PREFATORY NOTE. 
Tue 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 Zoédlogy since my last paper on these animals 
was published in the Proceedings of the United States National Museum, Feb. 7, 
1898, 20, p. 643-694, pl. 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 1uy 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, Ill., and Dr. A. E. Ortmann of the Carnegie Museum, Pitts- 
burgh, Pa., for the loan of specimens. 
