1918.] N. AnNandale: Fauna of the Inle Lake. 199 



Insects. — Insects are much scarcer than in the Marginal Zone. 

 Most if not all of the marginal species, however, make their way into it 

 occasionally. Several Chironomid and free-living Trichopterous larvae 

 were found in the canals of Ephydatia, together with one of the Neurop- 

 terous genus Sisyra (Hemerobiidae), a genus whose larva is always found 

 in sponges. 



Molluscs. — The most characteristic molluscs of the zone is Taia 

 elitoralis, which is not known elsewhere but is closely allied to the fossil 

 T. conica from the Hsin-Dawng valley in the same district. It reaches 

 a larger size than any other Gastropod of the lake except Amjyullaria. 

 Hydrobioides nassa lacustris grows larger here than in the Central 

 Region. Ampullaria winkleyi is fairly common at some places, but 

 Planorhis exustus does not come so far from the margin of the lake. 

 The smaller Limnaeidae are perhaps more numerous in this zone than 

 in any other ; their shells are often a little darker in colour than in the 

 Central Region. 



Fish. — There is no fish pecuhar to the Intermediate Zone, but the 

 little Cyprinidae Microrasbora rubescens and Sawbwa resplendens, which 

 are also common in the Central Region, perhaps breed in the former 

 only, for it was only in this zone that we found the males in full 

 breeding colour. Barilius auropurpureus, on the other hand, is neither 

 so big nor so brightly coloured, though common enough, as in the 

 Central Region. All weed-haunting species are abundant, e.g., the 

 Shan Carp {Cyprinus carpio intha), Cirrhina latia, Ophiocepjialus spp., 

 Mastacembelus spp., etc. 



Animal Life in the Central Region. 



This is the only part of the lake in which the fauna can be said to be 

 completely lacustrine. In it most of the peculiar species (excluding 

 insects) occur in abundance and in many respects it is the most 

 characteristic of the three regions. A curious feature is the complete 

 absence of sponges, a fact for which no explanation is at present 

 forthcoming. A similar lack is that of Phylactolaematous Polyzoa, 

 but this is a feature of other parts of the lake also. The bottom fauna 

 is perhaps richer than elsewhere, and it was only in the Central Region 

 that we found Pelecypoda. 



Platyhelminthes. — Small Planaria of very normal appearance 

 (P. burmaensis and P. (mnandalei) were dredged from the bottom. The 

 most interesting feature about them is the complete or partial absence 

 of rhabdites from their integument. The aberrant Trematode or 

 Temnocephaloid Caridinicola is common in the gill-chamber of Cari- 

 dina annandalei. 



Annelida.— The oidy Oligochaete we collected was Branchiura 

 sowerbyi, which in the semi-liquid mud of this region attains an unusual 

 size and has as a rule its gills less well developed than in the Marginal 

 Zone, in which the water is much less thoroughly qxygenated. Great 

 length is necessary for a cylindrical animal in the peculiar mud of the 

 Central Region, if it would maintain a vertical position. A small red 

 leech of the actively predaceous family Herpobdellidae is found occasion- 



