PISIDIUM. 9 



Var. 3. pallida. — Shell more ventricose, irregularly striate, 

 and of a paler colour, with occasionally a few darker rays which 

 diverge from the direction of the beaks to the lower margin. 

 Marshes and pools near Swansea, B.C. 



Var. 4. cinerea. — Shell larger and flatter, with fainter striae. 

 Widely diffused in this country, B.C. 



B. Oval. 

 3. P. pusil'luiM,* Gmelin. Pl. I. 



Body whitish, faintly tinged with rose-colour ; foot a little longer 

 than the shell, slender ; mantle bordered with reddish-grey ; siphon 

 short, somewhat conical, truncate, orifice small, edges entire. 



Shell nearly oval, somewhat compressed, but swollen, thin, not 

 very glossy, irregularly and finely striate concentrically, greyish 

 horn-colour ; epidermis extremely thin ; anterior side rounded ; 

 posterior side rounded and sloping gradually downwards ; lower 

 margin rounded ; beaks nearly central, short, blunt ; ligament 

 short, inconspicuous ; inside greyish, not very pearly ; hinge, 

 teeth, and scars as in P.fontinale. 



Inhabits weedy pools, ditches, swamps, &c., in most 

 parts of Great Britain. It may be distinguished from 

 P. fontinale by its oval form, and by its beaks being 

 blunter and more central. It is usually covered with 

 a reddish-brown incrustation. 



Var. " obtusalis. — Shell smaller and much more ventricose ; 

 beaks prominent, very obtuse. In similar situations with the 

 typical form, but more local and less abundant." — B.C. 



C. Roiuid. 

 4. P. Nl'TIDUM,t JENYNS. PL. I. 



Body whitish ; foot moderately long, finely pointed ; majitle 

 edged with grey ; siphon funnel-shaped, short, orifice wide, with 

 notched edges. 



Shell roundish, somewhat swollen above, compressed below. 



Small. t Shining. 



