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



daria annandalei Preston. It was usually taken with Modiola undulata on weeds or 

 algae. Until December, 1919, it was still common, but in April only a few individuals 

 were found alive. 



The two remaining species, or nominal species, of the Pelecypoda taken in 1914 

 belong to the family Anatinidae and are doubtfully distinct. Mr. Preston has named 

 them Anatina barkudensis and A. barkulensis. These molluscs can as a rule be 

 secured alive only by digging in sand when the lake is low, i.e. in the cold season 

 and the hot weather. None were obtained in 1919-20, but no special search was 

 made for them. Fairly fresh shells were observed on Cherriakuda in April, 1920. 



Considering the molluscs as a whole, we observed in 1914 that, in them as in other 

 groups of animals, changes in the physiography and hydrography of the lake had a 

 selective influence. This was also so in 191 9-1920. Some species have disappeared, 

 while others have survived without decrease of reproductive vigour. The species 

 moreover, that have survived are not always those that might have been expected to 

 do so à priori. Those of Modiola are, we know, tolerant, but Nassa is mainly a marine 

 genus. 



The changes observed in the invertebrate fauna of Rambha Bay in 1919-20 

 were doubtless correlated with the occurrence of abnormally low salinity of the 

 water, and were almost certainly of a temporary nature.. It is improbable that all 

 individuals of the species that were not observed in these years had perished, and, 

 indeed, observations made in June, July and August, 1920, proved that several of the 

 more conspicuous forms were already recovering their old status. 1 



It will be convenient to add here the description of a new species of Nudibranch- 

 mollusc discovered in Rambha Bay by Dr. Baini Prashad and myself. 



Stiliger pica Annandale & Prashad, sp. nov. 



The mollusc we call Stiliger pica is a very small aeolidiform Hermaeid with 

 simple ungrooved rhinophores and without other tentacular processes on the head or 

 foot. 



The total length of the living animal in an expanded condition was 87 mm. and 

 the breath of the foot i'5 mm. The foot was long and narrow with parallel sides and 

 sharply pointed but not produced into a filamentous process behind. In front it was 

 somewhat expanded and its antero-lateral angles formed small, broad, blunt lobes 

 separated by a deep emargination in front. The snout was truncate as a whole and 

 depressed over the front of the foot ; its anterior margin was separated into two lobes 

 like those of the foot but smaller. The dorsal surface of the anterior part of the head 

 was deeply concave. The rhinophores were long, slender, pointed and filiform ; the 

 eyes small but distinct and situated immediately behind the bases of the rhinophores. 

 The cerata were relatively long and slender, almost filiform and sharply pointed at 

 the tip. The longest were of about the same length as the rhinophores. They were 

 arranged in two bands, one running down each side of the notum from a little behind 



1 In October, 1920, Pachygrapsus propinquus and a species of hermit-crab reappeared at Barkuda. 



