202 Records of the Indian Musewn. [YoL. XlV, 



frequented them, clinging to them with its peculiar lip, gradually swim- 

 ming up them, browsing on the way on Hislopia and algae. 



Groups of Animals eepresented. 



Considered as a whole, the fauna of the lake is remarkably rich in 

 fish and molluscs, both of which are abundant in species and individuals 

 and include peculiar and apparently endemic forms. The Mollusca 

 exhibit extraordinary plasticity and in several instances a very high 

 degree of specialization in shell-form. The fish are almost equally 

 remarkable. Included among them are several minute brilliantly 

 coloured species and also the eel Chaudhuria, which is very small but 

 not brilliantly coloured — a form so peculiar that a new family has had 

 to be founded for its reception. A characteristic feature of most of the 

 fish, doubtless correlated with the clearness of the water, is the large size 

 of their eyes and the poor development of tactile organs such as barbels. 

 The lower vertebrates, on the other hand, are poorly represented and 

 in no way remarkable or highly specialized. Sponges are apparently 

 absent altogether from the Central Region, though one species {Ephy- 

 datia fluviatilis) is common in the Intermediate Zone, while the Polyzoa 

 are represented in the fauna only by the Ctenostomatous genus 

 Hislopia, a species (//. lacustris) of which is common all over the 

 lake. Notwithstanding a careful search, we were unable to find 

 any Amphipod or Isopod Crustacea. Only two species of Decapoda 

 penetrate as far as the Central Region, and the lower groups of 

 Crustacea are apparently scarce throughout the lake. In the Marginal 

 Zone numerous species of aquatic insects of the orders Odonata, Diptera, 

 and Rhynchota occur, but beetles are scarce in all regions. In the 

 Central Region the larvae of certain Diptera, Trichoptera and Ephe- 

 meridae swarm, but the number of species is limited. Dr. F. F. Laidlaw 

 has kindly given me the following note on the Odonata in our collec- 

 tion : — 



" The most interesting species in the collection is perhaps a small 

 orange and black IscJmeura, closely allied to /. rufostigma, Selys, from 

 Bengal and Assam but quite distinct, and apparently new to science. 

 A number of examples of the beautiful Rhinocypha iridea, Selys, hitherto 

 recorded from Burma, form an addition to the Museum list of species ; 

 and R. biforata, Selys, is also represented. Specimens of a species of 

 Ceriagrion present some difficulties in identification, they are possibly 

 examples of my C. olivaceum recorded from the Abor country. The 

 collection of larval forms is large and includes specimens belonging to 

 species not represented amongst the adults ; amongst others one that 

 is possibly the larva of a Disparoneura. The adults, with the exception 

 noted, are mostly to be referred to common and widely spread 

 species. Possibly the season of the year was unsuitable for the obtain- 

 ing of some species, but on the whole the collection of adults is not so 

 rich as one would have expected from the variety of the larvae." 



Some of these dragon-flies breed in the lake, notably the IscJmeura, 

 while others {e.g., Rhinocypha spp.) are jungle forms only found in 

 thickets on the hills. These latter probably breed in small streams. 



