INTRODUCTION. 23 



23. Voluta: Aperture effuse, the pillar plaited. 



24. Buccinum: Apertiu'e 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 trian- 



gular. 



28. 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. 



33. Dentalium : Shell slender, subulate, open at both ends. 



34. Serpula : Shell tubular, mostly serpentine, adhering 



to other bodies. 



35. Teredo: Shell thin, penetrating wood. 



36. Sabella: Shell composed of agglutinated grains of 



sand, &c. 



