FRESH-WATER SHELLS. 



having a spiral turn or twist are called snail shells, and are 

 to be studied first. 



3. Let the pupils pick out from their collections the 

 shells like these : 



FIG. 3. FRESH- WATER SNAIL-SHELLS. 



The different spiral turns, or twists, are called whorls, 

 and the whorls together form the spire. The opening into 

 the shell is called the aperture, and the line separating the 

 whorls is called the suture. The pointed end of the spire is 

 called the apex. 



apex. 



suture. ,;.---:"--. 



\ 



body-whorl. 



idiorh forming the spire. 



aperture. 



FIG. 4. SHELL, WITH PARTS NAMED. 



