550 Records of the Indian Museum. [Vol. XXII, 



lucent and conical, and (b) a pond phase (pi. I\^, figs. 4,5), in which 

 it is usually smaller, thicker, less translucent and less regular in 

 form, and has the mouth narrower and more pointed above. In 

 the latter phase large individuals occur, but they are never of 

 regular trochiform outline and the flattening of the whorls outside 

 the outline is much less oblique. The surface in specimens from 

 ponds is always more or less eroded. The sexual differences in 

 the shell are less marked than in the lake phase. 



Thus in the lake phase the shell is about i-J- times as high as 

 broad in females and li times in males, whereas in the pond phase, 

 in which sexual differences are concealed by individual variability, 

 the height is from i|- to li times the breadth. 



The pond phase comes nearer V. microchaetophora than does 

 the lake phase and has in all respects a less peculiar shell, nearer 

 that of the Viviparae bengalenses, from which the Viviparae 

 oxytropides are perhaps derived. The Japanese form that has 

 been assigned bj' some authors to the Manipur species has, as 

 Pilsbry has pointed out, no relation to it. 



V. oxytropis attains its maximum development and most 

 characteristic form in the more open parts of the l,oktak Lake, in 

 which it is abundant with Lecythoconcha lecythis. In ponds it is 

 much scarcer and it is apparently absent from the smaller swamps 

 of the Manipur valley. 



In the lake it is almost invariably infested by a leech of the 

 genus Glossostphonia, which often exists in the branchial cavity in 

 such numbers as to occupy practically the whole lumen. Major 

 Sewell, moreover, found Trematodes of the genus Leucochloridinin 

 encysted in the mantle of specimens brought living to Calcutta for 

 examination. 



Males in this mollusc seem to be considerably less abundant 

 than females, at any rate in the Loktak Lake. The young are 

 more numerous and smaller than those of L. Itcythis living in the 

 same conditions. 



Viviparae dissimiles. 



Vivipara micron, sp. nov. 



The shell is of ver\' small .size, moderatel}^ thick, acuminate, 

 narrowly rimate, with the spire and the upper part of the body- 

 whorl somewhat elongate but the basal part very short and con- 

 vexly flattened from below upwards. There are probably 4^ 

 whorls in the complete shell, but in the only specimen I have 



