I92I.J 



M am pur Molluscs. 



569 



and situated in a tropical climate. In many spots, however, one 

 or other of these forms may predominate and in some one or other 

 may be absent. For example the form gracilior is far the com- 

 monest, though by no means the only one in the pond in the 



/ 



9- 



d 



h. 



Fig. 12. — Series of shells of Limnaea acuminata from Manbhiim, Bengal. 



Fig. a may be taken to represent var. patula, Troschel and figs, g and h the 

 var. gracilior, von Martens. 



Museum compound, Calcutta, while no shell narrower than that of 

 the form rufescens was found at any place in Manipur. 



Other names again belong to phases associated with abnor- 

 mal types of environment. The phase nana, Annandale and 



