VARIOUS KINDS OF UNIO SHELLS 75 



many rivers, but is most abundant in the Illinois River. 

 Near Peoria, these grow to be very large. Some of them 

 are eight inches long and five inches wide. At Flor- 

 ence and Pearl, Illinois, they are about five or six inches 

 long, while near Grafton, Illinois, they are very much 

 smaller. 



In the upper part of the Illinois River these shells are 

 often stained or spotted, but in the lower part of the 

 river they are not so badly injured, and are flatter and 

 have a better luster. 



In the Cumberland River, in Kentucky and Tennessee, 

 the "washboards" are common, but are usually badly 

 stained and are sold there as a second grade. 



These are also found in Wabash, Mississippi and many 

 other rivers. The "washboards" yield many of our finest 

 pearls. Those which are found in the washboards are 

 often very large and therefore very valuable, if they are 

 perfect or nearly so. 



The most valuable fresh-water shell for the manufac- 

 ture of buttons is The Quadrula cbena, or "niggerhead." 

 This shell is shown in Fig. 9 in about one-fourth natural 

 size. This shell is very common in most rivers, and 

 especially in the Mississippi River. It was once plentiful 

 in the Illinois River, but is scarce there now. It is a fine 

 shell with a lustrous white nacre. The mussel delights 

 in deep waters and is not usually found near the head- 

 waters of rivers. It is very important to perpetuate the 

 supply of these mussels, yet the means of propagating 

 them have not been found. Pearls which are found in 

 "niggerheads" are of fine luster and good value. 



