82 PEARLS AND PEARLING 



of the Mississippi River are usually white, with a pearly 

 white nacre, and are excellent material for making but- 

 tons and knife handles. They are not always valuable, 

 however, for in some rivers in Tennessee these are pink 

 and in some Arkansas streams they are purple, and in 

 some of the rivers in Texas they are a deep purple color. 

 The "buck-horns" do not usually grow in colonies, but 

 are distributed among other shells. Some very valuable 

 pearls are occasionally found in them. 



The Quadrula lachrymosa, or "stranger," or "maple- 

 leaf," is illustrated in Fig 17, about one-third natural 

 size. This is very scarce in some rivers, and is not usual- 

 ly abundant in any of the rivers. It is similar to the 

 "three-ridge." It is used in the manufacture of buttons, 

 but the irregular surface of this shell slightly reduces its 

 value as button material. These also produce nice pearls. 



The Plagiola securis, or "butterfly," is a very pretty 

 shell, with pearly white nacre. This shell is shown in 

 Fig. 18, one-third natural size. A pair of these shells 

 open, and when viewed from the outside, have the ap- 

 pearance of a butterfly, and for this reason, their com- 

 mon name is used very appropriately. 



This variety is one of the most valuable ones for mak- 

 ing buttons. In some rivers the "butterfly" attains a 

 large size. It is not abundant in most rivers, although 

 there are some places where it is quite common. Some 

 very lustrous and valuable pearls are occasionally found 

 in this variety. 



The Lampsilis ventricosus, or "pocketbook," is shown 

 in Fig. 19, about one-third natural size. This variety 



