BIVALVES. — CARDIUM. 5S 



and compressed. In other species the contour exhibits 

 the figure of a perfect heart, as in the Cardium cardissa, 

 &c. &c. 



The shells are usuilly equivalve, and have their out- 

 sides adorned with longitudinal ridges and grooves, 

 crossed by transverse striae, something in the manner of 

 the common cockle, only much more articulate. 



In others, again, the ridges are beset with rows of 

 acute spines, as in the Cardium aculeatum and echina- 

 tum; but the exteriors of some, on the contrary, exhibit 

 a perfectly smooth and polished surface, as in the egg- 

 cockle, &c. 



The Cardium fragum and unedo exhibit a peculiar 

 formation, for they are sub-angular, and are only heart- 

 shaped when seen in one particular position. A similar 

 coincidence is observable in the Cardium retusum, though, 

 in other respects, it differs; for the fragum and unedo 

 have their ridges covered with crowded pink or yel- 

 low elevated lunules or crescents, whereas, the retusum 

 has nodules rath€r than imbricate scales. The interior 

 margin of this genus is almost universally crenate or 

 toothed. 



The hinge is furnished with two teeth, and a larger 

 remote lateral one on each side of it, each locking" into itg 

 opposite. 



The Cardium edule, or common cockle, is found in 

 great abundance beneath the sand on sandy coasts; the 

 fish afford a wholesome and nourishing food. 



The most rare and valuable species of the genus Car- 

 dium, is the costatum or pipe-ridged cockle, which ha* 

 rows of white hollow elevated ribs, situated at regular 

 distances on its surface, and proceeding in a longitudi- 

 aal direction from the beaks to the margin; the inter- 



