INTRODUCTION. 
SMITHSONIAN INSTITUTION, 
Washington, D. U., January 1, 1876. 
Str: A memoir on the J/uride is herewith transmitted as one of the 
series of ‘Monographs of North American Rodentia” in course of prepara- 
tion by Mr. J. A. Allen and myself, for publication by the Survey under your 
charge. : 
It is supposed that the series will consist of ten memoirs, each treating 
of a single family. Those to follow will probably occupy less space than the 
present one, the Murzde@ being much ‘the largest family of American Rodents. 
The successive articles will be entirely independent of each other, and may 
be issued separately if desired. As the complete series will doubtless make 
a volume of convenient size, it is suggested that the set of monographs will 
be available for one of the quarto “Reports” of original investigations, now 
publishing by the Survey. 
_ Circumstances having been unfavorable to the joint authorship which 
both Mr. Allen and myself cordially desired, it has been decided to divide the 
work in another way, each taking up certain families agreed upon. Neither 
author, therefore, is to be held responsible for the work of the other. Several 
additional articles are in an advanced state of preparation; and will be 
presented in the order of their completion, without reference to the natural 
sequence of the several groups. 
The present memoir, prepared in 1872, is based upon the material con- 
tained in the National Museum at Washington, the whole of its unparalleled 
collection of American Murid@ having been placed by the Secretary of the 
Smithsonian Institution in my hands for elaboration. The specimens 
collected by yourself, or by the Survey under your direction, will be 
found duly accounted for in the tabular lists. The swe consists of 
several thousand specimens, among them many of the types of American 
writers, and represents, I have no doubt, much more material than has hith- 
erto been made the basis of any monograph of a single group of mammals 
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