Indopecten margariticostatus (Diener, 1908)
DIENER, C. 1908. Ladinic, Carnic and Noric fauna of Spiti. Palaeontologia Indica [series 15], 5 (3): 1-152, pls. 1-24. [p. 97, pl. 18, figs. 1-3]
1908 Pecten (Variamussium) margariticostatus Diener, 1908
C. Diener, 1908, plate 18.
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«ThiIs species shows a distant external similarity with Lima serraticosta Bittner (Himál. Foss., Vol III, Pt. 2, p. 50, Pl. VIII, figs. 12, 13) from the Halorites limestone of the Bambanag section, but differences of specific and generic importance are revealed by a closer examination.
My specimens are not of oblique but of nearly equiIateral shape. The ears, which are not entirely known to me, are of almost equal size, triangular, and without any trace of a byssal notch. The thin shell is raised into five or six ribs of moderate strength, which are crenulated and covered with numerous pearl-shaped tubercles of very delicate shape. These tubercles are formed by the tronger development of the numerous striae of growth covering the entire shell, exactly as in Lima serraticosta. The generic difference between Lima serraticosta and the present species is clearly evident from a comparison of their casts. In the casts of the species from the Halorites limestone the ribs stand out more clearly than is the case on the surface of the shell itself. In the casts of our form, on the contrary, the surface is intersected by deep furrows corresponding to strong radiating ribs, which are developed on the inner side of the valve. Species of Pectines with thin shells, showing a delicate radiating ornamentation on their external surface and a strong ribbing on the inner side, have been united in the subgenus Amussium by Klein. My species is probably a triassic ancestor of the liassic representatives of this subgenus, although I do not know of any liassic form to which it could be compared more closely. I am, however, obliged to state that a grouping of the jurassic species resembling Amussium with that subgeuns is not in accordance with the views expressed by Philippi in his beautiful memoir on the morphology and phylogeny of Pectinidae (Zeitschr. Deutsch. Geol. Ges., LII, 1900, p. 82) who considers Amussium to be one of the youngest groups of the family and restricted to deposits of neogene and pleistocene age. By palaeontologist accepting this view our species might probably be referred to the section Variamussium Sacco of the subgenus Aequipecten. Locality.— Casts of this shell are represented numerously among the collections from the base of the Juvavites beds above Lilang, between Mani and Ensa, N. of Kágá.» CARL DIENER, 1908
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