1 92 1.] 



Manipur Molluscs. 



533 



As one of the chief objects of my visit to Manipur was to obtain 



material for a comparison between the fauna 



Comparison between ^f ^j^^ Loktak and that of the Inle Lake, a 



the Loktak Lake and the , r ji 1 • , 1 



Inle Lake. short summary oi the physical characters 



of these two bodies of water may be given. 



Both are situated in isolated valleys at altitudes between 2,500 

 and 3,000 feet. Their river-systems are connected with adjacent 

 watersheds, that of the Irrawadi in the one and that of the Salween 

 in the other. The climate of the two valleys also is similar, and they 

 are only some 340 miles apart as the crow flies. Even the appearance 

 of the two lakes is not dissimilar, for both lie in open plains between 

 ranges of rather bare mountains running almost due north and south, 

 and both are remarkable for the floating islands which cover a 

 considerable part of their surface. Both, moreover, are shallow, 

 and neither has well-defined shores or a definite permanent 

 area. 



On detailed comparison, however, it becomes clear that, in 

 this, as in so many instances the physical differences, though much 

 less apparent, are actually of greater importance from a biological 

 point of view than the pliysical resemblances. The structure of 

 the two valleys and of the hills surrounding them, as we shall see 

 when discussing the origin of the Loktak Lake, is very different, 

 the most im.portant feature characteristic of the Manipur valley 

 being probably the absence of limestone, for as a result of this the 

 composition of the water of the two lakes is quite unlike. 



This chemical divergence occurs in every particular. The 

 percentage of calcium and magnesium salts is very much smaller 



