122 CONCHACEA. 



Sliell compressed, subovate ; umbones but slightly produced, 

 obtuse at the points, where it is sometimes capped ; lower mar- 

 gins of the valves meeting at an acute angle; surface of a grayish 

 ash-colour, and finely striated concentrically; with a few deeper 

 sulci, which form deeper transverse zones. 



This shell is more ovate in its form than any of its con- 

 geners, excepting the Pisidiuin ohliquum, and will be at once 

 recognized by being more compressed than any of them, and 

 by its ashy hue. 



VatHetij 1. Someivhat more ventricose, toitli the umbones a 

 little more produced. 



Inhabits ponds near Newcastle, and other localities in the 

 North of England. Mr. Thompson says it is widely spread 

 throughout Ireland, although no where common. He par- 

 ticularizes Holywood House, Downshire ; Youngrove, near 

 Middleton, County of Cork, by Miss M. Ball; Killereran, 

 County of Galway, and Portarlington, by the Rev. B. J. 

 Clarke ; and neighbourhood of Dublin, by Thomas William 

 Warren, Esq. 



8. PiSIDIUM JOANNIS. 



Pisidium Joannis, Macgillivray, Moll. Ab., p. 248 ; Brown, 

 Illust. Conch., p. 132. 



Shell transversely-ovate, moderately convex, thin, glossy ; 

 both sides well rounded ; umbones tumid, obtuse, with smooth 

 beaks, and placed nearest the anterior side ; whole surface with 

 numerous, concentric stria;, the intervening furrows broader, 

 smooth, and glabrous, with several well marked lines of 

 growth ; hinge line a little arcuated ; colour greyish-yellow. 

 Length two-twelfths of an inch ; breadth two and a half 

 twelfths. 



Found by Mr. Leslie, in a ditch and pond of the Professor 

 of Medicine, and afterwards by Professor Macgillivray, in a ditch 

 near the Links of Old Aberdeen, where it is very abundant. 



9- Pisidium Jenynsii. 



Pisidium Jenynsii^ Macgillivray, Moll. Ab., p. 249 ; Pisidium 

 pulchellum, var., Jenyns ; Brown, Illust. Conch., p. 132. 



Shell transversely and obliquely ovate, somewhat tumid, very 

 thin, and glossy ; with regular, distinct, concentric striae, a few 

 more conspicuous lines of growth, and very faint radiating 



