52 Records of the Indian Museum. [VoL. XVIII, 
desert some two miles south of Nasratabad in Seistan. The pool 
in flood-time is connected with a branch of the Helmand river. 
The following are the measurements (in millimetres) of our Persian 
specimen :— 
Length ue ss Set § 
Maximum breadth Hs vie 27 
Length of aperture ; ne Bee 
Breadth of aperture ah ao. ea 
Family PLANORBIDAE. 
The three species belonging to this family and known from 
Baluchistan and Seistan are all small and all occur commonly 
throughout Northern India and the adjacent countries. It is with 
some reluctance that we feel obliged to recognize the two groups 
represented by the three species as distinct genera, but they differ 
so much not only in shell but also in anatomy that no other course 
seems possible to us. We assign, therefore, two of the species 
(Planorbis euphraticus, Mousson and P. convexiusculus, Hutton) to 
the genus Gyraulus, Agassiz, and one (Planorbis calathus, Benson) 
to the still more distinct genus Segmentina, Fleming. 
Genus Gyraulus, Agassiz. 
1837. Gyraulus, Agassiz, Nouv. Mem. Soc. Helv. 1 (fide Preston, Faun. 
Brit. Ind. Freshw. Moll., p. 118, 1915). 
In this genus the shell is small, thin, flat, pale, translucent 
or transparent, without strong transverse ribs, with or without 
spiral epidermal cilia, with or without peripheral keel, with few 
whorls, with'a simple lip, without teeth or partitions on the 
internal surface, with a dextral spiral. The radula has the central ~ 
tooth bicuspid and the laterals bi- or tricuspid, the marginals with 
several sharp cusps. The edge of the mantle is not thickened. 
The vas deferens is continued distally into a narrow penis, which 
projects straight into an elongate bulbous chamber or penis-sheath 
and is armed at its termination with a well-developed horny stylet. 
Type-spectes. Planorbis albus, Miller (Palaearctic). 
There has been much confusion about the two species of this 
genus that occur in Baluchistan and Seistan, chiefly because 
conchologists have rarely seen specimens from the original locali- 
ties. The correct names for these species are in our opinion 
G. convexiusculus (Hutton), of which G. saigonensis, Crosse and 
Fischer, is a synonym, and G. euphraticus, Mousson, to which 
Hutton and later Benson applied the preoccupied name Planorbis 
compressus. 
Gyraulus convexiusculus (Hutton). 
1850. Planorbis convexiusculus, Hutton, Fourn. As. Soc. Bengal (2), 
XVIII, p. 657. 
1864. Planorbis saigonensis, Crosse and Fischer, Fowrn. de Conchyl., XII, 
p. 362,pl. xii, fig. 7. 
