ZOOLOGY. ' 253 



12. Chama. Clamp-Shell. Inhabitant a Tethtfs. 



Shells strong, rugged ; hinge with a gibbous callous, or toothy 

 which is obliquely inserted into the opposite valve. 

 Plate4, fig. 13. 



These, like the last genus, are found in very deep water, 

 they all inhabit the sea, some of the kinds grow to a great 

 size, and all are edible. 



13. Area. Ark-Shell. Inhabitant a Tethys. 



Shell equivalve ; hinge with numerous teeth, alternately 

 inserted between each other. Plate 4, fig. 14. 



This genus is divided into four sections, * edge entire, 

 ' BEAK inflected : ** edge entire, beak reflected : *** 

 EDGE notched, BEAK recurved: **** edge notched, beak 

 inflected. 



The Ark-Shells are found in the sea, and on the sands and 

 mud on the shores of the ocean, generally between low and 

 high-water marks ; some of them are occasionally used as 

 food. 



14. Ostrea. Oyster. Inhabitant a Jethys. 



Valves in some unequal ; or one flat, and the other concave, 

 sometimes eared ; hinge without teeth^ with a hollow 

 cavity. Plate 4, fig. 15. 



