shells before you, and you will find that the re- 

 lative proportion of their parts varies very much. 

 In some you will perceive that the mouth is par- 

 ticularly large, in others the spire. Describe the 

 relative proportion of the parts of the cone. 



Child. The body whorl is very large, com- 

 pared with the other whorls. 



Teacher. This peculiarity is expressed by the 

 term turbinate, which is derived from the Latin 

 word turbin is, of a whirlwind. 



Child. Why is this form of a shell named 

 after a whirlwind. 



Teacher. Because the first sweep of a whirl- 

 wind describes a circle much larger than those 

 which succeed, when its power is in some degree 

 exhausted. Do you not now perceive how the 

 term is applicable to the form you were describing ? 



Child. Yes. The body whorl is very large 

 in proportion to the others, just as the first 

 sweep of a whirlwind is large compared with 

 those that succeed it. 



Teacher. You have now observed the general 

 appearance of the Cones ; what particular part 

 were you to take into consideration in order to 

 draw out the generic character ? 



Child. The mouth. 



Teacher. And what do you observe in the 

 mouth or aperture of the Cones ? 



Child. It is long and narrow. 



Teacher. When the mouth is very narrow in 

 proportion to its length, and also of a nearly 



