1921.] Maiiiptir Molluscs. 3^5 



except that the branchial process and the pulmonary siphon are 

 a little better developed. 



The radula is very minute with the dental formula approxi- 

 mately 14. 12. 1. 12.14. The central tooth is comparatively large 

 and bicuspid with sharp cusps. The laterals and marginals both 

 have a peculiar twinned structure, and the line of demarcation 

 between the laterals and marginals is not very sharp. The laterals 

 are tricuspid, the central cusps being much the largest. 



The male genitalia generally approximate to Simroth's Typus 

 I,' but differ in details. The vas deferens is very long and coiled. 

 The penis-sac is a well developed ovoidal structure with an elong- 

 ate tubular preputium in continuation of the sac. The penis is 

 massive with a lateral opening and without anv stylet. 



H. umbilicalis was originally de'^cribed from Svlhet, Assam, 

 but has also been recorded from Bengal in the plains of the 

 Ganges sy.stem; it is, however, a scarce species in India proper. 

 In theManipur Valley it is the most abundant Planorbid, occurring 

 in the Loktak I,ake and in ponds and swamps amidst dense 

 vegetation. In the dry swamp east of the L,oktak Lake large 

 numbers of shells, not long dead, were found in little damp 

 pockets under masses of peat. They had evidently migrated 

 there in hundreds as the swamp dried up. 



The largest shells obtamed in Manipur are from Looshipat, 

 where they were found attached to long grass-blades in ponds 

 with dirty water. One of them is 98 mm. in maximum diameter, 

 83 mm. in minimum diameter and 2-9 mm. in height. 



Segmentina, Fleming. 



1S17. Segment ilia. Fleming. Conchology in De BrcwsLer's Kni-yclope- 



dia, /ill cd., VII. 

 187H. Planorbis subgen. Segmentina (in part), Nevill, op. cit., p. 24O. 

 1915. Planorbis subgen. Segmentina (in part), Preston, op. cit., p. 124. 

 igig. Segmentina. .\nnand.ile and Prasliad, Rec. Ind. Mits. XVIII, 

 p. 56. 

 Preston in his account of the subgenus Segmentina has merely 

 followed Nevill, and unfortunately at the time of the publication of 

 Nevill's work nothing was known of the anatomy of these forms, 

 shell-characters alone being used for the discrimination of the vari- 

 ous subgenera. As a result of the study of a large collection 

 from Manipur of some of these forms in spirit, we find that the 

 positions assigned by Preston to several of the species are unten- 

 able. S. umbilicalis (Benson) is probably a Hippeutis and so are 

 S. caevosus and S. sindicus of the same author (see p. 584), while 

 5. canton is a Gyraulus. 



Segmentina calathus (Benson). 



1919. Segmentina calathus, Annandale and Pr.-ishad. op. cit.. pp. 56. 

 57, figs. 5D (.wrongly printed as 5E), 7C. 



1 SimrUh, bronn's Thier-keichs 111 ^supplement), Mollusca, p. 502, fig. 

 (IQIJ). 



