Bositra buchii (Roemer, 1836)

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

Bositra buchii (Roemer, 1836)

Plate 3, figs 1, 2

*1836 Posidonia Buchii Nob. - Roemer: 81, pl. 4, fig. 8.

1930 Posidonia ornati Quenstedt - Weir: 83, pl. 10, figs 14-21.

?1935 Posidonia somaliensis sp. nov. - Cox: 166, pl. 15, figs 7-8.

1938 Posidonia ornati Quenstedt - Weir: 45, pl. 3, fig. 6.

1940 Posidonia ornati Quenstedt - Cox: 103, pl. 7, figs 10-11.

?1965 Bositra somaliensis (Cox) - Cox: 50, pl. 6, fig. 2.

1994 Bositra buchii - Oschmann: 424, fig. 9b-d.

1995 Bositra buchii - Oschmann: 33, fig. 10b-e.

1995 Bositra buchi (Roemer 1836) - Jaitly et al.: 175, pl. 8, figs 6-9.

Material.

Numerous composite moulds from the basal silty black shales of the lower member at Langza (SNSB-BSPG 2020 XCIX 18-20).

Description.

Small-sized, feebly inflated, generally longer than high, obliquely ovate but occasionally suborbicular composite moulds. Dorsal margin short, straight, remaining margins well-rounded. Umbo inconspicuous, not protruding beyond dorsal margin and situated slightly anterior of mid-line of shell. Surface covered with 16-18 broad, rounded commarginal ribs, separated by narrow interstices.

Remarks.

Bositra buchii is a very widespread opportunistic byssate bivalve able to tolerate dysoxic conditions ( Oschmann 1994). It occurs profusely in black silty shales at the base of the lower member at Langza, where it forms near-monospecific assemblages.

The species is morphologically quite variable in outline, as has been documented by Conti and Monari (1992). Whether the more orbicular Bositra somaliensis (Cox, 1935) from the Kimmeridgian of Somalia falls within the range of variation of B. buchii requires a study of the type material of that species.

Order Pectinida Gray, 1854

Figures

Plate 3. (1, 2) Bositra buchii (Roemer, 1836). Composite moulds from the lower member at Langza. 1. a, articulated specimen in butterfly position, dorsal view (SNSB-BSPG 2020 XCIX 18 a); b, c, single valves, lateral view (SNSB-BSPG 2020 XCIX 18 b). 2. External mould of right valve (SNSB-BSPG 2020 XCIX 19). (3) Australobuchia spitiensis (Holdhaus, 1913). Composite mould of articulated specimen from the middle member, roadside close to Komic; right valve view (SNSB-BSPG 2020 XCIX 43). (4 - 5) Australobuchia blanfordiana (Stoliczka, 1866). upper member close to Demul Pass. 4. Right valve (SNSB-BSPG 2020 XCIX 46). 5. Right valve (SNSB-BSPG 2020 XCIX 45). (6 - 10)? Malayomaorica sp. upper member close to Demul Pass. 6. Left valve (SNSB-BSPG 2020 XCIX 51 a). 7. Right valve interior (SNSB-BSPG 2020 XCIX 52). 8. Fragment of right valve (SNSB-BSPG 2020 XCIX 51 b). 9. Left valve (SNSB-BSPG 2020 XCIX 51 c). 10. Fragment of right valve (SNSB-BSPG 2020 XCIX 51 d). (11) Entolium (Entolium) corneolum (Young & Bird, 1822). Internal mould of a left valve from the lower member at Langza (SNSB-BSPG 2020 XCIX 15). (12) Propeamussium (Propeamussium) sp. Internal mould of a small fragment from the lower member at Langza (SNSB-BSPG 2020 XCIX 12). a, natural size; b, enlarged. (13) Camptonectes (Camptochlamys) obscurus (J. Sowerby, 1818). Left valve interior from the lower member near the pass to Tashigeng (SNSB-BSPG 2020 XCIX 13).