352 Memoirs of the Indian Museum. [Vol. V, 



throughout the year. Its habits render it difficult to obtain except when the water is 

 low. Both young and old individuals were found. 



Meretrix ovum, Hanley, Reeve, Conch. Icon., XIV, Cytherea, pi. vi, fig. 19 (1864). 



This species is more common than the preceding in the outer channel, both 

 young and old individuals occurring in great abundance on the same ground and also 

 on clear sand nearer the mouth of the lake. M. ovum was described from Malabar. 



Tivela dillwyni (Deshayes), Reeve, Conch. Icon., XIV, Cytherea, pi. vii, fig. 24 

 (1864). 



A single small living specimen was obtained in Seruanaddi in the freshwater 

 season. 



Tapes pinguis, Chemn., Mart, and Chemn., Conch. Cab., Veneracea, p. 126, pi. v, 



figs- 3 _ 5j 8-10; 1869 (as V ernes). 

 The species is fairly common in the outer channel with M. casta and M. ovum in 

 March and probably at other times of the year. 



Tapes ceylonensis, Sowerby, Mart, and Chemn., Conch. Cab. t Veneracea, p. 236, 



pi. xl, figs. 10, 11 (1869). 

 The same remarks apply to this species as to the last. 



Clementia annandalei, Preston, 1914, p. 306, figs. 14, 14a, 14b; 1915, p. 301. 



All over the main area of the lake this is one of the commonest molluscs, occur- 

 ring in mud with Thsora opalina. In the inner part of the outer channel it is less 

 abundant, its place being taken to some extent by species of Diplodonta. Living 

 individuals were dredged at all times of the year, but it was noticed that dead shells 

 were relatively very abundant at the end of the freshwater season . The shell is so 

 brittle that it is difficult to obtain perfect specimens, but is much less transparent 

 than that of the Theora. 



The species also occurs at Port Canning in the Gangetic delta and has long been 

 represented in the collection of the Indian Museum by large numbers of specimens 

 from this locality labelled with the nomen nudum "Clementia blanfordii, Benson." 

 The genus is characteristic of estuarine waters in the tropics of Africa and Asia. 



Family Petricolidae, 



Petricola esculpturata ,* Preston, 1915, p. 301, figs. 13, 13«. 



This mollusc was found only in crevices between oyster-shells on the beds at 

 Manikpatna in the outer channel. It was obtained both in fresh and in salt water. 



Family Ungulinidae 

 Only two of the five species of Diplodonta by which this family is represented 

 were found in the main area of the lake. Considering the fact that several species 

 are known from the Gulf of Siam, all of which have a wide Oriental distribution, it is 

 remarkable that all the Chilka forms should prove to have been undescribed. The 

 first three species in the following list seem to prefer a bottom of sandy mud, but 

 D. ovalis and D. chilkaènsis live chiefly on clean sand. 



