PISIDIUM. 123 



P. pusxllum, Turton. 



Rounded oval, not greatly inequilateral, not distinctly striated ; 

 valves not swollen, always a little compressed below : umbones 

 usually broad and but little projecting. 



Plate XXXVII. fig. 10, and (Animal; Plate 0, fig. 9. 



Ci/clas fontinalis, Draparn. Moll. Terr, et Fluv. France, p. 130, pi. ]0, f. 8—12 ? 

 Lam. Anim. s. Vert. (ed. Desh.) vol. vi. p. 270 ? — Nilsson, 

 Moll. Suecise, Terr, et Fluv. p. 101. — Desh. Encyc. Meth. 

 Vers, vol. ii. pt. 2, p. 37 ? — Hanl. Recent Shells, vol. i. p. 

 90, suppl. pi. 14, f. 45.— ;Gras, Moll. T. et Fl. France, p. 

 73, pi. 6, f. 3,4? 

 Tellina pusilla, Turt. Conch. Diction, p. 167. 

 Cyclas „ Turt. Dithyra Brit. p. 251, pi. 11, f. 16, 17; Manual of Land 



and Freshw. Shells, p. 16, pi. 1, f. 7. 

 Cyclas gibba, Alder, Trans. Nat. Hist. Soc. Newcastle, vol. i. p. 41. 

 Pisidium pusillum, Jenyns, Trans. Cambridge Phil. Soc. vol. iv. p. 302, pi. 20, 

 f. 4, 5, 6.— Gray, Manual L. and F. W. Shells, p. 283, 



pi. 1, f. 7. — Macg. Moll. Aberdeens. p. 253 Brown, 



111. Conch. G. B. p. 95, pi. 39, f. 27. 



As in most Pisidia, there is a considerable latitude of 

 diversity in shape permitted to this species, which conse- 

 quently, although typically orbicular-oval, becomes some- 

 what oblong in certain individuals. It is small, thin, semi- 

 pellucid, and but slightly (for its genus) inequilateral ; the 

 valves, although not really compressed, appear so when 

 compared with P. obtusale, although actually they are ven- 

 tricose or nearly so. The surface is not regularly striolated, 

 is usually concealed by a rustlike coating, and is never 

 highly lustrous, but ranges from rather dull to rather 

 glossy. The colouring, which is generally uniform in tint, 

 displaying neither zones nor a marginal band, is of a light 

 fulvous hue, and occasionally so pale as almost to become a 

 squalid white. The ventral margin is regularly arcuated, 

 ascending much and almost equally at both ends. The 



