ANCYLUS. 189 



compartm. — Pult, Ilutchins, Hist. Dorset, p. 51. — Donov. 

 Brit. Shells, vol. v. p. 150. — Maton and Rack. Trans. Linn. 

 Soc. vol. viii. p. 233. — Rack. Dorset Catalog, p. 58, pi. 18, 

 f. 20*, and pi. 22, f. 8, a.— Turt. Conch. Diet. p. 138.— 

 Dillw. Recent Shells, vol. ii. p. 1042. —Wood, Index 

 Testae, pi. 37, f. 57. 



Patcl/a lacustris, Mont, (not Linn.) Test. Brit. vol. ii. p. 484. 



I r elhUa „ Gray, Manual L. and F. W. Shells, p. 251, pi. 10, f. 126. 



Shell but moderately elevated, with a more or less pro- 

 duced oblong base, extremely thin, semitransparent, and 

 beneath a dirty horn-coloured or palely olivaceous yellow 

 epidermis of an uniform smooth and shining snow-white hue 

 both within and without. Sides compressed, or pinched as 

 it were ; extremities moderately and often unsymmetrically 

 rounded, the anterior end slightly the broader. Apex 

 acutely peaked and hooked, decidedly behind the middle, 

 manifestly bending to the left (towards which side, indeed, 

 the entire shell is wont to incline); the slope from it forwards 

 arched, the declination from it backwards a little concave. 

 Margin acute, a little disposed to spread ; side edges but 

 little curved. Base simple, neither raised at the ends and 

 hollowed at the sides, nor hollowed at the extremities and 

 laterally elevated. Length a quarter of an inch ; breadth 

 a ninth or a tenth of an inch . 



Animal dark-grey, dextral ; in other respects resembling 

 the last. 



This little shell is found adhering to the stems and leaves 

 of water plants in ponds, lakes, and canals. It is generally 

 distributed, though somewhat local, in England, Wales, 

 and Ireland, but is rare in Scotland, occurring only in the 

 south, as in Duddingston Loch, near Edinburgh. 



