112 Records of the Indiari Museum. [Vol. XIV, 



mens from the Tale Sap in Peninsular Siam differ very little. The 

 species, therefore, seems to be a remarkably constant one, neither 

 plastic nor variable. It is common in the more swampy parts, close 

 inshore, of the marginal zone of the Inle Lake and in all ponds, etc., 

 in the district. It is found in similar situations in Bengal and Siam 

 and it does not appear to be anywhere a true lacustrine mollusc. 



I figure the shell of a very young individual, which puzzled me 

 greatly until I had seen a series. 



Planorbis saigonensis (?), Crosse & Fischer. 

 Plate xi, fig. 12. 



1909. Planorbis saigonensis, Germain, Bee. Ind. M^is., Ill p. 117. 

 1915. Planorbis (Gyraulus) compressus, Preston, Faun. Brit. Ind., Freshw. Moll. 

 p. 118. 



Germain has discussed the synonymy of this species in the paper 

 cited. I assign to it with some doubt a number of subfossil shells from 

 the banks of the He-Ho stream. They seem to be intermediate 

 between P. saigonensis and P. convexius cuius, which is perhaps no more 

 than a variety, but in none of them is the aperture definitely lunate. 

 In some a faint peripheral ridge can be detected, while in others there 

 is no trace thereof. The largest shell is only 5 mm. in greatest 

 diameter. 



The species is widely distributed in Mesopotaniia^ Afghanistan, India, 

 Indo-China, China, Japan and the Malay Region. 



Planorbis velifer, sp. no v. 

 Plate xi, figs. 7—11. 



Shell minute, delicate, transparent, colourless or faintly tinted with 

 yellow, with very fine close-set regular transverse striae, with 3| whorls, 

 slightly depressed above in the centre, with the upper surface very 

 slightly convex and the suture impressed, with the periphery angulate 

 and as a rule faintly carinate, with the centre of the lower surface 

 moderately depressed and with this surface otherwise almost fiat ; aper- 

 ture large, broad, moderately oblique, its lower margin slightly con- 

 cave, its upper margin moderately convex ; the edge of the lip sharply 

 defined without thickening ; no internal callus. Maximum diameter 

 4 mm., minimum diameter 3-5 mm., height 1-75 mm. 



Type-specimen. M. 11288/2 Zoological Survey of India {Ind. 

 Mus.). 



var. ciliata, no v. 



This variety only differs from the typical form in having a variable 

 number (usually five or six) of spiral ridges on both surfaces. These 

 ridges are formed entirely of very minute epidermal cilia closely pressed 

 together. They are often obsolete. 



The two forms of shell fade gradually one into the other. Both 

 exhibit considerable variation in the size and obliquity of the aperture 



