P1S1D1UM. 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. PUSII/LUM,* 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. Round. 



4. P. NI'TIDUM,! JENYNS. PL. I. 



Body whitish ; foot moderately long, finely pointed ; mantle 

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

 notched edges. 



Shell roundish, somewhat swollen above, compressed below, 



* Small. t Shining. 



