1918.] N. Annandale : Molluscs of the Inle Lake. 119 



differ from one another is the structure and position of the ridge that 

 rvms, nearer or further from the aperture, across the outer aspect of 

 the body-whorl. 



forma typica. 



The shell exhibits some variation, and possibly some local plasti- 

 city in size and shape. The spire is, however, in all cases sharply pointed, 

 unless eroded, and the colour dull. The condition of the ridges at or 

 near the mouth is fairly constant, the varix being separated from the 

 lip, to which it runs nearly parallel, by a broad groove. This groove 

 is, however, somewhat variable in breadth. There is no trace of an 

 intermediate ridge. 



Individuals of this type are abundant in ponds round Yawnghwe, 

 always living amongst dense weeds. They are also to be found, with 

 the race lacustris, at the edge of the Inle Lake, but never in the central 

 region. 



Type-specimen. M. 2237/2, Zoological Survey of India {Ind. Mus.) 

 (Theobald Coll.). 



subspecies lacustris, nov. 



This race differs from the forma typica in its narrower, more pointed 

 and more brightly coloured shell and in the structure of the varix and 

 lip. It also attains a larger size and the microscopic sculpture of the 

 surface of the shell is usually more strongly developed. In both these 

 latter characters, however, it is somewhat variable. Well-developed 

 shells are as much as 10-5 mm. long by 6-5 mm. broad. Microscopic 

 longitudinal striae run, close together, along all the whorls and the 

 shell is sometimes minutely decussated ; obscure spiral ridges are also 

 sometimes to be detected, while opaque, almost flat longitudinal ribs 

 can be seen on the body-whorl of some individuals. In fully developed 

 shells the edge of the aperture is always widely separated from the 

 varix, which does not run parallel to it but rather across the arc it 

 forms. The distance apart of the two ridges is variable. The inter- 

 mediate space, moreover, is not a groove but distinctly convex ; strong 

 transverse striae and often one or more incompletely developed trans- 

 verse ridges occur on it. 



The largest and most brightly coloured shells of this race are found 

 in the least congested part of the intermediate zone of the lake. 

 They are of a pale amber-yellow colour. In the central region shells 

 do not as a rule exceed 9-5 mm. in length and, when free from minute 

 algae, are of a pale cream tint. These shells also tend to have the 

 spire narrower and more sharply pointed. In all parts of the lake 

 this mollusc is found amongst dense growing weeds. 



Type-specimen. M. 11135/2, Zoological Survey of India {Ind. Mus.). 



subspecies rivulicola, nov. 



The shells of this form are much thinner than those of the others 

 assigned to the species. They are of a dull green colour and have the 

 longitudinal striae well-developed. The spire tapers less regularly 

 than in the forma typica, the whorls are more swollen individually and 



M 



