100 UNIVALVES. 



convoluted ; form more or less conical ; aperture 

 entire, quadrangular, sometimes approaching to 

 round, generally wider than it is long ; margins 

 separated ; columella oblique. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



Many of the Trochi so nearly resemble the 

 shells in the following genus Turbo, that it is 

 often difficult to discriminate between them. The 

 character by which the former are most readily 

 known, is the angular contour of the mouth. 

 Their true form is that of a pointed cone, capa- 

 ble of standing nearly perpendicular, or but little 

 inclined on its base. Some of these erect shells* 

 have their columella umbilicated, othersf are 

 imperforate. A few of the Trochi are elongated J 

 resembling in form the Needle Buccinum ; these 

 have an exserted columella, and when placed on 

 their base, fall on one side. These latter are 

 now arranged in the genus Pyramidella. 



Many of the shells of this genus have their 

 outside rough with tubercles, and many are 

 covered with a thick epidermis, on the removal 

 of which a bright surface appears, shining with 

 iridescent colours. The animals which inhabit 

 the Trochi have no proboscis, but a mouth 

 armed with two jaws, and thence it is concluded 



* Plate IV. figure 5. f Plate IV. figure 4. 



Plate IV. fig 6. 



