Hypothyridina Buckman, 1906

Ma, Xue-Ping, Sun, Yuan-Lin, Hao, Wei-Cheng & Liao, Wei-Hua, 2002, Rugose corals and brachiopods across the Frasnian- Famennian boundary in central Hunan, South China, Acta Palaeontologica Polonica 47 (2), pp. 373-396 : 388

Genus Hypothyridina Buckman, 1906 Hypothyridina linglingensis Wang, 1956a

Fig. 10G–I .

Hypothyridina linglingensis n. sp.; Wang 1956a: 173–174, pl. 3: C1–5. Material.—Ten shells.

Remarks.—Our specimens are in agreement with H. linglingensis Wang, 1956a in general shape and size. Shell width is slightly greater than length, with greatest width around mid−length of shell and greatest thickness at the anterior margin. The dorsal valve is much more convex than the ventral valve. Dorsal fold is very low posteriorly and becomes well developed at the anterior margin. Ventral sinus is very shallow, becoming geniculated in right angle to meet the dorsal fold near the anterior margin. Ventral beak is small, incurved against that of the dorsal valve. External surface is covered by simple, low, and rounded plications, with 8–10 in sinus, 9–11 on fold, and 16 or more on each flank. The interspaces are narrow and linear. Occasionally one or two plications next to the fold or sinus may bifurcate.

Wang (1956a) described two species of Hypothyridina from the Upper Devonian of central Hunan based on only three specimens: H. hunanensis and H. linglingensis . He did not mention any features distinguishing the two forms. Hypothyridina linglingensis is different from the former by its smaller shell and flatter sinal plications. Whether these are intraspecific variations or not requires additional specimens for further study.

Occurrences.—This species is very rare in the late Frasnian ( Pa. linguiformis Zone ), nevertheless it can be found in all latest Frasnian deeper water shelf deposits in the Chongshanpu, Shetianqiao, and Jiangjiaqiao sections.

Figures

Fig. 10. A–F. Sinalosia rugosa gen. et sp. nov., sample S−Y−2. A–C. Ventral, dorsal and lateral views of holotype PUM 00017; × 2. D. Ventral view of paratype PUM 00019 showing its chevron ornamentation, × 2. E, F. Ventral and dorsal views of paratype PUM 00021; × 2. G–I. Hypothyridina linglingensis Wang, 1956a; sample S−Y−4, lateral, ventral and posterior views of PUM 00027; × 1.25. J–Q. Hunanotoechia gamma (Tien, 1938), sample S−Y−2. J. Ventral view of PUM 00042 showing the presence of only two sinal plications, × 3. K–O. Lateral, dorsal, posterior, anterior and ventral views of PUM 00051; × 3. P. Dorsal view of PUM 00041 showing a specimen with growth bizarre ventral beak, × 3. Q. Dorsal view of PUM 00054 showing the deltidial plates, × 5. R, S. Hunanotoechia tieni Ma, 1993; sample S−25−2, PUM 00053, enlarged dorsal view (R) showing the deltidial plates and the foramen, × 4 and ventral view (S), × 3.