PELECYPODA. 39 



2. Genus : GRYPH.SIA, Lamarck. 

 Grtph^A VESiCTJLARis, Lamarck. PI. X. 1-la, 2-2b. 



(Synonymy in D'Orbigny, Pal^ont. franc. Terr. Crlt., Vol. Ill, p. 742.) 



The inequivalve shell attains a considerable size up to 112 mm. in height, but 

 in its general shape varies considerably. The left valve is irregular in shape ; some- 

 times it is rather narrow at the umbonal part and gradually expands towards the 

 ventral margin ; other specimens are nearly as broad at the umbonal region, as they 

 are at the ventral margiil ; it is, however, always highly inflated and very thick, par- 

 ticularly in the umbonal region. The umbo is low and depressed, the ligamental pit 

 deep, broad, and transversely striated. The surface is smooth but more or less foli- 

 aceous through the irregular striae of growth. 



The right valve is more or less circular, flat, or even somewhat concave, much 

 thinner than the left valve, and strongly bevelled all round, except on the hinge 

 margin ; ligamental pit short and triangular ; surface very foliaceous ; whether some 

 radiating striae on one of the specimens are only an accidental feature or not, cannot 

 be decided. 



Iiocality and stratigraphioal position. — Mazdr Drik, horizon 8. 



Remnrks. — The form here described has the greatest similarity with Grypheea 

 pina, Leymerie," and this author when creating the species states that it has the 

 oreatest likeness to Ostrea {OryphcBo) vexicularis, Lam., and it is chiefly on account 

 of its strati graphical position, which according to him is always lower than that of 

 Gryphcea vesicularis, that he considers it useful to distinguish it from the latter 

 species. It seems that its chief features are its considerable size, and its enormous 

 thickness. 



With regard to the latter features the specimens from Baluchistdn agree very 

 well with Leymerie's species, but there are other and in my opinion more important 

 features which seem to point to a close relationship of both species. Leym.erie's 

 figures are compressed ; for instance, with figure la it will be seen that the general 

 outline of the left valves agrees exceedingly well ; the wing-like expansion of the 

 posterior side is particularly well developed in both specimens ; there is further the 

 same thick, rounded, depressed, but not incurved umbo in both species, and the 

 features of the hinge are exactly the same ; a broad ligamental pit, bordered by 

 two broad ridges, both transversely striated, flanked on either side by a foliaceous 

 area more or less triangular, — all these are features which the specimens from 

 Baluchistan have in common with Ostrea lissa. Ley. On the other hand, I do not think 

 that to iudge from the general shape of the shell, the Baluchistan specimens should 

 be separated from Gryphcea vedcularis. Whether Gryphcea spina, Ley., is really 

 an independent species or not, would, in my opinion, require further examination. 



> Desor. QSoL et PaL dcs Pyrdndes, pi. I, fig. 1, a., b. 



