Our British Snails 63 



ponds. Oblong. Distinguished also from the 

 previous species by the body being milk-white, 

 and the shell is ashy-grey. 



SphcBvium lactistre. — Local. On the beaks is 

 a calcareous nucleus which distinguishes it. It is 

 thinner than corneum, and rounder than pallidum. 



Pisidmm amnicum. — (Our five pisidia resemble 

 SphcBvium, but are much smaller, all but amnicus 

 being minute. Very abundant where found. 

 P. amnicum and fortinale are triangular in shape, 

 P. pusillum oval, P. nitidum round, and P. roseum 

 or milium oblong ; but they are difficult to 

 distinguish on account of their similarity and 

 variation). P. amnicum is nearly twice the size 

 of the others, and this and fontinale may be 

 found in slow rivers, whereas the others prefer 

 stagnant waters. 



Pisidium fontinale. — Smaller and thinner, and 

 with more prominent beaks than P. amnicum. 



Pisidium pusillum. — The most common species. 

 Distinguished from the last by being oval and 

 by its beaks being blunter and more central. 



Pisidium nitidum. — Rare. Very glossy and 

 striated. 



Pisidium roseum (from the colour of part of its 

 body). — Like nitidum, but oblong, with a straight 

 lower margin, and with beaks placed away from 

 the centre. 



The last shell to be mentioned could not be 

 mistaken for any other. It belongs to the 



