i()i6.] Fauna of the Chilka Lake : Mollusca Gastropoda , etc. 355 



For the greater part of the year the little Solen is extremely abundant in the lake 

 and numbers were brought up in most hauls of our nets. Even when the shells were 

 absent, the peculiar siphons to which we refer below were often found. At the end 

 of the wet season, however, it was difficult to obtain living specimens, and only a few 

 were seen at this time of the year. 



The animal excavates, in the ordinary manner, a vertical burrow that is not 

 very much deeper than its own length, inserting its foot into the mud in a contracted 

 condition and then expanding it so as to force an entrance. If laid on its side it can 

 right itself instantaneously by turning its foot round at an angle and thus getting a 

 purchase on the bottom. It can dart rapidly for some inches backwards by squirt- 

 ing water from its siphon and can also swim forwards with moderate ease, compress- 

 ing its foot laterally and using it as a paddle. 



The most remarkable feature in the structure of the species lies in the great 

 development of the siphons, in their very distinct segmentation, in the arrangement by 

 which the segments are thrown off either singly on in groups by a process of autotomy, 

 and in the existence of a ring of minute tentacles round the distal end of each seg- 

 ment. Apart from the actual shortening effected by the autotomy of one or more 

 segments, it produces no apparent structural or functional disablement of the 

 siphons, and if, as seems not improbable, the tentacles have a sensory function, the 

 new tip is as well equipped as the old. 



The small form of Solen ? fonesi occurs in the backwaters of Cochin as well as in 

 the Chilka Lake. The species is recorded from the Philippines and Cebu, but with- 

 out particulars. 



Solen annandalei ,* Preston, 1915, p. 304, figs. 17, lya. Plate xvi, fig. 8. 



The shell of this form is easily distinguished from Chilka specimens of S. ? fonesi 

 by its larger size and relatively greater length ; in the only two specimens we have 

 seen the length is respectively 47 and practically 5 times the breadth. The shells 

 were found on sandy beaches at Nalbano and Satpara, in both cases with examples 

 of S. kempi. 



Solen kempi * Preston, 1915, p. 305, figs. 18, 18a. Plate xvi, fig. 9. 



The shell is still narrower than in 5. annandalei , the length being from 6-4 to 

 about 7 times the breadth. Several fresh shells were found at Satpara and Nalbano 

 and a single living example was dug from pure sea-sand near the mouth of the lake. 

 The siphons resembled those of 5. fonesi, but the animal, instead of being practically 

 colourless, had a distinct greenish tinge. 



Family Mactridae, 



Standella annandalei * Preston, 1915, p. 305, figs. 19, 19a, igb. 



This species is common on sandy ground at Nalbano, burrowing to a depth of 

 several inches. It also occurs in the outer channel, in which, however, we took only 

 dead shells. The only living specimens we obtained were taken in March, but the 

 habits of the species render it difficult of capture except when the level of the lake 



