AN ISLAND IN THE GHILKA LAKE. • 265 



such a way that they naturally cohere when the muscles of the fish rot or are removed, 

 and as the eagles are somewhat dainty in their feeding and only pick off the softer 

 and more accessible parts of the fish, this region of the skeleton remains, often in 

 perfect condition, and must in the course of time, if natural processes persist without 

 violent interruption, become a characteristic fossil. 



These facts are not without a bearing on the subfossil shells of the island, for 

 they suggest the questions : How far is the accumulation of them due to inanimate 

 forces, and is it possible that the molluscs they represent were originally brought 

 together by some animal, or even by man ? 



The shells found in a subfossil state on Barkuda belong to five species, two of 

 Gastropoda and three of Pelecypoda or lyamellibranchiata. 



IvIST OF THE MOI.I.USCAN ShKIvI^S FOUND SuBFOSSII. ON BARKUDA. 



Gastropoda. Pelecypoda. 



Potamides [Tympanatonos) cingulatus Area {Anadara) granosa, Iv. 



(Gmelin). Sunetta scripta (ly). ' 



Cuma disjuncta, sp. nov. Meretrix casta (Chemn). 



Three of these species, the Potamides, the Cuma and the Area still survive in 

 the lake — or rather did so a few years ago^ for considerable changes have apparently 

 taken place in the fauna since 1914.^ No difference between recent and subfossil 

 shells of P. cingulatus and C. disjuncta has been discovered, but the Area has been 

 profoundly modified. Sunetta scripta is a common species on the sandy coast of 

 Orissa but has not been collected in the lake, while the Meretrix casta apparently 

 belongs to an extinct race, shells of which are common in comparatively recent 

 brackish- water deposits on the east coast of India. Before discussing the significance 

 of these facts it will be as well to give an account of the species. 



GASTROPODA. 



Family Cerithiidae. 



Potamides^Tympanotonos) cingulatus (Gmelin). 



1916. Potamides (Tympanotonos) fluviatilis, Annandale and Kemp, Mem. Ind. Miis. V, p. 344. 

 This species is, on the coasts of India, a common and characteristic mollusc in 

 backwaters and lagoons, the water of which is of comparatively low and variable 

 salinity. In the Persian Gulf it is marine. In 1914 it was found living in all 

 the parts of the Chilka Lake in which the bottom was composed of sand or sandy 

 mud, except along the inner shore. ■ It was not uncommon in a ditch at the 

 head of Rambha Bay. On Barkuda subfossil shells occur, in no great abundance, in 

 the soil of the interior of the island, sometimes alone, sometimes with Meretrix casta. 

 These shells do not differ in any way from fresh specimens from the lake. Many of 

 them have a curious thickened broad and ill-defined varix on the body-whorl a short 



I See Annandale, Rec. Ind. Mus. (ined.). 



