1918.] N. x^NNANDALE : Mollvscs of the Inle Lake. 157 



or less evident reddish markings, and the sculpture consists of by 

 no means prominent granules or tubercles arranged more or less 

 definitely in longitudinal and spiral lines. Shells from some ponds 

 in Calcutta agree well with those of the forma typica. In the pond, 

 however, in the Museum compound — -it is about 150 yards square 

 and from 12 to 20 feet deep in the middle and has a fairly, but not a 

 very abundant vegetation of entirely sub-aquatic plants — a distinct 

 dwarfing is noticeable, shells (fig. 6d) rarely, if ever, exceeding 23 mm. in 

 length ; the sculpture is also as a rule somewhat obliterated and the shell 

 rather narrow. The only reason I can give for the dwarfing of the shells 

 from this pond — a feature which is also noticeable in M. variabilis and 

 in Vivipara bengalensis — is extreme overcrowding. Individuals of these 

 three species abound to such an extent that we find it impossible to grow 

 any kind of water-lily, because the snails congregate in such large num- 

 bers on the stems of young leaves shooting up from the bottom that they 

 bear them down and prevent them reaching the surface of the water. 

 In the same compound there is a small fern-house, thatched with an 

 open layer of straw on wire-netting, but not enclosed with glass. In 

 this fern-house there is an oval concrete basin 5 feet long by 4 feet broad 

 by 1 ft. 4 inches deep. It is supplied with filtered water by a tap and 

 is never entirely stagnant for long, as it overflows in wet weather and the 

 gardeners are apt, contrary to municipal regulations, to leave the tap 

 running. There is, moreover, in it a fairly dense growth of Vallisnieria 

 spiralis. Some years ago one or two plants of the water hyacinth were 

 introduced into the basin, and apparently brought with them, probably 

 from a pond in Calcutta, the eggs or young of AI. tuberculata. The 

 molluscs (fig. 6e) have flourished so far as numbers are concerned, and 

 must have gone through several generations. None of the shells are 

 longer than 17 mm., and the shape is broader and shorter than that of 

 individuals from ponds. Similar peculiarities are to be noted in shells 

 from pools and canals of brackish water in both the Gangetic Delta 

 and Orissa, except that the shell (fig. 6/) is a little more elongate. 



Individual variability is not usually characteristic of Melania tuber- 

 culata, but in the Lake of Tiberias, and apparently also in other parts of 

 Palestine, two varieties (fig. 6g, h) occur. Both have the sculpture well 

 developed and both are of relatively large size. In one, however, the 

 shell is rather smaller and distinctly narrower than in the other. (There 

 is some doubt as to the proper name to be applied to the narrower form.) 

 The interesting points, however, about these two forms from Palestine 

 are (1) that they are found together under identical conditions and 

 (2) that even though they live in water of very abnormal chemical 

 composition they are not dwarfed, but rather above the average 

 size. 



All these facts about M. tuberculata are illustrated in the outlines of 

 shells reproduced in text-figure 6. 



Two other species of the genus Melania are found in the Yawnghwe 

 river, viz., M. terebra and M. baccata. There is very little difference 

 between the shells of the former species from this stream and specimens 

 from Cachar, the original locality. Our series is not a large one and does 

 not exhibit any marked individual variation. 



