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12. CHAMA : Hinge on one side with an oblique obtuse tooth inserted 



into a corresponding cavity. 



13. ARC A : Hinge with numerous penetrating teeth. 



14. OSTREA : Hinge without teeth, but an Ovate hollow. 



15. ANOMIA : Hinge without teeth, but generally a linear depression on 



the rim, the beak of one valve curved over the hinge. 



16. MYTITUS : Hinge without teeth, with a subulate depression. 



17. PINNA : Hinge without teeth, valves united at one end and open at the 



other. 



3. UNIVALVES. 



I. WITH A REGULAR SPIRE. 



18. ARGONAUTA : Shell with one cell spiral involute. 



19. NAUTILUS: Shell with many chambers communicating by a tube. 



20. CONUS: Aperture effuse, longitudinal, without teeth. 



21. CYPRiEA : Aperture effuse, linear, longitudinal, toothed on each side. 



22. BULLA : Aperture rather contracted and placed obliquely. 



23. VOLUTA : Aperture effuse, the pillar plaited. 



24. BUCCINUM : Aperture with a small canal leaning to the right. 



25. STROMBUS : Aperture with a small canal leaning to the left. 



26. MUREX : Aperture with a small straight canal. 



27. TROCHUS : Aperture contracted nearly rectangular. 



28. TURBO : Aperture contracted and orbicular. 



29. HELIX : Aperture contracted lunate on the inner side. 



30. NERITA : Aperture contracted and semi orbicular. 



31. HALIOTIS : Shell with a row of orifices along the surface. 



II. WITHOUT A REGULAR SPIRE. 



32. PATELLA : Shell conic, the aperture widened like a basin. 



33. DENTALIUM : Shell slender subulate open at both ends. 



34. SERPULA : Shell tubular, generally serpentine adhering to other bodies. 



35. TEREDO : Shell thin penetrating wood. 



3G. SAB ELL A : Shell composed of agglutinated grains of sand. 



