6 cardial. 



ed, enlarging at their bases parallel to the ribs ; the central 

 series are similarly shaped, but bend posteriorward ; and 

 the front ones, which are shorter, and more solid, are com- 

 pressed (in the mature shell) horizontally (or at right 

 angles to the ribs), and are either blunt-topped, or bend up- 

 ward at their apices. The interstitial sulci, which are 

 scarcely as broad as the ribs, are only delicately marked 

 with very fine and regular-raised concentric striulae, which 

 are not developed in the immature examples, and conse- 

 quently are absent from the umbonal region of the adult ; 

 they are not at all flexuous, a character which affords a 

 ready means of distinguishing this species from the two 

 succeeding ones. The lateral teeth, particularly the front 

 one, which is generally the more approximate, are very large. 



The external colouring is also of a less yellow cast than 

 in the next species, being usually of a pale-brownish flesh- 

 colour, with livid or rufous zones. The sides of the adult 

 are always very unequal, the outline being then oblique, 

 and the umbones much nearer to the anterior commence- 

 ment of the shell. The British specimens appear generally 

 more elongated than the Mediterranean ones, which 

 are more orbicular, less flattened behind, and more fully 

 weaponed. 



The young shell is less inequilateral and oblique, and de- 

 void of any inferior angle at the hinder extremity. The 

 dorsal line is much more sloping than in echinatum, ascend- 

 ing slightly on the hinder side. 



A good-sized example will measure four inches in length, 

 and three and a third inches in breadth. 



Poli states that the animal of this species is of a cinna- 

 bar colour ; the foot long, subulate ; the bases of the tubes 

 not fimbriated ; the last statement, however, is probably 

 a mistake. 



