104 Records of the Indian Mvscum. [Vol. XIV, 



and also of magnesium. Though now shrunken and shallow, the lake 

 is the last relic of a once extensive lake-system and was at a period 

 geologically not remote both larger and much deeper than it is at 

 the present day. The water of its central region is remarkably clear 

 and its bottom covered with a peculiar semi-liquid mud formed of 

 calcareous particles and fragments of decayed vegetable refuse. Round 

 the margin there is a curious rim of floating islands composed of dead 

 and living plants, and the formation of peat is proceeding with great 

 activity. The water of the marginal zone is, therefore, much con- 

 taminated. Considerable differences exist in the fauna of the two 

 regions. Certain peculiarities can also be observed in that of the 

 intermediate zone between the two. As there are no rocks or stones 

 in the lake rupicolous molluscs are absent. 



Many of the specimens from the lake were obtained by dredging, 

 others by the careful examination of masses of weeds. We also searched 

 several of the small streams that flow into the lake, as well as the larger 

 streams and swamps of the He-Ho plain, which lies a few miles to the 

 south-west at an altitude about 800 feet higher. Further, we obtained 

 good series of fossil and subfossil shells from several deposits both in 

 this plain and in the Hsing-Dawng valley some five miles north-east of 

 the lake. 



So far as I am aware, no molluscs have been recorded from the Inle 

 Lake, but several of the species common to it and neighbouring waters 

 have been described by Theobald,^ by Nevill,^ by von Martens,^ by 

 Kobelt* or by Pilsbry,^ from the Northern Shan States and Upper 

 Burma. The species described by Theobald have been admirably 

 figured in Theobald and Hanley's Conchologia Indica (1876). I have 

 found the references to literature in Mr. H. B. Preston's volume on 

 the freshwater Mollusca (1915) in the Fauna of British India series of 

 great value, though they are far from complete. I have to thank my 

 friends Mr. E. Vredenburg of the Geological Survey of India and 

 Mr. Stanley Kemp of my own department for going through certain 

 parts of the proofs of this paper and making valuable suggestions. 



Part I.— SYSTEMATIC. 

 Gastropoda. 



Order PULMONATA. 



Family SUCCINEIDAE. 

 Genus Succinea, Draparnaud. 



It is only by some stretching of terms that a species of Succinea 

 can be dealt with in a paper exclusively on aquatic molluscs, for there 



1 Journ. As. Soc. Bengal (2), XXXIV, pp. 273-279 (1865). 



2 Journ. As. Soc. Bengal (2), XLVI, pp. 14-41 (1877). 



3 Wiegm. Arch. Naturg., LXV (1), pp. 30-48 (1899). 



* Pnhidinen in Martini and Themnitz's Conch. Cab. (ed. Kiistcr), (1909). 

 ^ Pmc. Ac. Nat. Sci. Philadelphia, pp. 188-190 (19011 



