1918.] N. Ani^andale : Molhiscs of the InU Lake. 137 



obscure, broad spiral ridge appears ; on the third this grows stronger 

 while on the fourth it becomes double ; on the fifth whorl there are 

 three ridges of this kind, and on the sixth, which represents the upper 

 part of the fifth whorl in the adult shell, there are five. On this whorl 

 the two upper ridges become definitely nodular. 



The operculum of T. intha closely resembles that of T. elitoralis, 

 but is thinner and less produced posteriorly. The radular teeth are 

 of a bright golden colour. They differ from those of T. elitoralis mainly 

 in proportions ; a characteristic feature that both have in common is 

 the coarseness of the lateral denticulation of the central tooth. The 

 differences are that the upper margin of the central teeth is convex, 

 the teeth of the inner lateral row are rather larger, only a little longer 

 than the central teeth, and distinctly shorter than the marginal teeth. 



Type- specimen. M. 11004/2, Zoological Survey of India {hid. Mus.). 



Habitat, etc. — This species only lives in the central region of the 

 Inle Lake, where it is extremely abundant. It crawls slowly on the 

 bottom, on weeds and on posts, but is very sluggish, and often remains 

 for days without moving. Its food consists of minute algae of a very 

 soft consistency. 



As I have examined many hundreds of specimens of this remark- 

 able species I am able to speak with confidence of its constancy. There 

 is very little sexual variation in the shell and I did not always find it 

 possible to distinguish males from females by the shell alone. The 

 only characters in which individual variation was found were the 

 development of the spiniform processes, the number of spiral ridges, the 

 degree of attenuation of the spire, and changes in the direction of the 

 spiral. In all these points, moreover, the shells that exhibited variation 

 were what a lepidopterologist would call aberrations. Shells occur 

 occasionally, but very rarely, in which the spiniform processes are 

 developed on the basal ridge of the penultimate whorl as well as on the 

 body-whorl. A shell of this kind is figured on pi. XV, fig. 2. Shells 

 in which there are three instead of two tubercular ridges above the 

 main ridge of the body-whorl are less rare, and others in which the 

 spire is considerably more attenuated than usual are still more common, 

 while shells in which there is an abrupt change in the spiral at more 

 than one point are not uncommon. In no case, however, is the ab- 

 normality at all extreme. Towards the edge of the lake shells are a 

 little larger than those out in the middle, but the average difference 

 in length is not more than 2 mm. The larger shells, moreover, some- 

 times have the sculpture slightly less regular and the body-whorl 

 broader. There is, however, no transition to T. elitoralis. 



Family AMPULLARIIDAE. 



1915. Pilidae, Preston, op. cit., p. 96. 



Genus Ampullaria, Lamarck. 



1911. Pachylahra, Kobelt, in Martini and Chemnitz's Conch. Cah. (ed. Kiister), 



I, pt. II Ampullaria, p. 44. 

 1915. Pila, Preston, op. cit., p. 06. 



Kobelt has shown that the American species to which the name 

 Am'pulhria belongs in a restricted sense differ from those of Africa and 



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