86 PEARLS AND PEARLING 



about the same value as the "pig-toe" shells. Small 

 pearls are some times found in the "monkey faces." 



The Unio gibbosus, or "lady-finger," or "spectacle- 

 case," is shown in Fig. 23, one-third natural size. It is 

 usually an unsalable shell on account of its color. It is 

 not often found with white nacre, but in such cases it is 

 usually of commercial value. They are very widely dis- 

 tributed and are found in both lakes and rivers, and are 

 especially plentiful in the headwaters of the rivers. They 

 are some times infected with the marginal cyst distomid, 

 and occasionally contain slugs, baroques and pearls. 



There are some other shells which occasionally are of 

 commercial value, but the ones illustrated and described 

 are practically all of the valuable fresh-water shells of 

 the United States. 



If the present styles should change, and a demand be 

 created for colored buttons, then the colored shells would 

 become valuable. It is not likely, however, that there will 

 be a change from the present styles of buttons. 



Amateur pearl hunters should remember that while 

 some varieties of shells do not have a commercial value, 

 all varieties of shells occasionally yield pearls. 



