280 LETTER OF TRANSMITTAL. 



A considerable number of the illustrations which accompany this 

 memoir have been drawn from specimens belonging to the United States 

 National Museum, by i>ermission of the Director. He has also per- 

 mitted the use of electrotypes of a portion of those illustrations which 

 were already engraved and in possession of the Smithsonian Institu- 

 tion. 



Eespectfully submitted. 



r. A. WHITE. 



Hon. J. W. Powell, 

 Director of the United States Geological Survey. 



