INTRODUCTION 



Smithsonian Institution, 

 Washington, D. C, January 1, 1876. 



Sir: A memoir on the Muridce 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 Muridce 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 Murida 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 suite 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 



