1 92 1.] Manifur Molluscs. 559 



Presidency. In it I find all intermediate stages between the typi- 

 cal M. scabra (Miiller) and M. acanthica (Lea) in the one direction 

 and between M. scabra and the form we called M. pyramis var. 

 puteicola on the other. The only constant difference that can now 

 be claimed between M. scabra and M. pyramis as species is that in 

 the former the lip of the shell is always strongly sinuate, its upper 

 extremity as seen in ventral view being situated at a somewhat 

 lower level than that of the columellar margin, though the central 

 part of its margin lies level. This, as is shown in our original 

 figures of the var. puteicola, is a marked feature of that form. The 

 variety must, therefore, be retransferred to M . pyramis^ with which 

 Nevill originally associated it, and known a.sM. scabra var. puteicola. 

 I can find no justification for separating Tarebia generically from 

 forms like the typical M. scabra. 



Melanoides tubcrculatus (Miiller). 



I()i<). Melanoides tuber cnl at us, Ann.ind.ile and Prashad. op. cit., pp. 2g, 

 31, fig-. 3A, pi. iv. fijf. 1. 



Specimens from Manipur have no striking peculiarities. The 

 species is common in ponds in the valley l)ut was not found in the 

 Loktak Lake. 



The processes 011 the edge of the mantle arise on the ventral 

 surface a short distance behind the actual margin. The largest is 

 situated on the left side and they grow smaller as the series pro- 

 ceeds towards the right. 



Genus Acrostoma, Brot. 



1854. Melanoides, H. and .\. ,-\danis (nee Olivier i, 



1874. Melanoides, Acrostoma, Brot. Conch. Cab., p. 7. 



iSq;. Brotia, von Martens, in Welder's Zool. Erqebn. Nieiierl. Ost. Ind. 



IV, p. 33- 

 1915. Melanoides. Acrostomn. Preston, Faun. Brit. Ind.. Freshw.-Moll. 



pp. 21, 31). 

 iqjii. Acrostoma, .\nnandale, Rec. Ind. Mas. XIX, p. 109. 



I cannot find any constant difference between the shells, oper- 

 cula, soft parts or radulae of Brotia, von Martens (^Melanoides, 

 auct.) and Acrostoma, Brot. Indeed such forms as the one des- 

 cribed here as Acrostoma variabilis var. laevis, though clearly falling 

 within the limits of Brotia, are very closely related to .4. hugeli, 

 the type-species of Acrostoma. 



In this genus some of the heaviest shells among the freshwater 

 Gastropods occur. 



The edge of the mantle of A . variabilis, in living individuals 

 as in preserved specimens, is quite smooth. It is marked out, 

 however, on the inner surface into well-defined areas by vertical 

 lines of bright yellow pigment on a dark background. In pre- 

 served specimens of A . hugeli , the type-species of the genus , a similar 

 condition is found. There is no difference in this respect between 

 individuals of .-1. variabilis with smooth and those with highly 

 sculptured shells. 



