I92I.] N. Annandale & R. B. S. Seweli, : Vivipara. 269 



Soft parts. — As yet we know too little about the details of the 

 comparative anatomy of the Viviparidae to say with certainty what 

 characters in the soft parts are of specific importance, but the 

 following four points may be noted wherein a definite anatomical 

 difference exists between V. vivipara and other species for which 

 information is available : — 



1. The marginal processes of the mouth are moderately 

 well developed, less so than in V. oxytropis, but more so than in 

 the adult of V. dissimilis and V. vivipara. Three are much larger 

 than the others. 



2. The testis consists of a single lobe, not of two subequal 

 lobes as in V. vivipara or of a large primary lobe with an ill-deve- 

 loped second lobe as in V. dissimilis. 



3. The male tentacle is less differentiated than in V . vivipara^ 

 but not less so than in V. dissimilis and other Indian species 

 examined. 



4. The right jjleural ganglion is almost completely fused with 

 the right cerebral ganglion, whereas in V. vivipara there is a short 

 but distinct commissure. 



Radula. — The radula is chiefly noteworthy for the following 

 points : — 



1. The teeth are moderately large and stout and have their 

 denticulation well but not immoderately prominent. 



2. The centra) is relatively large and considerably broader 

 than long. Its distal margin is distinctly concave. The lobe in 

 the middle of its cutting edge is quadrate, much broader than 

 deep and relatively large. It has on each side of it at least five 

 triangular denticulations ; which are sharply pointed and decrease 

 in size gradually from within outwards. 



3. The two laterals and the marginal on each side are rela- 

 tively broad and not very much longer than the central. Their 

 denticulations are comparatively coarse and on the laterals closely 

 resemble those on the central. On the marginal they are much 

 finer and there are over twenty. The upper extremity of the 

 edge of this tooth is usually expanded to form a small triangular 

 process. 



The foregoing description and observations are intended to 

 apply to the species as a whole. I will describe separately the 

 various races that occur in different parts of the Indian Empire, 

 and then the phases, whose peculiarities are probabl}^ due to some 

 physical factor in their environment acting directly on the 

 individual, rather than to geographical isolation of the race. 



The anatomy of the Viviparidae, so far as it has been studied, 

 is strikingly uniform in most respects and little or no recognisable 

 difference has been found in the different forms of V . bengalensis 

 so far as the radulae and soft parts are concerned. In the radular 

 teeth slight racial peculiarities might perhaps be found, but thej^ are 

 so ill marked that it would be misleading to lay stress upon them. 



The different local races of V. bengalensis have the following 

 distribution. The forma typica is peculiar to the lower Ganges 



