272 N. ANNANDALE. 



Most of the shells on Barkuda, where they occur in the red soil of the island, 

 often in large numbers, are broken and have the surface corroded. 



The typical form of M . casta still lives in the outer channel of the Chilka Lake, 

 but all forms of the species have disappeared from the main area, in which the dense 

 mud of the bottom is now quite unsuitable for the activities of a mollusc with so 

 heavy a shell. The race satparaensis is found in sandy deposits all round the lake as 

 well as in the soil of Barkuda and other islands. This race, shells of which are also 

 abundant (/. Hornell) in deposits of subfossil age at the edge of other backwaters 

 and lagoons on the east coast of India, is apparently extinct, or at any rate has not 

 yet been found in a living condition. In considering the age of Barkuda I 

 will discuss the probable nature of its habitat. 



Sunnetta scripta (Ijnn.). 



A few, quite typical but colourless valves of this species were found amongst an 

 accumulation of those of Meretrix casta near the middle of the island. The surface 

 is somewhat worn. 



5'. scripta is one of the commonest bivalve molluscs on the sandy coast of 

 Orissa and Ganjam, but it has not been found living in any part of the Chilka Lake. 



Comparison between the Deposits of Sheels on Barkuda and 



THOSE AT THE HEAD OF RAMBHA BAY. 



Blanford ' in his "Sketch of the Geology of Orissa" says of the Chilka 

 Lake : — 



" The lake itself is a part of the sea first rendered shallow by deposits from the 

 mouths of the Mahanaddi and from the silt carried up the bay round the hills near 

 Ganjam by the violent southernly winds of the monsoon, and then entirely cut off by a 

 spit, formed bj^ the same agency of sand drifted along the coast. Near the south- 

 western extremity of this spit there is a considerable deposit of estuarine shells, at a 

 height of 20 to 30 feet above the present flood level of the Chilka. The shells found, 

 Cytherea casta and Area granosa, have not been observed living in the Chilka, 

 and both are estuarine species, not occurring in the sea itself, but the former is now 

 abundant in the estuary connecting the lake with the sea. This deposit appears to 

 afford evidence of a recent elevation of the land." 



As we have seen, his statement as to living molluscs must be modified in 

 accordance with knowledge more recently acquired. Further it may be noted that the 

 deposits of Area and Meretrix at certain places extend right down to the shore of the 

 lake and are even partially submerged in its waters in high floods. With the two species 

 Blanford mentions are mingled occasional shells of Cuma disjuncta and Potamides cingu- 

 latus. Bleached shells also occur of freshwater species such as Indoplanorhis exustus, 

 Melanoides tuber cut atus, Vivipara dissimilis and Pachvlabra globosa carinata. All these 

 species are found living in the neighbouring rice-fields and village-ponds and it is 



I Rec. Geol. Surv, Ind., V, p. 6i (1869). 



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