LETTER TO THE SECRETARY. 



Office of the United States Geological and 



Geographical Survey of the Territories, 



Washington, D. C, May 31, 1877. 



Sir: I have the honor to transmit herewith, for your approval and for 

 publication, the Eleventh Volume of Final Reports of the Survey under my 

 charge. 



This Report consists of a series of Monographs of the several North 

 American Families of Rodentia, prepared by Dr. Elliott Coues, of the United 

 States Army, now Secretary of the Survey, and Prof. J. A. Allen, of Cam- 

 bridge, Mass., one of the special collaborators of the Survey — gentlemen whose 

 names guarantee the high scientific character of the work here accomplished. 



It has become the settled policy of the Survey to devote a reasonable 

 and proper share of attention to the Zoology of the Territories explored, as a 

 subject entirely germane to the main purposes for which the Survey was 

 established, and as one having an important bearing upon the agricultural 

 and other industrial resources of the West. To this end, zoologists have, 

 from time to time, been attached to the various surveying parties, and have 

 been instructed to avail themselves of every opportunity to acquire informa- 

 tion respecting the Fauna of the regions visited, as well as to make collections 

 of specimens illustrating all branches of Zoology. The material thus secured 

 has been deposited in the National Museum, where it now remains. 



The present series of Monographs is based primarily upon the collections 

 furnished by the Survey; and a glance at the "Lists of specimens examined" 

 which the authors have given in this volume will show the extent of the 

 material thus contributed. Through the liberal policy pursued by the author- 

 ities of the National Museum and of the Museum of Comparative Zoology of 

 Cambridge, the authors have been enabled to avail themselves also of the 



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