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



recent connection with Burma is by no means strong, and the As- 

 samese and Bengali element in the fauna is clearly shown. 



The three genera of Cyrenidae represented in the Manipur 

 fauna are all of exceedingly wide range, Sphaenu-in and Pisidium 

 being almost cosmopolitan, while Corbicula is found in the warmer 

 parts of all regions.' The species of these genera known from 

 Manipur, with two possible exceptions, have a wide range in north- 

 ern India, the two exceptions being C. suhradi'.da, for which the 

 Manipur Valley' is the only precise locality recorded, and S. austeni 

 which is only known from Manipur and the Naga Hills. Of the 

 others, C occid ns and C striatella occur a'l over the plains of In- 

 dia, while S. inuiciim, P. clarkeanitm and P. hydaspicola have been 

 found at considerable altitudes in northern India as well as in 

 widely sepirate:! localities in the Inilo-Gangelic plain. 



The Cyrenidae, indeed provide as little evidence for long-estab- 

 lished connection between the Manipur Valle}' and Burma as any 

 other family of aquatic molluscs. 



To sum up, therefore, the geographical affinities of the aqua- 

 tic and amphibious ]Mollusca of Manipur as revealed by the distri- 

 bution of genera and species, it may be stated briefly that these 

 affinities are rather with the molluscs of Assam and the Gangetic 

 Valley than with those of the valley of the Irrawadi or the Salwtea 

 and that the Burmese element is much smaller than might be ex- 

 pected from the close connection between the river-system of the 

 Manipur Valley and of the Irrawadi. 



Ecological Distribution. 

 As might be expected in a swampy valley like that of Manipur, 

 the aquatic fauna is largely paludine. Even in the Loktak Lake 

 there has bten no evolution of a true lacustrine fauna, and, indeed, 

 the number of species of aquatic molluscs is comparatively small. 

 The species found actually in the lake are — 



Vivi-para oxytropis. Gyrauliis canton. 



Lecythoconcha lecythis. Hippeutis (?) nmhilicalis. 



Liiinaea ocmninata. Lamellidens corrian-us. 



Indoplunorbis exustus. Sphaerium indicum. 



Pisidium clarkeanum. 



The majority of these species are common in small ponds in 

 the Gangetic Delta and none of them have been found in a true 

 lake, except Indoplanorbis exustus, which in the Inle Lake haunts 

 only the swampy marginal zone and in the Tale Sap in Siam is 

 found only among beds of weeds near the shore. The only species 

 that are in any way characteristic of the Loktak Lake are the two 

 Viviparidae. These attain their maximum de\elopment onlj' in 

 the deeper part of the swamp, but both are found also in ponds 

 and smaller swamps throughout the valley. No definite zones of 

 life can be recognized here, but Laiiiellidens marginalis and Pisi- 



i It occurred in England in 'I'ertiarv times. 



