176 BIVALVES. 



and muricated ; * posterior slope heart-shaped, 

 closed ; margin in front deeply sinuous ; the co- 

 lour is white or yellowish, with scattered reddish 

 or purplish spots; commonly about two inches 

 long, and three inches and a quarter inside, but 

 it sometimes occurs double this size. 

 It inhabits the East Indian ocean. 



Genus. ARC A. f Plural, Area. 



ARK. 



Generic Character. Shell bivalye, equivalve, 

 inequilateral ; form various, often oblong, some- 

 times orbicular ; hinge with numerous small sharp 

 teeth in each valve, alternately inserted between 

 each other, arranged sometimes in a straight, 

 sometimes in a curved line ; beaks generally re- 

 mote ; ligament external. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



The shells of this genus are very readily 

 known, by their numerous small teeth. Some 

 of the species attach themselves to rocks by a 

 kind of byssus : these have always the shell more 

 or less gaping ; but the greater part of the Arks 

 live buried in the sand at a short distance from 



* Muricated, having little pointed knots, from the Latin 

 murex, the sharp point of a ro^k. 



t Plate IX. figures 4, 5,6. 



