1916.] Fauna of the Chilka Lake : Mollusca Gastropoda , etc. 349 



American shells, suffuses parts of the valves, especially the muscular scar. This 

 pigment is certainly absent in the large variety from Cuttack, but it is developed' 

 to a most pronounced degree in the specimens which we have lately obtained from 

 the Chilka Lake, the Andamans, Madras and Siam. The absence or presence of the 

 colour is probably due to circumstances of environment. Amongst many species of 

 Ostrea the colour is very variable. 



The Cuttack shell is regarded by Newton and Smith as specifically identical with a 

 fossil form from the miocène of Europe, Ostrea gryphoides, Schlotheim (better known 

 as Ostrea crassissima, Lamarck) the close affinity of which to the species living along the 

 coast of North America has been commented upon by every palaeontologist who has 

 had occasion to deal with the form. In most instances specific identity between the 

 fossil form and the living Ostrea virginiana has not been admitted. The identity 

 would, nevertheless, have to be conceded, if, on the one hand, we accept Mr. Vreden- 

 burg's identification of the living Indian shell with the North American Ostrea virgi- 

 niana, and, on the other hand, Messrs. Newton and Smith's reference of the living 

 form to a miocène species. Mr. Vredenburg, while admitting that there exists the 

 closest relationship between the living and tertiary forms, is not prepared to admit 

 actual specific identity without further research. In any case, as regards nomencla- 

 ture, if the identity of the Indian and American species is accepted, the specific name 

 virginiana is older than any of the others bestowed upon its fossil relatives. 



Mr. Preston regards the small Indian form with deep pigmentation of the inner 

 surface as specifically distinct and has described it under the name 0. madrasensis.' 2 



Ostrea lentiginosa , Sowerby, Preston, 1910, p. 36. 



A few shells of this species from Manikpatna have been identified by Mr. Preston. 



Ostrea cucullata, Born, Test. Mus. Caesarei Vindobon. , p. 114, pi. vi, figs. 11, 12 



(1780). 

 Individuals of this common oyster are sometimes found attached to clumps of 

 0. virginiana on the beds at Manikpatna (see pi. xiv, fig. 2). 



Ostrea sp. 



Several shells of a flat circular form were found attached to the post in the 

 channel off Satpara to which reference has already been made. Unfortunately they 

 have been mislaid, but there can be no doubt that they represent a species different 

 from any of those recorded above. 



Family Mytilidae. 

 Mytilus smaragdinns , Chemnitz, Reeve, Conch. Icon., X, Mytitus, pi. vii, fig. 28 



(1858). 

 A single small shell, in a fresh condition but empty, was found on the oyster- 

 beds at Manikpatna in fresh water. The animal had evidently entered the lake in a 

 larval condition, but had been unable to survive the floods. The species is very com- 



1 The corresponding soft parts of the animal are similarly pigmented. 



2 Rec. Ind. Mus., XII, p. 33, figs, ir, 11« (1916). 



