148 



MOLLUSCA 



propagation of mussels in the Mississippi basin. Valuable pearls 

 are secured from the adult mussels, and pearl buttons are manu- 

 factured from certain mussel shells. Their larvae (glochidia), 

 parasitic on the gills and fins of fishes, become dispersed widely. 

 (Figure 64, A and .S.) 



Fig. 64//. Unto gibbosus Barnes. (After Simpson, U. S. B. F. Bull., 1898.) 



The sa/f water or edible mussel {Mytilus edulis), cultivated for 

 many years in France and England, has only recently come into 

 general use in the United States. Through the activities of the late 



Dr. I. A. Field,3 the 

 many mussel beds on 

 the Atlantic coast are 

 now being utilized. In 

 mid-summer, mussels 

 may sometimes become 

 poisonous. 



The " pearl-oyster " 

 (Meleagrina), which is 

 not a true oyster but a 

 mussel, is found in the 

 Fig, 645. Lampsilis luteolus La. Female. (After South Sea Islands, Ja- 

 Simpson, U. S. B. F. Bull., 1898.) pan, Ceylon, the East 



Indies and the West 

 Indies. Pearls are an accumulation of layers of " nacre " laid down 

 around foreign substances. (See page 157, Culture Pearls.) 



The softs helled clam {My a arenarid)^ sometimes called the long- 



^Field, I. A. 191 1. The food value of sea mussels. Bull. Bur. Fish., vol. 29. 



