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edly esteemed a delicious and wholesome food in Great Britain; in France 

 little regarded. They are in season during March, April, and May, after 

 which they become milky. They are not used generally as a bait. This 

 genus is divided into three divisions, with families. 



DIVISION I. Heart-shaped valves, compressed umbones alternating. 



Scientific name. 



Cardissa, 



Humanum, 



Locality. 

 East Indies, 

 do. do. 



Scientific name. 



Roseum, 



Monstrosum, 



Locality. 

 Malay Coast. 

 South Sea Isles. 



DIVISION II. Sub-cordate, longitudinally ribbed. 



One of the most rare species of this division is the C. costatum, which 

 has rows of white, hollow, elevated ribs, situated at regular distances, pro- 

 ceeding from the umbones to the margin ; and the spaces between them are 

 imperfect specimens of a fine dark brown color. 



Family 1st. Having a crescent-shaped cavity beneath the umbones. 

 Retusum, India. 



Family 2d. Ribs armed with nodules, elevated, rough strias, wrinkles or scales. 



