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



general scarcity of solid bodies to which attention has already been called with 

 respect to the outer channel. The hedges of screw-pines by which the fields are 

 protected from trespassing cattle are, however, when the water is high, sometimes 

 partially submerged ; they then afford shelter to many Decapod Crustacea, while 

 broken fragments stranded on the shore give lodgment to amphibious insects and 

 Crustacea, as well as to several terrestrial vertebrates that feed on these animals. 



General Character of the Fauna. 



When all the reports contributed by specialists to this volume have been 

 completed we propose to discuss the fauna of the Chilka Lake in considerable detail. 

 It will be well, however, to preface these reports by a brief statement as to the 

 general nature of the fauna with which they will deal. To do so it will be convenient 

 to consider the animals first under the following headings: — 



(i) Mud fauna. (4) Weed fauna. 



(2) Sand fauna. (5) Free-swimming organisms. 



(3) Rock fauna. (6) Plancton and surface fauna generally. 



i. The organisms that live in mud or crawl on its surface form what is perhaps 

 from a zoological point of view the most conspicuous element in the fauna of the 

 lake. Considering the great proportion of the bottom that is covered with mud this 

 fact is not surprising. Among the mud-dwellers are included several coelenterates, 

 several polychaete worms, a large proportion of the molluscs, several Decapod and 

 other Crustacea, a few small Teleostean fish and several comparatively large rays. In 

 nearly every case the number of spades present in any one group is extremely 

 small, indeed it is probable that in many cases even families are each represented by 

 a single form. The number of individuals on the other hand is as a rule ver} 7 

 large. In this section of the fauna we find many noteworthy adaptations for burrow- 

 ing and for protecting the gills or other breathing apparatus from being clogged with 

 particles of silt 



2. The arenicolous animals of the lake are mainly confined to the outer part 

 of the outer channel and have as a rule a less specialized character than the mud- 

 dwellers. Among them are to be found at least one species of sponge, two species of 

 oligochaete worms, several polychaetes, and the majority of the Decapod Crustacea 

 and molluscs. This element is not entirety confined to the outer channel, for several 

 of its representatives are found on the shores of Nalbano Id. and a few even so far 

 inland as Barkuda Id. near the mouth of Rambha Bay. 



3. The rock fauna is much more restricted as to number of species and genera 

 than might at first sight seem probable. The sponges are represented by two abun- 

 dant forms, the coelenterates by a single hydroid, the Crustacea and worms by a few 

 small species that crawl among sponges and algae or hide under stones ; the molluscs 

 by one or two sessile Lamellibranchs and one or two Gastropods. The poverty 

 of this element is due very largely to two facts, firstly that most of the rocks are 

 only covered by water for a small part of the year, and secondly that any animal 



