Grammatodon (Cosmetodon) sp.

Fuersich, Franz T., Alberti, Matthias, Pandey, Dhirendra K. & Ayoub-Hannaa, Wagih S., 2022, Jurassic bivalves from the Spiti area of the Himalayas, northern India, Zitteliana 96, pp. 153-178 : 153

Grammatodon (Cosmetodon) sp.

Plate 1, figs 8, 9

Parallelodon ?1998? Parallelodon sp. indet. - Kanjilal and Pathak: 33, pl. 1, fig. 2.

Material.

Two right valves from the lower member at the Kaza-Hikkim road (SNSB-BSPG 2020 XCIX 2).

Description.

Shell strongly elongated, hinge line long, straight, position of umbo distinctly anterior of mid-line of the shell. Shallow umbonal sulcus widening ventrally and resulting in slight indentation of ventral margin. Umbonal ridge broadly rounded, area posterior of umbonal ridge concave. Surface covered with numerous delicate radial riblets and fine commarginal growth lines and, towards ventral margin, with several commarginal grooves corresponding to growth halts. Cardinal area narrow, attaining its greatest width below umbo. Posterior teeth long, extending parallel to dorsal margin of hinge plate, anterior teeth shorter, oblique, and directed posteriorly towards point below the hinge line.

Remarks.

The specimens, in which the anterior and posterior ends are missing, has been dorso-ventrally compacted. As a result, the two valves have become separated and slightly distorted so that the inflation has been artificially increased. Due to its poor preservation, an identification at the species level is not possible. However, the specimen exhibits the characteristic features of the subgenus Parallelodon Cosmetodon , such as a strongly elongated shell, long, straight hinge line, a position of the umbo distinctly anterior of the mid-line of shell, and a shallow umbonal sulcus that widens ventrally and is responsible for a slightly indented ventral margin.

Order Myalinida Paul, 1939

Figures

Plate 1. (1, 2) Palaeonucula cuneiformis (J. de C. Sowerby, 1840). 1. Left valve from the lower member at Langza (SNSB-BSPG 2020 XCIX 26 a). 2. Left valve from the lower member at Langza (SNSB-BSPG 2020 XCIX 26 b). (3) Palaeonucula stoliczkai Cox, 1940. Laterally crushed articulated specimen, lower member at Langza (SNSB-BSPG 2020 XCIX 34); a, left valve view; b, right valve view. (4) Megacucullaea cf. kraussii (Tate, 1867). Internal mould of articulated specimen with remains of shell from the lower member near Chichim (SNSB-BSPG 2020 XCIX 1); a, right valve view; b, dorsal view. (5 - 7) Grammatodon (Indogrammatodon) egertonianus (Stoliczka, 1866). 5. Articulated specimen from the lower member near the pass to Tashigeng (SNSB-BSPG 2020 XCIX 4). a, left valve view; b, dorsal view. 6. Laterally crushed articulated specimen from the lower member along the Kaza-Hikkim road (SNSB-BSPG 2020 XCIX 3 b); right valve view. 7. Dorso-ventrally compacted articulated specimen from the lower member at Langza (SNSB-BSPG 2020 XCIX 6); right valve view. (8, 9) Grammatodon (Cosmetodon) sp. from the lower member along the Kaza-Hikkim road. 8. Right valve (SNSB-BSPG 2020 XCIX 2 a). 9. Right valve (SNSB-BSPG 2020 XCIX 2 b). a, lateral view; b, dorsal view. (10) Anopaea? Fragmented right valve from the upper? member at Langza (SNSB-BSPG 2020 XCIX 67).