46 CATECHISM OF CONCIIOLOGY 



Q. What is the apex ? 

 A. It is the tip or summit of the spire. 

 Q. What are the articuli ? 

 A. They are joints, or parts of the whole. 

 Q. Describe the basis, or base. 

 A. It is the opposite extremity to the apex ; 

 in some shells that part of the body which is next 

 the aperture, in others the lowest part of the 

 beak. In this sense it is either emarginate, 

 indented by a deep canal, or entire, without 

 indentation. 



Q. What is the canalis, or canal ? 

 A. It is a continuation or prolongation of the 

 aperture along the beak, which forms a kind of 

 gutter or groove. 



Q. What part is the rostrum, or beak ? 

 A. It is a narrow channel, formed by a gra- 

 dual approach of the lips of the shell towards the 

 base. 



Q. Will you explain the meaning of the term 

 costae ? 



A. Costae signifies ribs; keel-like processes 

 reaching from the apex to the circumference of 

 the shell. 



Q. I will also thank you to explain the mean- 



