CLASSIFICATION. XV 



/^. 27- Trochus : Aperture contracted, nearly rectangular. 



//^ 28. Turbo: Aperture contracted, and orbicular. 



yy 29. Helix: Aperture contracted, lunate on the inner side. 



yo SO. Nerita: Aperture contracted, and semiorbicular. 



y/ 31. Haliotis: Shell with a row of orifices along the surface. 



2. Without a reyular Spire. 



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

 //? 3S. Dentalium: Shell slender, subulate, open at both ends. 

 y^ 34. Serpula : Shell tubular, generally serpentine, adhering 



to other bodies. 

 /J) 35. Teredo: Shell thhi, penetrating wood. 

 //, 36. Sabella: Shell composed of agglutinated grains of sand. 



