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



appears at first sight to be colourless, but even in G. velifer the 

 tentacles of the living animal have a faint pink tinge under a high 

 power of the microscope and if the mollusc be killed suddenly, as 

 with hot corrosive solution, a distinct pink drop can be seen in the 

 region of the heart through the transparent shell. Intensity of 

 colour in the blood is, however, not correlated with size, for the 

 tint is a deep scarlet both in Indoplanorbis exustus, the largest, 

 and in Intha capitis, the smallest Indian species known to me. It 

 is, perhaps, correlated in some species and to some extent both with 

 external pigmentation of the body and with habitat. G. velifer has 

 as a rule very little external pigment and even in pigmented indivi- 

 duals from the Inle Lake the blood is only a faint pink, though it is 

 deep red in /. capitis from the same habitat ; but in individuals of 

 the former species from canals and swamps, where pigmentation of 

 individuals of G. velifer is more general and as a rule more intense, 

 the blood is slightly pinker, but still much paler than it ever is in 

 the closely allied G. convexiuscuhis and G. euphraticus, species that 

 are always pigmented. In both Bullinus and Camptoceras it is 

 bright red. 



The Planorbidae may, as a matter of convenience, be separ- 

 ated, as already indicated, into two subfamilies : the Bullininae 

 (or Isidorinae) and the Planorbinae. In the former the shell is 

 hardly to be distinguished from that of the Physidae, while in 

 the latter it is disc-shaped or at least discoidal. These differences 

 in the shell do not seem to be correlated with any important 

 differences in the soft parts, which show considerable generic 

 variation in both subfamilies. 



Subfamily PLANORBINAE. 



In dealing with the Planorbinae most European authors 

 include the species in a single genus with many subgenera. These 

 subgenera were founded, almost without exception, on shell- 

 characters only, but subsequent investigations have shown that 

 shell-characters are supported by others in the radulae and soft- 

 parts, and it seems to me preferable to regard the ' f subgenera " 

 as true genera. In his invaluable Catalogue of the Planorbidae in 

 the Indian Museum, of which only a part has yet appeared (Rec. 

 Ind. Mus. XXI, 1921), Germain regards Segmentina as distinct 

 from Planorbis, in which he includes as subgenera Gyraulus, 

 Dipiodiscus and Hippeutis, here treated as genera ; but in so do- 

 ing he relies solely on conchological evidence. I have found it 

 necessary not only to recognize the one large Indian discoidal 

 Planorbid {Planorbis exustus Deshayes) as representing a distinct 

 genus on anatomical grounds, but also to describe a new genus 

 based both on shell and on anatomy, with a minute Burmese 

 species as genotype. 



In the structure ot the soft parts the Planorbinae show much 

 greater diversity than the allied families. In the genitalia Simroth ' 



■ Simroih, in Bronn's Tisr-Reichs, Mollusca 111, p. 502, tigs. (nju). 



