8 SPH^RIID^. 



near Dublin ; and it is one of our upper tertiary fossils. 

 It is a local species. On the continent it ranges from 

 Holland to Italy. 



This fine species may be distinguished from S. corneum 

 by its much greater size, its form being oval instead of 

 globular, the strong transverse ridges, and the con- 

 spicuous ligament. The young of this are also much 

 flatter in proportion to their size. Both species occur 

 together. >S^. rivicola was first indicated by Lister as 

 having been found at Doncaster. 



3. S. ova'le^, Ferussac. 



Cijclas ovalis, Fer. in Ess. Meth. 1807, pp. 128, 136. 8. pallidum, Gray 

 in Ann. N. H. ser. 2. xvii. p. 465, woodcut. 



BoBY milk-white : tuhes long, united nearly all the way : 

 foot tongue-shaped, very extensile and flexible : gills of a 

 faint blush-colour. 



Shell oblong, somewhat compressed, not so equilateral as 

 the two preceding species, owing to the greater development of 

 the posterior side, thin, semi transparent, not very glossy, 

 yellowish, with sometimes a brown tint and darker zones of 

 growth, with occasionally some faint rays in the direction of 

 the lower margin, finely striate concentrically : epidermis thin : 

 anterior side rounded : posterior side truncate, and sloping 

 towards the lower margin, which is curved and sharp : heaks 

 small, nearly central, and slightly prominent : ligameiit long 

 and narrow, distinctly visible on the outside: inside ashy- 

 white : hinge straight on the posterior side, and incurved on 

 the other side ; cardinal and lateral teeth arranged as in S. 

 corneum, but the former are exceedingly small and difficult to 

 distinguish : muscular and pallial scars very faint. L. 0-4. 

 13. 0-6. 



Habitat: Exmouth (Clark) ; PaddingtonCanal(J.G.J.); 

 canals and ponds in Lancashire (Darbishire) . A speci- 

 men also exists in the late Dr. Turton's collection of 

 British shells, but without any note of the locality. 



* Egg-shaped. 



