PISIDIUM. Te 
Var. I. Henslowana. The valves have a plate-like 
appendage near the beaks. 
Var. II. pulchella. Strongly grooved, glossy. 
Var. III. pallida. More tumid, paler, irregularly 
striate. 
Var. LV. cinerea. Larger and flatter. 
3. P. pusittumM (small). 
Oval, thin, moderately glossy, finely striate concen- 
trically, yellowish white; beaks nearly central; ligament 
inconspicuous. 
Common in ditches and swamps. Its oval form, as 
well as its blunter and more central beaks, distinguish 
it from the last species. 
Var. I. obtusalis. Smaller and more tumid. 
Var. IL. grandis. Much larger (near Manchester). 
4, P. nitipum (shining). 
Roundish, tumid above, compressed below, very glossy ; 
scars distinct. 
It is found in ponds throughout the country. Its 
outline is rounder and its epidermis more glossy than 
the rest of the Pistdia. Its siphon is funnel-shaped. 
Var. I. splendens. Liemon-coloured. 
Var. IL. globosa. Spheroidal in form. 
Cc 
