22 FIRST BOOK OF ZOOLOGY. 



examining pools left at low tide, many little sea snails may 

 be seen creeping about. 



A good place to collect dead shells may be found along 

 an exposed beach. After a violent storm, when the waves 

 have been running high, a great many animals are thrown 

 up from the sea, and among them many shells may be 

 secured. 



The following will be some of the shells collected : 



FIG. 26. COMMON SEA SNAILS. 



22. With very few exceptions, all sea snails are water- 

 breathers ; that is, they are furnished with gills, instead of a 

 simple lung. Most of them are operculated. 



In the shells collected the pupil will find two well- 

 marked groups. 



In the two lower right-hand figures of Fig. 26, the 

 shells have an aperture with a continuous border ; that is, 



