120 Records of the Indian Mvseuvi. [Vol. XIV, 



the suture more impressed. The varix is very low and the thickening, 

 of the margin of the aperture comparatively slight ; the relation between 

 the varix and the edge of the shell is similar to that noticed in the forma 

 typica. 



We found a few specimens of this race among weeds in the back- 

 waters of small streams at Thamakan, which lies some 1000 — 1200 

 feet higher than the Inle Lake. 



Type-specimen. M. 11139/2, Zoological Survey of India {Ind. 

 M.us.). 



subspecies distoma, nov. 



The shell is small and compact, not exceeding 8 mm. in length and 

 5 mm. in greatest breadth. The longitudinal striae are often well- 

 developed, but the surface has a smooth appearance. The varix, which 

 is prominent, is situated very close to the edge of the shell. 



Shells of this race are abundant in a fossil and subfossil condition 

 on the He-Ho plain in all the deposits that we examined. It must 

 be regarded as the most primitive in the series of forms to be included 

 under the name Hydrohioides nassa. 



Type-specimen. M. 11140/2, Zoological Survey of India {Ind. 

 Mus.). 



Hydrobioides avarix, sp. nov. 



Plate xiv, figs. 1, 2, 2a, 2b, 2c. 



In this species the shell, though the peristome is thickened, entirely 

 lacks a varix on the body-whorl. I can find no trace of a ridge. Other- 

 wise the shell closely resembles that of H. nassa distoma. It is 

 small (not longer than 7 mm. and broader than 3-5 mm.), moderately 

 thick, with longitudinal striae, of a dark olivaceous colour. I have 

 examined the animals of several individuals. The females agree pre- 

 cisely with those of the typical form of H. nassa in external anatomy. 

 I have found only one male. Its external male organ only differs from 

 that of H. nassa typica in that the internal branch is much shorter. 

 This, however, may be due to immaturity or contraction. The radula 

 closely resembles that of H. nassa (see figures), except that the outer 

 lateral tooth is slightly broader and the marginal tooth a little shorter. 



Measurements of shells. 



Length of shell 

 Greatest breadth 

 Length of aperture 

 Greatest breadth of aperture 



The operculum is a little broader than that of H. nassa and less 

 clearly spiral in the centre ; it lacks the membranous margin. 



Most of our specimens have the tip of the shell eroded. 



This species was found in great abundance among weeds {Hydrilla) 

 in a stream of slightly warm water flowing out of a spring about a mile 

 from the edge of the Inle Lake near Fort Stedman. I have discovered 

 in the collection of the Indian Museum some shells from Moulmein in 



