10 CYCLADTD^E. 



Hal. It is very generally distributed, inhabiting 

 stagnant pools, frequently in great abundance. 



P. CINEREUM. Alder. PL I, fig, 8. 



Shell broadly ovate, greyish, rather compressed, finely striated with 

 one or two evident sulcations which form darker zones across the 

 shell; umbones obtuse, and slightly produced. 



The peculiar milky ash colour and dark zones, to- 

 gether with the compressed shape of this shell, readily 

 distinguish it from the other Pisidia, independently 

 of its being much larger (P. amnicum excepted.) We have 

 found specimens about a quarter of an inch long, and 

 one fifth broad, in a running stream in the neighbour- 

 hood of Guisbro' in Cleveland, though it is generally 

 rather less. 



Hab. It is by no means so common as some of the 

 other species. Stagnant or still pools it most frequently 

 inhabits, though sometimes found in running streams 

 and even rivers. Scabro', near Newcastle, Preston, 

 Croydon Canal, Bath, and Exmouth are recorded locali- 

 ties. It is distributed sparingly over Ireland and Scot- 

 land. 



P. NITIDUM. Jenyns. PI. I, fig. 9. 



Shell orbiculate, very shining, oval, with fine striae, more deeply 

 marked on the umbones. 



The animal, according to Jenyns, is white ; siphon 

 short and funnel shaped, with a patulous aperture, the 

 margin of which is more or less crenated or plicated. 

 The shell of this species is difficult to distinguish from 

 P. pusillum, except by the deeper striae upon the um- 

 bones (which require a searching examination), and its 

 lustrous appearance, being seldom coated with mud. 

 The larger specimens are an eighth of an inch in 

 length, and nearly as broad. Jenyns first described 

 this shell in the Trans, of Cambridge Phil. Soc., from 

 specimens obtained in the ditches in Battersea Fields 

 and other parts of Surrey, where, he says "it is widely 

 distributed but seldom abundant." 



Hab. Streams of clear water, Surrey. It has also 

 been found near Scarbro', in Northumberland, near 



