i6 Memoirs of the Indian Museum. [Vol. V, 



in environment that most of them possess. It seems strange to find a Rhizostomous 

 medusa or an Oxystome crab living in lacustrine conditions, but it is even more 

 remarkable that individuals of such forms are able to flourish at one season in fresh 

 and at another in salt water. 



Aims of the Zoological Survey of the Lake. 



The origin of our zoological survey of the Chilka Lake has been explained in the 

 note prefixed to this volume ; the main object we have had before us in its execution 

 has been to lay a foundation for the study of the fauna of brackish water and of 

 water of variable salinity on the coast of India on the same lines as our predecessors 

 in the Indian Museum have done for that of the abyssal fauna of Indian seas. For 

 this object it has seemed necessary in the first place to make our collections as 

 comprehensive as possible, noting the circumstances of each capture and deducing 

 from our notes facts as to the biology of the commoner species. It has not been 

 possible, and perhaps it has been hardly desirable, to make any attempt at a detailed 

 biological or morphological study of any particular group or species. That can 

 come later, and if our researches prove useful to future naturalists who may under- 

 take investigations of the kind, we feel that our labours will be amply rewarded. 

 In a field so little explored we think it is as well not to specialize too soon. 



The methods employed and the apparatus used in the survey may be described 

 in some little detail. 



Methods and Material. 



In making our investigations we were fortunate in obtaining from the Kallikota 



raj the use of a small launch, the c< Lady of Chilka", 

 the only steamship on the lake. From this launch we 

 were able to trawl systematically over a considerable part of the main area and, 

 in the flood-season, over the whole of the outer channel. In the latter area, in 

 the salt-water season, we worked from a row-boat kindly lent us by the Salt 

 Department. 



The very soft mud of which the bottom is for the most part composed proved a 

 considerable difficulty, and we believe that a really satisfactory instrument for the 

 zoological investigation of regions such as the Chilka Lake yet remains to be devised. 

 A net with mesh fine enough to retain small bottom organisms, such as Cumacea 

 and minute Mollusca, does not permit the mud to escape and in a very short space 

 of time becomes filled to bursting point. 



For bottom work we used chiefly two sorts of net. The first of these was a 

 miniature beam- trawl, six feet in breadth, of a size that could be fished comfortably 

 from the stern of the launch. At the cod-end the mesh of this net was \ in. (stretched) 

 and it therefore permitted the greater part of the mud to escape, except in particular 

 places where it was of a lumpy character. To the back of this net, on the outside, 

 we attached a shaped bag of mosquito-netting or coarse-meshed canvas, placed in 

 the path of the swirl caused by the foot-rope. This net caught numbers of small 



