114 CLASS IX. ORDER IH, 



ORDER 3. BIVALVA. 



Soft animals, having shells with two valves. 



MYA, (pearl-muscle, gaper,) animal an ascidiaf 

 shell bivalve, generally gaping at one end ; hinge 

 with broad thick strong teeth, seldom more than 

 one, and not inserted into the opposite valve. 



SOLEN, (razor- sheath,) animal an ascidia; shell 

 bivalve, oblong, open at both ends ; hinge with a 

 subulate reflected tooth, often double, and not in- 

 serted in the opposite valve* 



TELLINA, animal a tethys ; shell bivalve, gen- 

 erally sloping on one side ; in the forepart of one 

 Valve a convex, of the other a concave, fold ; hinge 

 usually three teeth, the lateral ones smooth in one 

 shell. 



CARDIUM, (cockle,) animal a tethys ; shell bi- 

 valve, nearly equilateral, equivalve, generally 

 convex ; longitudinally ribbed, striate or grooved, 

 with a toothed margin ; hinge with two alternate 

 teeth near the beak in the middle, and a larger re- 

 mote lateral one each side, each locking into the 

 opposite. 



MACTRA, animal a tethys ; shell bivalve, une- 

 qual sided, equivalve ; middle tooth of the hinge 

 complicated, with a small hollow each side, late- 

 ral ones remote and inserted into each other. 



DON AX, animal a tethys; shell bivalve, with 

 generally a crenulate margin, the frontal or ante- 

 rior margin very obtuse ; hinge with two teeth, 

 and a single marginal one placed a little behind^ 

 which is rarely double, triple or none. 



VENUS, (common clam,) animal a tethys ; shell 

 bivalve, the frontal mapgitt flattened with incura- 



