1918. J N. Annandale : Fauna of the InU Lake. 201 



and H. fhyscus are much the most abundant species. Amnicola alticola 

 is also very common, and Phi/sunio ferrugineus fairly so. The smaller 

 Limaeidae occur in small numbers among weeds. 



E'isH. — All the fish of the lake (excej)t the mud-loving eels and cat- 

 fish and Microrashora erythromicron) probably enter this region, but 

 Barhus schanicus, which is not a true lacustrine hsh, avoids it habitually 

 and we have no evidence as to the occurrence of Lepidocephalus herd- 

 morei, which is httle more than a stray immigrant in the lake. The most 

 characteristic species is Barilius auropurpureus, which swims in large 

 shoals just below the surface of the water. Chaudhuria caudata is 

 found among weeds. 



The fauna of the Central Region {i.e., the true lacustrine fauna) 

 of the lake consist mainly, from a biological point of view, of two ele- 

 ments, viz., animals that live among weeds and bottom forms. Surface 

 organisms of all kinds are, at any rate in early spring, very scarce and 

 even Barilius auropurpureus descends to the bottom in the heat of the 

 day. 



The bottom fauna includes comparatively few burrowing forms, 

 probably on account of the tenuity of the mud, which renders burrowing 

 for any but very small and light or extremely elongate animals difficult. 

 Among the few burro wers are Physunio ferrugineus, which works its 

 way through the mud with the aid of a sharp projecting " wing " 

 and is never entirely submerged, a very small form of Pisidium caser- 

 tanum, the Oligochaete worm Branchiura sowerhyi (which is much longer 

 than usual in this position and, like the Unionid, only buries the anterior 

 part of its body) and small red Dipterous (Chironomid) larvae. Melania 

 tuherculata crawls habitually on the bottom, on which, as well as among 

 weeds, Taia intlia and the species of Hydrobioides are also to be found. 

 We dredged a few small Planarians of normal appearance and some 

 flattened Libellulid dragon-fly nymphs, also mud-crawlers. 



Life is rich among the weed-thickets of this region. Most of the fish 

 conceal themselves and probably spawn among them. The small Lim- 

 naeidae so characteristic of the lake as a whole, Caridina annandalei 

 and the larvae of Agrionid dragon-flies and of the Trichoptera and Ephe- 

 merids that swarm in the evening in a winged state find their home 

 here. The peculiar larva of the midge Polypedilum in its case (which 

 is also its larder) decorated with living Vorticellid Protozoa, a\so lives 

 amidst the thickets of Ceratophyllum. A prolonged search would 

 certainly reveal other interesting forms. A peculiarity of the weeds 

 of this region is the total absence of sponges and polyzoa. 



The house-posts of our dwelling in the middle of the lake had an 

 interesting fauna, which it was possible to observe in almost ideal con- 

 ditions. The house had been erected only a few weeks before our visit, 

 but the surface of some of the posts on which it stood was almost com- 

 pletely covered with large colonies of Hislopia lacustris, the upper parts 

 of which were perishing as the water sank. Considerable numbers of 

 the mollusc Taia intha sat on the posts, sometimes without moving 

 from day to day, and the two commonest species of Hydrobioides crawled 

 on them more actively. The curious fish Discognathus lamta also 



