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. The 

 true form of the shell is that of a pointed cone, 

 capable of standing nearly perpendicular, or but 

 little inclined on its base. Some of these erect 

 shells* have their columella umbilicated, other sf 

 are imperforate. A few of the Trochi are elon- 

 gatedj 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 



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



Plate IV. fig. 6. 



