudodeltidium with high sharp monticulus; umbo conical posteriorly; lateral slopes steep; median sulcus absent. Dorsal valve evenly convex, most convex at umbo; median sulcus broad, originating at beaks as shallow groove, abruptly broadening and deepening at umbonal region, forming deep lingual extension anteriorly.

Costellae fine, dense, rounded, frequently intercalate or bifurcate, about 40 per 10 mm at midlength, irregularly, moderately plicate; four plicae in 10 mm at midlength, those on umbo more conspicuous than others. Ventral interior dental plates high, long, slightly convergent anteriorly, extending to midlength. Cardinal process long, slightly projecting posteriorly; dorsal socket ridges strong; crural plates fused to base of cardinal process ( Fig. 9 ).

Remarks.— Liao (1980b) described three new species Meekella langdaiensis, Me. deltoides, and Me. pusilloplicata from the Lungtan Formation of Guizhou, South China. They are contemporaneous to Me. beipeiensis , but all are distinct from the new species in the loss of a dorsal median sulcus. In addition, Me. deltoides is much smaller; Me. pusilloplicata has a proportionally longer hingeline; Me. langdaiensis embraces coarser plicae with sharper crests. Shen et al. (1992) created two new species, Meekella sichuanensis and Me. perigeyerelloides, from the Changhsingian of Chongqing, South China; they possess a higher, flat ventral interarea and a slightly shallower dorsal median sulcus, and thus cannot be confused with Me. beipeiensis .

Figures

Fig. 9. Selected serial sections of the ventral umbo of Meekella beipeiensis Chen sp. nov. (based on specimen NMV P309627) showing closely situated, parallel dental plates. The numbers are distance from the ventral beak; the orientation of the sections is with ventral surfaces upward.