OONCHACEA. 121 



Shell obliquely oval, much intlated; with regular, well defined, 

 concentric grooves ; beaks very tumid, considerably produced, 

 and somewhat tubercled. Length an eighth and a half of an 

 inch ; breadth not quite a quarter. 



Found in slow running streams, but is very rare. Thompson 

 says it is met with at Finnoe, Tipperary, Ireland. 



This shell seems nearly allied to P. obliquum, from which, 

 however, it differs, in its greater convexity, and the protrusion 

 of the beaks, at the base of which is a groove, or dark zone, 

 giving them the appearance of tubercular appendages. 



5. PiSIDIUM NITIDUM, pi. XXIII, f. 11. 



Pisidium nitidurn, Jenyns, Monog., p. 16, pi. 20, f. 7, 8; 

 Thompson, Ann. and Mag. Nat. Hist., VI, p. 53; Brown, Illust. 

 Conch., p. 95, pi. 39, f. 2G. 



Shell suborbicular, or slightly oval; umbones large, and blunt; 

 external surface very glossy, of a pale horn-colour, and covered 

 with fine, concentric stria;, which are wider-set and deeper on 

 the umbones. 



Inhabits Battersea Fields, some ditches in Cambridgeshire, 

 and ditches near Worcester; in a pond at Wolf hill, near Belfast, 

 and other places in that neighbourhood; Lough Gill, County 

 Sligo, Portarlington, and Finnoe, Ireland. 



6. Pisidium pusillum, pi. XXIII, f. 12. 



Pisidium pusillum, Jenyns, Monag., p. 14, pi. 20, f . 4 and 6; 

 Thompson, Ann. and Mag. Nat. Flist., VI, p. 53; Brown, Illust. 

 Conch., p. 95, pi. 38, f. 27 ; Cyclas pusilla, Turton, Brit. Biv., 

 p. 251, pi. 11, f. 16, 17 ; lb., Man., p. 16, pi. 1, f. 7; Alder, 

 Mag. Zool. and Bot., II, p. 119- 



Shell nearly orbicular, slightly ovate, subcompressed ; um- 

 bones prominent, and very obtuse at the points ; sides some- 

 what flattened, and very slightly inequilateral ; surface of an 

 olivaceous-brown, with very fine, concentric stria:;. 



Inhabits ponds near London, and many other localities. In 

 Ireland, according to Thompson, it is the most common of the 

 genus, frequenting ponds and drains. 



7. Pisidium cinereum, pi. XXIII, f. 13. 



Pisidium cinereum, Alder, Cat. Sup., p. 4 ; lb., Mag. Zool. 

 and Bot., II, p. 119; Thompson, Ann. and Mag. Nat. Hist., 

 VI, p. 54 ; Brown, Illust. Conch., p. 95, pi. 39, f. 28. 

 R 



