26 CARDIAD^. 



was sent after his decease), we have yiekled, though not 

 silently, to the dictum of Tuvton, who prohahly founded 

 his recognition on some original types which are no longer 

 accessible. The name ovale was only introduced to 

 remedy the pre-occupation of the epithet elongatum by 

 a magnificent exotic species ; fasciatum^ notwithstanding 

 its having been already bestowed on a Cardium, is allow- 

 able, since Gmelin has merely used it to designate a wretched 

 figure of Knorr's, from which drawing solely he has derived 

 his bald and undefining diagnosis. 



The form is more or less oblique and oboval, with, 

 at times, a tendency to be heart-shaped ; at times, to be 

 subquadrate. The texture is thin and fragile, but not at 

 all diaphanous, and the valves are more or less ventricose. 

 The colouring is white, with often a slight livid tinge, and 

 almost invariably with short concentric bands of undulated 

 brown streaks, which do not traverse the entire shell but 

 are confined, excepting near the beaks, to the posterior 

 side. These bands, moreover, are less evident and more 

 livid in the adult ; but even when almost obsolete exter- 

 nally, their presence may be traced in the interior. The 

 surface is divided by about twenty-six radiating ribs, 

 which are by no means prominent, the central being 

 scarcely raised in the slightest, and merely a little convex, 

 and those at the sides, with the exception of a few rounded 

 ones upon the umbonal ridge (which is very oblique and 

 rendered tolerably distinct by the surface being flattened 

 behind it), are at most convex. The central ribs (except 

 in the fry) are smooth and unarmed ; but the lateral are 

 sculptured by oblique tubercles, of which those upon the 

 front ones are rather depressed, linear, crowded, transversely 

 occupying the entire surface, and sloping down anterior- 

 ward ; those upon the hinder ones are elevated horizontally 



