1918.] N. Annandale: Fauna of the Inle Lake. 197 



Animal Life in the Marginal Zone. 



The most striking feature of the fauna of this zone is its wealth of 

 insect life. Characteristic species occur among the fish and molluscs, 

 but most of them are also found in marshes and pools and the fauna as 

 a whole is paludine. 



Sponges. — Ephydatia fluviatilis var. intha is occasionally found and 

 Spongilla jragilis var. calcuttana and S. locustris var. proliferens occur. 



Annelids. — In mud at the edge of the lake we found two species of 

 Oligochaeta, the Tubificid Branchiura sowerhyi, one of the few species 

 with external gills, and the Megascolecid Perionyx fulvus, a form that 

 possesses no obvious modification for an aquatic life. The specimens 

 of Branchiura are of normal size with the gills long and as a rule nu- 

 merous. A small almost colourless leech of the genus Glossosiplionia is 

 common on the gastropod molluscs Taia shanensis and Ampullaria 

 umikleyi, and we found specimens of a larger species of the same family 

 on the tortoise Cyclemys dhor shanensis. 



PoLYZOA. — The Ctenostome Hislopia lacustris sometimes grows on 

 Gastropod shells, but not so commonly or so luxuriantly as in other 

 parts of the lake. 



Decapod Crustacea. — The little Atyid prawns Caridina annan- 

 dalei and C. weheri occur, but C. weberi, which apparently enters the 

 lake occasionally from small streams, is much less abundant than its 

 congener. The crab Potamon acanthicum is fairly common among 

 the roots of floating islands and P. curtohates probably wanders in 

 occasionally from the rice-fields and marshes it usually inhabits. 



Insects. — Both larval and adult aquatic insects are very abundant, 

 but the latter are mainly surface-forms, the family best represented 

 both in species and individuals being the Hydrometridae, which are 

 attracted both by the shelter afforded by the islands and the floating 

 plants on the waterways, and also by the abundance of food. As all 

 members of the family are rapacious or feed on dead insects that have 

 fallen into the water it is important for them to live in places where 

 other insects are abundant, while their movements on the surface are 

 greatly impeded by even small waves. The commonest species of 

 Hydrometridae on the Inle Lake are Gerris fossarum and G. nepalensis. 

 Another family of Rhynchota, not surface forms, is well represented 

 in the Corixidae, but Nepidae are comparatively scarce. Water-beetles 

 of all famihes are also rather scarce. Dragon-fly larvae (Agrionidae 

 and Aeschnidae) are abundant. Among Dipterous larvae we observed 

 those of Culicidae (both Culicinae and Anophelinae,^ both very scarce), 

 Chironomidae and Stratiomyidae. Caddis-worms were not very common. 



Speaking generally, therefore, the insects of this zone are just such as 

 would be found in any Oriental marsh, though the number of apparently 

 endemic species is large. No special modifications were observed. 



Molluscs. — The characteristic molluscs of this zone are Planorhis 

 exustus, Ampullaria winUeyi, Hydrohioides nassa typica, Hyrobioides 

 nana and Taia shanensis. All of these but the last, which has not 



1 Anopheles barbirostris, v. d. Wulp. I have to thank Dr. Baini Prashad for 

 naming specimens of larvae. 



