ZOOLOGY. 



251 



Shells generally sloping to one side; hinge witli three 

 teeth, the side ones either plain or wanting, in ©ne 

 valve. Plate 4, fig. 7. 



They are divided into three families, * OvATEand thickish, 

 Ovate, compressed, Suborbiculae. Their shells 



are usually found buried in the sand or gravel on the sea 

 shores, and some kinds in rivers or ditches. 



7. Cardium. CocKLTE, Inhabitant a Te^^yj. 



Shells mostly equilateral, equivalve, usually convex, longi- 

 tudinally ribbed ; margin toothed ; teeth two near the 

 beak, with larger side ones, each locking into the op- 

 posite valve. Plate 4, fig. 8. 



The Cockles are generally natives of the ocean, residing 

 immediately beneath the sand on the sea shore; most of 

 them are applicable to the purposes of food. 



8. Mactra. Flat-Sided Cockle. Inhabitant a Tethys. 



Sides of the shell unequal ; valves equal, the middle tooth 

 complicated with a small concavity on each side ; lateral 

 teeth remote, and mutually inserted. Plate 4, fig. 9. 



These are generally found at the mouths of rivers, imme- 

 diately beneath the surface of the sand, or among rejecta- 

 menta of the sea, 



9. Donax. Wedge-Shell. Animal a lethyi\ 



