LETTER OF TRANSMITTAL. 



U. S. Department of Agricultube, 



Bureau of Biological Survey, 

 WasMngtorij D, C, November 16, 1915. 

 Sir: I have the honor to transmit herewith for publication as 

 North American Fauna No. 40, a systematic account of the prairie- 

 dogs of North America, by Mr. N. HolUster, Assistant Curator of 

 Mammals, of the United States National Museum. This review of 

 the group is based largely upon material in the collection of the 

 Biological Survey. Prairie-dogs are distributed over a large part of 

 the Great Plains and Rocky Mountain regions. Their colonies often 

 number thousands of individuals, and their destruction of grasses 

 and other forage plants makes them of considerable economic im- 

 portance. Drastic measures are frequently necessary to prevent 

 their destroying crops of grain and hay. The Biological Survey is 

 engaged in exterminating these rodents in national forests and on 

 the pubhc domain. The definite information in this report in regard 

 to the several species and their distribution, as indicated by maps, 

 will materially aid in efforts, National or State, to control or exter- 

 minate them. 



Respectfully, 



Henry W. Henshaw, 

 Chief, Biological Survey, 



Hon. David F. Houston, 



Secretary of Agriculture. 



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