﻿21 



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 umboncs alternating. 



Scientific name. 



Cardissa, 



Humanum, 



Locality. 

 East Indies, 

 do. do. 



Scientific name. Locality. 



Roseum, Malay Coast. 



Monstrosum, 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, 

 Family 2d. 



Edule, 



Unedo, 



Fragum, 



Hemicardium, 



Tuberculatum, 



Isocardia, 



Pectiniforme, 



Regulare, 



Flavum, 



Spinosum, 



Echinatum, 



Lima, 



Muricatum, 



Costatum, 



Medium, 



Donaciforme, 



Exiguum, 



Ringens, 



Oblongum, 



India. 



Ribs armed with nodules, elevated, rough stria;, tvrinkles or scales. 



Britain. 

 India. 



do. 



do. 

 Mediterranean. 

 E. and W. Indies. 



Glaucum, 



Fasciatum, 



Elongatum, 



Leucostomum, 



Magnum, 



Rigidum, 



Maculatum, 



Mediterranean. 

 Britain. 



do. 

 West Indies. 



Ceylon. 



West Indies. 

 Family 3d. With ribs armed, more or less spined. 



Ceylon. 



Mediterranean. 

 Britain. 

 East Indies. 

 West Indies. 



Rugatum, 



Latum, 



Ciliatum, 



Aculcatum, 



Muricatum, 



Family 4th. With ribs unarmed. 



Africa. 



W. Indies, Britain. 



do. do. do. 



Britain. 



Africa. 



Mediterranean. 



Papyraceum, 



Fimbriatum, 



Rusticum, 



Islandicum, 



Parvum, 



E. and W. Indies. 



East Indies. 

 Greenland. 

 Britain. 

 Coast of Kent. 



Med. and Ind. Ocean. 



Mediterranean. 



Greenland. 



Coast of Hampshire. 



