360 Records of the Indian Museum. [Vol,. XXIV, 



B. Shell without internal ridges. Male organ not of 

 type II. 



1. Shell flattened and disc-like, often cari- 

 nate, but never excessively so, its 

 aperture lunate. Male organ of type 

 IV. 

 a. Whorls not more than four, in- 

 creasing rapidly ; the body- 

 whorl much broader than the 

 penultimate ... ... Gyravlus. 



/>. YVhorls more than four, increas- 

 ing gradually ; the body-whorl 

 not much broader than the 

 penultimate ... ... Diplodiscus. 



2. Shell more or less of the form of a 

 flattened conoid, with the aperture 

 cordate. Male organ not of type IV. 



a. Spire partly exposed on upper 



surface of shell. Male organ of 

 type V, but with the penis coiled 

 inside the sheath ... ... Hippeutis. 



b. Body-whorl completely occlud- 



ing spire. Male organ of type 



I ... ... ... /.tit ha, now 



Genus Planorbis Geoffroy (1776). 



1921. Planorbis s.s., Germain, " Catalogue of the Planorbidae in the 

 Indian Museum," Rec. Ind. Mus. XXI, pp. 619. 



There is great doubt as to the occurrence of the true 

 Planorbis (taking Helix corneus Iy. as type-species) in the Indian 

 Empire. I include it here on the evidence of Clessin's figure of 

 Planorbis hindu, 1 but both the provenance and the generic posi- 

 tion of this species are doubtful. It may be a Gyraulus, and may 

 not be Indian. 



Genus Indoplanorbis Annand. & Prashad (1920). 



1920. indoplanorbis, Annandale and Prashad, fourn. Ind. Med. Res. 



VIII, p. 112. 



192 1. Indoplanorbis, iid., Rec. Ind. Mus. XXII, p. 537. 



In our recent account of this genus we failed to observe the 

 retractor muscles of the penis-sheath, and also to recognize the 

 fundamental agreement in structure of the male organ with 

 Simroth's type III. The muscles are two in number, one situated 

 at the upper end of the sheath, the other a short distance down 

 its side, but relatively higher than in Simroth's diagram. When 

 not distorted by the presence of spermatophores the sheath is 

 more sausage-shaped than our figure would indicate (op.cit., 

 1921, p. 579, fig. 14) and the penis can be much contracted, but 

 without losing its straight cylindrical form. 



The only species of the genus with which I am acquainted is 

 Planorbis exustus Deshayes. Germain has discussed the variations 

 and growth of the shell in a masterly manner [op. cit. y 192, pp 

 34-41, figs. 2-16). 



' Clessin on Planorbis in Martini and Chemnitz's Conch. Cab. (ed. Kuster and 

 Duncker). 



