CATECHISM OF CONCHOLOGY. 59 



A. Yes, in some instances ; but the most 

 simple, though not an unexceptionable rule, is 

 to consider all specimens as belonging to this 

 genus which have any angular tendency in the 

 contour of the mouth, and are, as to their gene- 

 ral appearance TOP shaped, in conformity with 

 the meaning of their name, derived from the 

 Greek. 



Q. What is the true form of the Trochus ? 



A. It is that of a pointed cone, capable of 

 standing nearly perpendicularly, or but little 

 inclined, upon the flattened base of the last 

 whorl ; the aperture broader than long, angular 

 at the lower extremity of the columella, and 

 having the carinate (having the form of a boat- 

 keel) margin f the outer lip so situated as to be 

 nearly horizontal when the shell is placed in an 

 upright position. 



CHAP. XXXI. 



UNIVALVES: 

 TURBO; Wreath, or Turban Shell. 



Q. How is the Turbo to be distinguished from 

 the Trochus ? 



A. By observing that the Turbo has a round 



