1918.] N. Annandale : Molluscs of the Inle Lake. 117 



Genus Hydrobioides, Nevill. 



1884. Hydrobioides (subgenus of Bithynia), Nevill, Hand List Moll. Ind. Mus 

 II, p. 42. 



The shell is thick, of moderately small or minute size, imperforate, 

 of somewhat variable shape but not definitely neritiform. The aper- 

 ture is large, ovoid or subtriangular. There is a very stout columellar 

 callus, which is in continuation at both ends with a thickening of the 

 outer lip. The lip is often fortified also by a strong ridge or varix 

 that runs across the outer surface of the shell a short distance from 

 the margin. 



The operculum is calcified and thick but often surrounded by a 

 membranous margin. The nucleus is almost central and surrounded 

 by numerous well-defined concentric striae. 



The soft-parts, externally at any rate, closely resemble those of 

 Bithynia, the penis in particular being bifid. Both of its branches 

 are well-developed. There is a deep but narrow transverse groove 

 on the sole of the foot parallel to and close behind the anterior margin. 



The radula is like that of Bithynia. 



Type-species. Bithynia (?) turrita, Blanford. 



The genus is closely allied to Bithynia, of which it might, but for 

 the inconvenience of multiplying subgeneric names, rank as a subgenus. 

 Of the five species assigned to it, one approaches the stouter and shorter 

 forms of Bithynia such as B. orcula, one is elongate, while the other 

 three agree in general appearance with more normal species of Bithynia 

 such as B. tenfacidata. The most characteristic feature is the peculiar 

 armature of the mouth of the shell. 



The shells may be distinguished as follows : — 



I. Shell more or less elongate, with the spire in the same 

 axis as the body-whorl. 



A. A ridge or varix running across the outer aspect 



of the body- whorl 



B. No varix. 



1. Shell at least 6 mm. long. 



(a) Shell twice as long as broad 

 {b) Shell much less than twice as long as 

 broad 



2. Shell not more than 3 mm. long 



II. Shell globose, with the spire short, directed backwards 

 and outwards! 



Hydrobioides turrita (Blanford). 



1869. Fairbankia ? (an Bithynia ?) turrita, Blanford, Proc. Zool. Soc. London, 



p. 446. 

 1881. BUhinea («') turrita, Nevill, Journ. As. Soc. Bengal, L (2), p. 157, pi. vi, fig. 15. 

 1884. Bithinea {Hydrobioides) turrita,- Nevill, op. cit., II, p. 42. 



Blanford describes the shell as follows : — 



" Testa subperforata, turrita, solidula, fulva, glabra, nitidula. Spira elongata- 

 conica, sutura impressa. Anfr. 7, convexi, ultimus antice subasccndens, subtus rotun- 

 datus. Apertura ovata, postice vix angulata, varice externo mediocri in.structa ; peris- 

 toma undique expansiusculum, marginibus callo junctis, externo leviter arcuato, colu- 

 mellari obliquo, antic ecum basali subangulatum juncto. Operc. ? Long. 6;^^ diam. 

 3 mm. ; aperturae long. 2J, lat. If mm." 



