Leptagonia cf. analoga ( Phillips, 1836 )

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 : 495-496

Leptagonia cf. analoga ( Phillips, 1836)

Fig. 7 .

cf. 1836 Producta analoga Phillips ; Phillips 1836: 215, pl. 7: 10.

cf. 1968 Leptagonia analoga (Phillips) ; Brunton 1968: 29–31, pl. 3: 26, 27.

1999 Leptagonia analoga ( Phillips, 1836) ; Baliński 1999: 441, fig. 3F, G.

Material.—Over 20 specimens, all are fragmentary single valves.

Remarks.—This is a relatively rare species in the fauna from the Muhua Formation. As in the majority of other forms in the fauna, the species is represented by fragmentary disarticulated valves. Even thick−shelled large individuals are broken indicating high hydrodynamic activity prior to burial.

Externally the visceral region is covered with quite regular concentric rugae and rounded, rather weak radial costae. There are about 6–7 costae in 2 mm measured at 10 mm distance from valve beak. Inside ventral valves there are low dental plates which are continuous with the lateral edges of the wide, circular muscle platform. The platform is clearly elevated above valve floor laterally, but rather low in its antero−median region. The umbonal region of the ventral valve is pierced by a quite large pedicle foramen, which is clearly seen both internally and externally ( Fig. 7E ). The interior of the dorsal valve is well seen in three incomplete specimens from samples GT and Mu−42 ( Fig. 7C, D, F ). Their cardinal process and muscle scars are reminiscent those illustrated by Brunton (1968: pl. 4: 7; text−fig. 9) in juvenile dorsal valve of Leptagonia analoga from D zone of County Fermanagh, Northern Ireland. Several specimens of L. analoga from Redesdale (Northumberland, England) illustrated by Brunton (1968: pl. 3: 28, pl. 4: 2) were attributed by Brand (1972) to his new species Leptagonia caledonica Brand, 1972 , which occurs in Britain in the Viséan and basal Namurian. Generally, the specimens from the Muhua Formation resemble L. analoga in the shape of valves and external ornamentation as well as in details of the internal structure. The broken material, however, precludes more definite taxonomic identification.

Stratigraphic and geographic range.—This species was found in samples GB, GT, MH 1, and Mu−42. According to Brand (1972) L. analoga occurs in England, Ireland, and Wales in Tournaisian and early Viséan strata. In China, L. analoga was described from Anhui and Jiangsu ( Wang et al. 1982), Hunan ( Tan 1987), Guangxi ( Yang et al. 1977; Xu and Yao 1988), and Sichuan ( Tong 1978) provinces. Furthermore, the species was mentioned also in Hubei Province by Xu (1984).

Figures

Fig. 7. Strophomenoid brachiopod Leptagonia cf. analoga (Phillips, 1836) from the Muhua Formation. A, E. Incomplete ventral valves, PKUM02−0209 (A) and PKUM02−0210 (E), in exterior (A1, E1) and interior (A2, E2) views. B–D. Incomplete dorsal valves, PKUM02−0211 (B), PKUM02−0212 (C), and ZPAL V. 26/6 (D), in exterior (B1, C1, D1) and interior (B2, D2) views. F. Incomplete dorsal valve, PKUM02−0213, in exterior (F1), interior (F2), and enlarged postero−dorsal (F3) views; notice massive chilidium.Samples MH1 (A, B), GB (E), GT (C, F), and Mu−42 (D; figured in Baliński 1999: fig. 3F, G).