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



Prashad, for instance, was described from a small ditch, liable to 

 desiccation , in the Western Ghats and has since been found in a 

 shallow pond at Rangoon. The phase Jiians, Sowerby, originally 

 described from " Malabar," occurs, without much individual varia- 

 tion, in a swampy artificial lake situated at an altitude of 7,000 ft. 

 in the Nilgiri Hills. A somewhat similar but more delicate phase, 

 ventricularis, Kustei, has been found in the Lake Nainital (altitude 

 6,400 ft.) in the Western Himalayas, and these two forms may prob- 

 ably be regarded as dwarfed mountain phase;. 



Differences in shell colour are probably correlated in most cases 

 with differences in the water in which the specimens are found. 



We are in some doubt about Benson's L. chlmnys, which dif- 

 fers from all other forms of L. acuminata with which we are 

 acquainted in the brilliant golden colour of its shell, the relative 

 width of the bodj'-whorl and its strong spiral sculpture. On the 

 only occasion on which either of us has found L. chlamys it was 

 discovered living in abundance on rocks covered with algae in an 

 artificial reservoir in the hill-fort of Satara — a tj^pe of environment 

 very unusual for L. acuminata. The specimens were small and 

 rather narrow but exhibited the diagnostic characters clearly. 



L. acuminata is common in the Manipur Valley, in which, how- 

 ever, we obtained no specimens of the extreme narrow type (gra- 

 cilior, von Martens). Indeed the shells obtained showed less indi- 

 vidual variability than in many districts and were for the most 

 part of a type approaching the mean in shell form, neither very 

 narrow nor particularly broad. No very large specimens were seen, 

 and none that could be called dwarfed. The averge size of shells 

 was, however, distinctly smaller than usual. One or two points of 

 interest may be further noted in detail as regards plasticitj* and 

 aberration. 



Our collection is from different parts of the Loktak Lake, from 

 ponds, swamps and small bathing-pools and from a stream. The 

 specimens from the Loktak Lake provide evidence of distinct but 

 not extreme plasticity. If shells from clean beds of Potamogcton 

 in the lake (pi. VII, fig. 2) be compared with those from its rather 

 foul and swampy margin (pi. VII, fig. i), the following differences 

 are apparent : — (i) the shells from the open lake are in most in- 

 stances distinctly smaller and have a shorter spire (see table of 

 measurements) than those from the margin. In both series the 

 colour is a deep chestnut brown, but those from the margin are 

 coated externally with a black deposit. The shell in the latter is 

 also a little thicker and the sculpture coarser and more regular. 



The most characteristic series in our collection, however, 

 consists of specimens from running water. These were found on 

 floating grass-stems and among green filamentous algae in the 

 small stream that runs past Potsengbam into the north end of the 

 Loktak Lake. Thej^ occurred onlj' at places at which the water 

 was clean and deep and flowed fairty rapidly. The shells in this 

 series are almost colourless and so thin and brittle that we found 

 it difficult to secure perfect specimens. Their surface is deeply 



