Tihkia, SAHNI & TEWARI, 1958

Skawina, Aleksandra & Dzik, Jerzy, 2011, Umbonal musculature and relationships of the Late Triassic filibranch unionoid bivalves, Zoological Journal of the Linnean Society 163 (3), pp. 863-883 : 877-878

GENUS TIHKIA SAHNI & TEWARI, 1958

TYPE SPECIES: TIHKIA CORRUGATA SAHNI & TEWARI, 1958

Original diagnosis: ‘The shell is thick and varies in shape from broadly oval to narrow sub-quadrate. Anteriorly, the shell is broadly, and posteriorly somewhat narrowly rounded or sub-angular. The length is in all cases greater than the height, relative proportions varying within wide limits. The beaks are anteriorly situated but are not terminal; they are inconspicuous and curved inwards and very slightly forward. The umbo is comparatively flat and smooth but is not otherwise distinguished from the rest of the shell by any distinctive character. The lunule is present and there is a well defined opisthodetic ligament’ ( Sahni & Tewari, 1958: 4101).

Remarks: Among Triassic unionoids of this kind the diagnostic umbonal musculature and gill structure is known only in two populations from Silesia. Shells of the Rhaetian species, of generalized appearance, are closely similar to those from India, Tanzania, and Zambia, but differ in geological age: about 10 Myr from T. corrugata and perhaps 20 Myr from Tihkia karooensis ( Cox, 1932) . Until at least umbonal musculature is known in these Gondwanian forms, their generic level identification with the Polish species remains only a hypothesis. The generic affiliation of the Rhaetian species from Silesia is based on the assumption that its compact set of umbonal muscles near the umbo tip is a generic rank distinction, and that it may be shared with the Gondwanian species of Tihkia .

Species included: Tihkia corrugata Sahni & Tewari, 1958 from the Late Triassic (late Carnian or early Norian) Maleri Formation of the Hyderabad State and the region of Tihki, Vindhya Pradesh, India ( Sahni & Tewari, 1958), T. karooensis ( Cox, 1932) from the supposedly Mid Triassic Manda Beds of Tanzania and Ntawere Formation of Zambia ( Cox, 1932), and T. silesiaca sp. nov. from the early Rhaetian of the Upper Silesia, Poland.