XxXvVI PREFACE. 
a general and popular interest far greater than can attach to the present account of mere zoologi- 
cal and technical details. ' 
The large size of this report on the mammals collected by the railroad parties is owing to 
several causes. In the first place, the amount of new or little known material obtained was 
extraordinarily great, The summary of the species at the beginning of the systematic list 
hereafter presented, will show that very many entirely undescribed animals were procured, and 
that of a.large number of others, previously little known, the specimens were sufficient to 
furnish many new and interesting details of characters, both external and internal. 
As, too, the object in calling for complete reports from the several parties was not merely to show 
the actual results of the several expeditions, but likwise to ascertain the general character of 
the western territories, I heve not hesitated to include in this work all such materials derived 
from officers stationed at military posts, and other persons elsewhere in the west, as fell under 
my notice. 
In view of the large amount of new or little known species at hand, in the preparation of the 
present report, sometimes embracing entire genera and even families, it soon became evident 
that none of the published descriptions of the old and standard species were sufficiently minute 
and detailed to furnish the necessary means of comparison. With the discovery of forms very 
closely allied to or intermediate between those already known, the descriptions of the latter on 
record did not show sufficiently in what the differences consisted. It became necessary, therefore, 
to re-describe, as far as they could be procured, all such species, which, in fact, proved finally to be 
nearly all previously known. The present monograph of American mammals has, in the end, 
grown out of the necessities referred to. 
It will be sufficiently evident that, without the extraordinarily rich and full collection of North 
American mammals belonging to the Smithsonian Institution, the monographs and comparisons of 
species, in the present report, could not have been prepared. Independently of the specimens 
brought in by the Pacific Railroad surveying parties, the series in its museum, from other sources, 
was found to embrace nearly all the previously known species, and many entirely new ones. 
I have also made free use of the collections and library of the Philadelphia Academy of 
Natural Sciences, for which every facility has been furnished in its hall. The examination of 
the specimens collected by Townsend, and described by Dr. Bachman, has contributed to settle 
some quite doubtful points, while in some rare or very costly works of its unequalled natural 
history library I have been enabled to verify many references which would otherwise have 
remained uncertain. 
I regret not to have been able to examine any of the types of the new species of Audubon 
and Bachman, as presented by the latter gentleman to the Charleston museum. The rules of 
that establishment do not permit specimens to leave its hall, and it was not possible to visit it 
during the preparation of this report. 
I have endeavored to make all acknowledgments of aid from systematic writers in the body 
of the report, although it may be well to mention here that much use has been made throughout 
of the works and articles of Wagner, Waterhouse, Gray, Brandt, Burmeister, Keyserling and 
Blasius, Giebel, Richardson, Agassiz, Engelmann, and others, as enumerated in the synonymy 
and list of authorities. To the 1abors of Messrs. Audubon and Bachman, however, either singly 
or collectively, are acknowledgments especially due for whatever facilities may have previously 
existed for the preparation of a report on American mammals. The necessity or propriety of such 
a report is only to be found in the fact that, when the crowning work of these gentlemen, ‘‘The 
