1918.] N. Annandale : Molluscs of the Inle Lake. 



163 



among the shells included in Theobald's series, but it is evident from 

 his description and figures that he did not examine adult shells only. 



We may legitimately conclude from this statement that Theolaald 

 and I are dealing with the same species, but that races from different 

 localities differ considerably in details of variation. I have not been 

 able to find a single specimen from He-Ho in which the shell is absolutely 

 smooth, or in which even approximate smoothness is correlated with 

 absence of spiral bands. But Nevill called the typical smooth form 

 from Theobald's series " var. concolor." 



There is, therefore, evidence that details of variation differ in differ- 

 ent localities. This is further proved by an examination of a series from 

 Yawnghwe, 800 feet below the He-Ho plain. This series was taken 

 in a large pond and a canal. In fifty specimens, twenty-nine are un- 

 handed and carinate, fifteen banded and carinate, two smooth and 

 banded, two smooth and unhanded. These results may be expressed 

 in a table of percentages. 



Tn addition to this difference in individual variation between the 

 shells from the two localities (and also from two types of environment) 

 there is a distinct racial difference in structure. The shells of the 

 Yawnghwe race are all thinner than those of the He-Ho race. They 

 are smaller, fully adult shells being from 30 mm. to 32 mm. long. When 

 bands are present they are rarely so dark, and it is often difficult to say 

 whether they are present or absent, so faint may the bands be. More- 

 over, the shells are constantly a little more globose (c/. figs. 17, 16, pi. 

 XV, and figs. 3, 4, pi. xvii), the smooth examples are smoother, and the 

 carinate ones never quite so nodular. Finally the chief ridge of the 

 body-whorl is often more distinctly squamous than it ever is in the 

 He-Ho race, thus affording some approach to T. shanensis. The radulae 

 of the two races are very similar, but the teeth of the Yawnghwe race 

 are paler in colour and probably less stout than those of the He-Ho race. 



We have no evidence of the existence of this variable and plastic 

 species in a fossil state, but to it all except one of the lacustrine forms 

 of the three basins can be traced directly. The exception is T. obesa, 

 with which I shall deal when discussing the Hsing-Dawng group, but the 

 He-Ho species must be discussed first because they are less highly spe- 

 cialized than those of the other two lakes. It is with the more highly 

 specialized individuals of T. naticoides that all the lacustrine species 

 must be associated. Indeed, it is not always easy to distinguish between 

 the more strongly carinate shells of the former and the typical shells 

 of T. mtermedia, the simplest of the He-Ho forms. 



In T. intennedia the shell, however, is constantly more tubercular 

 and a little more globose than T. naticoides, and no even approximately 

 smooth specimens are found. There is considerable variation both in 



