1919. | N. ANNANDALE & B. PrAsHaD: Mollusca. 57 
much the same relation as Gyraulus convexiusculus does to G. 
albus. The radula has approximately the formula I3.10.1.10.13. 
The teeth are rather small. The terminal part of the central 
tooth is distinctly bilobed. The inner laterals have six small, 
sharp cusps, the other teeth of the same series five. The inner 
marginals have six cusps very similar to those of the inner later- 
als, while the outer marginals have seven cusps, the central cusp 
being considerably larger than the others. 
Our material is not well preserved for anatomical investiga- 
tions, but in a specimen from the Punjab the terminal part of 
the male duct belongs to Simroth’s Typus II. ‘The blind sac-like 
appendages shown in his diagram (op. cit., p. 502, fig. 165) are, 
however, very poorly developed. 
The species is common in swamps in Northern India, but 
somewhat local in its distribution. It is recorded from several 
places in the Himalayas, Bengal, Assam, Burma, Ceylon and 
Siam. Oneof us recently found it to be common in a swamp near 
Peshawar on the North-West Frontier of India and also obtained 
a specimen in a similar situation at Gurdaspur in the Punjab. 
Two dead and whitened shells were found at the edge of a pool in 
the desert near Nasratabad, Seistan. The shells are very small, 
but otherwise fairly typical. 
Crass LAMELLIBRANCHIA (==PELECYpopa). 
This class is represented in our collections from Seistan and 
Baluchistan by large series of specimens of two species, Corbicula 
fluminalis (Miller) and Lamellidens marginalts (Iramarck). Hutton 
(Journ. As. Soc. Bengal, XVIII, p. 659: 1850) has described under 
the name Pisidium paludosum a third species from Chaman, now 
on the Afghan frontier of Northern Afghanistan, but we have seen 
no shells of this form. It may be a young Corbicula. 
Corbicula fluminalis, which also occurs in ponds and streams 
at Quetta, and the Unzo are both so abundant in Seistan, both 
recent and subfossil, that their shells are a feature of the country. 
They are found lying on the surface, wherever the land is occa- 
sionally flooded, in thousands and the banks of ancient streams 
and lakes are full of the shells of Corbicula. This is the case at 
many places now completely desert. Though the shells are fre- 
quently bleached and sometimes wind-worn and sand-eroded, they 
are usually in a remarkably perfect condition. 
Family CYRENIDAE. 
Genus Corbicula, Megerb. 
This genus provides many difficult problems in taxonomy, 
increased by the fact that there is no recent, well-illustrated 
monograph. Undoubtedly many of the socalled species now 
generally accepted will have to retire into the synonymy of others. 
