ZOOLOGY. 251 



Shells generally sloping to one side; hinge with three 

 teeth, the side ones either plain or wanting, in one 

 Talve. Plate 4, fig^ 7. 



They are divided into three families, * OvATEand thickish, 

 ** Otate, compressed, *** Suborbiculab. Their shell* 

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

 shores, and some kinds in rivers or ditches. 



7. Cardium. Cockle. Inhabitant a Tethys. 



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 /oo/A 

 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. DoTMx. Wedge-Shell. Animal a lethyt. 



