SPH^ERIUM. 7 



which is another variety of the present species. Dr. 

 Baudon and M. Bourguignat both agree with* me in the 

 above opinion. This species is widely distributed in 

 Europe ; its northern limit being (according to Von 

 Wallenberg) Lapland, and its southern limit being (ac- 

 cording to Philippi) Sicily. Young shells are extremely 

 flat, and might be easily mistaken for a different species. 

 This common species was first made known by our 

 countryman, the celebrated Dr. Lister, in his Treatises 

 on the history of English animals, in 1678. It is the 

 Tellina rivalis of 0. F. Miiller, and the Cyclas rivalis of 

 Draparnaud, who evidently described and figured the 

 next species (8. rivicola) as the Tellina cornea of Linne*. 



2. S. RIVI'COLA*, Leach. 



Cydas rivicola, (Leach) Lamarck, An. sans Vert. vi. p. 267 ; F. & 

 H. ii. p. Ill, pi. xxvii. f. 1, 2, and (animal) pi. Q. f. 1. 



BODY yellowish-grey, or light brown : tubes short, white, 

 and nearly of equal length : foot thick, and capable of great 

 extension, greyish-white : gills sometimes slightly tinged 

 with red. 



SHELL oval, ventricose, nearly equilateral, much compressed 

 in front, rather solid, glossy, yellowish horn-colour, or olive- 

 green, with often darker bands or zones, deeply ridged con- 

 centrically, especially towards the lower or front margin, the 

 ridges being crossed by obscure lines which radiate from the 

 beaks : epidermis rather thick : anterior side rounded : pos- 

 terior side more produced and subtruncate : beaks central, 

 small, and flattened : ligament short, prominent, and dis- 

 tinctly visible on the outside : inside white and nacreous, 

 with sometimes a yellowish tinge : hinge and teeth stronger 

 than in S. corneum, but nearly of the same form : muscular 

 and pallial scars distinct. L. 0*7. B. 0'9. 



HABITAT : Slow rivers and canals in the metropolitan, 

 midland, and northern counties of England, as well as 



* Inhabiting brooks. 

 I 



