CLASSIFICATION. 



II. BIVALVES. 



Shells with two Valves.—Conchs. 



4. Mya : Hinge with generally a broad thick tooth, not 



let into the opposite valve. 



5. SoLEN : Shell open at each end; hinge with a single 



or double subulate reflected tooth, not let into tlie 

 opposite valve, ^^y f'<»^ ^-<' , 



6. Tellina: Hinge ^with the lateral teeth of one valve 



not let into the other. 



7. Cardium: Hinge with remote penetrating lateral 



teeth. 



8. Mactra: Hinge with a complicated triangular mid- 



dle tooth, and an adjoining hollow. 



9. DoNAX : Hinge with a generally remote lateral tooth, 



not let into the opposite valve, 

 to. Venus : Hinge with generally three approximate di- 

 varicate teeth. 



11. Spondylus: Hinge with two teeth, separated by a 



small hollow. 



12. (^hama: Hinge in one shell, with two oblique ob- 



tuse teeth. 



15. Arc a: Hinge with numerous penetrating teeth. 



14. Ostrea: Hinge without teeth, but an ovate hollow. 

 1 .5. Anomi A : Hinge w ithout teeth, but generally a linear 



depression on the rim, the beak of one valve curved 



over the hinge. 



16. Mytilus: Hinge without teeth, with a subulate de- 



pression, and generally fixed by a silky beard. 



17. Pinna: Hinge without teeth, valves united at one 



end, and open at the other. 



