ADVEETISEMENT. 



This work is tlie twentieth of a series of papers intended to illustrate 

 the collections of natural history and ethnology belonging to the 

 United States, and constituting the National Museum, of which the 

 Smithsonian Institution was placed in charge by the act of Congress of 

 August 10, 1846. 



It has been prepared at the request of the Institution, and printed by 

 authority of the honorable Secretary of the Interior. 



SPENCEE F. BAIED, 

 Secretary of the Smitlisonian Institution. 

 Smithsonian Institution, 



Washington, May, 1880. 



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