5o PEARLS AND PEARLING 



hunting. Mussel beds are of various sizes. Some are 

 several miles long, while the length of others may not 

 be more than a few hundred yards. 



In young colonies, the mussels have plenty of room, 

 but in some of the old beds like those mentioned, the 

 mussels are so large that they occupy more space and in 

 many instances they are piled on top of each other, and 

 a small area will contain a large number of shells. As 

 many as sixty mussels of various sizes have been taken 

 from an area of one square foot of river bottom. 



There are over four hundred varieties of mussels in 

 the United States streams, but of this large number there 

 is only a small per cent, of them that are especially com- 

 mon in most of our rivers. Some thrive best in swift, 

 deep water and have heavy strong shells and large hinges 

 and teeth to protect against injury in accident. In this 

 class the quadrula group is prominent. 



Some mussels prefer to live in quiet, shallow water. 

 Their shells are not so heavy and they do not have heavy 

 hinges like the quadrula. Many of these are in the 

 Lampsilis group. 



Illustration No. 4 shows the interior of a Quadrula 

 heros, or "washboard." In the living mussel the shells 

 are joined together by a tough ligament which acts as a 

 spring in opening the shell when the adductor muscles are 

 cut. In front of the ligament on the outside of each 

 shell are elevated portions called the beaks or umboes, and 

 are the oldest part of the shell. The heavy, thick, 

 rounded e'nd of the shell is the front or anterior part, and 

 is always ahead when the mussel is moving. The thin 



