PREFATORY NOTE. 



The following notes on Crayfishes were made during an examination of 

 all the Crayfishes that have been received at the United States National Museum 

 and the Museum of Comparative Zoology since my last paper on these animals 

 was published in tlie Proceedings of the United States National Museum, Feb. 7, 

 1898, 20, p. 643-694, pi. 62-70. I am deeply indebted to the authorities of the 

 National Museum for sending to me the vast amount of material that has come 

 to Washington since my last review of the subject. I am also indebted to Mr. 

 W. P. Hay of Washington, Prof. S. E. Meek of the Field Museum of Natural 

 History, Chicago, 111., and Dr. A. E. Ortmann of the Carnegie Museum, Pitts- 

 burgh, Pa., for the loan of specimens. 



