MATERIALS FOR A GENERIC REVISION OF THE 



FRESHWATER GASTROPOD MOLLUSCS OF 



THE INDIAN EMPIRE. 



No 5. — The Indian Pi,anorbidae. 



By N. Annanpale, D.Sc, F.A.S.B., Director, Zoological 

 Survey of India. 



The Planorbidae are distinguished from their allies the 

 Limnaeidae and Physidae b}- well-defined conchological, anatomi- 

 cal and physiological characters. In their dextral bodies they 

 come nearest the Physidae (which are not represented in* the 

 Indian fauna) and in the sinistral more or less ovate shells of one 

 of their two subfamilies (the Bullininae) there is also a close resem- 

 blance to the same family, but important differences are to be 

 found in the radulae, the lateral teeth of which in the Planorbidae 

 are simply cusped, while in the Physidae they bear a curious 

 lateral process. A still more important difference is to be found in 

 the colour of the blood, which is red in both subfamilies of the Plan- 

 orbidae and colourless in the Physidae and also in the Limnaeidae 

 and Ancylidae. The Bullininae, moreover, comprise comparatively 

 few species and the much more numerous Planorbinae have disc- 

 shaped shells quite unlike those of any of the other two families. 



The genitalia of the Planorbidae show great diversity in the 

 structure of the male organ, but otherwise conform to the same 

 type as those of the Limnaeidae. The digestive system is also 

 similar, allowance being made for the more elongate type of body, 

 correlated with the difference in shell-form, in the Planorbinae. 

 The jaws in most genera consist, as in Limnaea, of a central more 

 or less lunate or sublinear upper transverse piece and of two slender 

 vertical sidepieces, but in some species the}* are broken up into 

 many horny teeth as in the Ancylidae. The radulae bear smaller 

 teeth with shorter and often more numerous cusps than in Limnaea. 



There is present on the left side of the body in the Planorbidae 

 a vascular outgrowth (pseudobranch) of more complex structure 

 in some genera than in others. 



Before discussing the subfamilies and genera I wish to say a 

 few words about the colour of the blood. In all the Planorbid 

 genera I have examined, including Bullinus and Camptoceras among 

 the Bullininae, it is some shade of red or pink, but its colour is 

 much more intense in some species than in others. In certain 

 minute lacustrine forms, indeed, such as Gyraulus velijer ' it 



1 Annandnle. Ree. Tnd. Afrit. XIV. p. 112, pi. xi, figs. 7-11 (1918). 



