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■METAZOAN PHYLA 



product was $88,000. In the past Ohio, Illinois, and Iowa have furnished 

 our chief supply of fresh-water mussels, but the supply of shells is rapidly 

 diminishing, and the future prosperity of the industry will rest on the 



Fig. 143. — Mollusca of considerable economic importance. A, shell of the edible 

 oyster, Ostrea virginiana. B, shell of a fresh-water clam, Lampsilis sp., from which pearl 

 buttons have been cut. C, shell of a snail from which many cameos are made by cutting 

 the design in one layer and allowing it to remain affixed to the underlying layer of a different 

 color. D, shell of a Japanese oyster, Meleagrina sp., showing a "cultured pearl." 



success of experiments in artificial propagation now being conducted. 

 Fresh- water mussel shells purchased by manufacturing plants in 1936 

 amounted to 58,484,000 pounds. These were bought from 18 states in 



