ZOOLOGY. 



§51 



Shells generally sloping to one side; hinge livitli three 

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

 valve, i'late 4, fig. 7. 



They are divided into three families, * OvAXEand thickish, 

 ** Ovate, compressed, *** Suboubicular. Their shells 

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

 shores, and some kiuds in rivers or ditches. 



7. Cardium. Cockle. Inhabitant a T6"//i_?/j. 



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-Sioed 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-Shet.l, Anima! a Tethys, 



