156 MOLLUSCOUS ANIMALS. 



are slow, and confined to creeping and swimming 

 One or two of the bivalve shell-fish can. however, 

 leap very short distances, as the scallop, and the 

 muscles found in our rivers. 



Many of this class of animals afford excellent 

 food, and are largely used for that purpose in all 

 parts of the world. The pinna, a bivalve shell- 

 fish, is famous for furnishing a kind of thread^ 

 which may be made into dresses ; fine pearls are 

 also sometimes found in it. 



The engraving at the head of this lesson re- 

 presents the paper nautilus. The Mediterranean 

 sea, and warmer parts of the Atlantic, abound in 

 these beautiful little creatures. In calm summer 

 days they may be seen in considerable numbers, 

 steering themselves on the surface of the water. 



Questions. 



What kind of covering have many molluscous animals 1 



In what way do they enlarge their shells "? 



What is the meaning of bivalve and univalve shells ? 



From what are pearls procured ? 



Can you mention what rivers furnish them in our own 

 country ? 



Where are they found most abundantly 1 



How does the snail support itself when at rest 1 



By what other means do molluscous animals fasten them- 

 selves ? 



Are they capable of much and quick motion ? 



What shell-fish can leap ? 



Mention some which are useful as food 1 



For what is the pinna celebrated ? 



