248 Records of the Indian Museum. [Vol. XXU 



paridae in which the shell attains a relatively large number of 

 whorls before birth, a colour-pattern appears on the lower whorls^ 

 while in V. hengalensis, in which there are only 3i- whorls at birth^ 

 this pattern appears later. It cannot, therefore, be regarded as 

 belonging to the primitive shell. Generally speaking, the shells 

 of the Viviparidae may be divided into two categories so far as 

 colour is concerned ' The external surface in one category is of 

 an almost uniform clivaceous colour, occasionally with irregular 

 black longitudinal streaks. In the other type it is marked "with 

 dark spiral bands. 



Structure of the Marginal Region of the ^Iantle. 

 By the phrase marginal region of the mantle I mean the 

 free edge of the roof of the branchial chamber and the immediate- 



Tag. -mp 



ra.g, 



m.p 



iS'iisMi'^. 



-s.gr. 







s.g. 



B 

 Fig. 12. — Kdge of tin- iiiainlc in ]'ivipar(i beiiga/ensis ( l.aiiiarcl<). ns seen 

 by transmiUed light (x 80). 



A. In new-born young. 



B. In half-grown individual at the end of a period of growth 



r,i.g., marginal groove; m.p., primary marginal process; m.p.', secondary 

 marginal process; 11, nerve; s.g.. calciferous glands; s. gy.. .supraraarginai 

 groove. 



ly adjacent parts. For the sake of brevity I shall refer to it merely 

 as the marginal region. I do not propose to discuss the structure 

 of other parts of the mantle except in so far as it may be necessary 

 to elucidate that of this region. 



External Structure. — The external structure of the mar- 

 ginal region is uniform in all the Viviparidae examined, so far at 

 any rate as its main features are concerned, but exhibits certain 

 minor generic and even specific characters, and differs in details at 

 different periods in the life of the individual. The free edge is 

 sharp at birth in Vivipara and Taia, blunt in Lecyihoconcha and 



I The only real exception I know to this rule is to be found in K. iu'lm<iii<iica 

 Annandale, from Eastern Persia, the shell of which is olivaceous with rounded 

 pale spots, but there is often an obscure pale band round or just below the peri- 

 phery of the bod\-\vhorl of the shell in forms of the I', dissimilis group, 



