14 PEARLS AND PEARLING 



eral term and includes all fresh-water mussels, which are 

 distributed over the entire globe and are found through- 

 out the streams and lakes of all continents, as well as 

 all the larger islands and some smaller islands. 



The Unio Margaritifera is very common in North 

 America and especially in the United States. These 

 have a large variety of species also, and there are known 

 to be living in North America nearly 600 different species 

 of them. Most of these are found in the Mississippi 

 drainage area and other streams emptying into the Gulf 

 of Mexico from the north. 



Many Mollusks are found in the streams emptying 

 into the Great Lakes and St. Lawrence River. Many are 

 also found in rivers that flow into the Atlantic Ocean. 

 The rivers emptying into the Pacific Ocean do not con- 

 tain many Mollusks and are not known as pearl streams. 



Most of the Fresh- Water Pearls come from the United 

 States. In this book we shall give our attention almost 

 entirely to subjects relating to Fresh-Water Pearls. Most 

 of the Unionidae are Margaritiferous, or pearl bearing, 

 although many of these varieties are uncommon and so 

 we get most of our pearls from the varieties that are 

 most abundant. Although these are very plentiful, the 

 pearls are very scarce and one has no assurance of find- 

 ing a pearl in a given number of shells. In some locali- 

 ties there are more pearls than other places; yet they 

 are scarce, everywhere. This is not a bad feature after 

 all as the scarcity of the pearls increases the value of the 

 few that are found. 



In Europe the Fresh- Water Pearls have held an im- 



