A GROUP OF SAND-DWELLERS. 87 



Sometimes a great number of these olives live 

 together, and the bed of sand will be quite alive 

 with them; but if you go again to the same place, 

 you may find that they have all decided to move; 

 and though you search for an hour, you may not 

 be able to find a single shell. 



They never like to be in the air, and if you 

 wish to find them at home, you must go when 

 the tide is the very lowest, and then be prepared 

 to get wet while you are searching for them. 

 But their shells are so pretty that you 

 ought to get at least a few for your cab- 

 inet. 



The common California Olive-shell, 

 when full-grown, is almost the size of 

 the picture (Figure 40), and varies in 

 color from almost pure white to a 



Figure 40. 



brownish purple. The animal which 

 lives within the shell spreads out folds of soft, 

 moist skin, or mantle, as it is called, and covers 

 the shell most of the time, thus keeping it smooth 

 and free from injury. But when the mollusk dies, 

 the shell is tossed about by the waves, and gets 

 worn and battered. 



This last is true of all sea-shells, and it is easy 

 to tell what are called dead shells from those 

 which were taken with the animal still in them, 



