100 UNIVALVES. 



OBSERVATIONS ON THE SHELL AND ITS 

 INHABITANT. 



Many of the Trochi so nearly resemble the 

 shells in the following genus, that it is often dif- 

 ficult to discriminate between them. The cha- 

 racter by which they are most readily known, is 

 the angular contour of the mouth. Their true 

 form is that of a pointed cone, capable of stand- 

 ing nearly perpendicular, or but little inclined on 

 its base. Some of these erect shells* have their 

 columella umbilicated, somef 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. 



Many of the shells of this genus have their 

 outside rough with tubercles, and many are co- 

 vered with a thick epidermis, on the removal of 

 which a bright surface appears, shining with iri- 

 descent colours. The animals which inhabit 

 these shells have no proboscis, but a mouth 

 armed with two jaws, and thence it is concluded 

 that they feed upon vegetables ; the shell also 

 has neither notch nor canal, and the mollusca no 

 siphon. 



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



I Plate IV. figure 6. 



