of Cyclas, which has so long received the sanction of 

 naturalists, the principle of usage may be to some extent 

 violated, and that it may be urged, with great reason, 

 that Limncea and Succinea ought to give place to Nerito- 

 stoma and Auricula, which Klein had previously pro- 

 posed, as well as Physa to that of Adanson's genus 

 Bulin ; but I am only in the present case following the 

 lead of experienced naturalists, and the conflict of au- 

 thorities ought to be determined by the strict rules of 

 justice. The word being derived from o-^cuptoi/, it ought 

 not to be spelt Sphcerium, as has been done by some 

 authors. 



1. SPHJERIUM COR'NEUM *, Linne. 



Tdlina cornea, Linn. Syst. Nat. ed. xii. p. 1120. Cyclas cornea, 

 Forbes & Hanley, Brit. Moll. ii. p. 113, pi. xxvii. f. 3, 4, 5, 6. 



BODY white, greyish, brown, or yellowish : tubes rather 

 long, slightly tinged with flesh-colour : foot somewhat longer 

 than the shell, of a faint rosy hue towards its extremity. 



SHELL subglobular, nearly equilateral, compressed in front, 

 rather thin, glossy, yellowish horn-colour, with often paler 

 bands or zones which denote the periods of growth, and occa- 

 sionally having faint streaks of brown which radiate from the 

 beaks towards the front margin, slightly but closely striate 

 transversely, and marked by obscure lines in a longitudinal 

 direction, so as to give the surface a reticulated appearance 

 under a high magnifying power : epidermis rather thin : beaks 

 almost central : ligament short and narrow, scarcely visible on 

 the outside : inside bluish- white : hinge strong, having a double 

 cardinal tooth in each valve, besides two lateral teeth in the 

 right, and four in the left valve ; the cardinal teeth are very 

 small, but distinct ; the lateral teeth form elevated ridges or 

 plates, and are subtriangular at their extremities, those on the 

 anterior side being the largest : muscular scars or impressions 

 faint, owing to the thinness of the interior lining : pallial scar 

 scarcely discernible. Length O35. Breadth 0'45. 



Var. \.flavescens. Smaller and rounder ; body and shell 

 * Horn-colour. 



