30 BIVALVES CARDIUM. 



the Cardia to be separated into three divisions, and 

 those divisions into families. 



Specimens of this shell are found in almost every 

 sea, and some, though rarely, at the mouths of the 

 rivers Tees, Thames, &c. 



This genus has been named Cardium from the re- 

 semblance which its species bear to a heart (/capSi'a). 



Division I. — Heart-shaped, valves compressed, umhones alter- 

 nating. 



Scientific Name. Locality. Common Name. 



Cardissa East Indies Venus's Heart • • 



Humauum East Indies • • • • Concave • . . . do • • 



Roseum Malay coast Rose do — 



Monstrosuni South Sea Isles Recurved • • • do • • 



Division II. — Sub-cordate, longitudinally ribbed. 



One of the most rare species of this division is the 

 C. costatura, which has rows of white, hollow, elevated 

 ribs, situated at regular distances, proceeding from 

 the umbones to the margin ; and the spaces between 

 them are, in perfect specimens, of a fine dark brown 

 color. 



The C. fragum and C. unedo differ from the other 

 species of this division, their ribs being armed with 

 small crescent-shaped scales. 



Family 1. — Having a crescent shaped cavity beneath the umbones. 

 Retusum India Diana's Heart • • • 



