igzi.j Manifiir Molluscs. 549 



broadly oval, slightly narrowed at both extremities. The columel- 

 lar margin is sharp and narrowly prominent. The umbilicus, 

 though narrow, is circular and is approached from below by a deep 

 and clear-cut channel. The aperture extends for some distance 

 below the apparent base of the shell. The peristome is continuous. 

 The outer lip is thin but not sharp, broadly and regularly arched, 

 with a distinct prominence at the termination of the peripheral 

 ridge. There are two smooth prominent spiral ridges on the three 

 last whorls of the spire, three including the peripheral ridge or 

 keel on the upper part of the body-wliorl, and three rather less 

 prominent ridges below the peripheral keel. All these ridges are 

 darkened. Between each pair finer spiral ridges can be detected 

 with a low power lens, crossed at regular intervals by straight, 

 oblique striae, which do not interrupt the stronger ridges. The 

 ape.x of the spire is darkened and the second complete whorl tinged 

 with chestnut. The interior of the shell is washed with bluish 

 white and the periphery of the aperture narrowly blackened and 

 highly polished. 



The female shell is distinctly broader than the male. The 

 embryonic shell is extremely like that of V. microchactophora but 

 considerably larger. 



The operculum is thin, relatively large and broadly ovate, 

 bluntly pointed above, of a pale translucent brown colour, almost 

 flat externally, with the concentric ridges feeble, the margin almost 

 membranous and the scar small poorly developed and only slight- 

 ly darkened. On the peripheral region of the ventral surface 

 radiating striae are well developed. 



The radula is distinguished from that of Vivipara bengalensis 

 by the much smaller denticulations of the teeth and narrower 

 marginals (fig. 3B). 



The animal is like that of Vivipara bengalensis (fig. 7B), 

 except for the strong development on the free edge of the mantle in 

 the adult of a number of finger-shaped processes three of which are 

 larger and one much larger than the rest. Each process cor- 

 responds to a ridge on the shell and its size is proportionate to the 

 development of the ridge. These processes are concealed in life 

 when the animal is expanded. Their function, as hypertrophied 

 structures, is probably that of accessory breathing organs and may 

 be correlated with the fact that the branchial chamber is often 

 almost completely filled with parasitic leeches {vide postea) 

 There is no material difference in the gross internal anatomy of V. 

 bengalensis and V . oxytropis. 



The latter species has .frequently been recorded in error from 

 Bengal. The Manipur valley is apparently the only district in 

 which it is common, but I collected some young shells apparently 

 identical in a swampy lake near Kavvkareik in the interior of the 

 Amherst district of Tenasserim in 1908. 



Two phases can be distinguished in the Manipur valley: — 

 ia) the typical phase fiom the Loktak l,ake (pi. IV, figs. 2, 3), in 

 which the shell is normally large and well developed, thin, trans- 



