INTRODUCTION. ^ 15 



2 1 . CYPR.EA : Aperture eflfuse, 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 effuse, the pillar plaited. 



24. Buccinum: Aperture with a small canal leaning to 



the right. 

 25- Strom BUS : Aperture with a small canal leaning to 

 the left. 



26. MuREX : Aperture with a small straight canal. 



27. Trochus: Aperture contracted, and somewhat 



triangular. 



28. Turbo: Aperture contracted and orbicular. 



29. Helix : Aperture contracted, lunate on the inner 



side. 

 SO, 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. 



S5. Teredo : Shell thin, penetrating wood. 



36. Sab ELLA: Shell composed of agglutinated grains of 

 sand, &c. 



