POND SNAIL 193 



a. The "wliorls or turns of the spiral. — How many are 

 there ? "What is their arrangement ? "What vari- 

 ations in shape, size, and color do you find ? Trace 

 the suture or line of junction between two 

 whorls. 



h. The body-whorl or first turn of the spiral. — "What 

 is its position % Shape ? Size as compared with 

 others? How much of the entire shell does it 

 form? 



0. The spire. — "What is its structure? "What is the 

 number of whorls composing it ? "What is the di- 

 rection of the spiral? 



d. The apex. — "What is its structure ? Compare in age 



with other parts of the same shell, also compare 

 with the umbo of JJnio or Anodonta. 

 Cut a shell in two lengthwise and notice 



e. The columella or axis around which the whorls 



turn. — How is it formed ? Does it extend 

 throughout the length of the shell? Is it solid 

 or hollow ? 



/. The mouth. — "What is its shape ? Is it the largest 

 part of the cavity of the shell ? Notice the in- 

 ternal lip or side towards the columella, and the 

 external lip or side away from the columella. 



g. The peristome or rim of the mouth. — "What is its 

 shape ? Size ? Does it bear any outgrowths, as 

 teeth, etc. ? 



h. The muscular impression. — Where is it? What 

 is its shape ? Color ? How is it formed ? 

 Draw the shell as seen from the front, also a longitu- 

 dinal section. 

 13 



