10 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 withasingle 



or double subulate reflected tooth, not let into the 

 opposite valve. 



6. Teli.in A : Hinge with the lateral teeth of one valve 



not let into the other. 



7. Cardium : Hinge with remote penetrating lateral 



teeth. 



8. Mactra: Hingewith 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. 



10. Venus : Hinge with generally three approximate di- 



varicate teeth. 



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



small hollow. 



12. Chama: Hinge in one shell, with two oblique ob- 



tuse teeth. 



13. Arca: Hinge with numerous penetrating teeth. 



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



15. Anomia: Hingewithoutteeth, but generally a linear 



depression on the rim, the beak of one valve curved 

 over the hinge. 



16. Mytilus: Hingewithoutteeth, 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. 



