CONUS CONE. 59 



Teacher. It does ; but which is the broadest 

 part of a cone ? 



Child. The base. 



Teacher. And is the base the broadest part 

 of these shells I 



Child. No ; quite the reverse. 



Teacher. They are therefore said to be in~ 

 versely conical. 



Child. The cones are spiral. 



Teacher. Observe how the spire is formed. 



Child. By the whorls. 



Teacher . And how are the whorls arranged ? 



Child. They are spirally convoluted. 



Teacher. Compare the spires of the cones 

 with those of the other shells before you, and tell 

 me what you remark. 



Child. The whorls scarcely rise one above 

 the other. 



Teacher. You remember what a spire is 

 called, when the whorls have the appearance of 

 being pushed into the body whorl. 



Child. Such a spire is called retuse. Here 

 is a cone in which the upper whorls appear so 

 pushed into the body whorl* that the spire forms 

 almost a flat surface. 



Teacher. What then is the character of the 

 spire of the cones. 



Child. The spire of the cones is retuse. 



Teacher. Compare together all the different 

 shells before you^ and you will find that the 

 relative proportion of their parts varies very 

 much. In some you will perceive that the 

 mouth is particularly large, in others the spire* 



