CARDIUM. 9 



attenuates the anterior side ; it is well arcuated, and rises a 

 little behind likewise, so as to round off the incipient basal 

 angulation of that extremity. The dorsal edges are almost 

 straight, or barely convex ; the front declination is the 

 more manifest, but both are very trifling. The posterior 

 edge, which is not much curved, forms a distinct angle at 

 the upper corner ; a less decided angulation takes place at 

 the opposite end of the dorsal margin, where it is modified 

 by the arcuation of the anterior edge ; the front extremity 

 is narrowed, the hinder is moderately broad. The liga- 

 ment is rather large and projecting, but not elongated : the 

 umbonal ridge is obsolete, the space beyond it being 

 scarcely, if at all, flattened. The umbones are prominent, 

 and more ordinarily subcentral ; in very large examples, 

 however, they closely approach the anterior end ; the 

 beaks are inflected, and lean slightly forwards ; there is no 

 lunule in front of them, but usually a somewhat heart- 

 sliaped area, devoid of costae, of which the lips are generally 

 elevated and pouting. The interior is white or pale, and 

 neither stained at the hinge margin nor posteriorly with 

 any colouring matter ; the position of the external sulci is 

 occasionally indicated by the internal surface being rather 

 of a browner tint. The lateral teeth are large, and, the 

 front one especially, tolerably approximate. 



The diameter of the average of examples does not exceed 

 two iaches ; we have taken a specimen at Torquay, how- 

 ever, which is three inches long, and more than two inches 

 and a half broad. 



The animal has been more than once figured, and was 

 well delineated in the Zoologia Danica. It is shaped like 

 the shell, and of a yellowish white or pale yellow colour, 

 palest when young. The mantle is very muscular, and 

 simple at its edges, white in the young shell, pale brown in 



VOL. II, c 



