i 9 i6.J 



Fauna of the Chilka Lake ; Mollusca Gastropoda, etc. 



357 



Fig. 6. — Theora opalina (Hinds). 

 Living animal, with siphons contracted 

 and foot partially extruded, 

 by Mr. G. M. Henry. 



From a sketch 



in mud, or muddy sand, and the siphons are capable of elongation to at least three 

 times its length ; but so far as we could dis- 

 cover the burrow is always quite superficial. 

 The animal is capable of giving sudden leaps 

 by ejecting water. The shell when not eroded 

 is of a glassy transparency (see fig. 6) but 

 becomes somewhat clouded after death. 



Theora opalina was originally described 

 from a muddy bottom in shallow water in 

 the Philippines. It probably occurs in all 

 estuaries and backwaters on the Indian 

 coasts, at any rate it is fairly common in 

 those of Bengal, Madras and Cochin. 



Cumingia hinduorurn* Preston, 1915, p. 308, figs. 22, 22a. 



This species was found living at the inner end of the outer channel at all times 

 of the year. Living specimens were also obtained off Parikudh in the main area in 

 November in water of very low salinity (sp. gr. 1-00225), the bottom at this point 

 being somewhat sandy. 



Family Cuspidariidae. 



Cuspidaria annandalei , Preston, 1915, p. 308, figs. 23, 23a, p. 482 ; 1916, p. 39. 



This species is common all over the lake-system except at the seaward end of 

 the outer channel. It sometimes occurs on bare mud, but. is particularly abundant 

 in thickets of Potamogeton, to which young shells are frequently found attached. 

 It seems to flourish equally well in fresh, salt and brackish water. Many shells have 

 a number of small greyish spots on the swollen part ; these are more conspicuous in 

 fresh examples. The species has also been found in backwaters at Madras and Cochin 

 and in the Gangetic delta. 



Family Lyonsiidae. 



Lyonsia satnalinsulae* Preston, 1914, p. 310, figs. 16, 16a; 1915, p. 309. 



There are not many specimens of this species in our collection; but they were 

 found living at widely separated places in the outer channel and the main area both 

 in the salt and fresh-water seasons. Their scarcity is probably due to the fact that 

 they burrow in sandy mud near the shore and were therefore rarely taken in our 

 nets. 



Family Anatinidae. 



Broken shells belonging to the genus Anatina were observed in considerable num- 

 bers on the shore, when the level of the lake was low. wherever a certain amount of 

 sand was mixed with the mud of the bottom. Good specimens were difficult to obtain 

 on account of the fragility of the shells and of the fact that the animals burrow 

 to a depth of at least two feet. 



Lynge draws attention to the variability of A. anatina (Linn.) and expresses the 

 opinion that many species of the genus will ultimately have to be withdrawn. We 



