54 Records of the Indian Museum. [Vo,. XVIII, 
5mm. in maximum diameter. The figure of the mouth in Concho- 
logia Indica is not very good, the upper margin being represented 
as too much elevated. Some variation, however, exists in this 
respect. 
It is undoubtedly to G. convexiusculus and not to Hutton’s 
P. compressus that Crosse and Fischer’s P. saigonensis belongs. 
Specimens from Tibet identified by Germain (who had probably 
had access to the collections described by the latter authors) as 
P. saigonensis agree closely with shells from Quetta, one of the 
type-localities of Hutton’s species. 
The radula has approximately the dental formula I1.9.1.9.11. 
The two cusps of the central tooth are well developed and sharply 
pointed. The inner laterals have two stout, sharply pointed cusps, 
the outer laterals or transitional teeth three. The marginals have 
from four to six similar but more slender cusps. Von Martens’ 
figure of the teeth is on too small a scale to show their structure 
clearly. 
The genitalia (fig. 5 E, p. 40) belong to Simroth’s ' Typus III and 
closely resemble his figure of those of Planorbis vortex in general 
structure. All the ducts are, however, much shorter, the penis- 
sheath is larger and more elongate and the spermatheca smaller 
and also more elongate. 
Planorbis convexiusculus is common with the succeeding 
species among weeds in water-channels and in pools in the reed- 
beds in Seistan, also in ponds near Quetta, where it occasionally 
occurs in large numbers on the muddy bottom of open water- 
channels. It is almost invariably found with P.saigonensis. Its 
geographical range extends from Lower Mesopotamia through 
Eastern Persia, Afghanistan and, Northern India to Upper Burma, 
French Indo-China, China, Japan, and the Malay Archipelago. 
Like many aquatic Pulmonates this species rises to the 
surface of the water in the evening and crawls shell-downwards 
on the surface film. It is, however, apparently unable to swim 
actively in this position as G. euphraticus does (post., p. 56). 
Gyraulus euphraticus, Mousson. 
1834. Planorbis compressus, Hutton (nec Michaud), Fourn. As. Soc. 
Bengal (2) Ill, p. 93. 
1850. Planorbis compressus. id., ibid., XVIII, p. 117. 
1874. Planorbis (Gyraulus) devians var. euphratica, Mousson, Fourn. de 
Conchyl. (3) XIV, p. 44. 
1918. Planorbis saigonensis, Annandale, Rec. Ind. Mus, XV, p. 166. 
1918. Planorbis satgonensis, id., Mem. As. Soc., Bengal V1, p. 304. 
The shell of this species is so like that of G. convexiusculus, 
and the two are so frequently found together, that we would have 
felt inclined to regard them merely as dimorphic forms had it 
! Simroth, ‘ Mollusca (Weichtiere) ’’ III, p. 502, fig. 165, pl. xxvi, figs. 4, 6 in 
Bronn’s Tier-Reich (1912). 
