Jurassic bivalves from the Spiti area of the Himalayas, northern India Author Fuersich, Franz T. https://orcid.org/0000-0002-0844-9297 Universitaet Erlangen-Nuernberg, GeoZentrum Nordbayern, FG Palaeoumwelt, Lowenichstrasse 28, 91054 Erlangen, Germany franz.fuersich@fau.de Author Alberti, Matthias State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Centre for Research and Education on Biological Evolution and Environment and Frontiers Science Center for Critical Earth Material Cycling, Nanjing University, Nanjing 210023, China Author Pandey, Dhirendra K. https://orcid.org/0000-0002-7721-9604 Department of Earth and Environmental Science, KSKV Kachchh University, Bhuj, India Author Ayoub-Hannaa, Wagih S. Geology Department, Faculty of Science, Minufiya University, El-Minufiya, Shibin El Kom, Egypt text Zitteliana 2022 2022-08-11 96 153 178 http://dx.doi.org/10.3897/zitteliana.96.87253 journal article http://dx.doi.org/10.3897/zitteliana.96.87253 2747-8106-96-153 191199E07F3E4E09A3774ADFBF93A248 AFA9059B36235BFF9BA3E9B7BE816DC1 Megacucullaea cf. kraussii (Tate, 1867) Plate 1, fig. 4a, b cf. 1850 Cucullaea cancellata - Krauss: 452, pl. 48, fig. 2a, b (non Phillips, 1829) *cf. 1867 Cucullaea kraussii - Tate: 161. cf. 1882 Cucullaea Kraussi Tate - Holub and Neumayr: 375, pl. 2, fig. 2a-c. cf. 1940 Cucullaea (Megacucullaea) kraussii Tate - Cox: 57, pl. 4, figs 3-4. cf. 1998 Megacucullaea kraussi (Tate, 1867) - Kanjilal and Pathak: 34, pl. 1, fig. 6. Material. A single poorly preserved articulated internal mould with remains of shell from the lower member of the Spiti Shale Formation (Oxfordian) near Chichim (SNSB- BSPG 2020 XCIX 1). Description. Specimen large, longer than high (L ~79 mm, H ~60 mm, I ~70), thick-shelled, strongly inflated. Maximum inflation at around one-third of shell height from umbo. Ventral margin faintly arched, anterior margin convex, forming an angle of ~90° with hinge margin. Posterior margin straight, oblique, posteroventral corner rounded. Umbones only partly preserved, prominent, straight, incurved, situated anterior of mid-line of shell. Posterodorsal carina distinct but rounded, posterodorsal area flat to slightly convex. Cardinal area large, largest width anterior of umbo, slightly concave. Ornamentation poorly preserved; there are at least four widely spaced, strong, rounded radial ribs with concave interstices. Hinge line straight, dentition and other internal features not seen. Remarks. The two valves are sligthly laterally sheared. Moreover, the specimen may be somewhat compressed dorso-ventrally. In this case, the inflation would be lower and the height greater than decribed above, and the point of maximum inflation would also be slightly off. The umbones are only partly preserved. The various Jurassic species of Megacucullaea , i.e. M. eminens Cox (1940 , p. 59, pl. 4, figs 5-7), M. kraussii ( Tate 1867 , p. 161), and " M. sp. nov. aff. C. (M.) eminens Cox" of Agrawal (1956 p. 14, pl. 1, fig. 1) differ in outline and the number of radial ribs ( M. kraussii : 6-8; M. eminens : 16-19; Agrawal's specimen: approximately 10). The present specimen is closest to M. kraussii , having a similar number of ribs, whereas in the other two species the number of ribs is distinctly higher. Due to the poor preservation of the specimen, a detailed comparison with M. kraussii is not possible. The material of Cox (1940 , p. 57, pl. 4, figs 3-4) exhibits eight radial ribs, of which three are only faintly developed on one out of two specimens. Interestingly, M. eminens and M. kraussii co-occur in Upper Tithonian rocks of the Kachchh Basin. M. eminens Cox (1940 , p. 59, pl. 4, figs 5-7) is shorter, carries about 16 radial ribs differing in strength (weak close to the umbonal carina and strong on the remainder of the shell), and the area posterior of the umbonal ridge is distinctly concave. " Cucullaea Kraussi Tate" of Barrabe (1929 , p. 147, pl. 8, fig. 13) has more radial ribs and resembles M. eminens . The early Tithonian specimen figured as Megacucullaea kraussii by Kanjilal and Pathak (1998) has seven ribs.