48 CATECHISM OF CONCHOLOGY. 



Q. Where are the varices situated ? 



A. They are longitudinal swelling sutures, 

 formed in the growth of the shell, at certain dis- 

 tances on the whorls. 



Q. Will you explain to me the meaning of 

 ventricose, vertex, and umbilicus ? 



A. Ventricose signifies bellied. Vertex, in the 

 Patella, signifies the uppermost point of the shell. 

 Umbilicus, a hole in the base of the columella, 

 visible underneath. 



CHAP. XXI. 



UNIVALVES: 

 ARGONAUT A ; Paper Sailor. 



Q. WILL you describe the form of this shell ? 



A. The shell is spiral, involute, membrana- 

 ceous, unilocular, or without chambers. 



Q. What has given rise to the name? 



A. This genus has been denominated Argo- 

 naut a, from a companion of Jason, in the cele- 

 brated voyage of the ship Argo. The art of 

 navigation is supposed to owe its origin to the 



