626 



Records of the Indian Museum. [Vol. XXII , 



tures in common, others, which are perhaps more important, 

 widely divergent. Comparatively few species of molluscs are iden- 

 tical in the two localities, and the general facies and composition 

 of the fauna is very different. In the Inle Valley the two families 

 of molluscs most remarkable for their plasticity are the Vivipari- 

 dae and the lyimnaeidae. As this is also so in the Manipur Valley, 

 it will greatly simplify my comparison if I confine my remarks to 

 these two families. I will begin to do so by drawing up in tabular 

 form the main differences between the Viviparidae of the Inle Lake 

 and those of the Manipur Valley. 



In considering the meaning of the differences thus summarih' 

 expressed we have to take into account not only the differences in 

 environment but also the idiosyncracies of the different genera 

 represented, for there is no fact more evident in the stud}- of the 

 freshwater molluscs than that different genera have different ten- 

 dencies in the matter of variation and plasticity. At present we 

 have three genera to consider, Vivipara, Lecythoconcha and Taia. 

 It will be convenient to take Lecythoconcha first. 



Although this genus is present in both valleys it is so scarce 

 in the Inle Valley, and I know so little about it there, that I must 

 confine va.y remarks, so far as my own observations go, to its pecu- 

 liarities in Manipur. I have selected this genus as the protagonist 

 in my argument because its case is not complicated by the produc- 

 tion of an abnormal and exuberant shell-sculpture. We may 

 indeed, so far as Manipur is concerned, regard Lecythoconcha as a 

 smootli-shelled genus. Further east, especially in Japan, we find 

 shells presumably of this genus with a type of sculpture very like 

 that of Vivipara oxytropis, but we know nothing of their anatomy 

 and they must for the present be ignored. It is probable that 

 their case is similar to that of the species of Vivipara already 

 mentioned and to be discussed further. 



The one species of Lecythoconcha found in Manipur extends 

 the range of the genus a considerable distance westwards from its 



