INTRODUCTION. 15 



21. Cypr^a: Apertureeffuse, linear, longitudinal, tooth- 



ed on each side. 



22. Bulla: Aperture a little contracted, and placed ob- 



liquely ; toothed on one side only. 



23. Voluta: Aperture eflfuse, 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, and somewhat 



triangular. 

 2§. Turbo : Aperture contracted and orbicular. 



29. Helix: Aperture contracted, lunate on the inner 



side. 



30. Nerita: Aperture contracted, and semiorbicular. 



31. Haliotis: Shell ear-shaped, aperture dilated, with a 



row of orifices along the surface. 



2. WITHOUT A REGULAR SPIRE. 



32. Patella: Shell conic, the aperture widened like a 



basin. 

 S3. Dentalium : Shell slender, subulate, open at both 

 ends. 



34. Serpula: Shell tubular, mostly serpentine, adher- 



ing to other bodies. 



35. Teredo : Shell thin, penetrating wood. 



36. Sabella: Shell composed of agglutinated grains of 



sand, &c. 



