48 LESSON VIII. 



Child. To the class of univalve shells. 



Teacher. I intend that you shall study the 

 univalve shells first, because they are the most 

 simple, and their distinguishing characters well 

 marked ; but before you can describe these 

 shells, you must be well acquainted with their 

 parts. Here are some univalve shells, examine 

 them carefully ; I will give you the names for 

 the parts, as you discover them. First, consider 

 which appear to be the principal parts. 



Child. These shells have two principal parts, 

 this which swells out, and this which is tapering. 



Teacher. The swelling part is called the 

 body,* and this which is tapering, the spire. 

 Observe how the spire is produced. 



Child. It seems formed by the rolling round 

 of a part of the shell. 



Teacher. These parts that roll round are 

 called whorls, from an old Saxon word signifying 

 a round. What do you remark in these whorls'? 



Child. That they gradually increase in size. 



Teacher. Yes ; and as they successively roll 

 one round another, what difference is there in the 

 circles they describe ? 



Child. They gradually increase in diameter. 



Teacher. It is from this circumstance that 

 the set of whorls is called the spire, a word de- 

 rived from the Greek root <nrp, (speir,) which 

 signifies convolutions gradually increasing in 

 diameter, just as would be the case in a rope 

 coiled up. In the coiled rope you have the cir- 



See Plate L 



