LETTER TO THE SECRETARY. 
OFFICE oF THE Unirep States GEOLOGICAL AND 
GEOGRAPHICAL SURVEY OF THE TERRITORIES, 
Washington, D. C., May 31, 1877. 
Str: 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 Zoélogy 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, zodlogists 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 Zodlogy. 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 Zodlogy of 
Cambridge, the authors have been enabled to avail themselves also of the 
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