416 APPLIED BIOLOGY 



variety of purposes, ornamental and useful. In some bar- 

 baric tribes of Central Africa shells still pass as money, and 

 the " money cowry " is the standard currency. The North 

 American natives (" Indians ") once cut cylindrical beads 

 from the purple spots on shells of the hard-shelled clam 

 (Venus), and this was the " wampum " mentioned in early 

 colonial history of the United States. 



Civilized men make extensive use of shells. Some are 

 used for inlaying and for other ornamental work. Vast 

 quantities are used for pearl buttons. Pearls of great value 

 are each year collected from clams of various species. In 

 North America many pearls are found in the rivers of the 

 Mississippi system and in Lower California. 



Reference : Roger's " The Shell Book." 



Important Classes of Mollusca 



Amphineura chitons, eight-valved shell. 

 Gasteropoda snails, univalved shell. 

 Lamellibranchiata clams, bivalved shell. 

 Cephalopoda squids, nautilus. 



