PREFACE. 
The present report is intended to embrace a systematic account of all the species of North 
American mammals collected or observed by the different parties organized under the direction of 
the War Department for ascertaining the best route for a railroad from the Mississippi river to 
the Pacific ocean. It was originally proposed to furnish a separate report in detail, on the 
collections of each party, but a consideration of the fact that, with scarcely an exception, almost 
every species was found on two or more lines of survey, and thus not peculiar to any one expe¬ 
dition, led to an abandonment of the first intention. It was considered to be worse than useless 
to repeat the same descriptions and details over and over again, while, at the same time, under 
the circumstances, it would have been difficult to say in what report any particular article could be 
best placed. As, too, the interest of North American zoology depends not merely on the character 
of the species, but also on their generic and family affinities, as well as on their relationships to lati¬ 
tude and longitude, climate, soil, elevation, &c., it would have been impossible to do justice to the 
subject by cutting up the report into several isolated portions without any special Connexion as 
parts of a systematic whole. 
At the same time, however, as it was desirable to present a picture of the zoological character 
of the several routes, as well as to show what each party accomplished, and as many very im¬ 
portant notes of habits and local peculiarities were made by tbe naturalists of the different lines, 
it would have been clearly an act of injustice to these gentlemen as well as to their chief officers 
to merge all their results into one common report. For these and other reasons it was finally 
determined that there should be prepared one general report on the entire collections of the 
railroad surveys, to consist solely of the technical description of the families, genera and species, 
and of such remarks as might be necessary to show their place in the systems, each species to be 
preceded by its synonymy, and followed by an enumeration of all the specimens collected, so 
arranged in tables as to show their geographical distribution. 
In addition to this general report, however, special reports by the naturalists of each line were 
also to be prepared and published, to embrace the systematic and vernacular names of their 
species, with a list of the specimens collected. To these special reports were to be confined all 
the biographies of the animals seen, all notices of their habits, peculiarities, and distribution, as 
observed and recorded during the route. In order, that there might be no misconcep¬ 
tion of the species referred to, it was concluded to give a short diagnosis of each with a 
reference to the page of the general report where the purely zoological details might be found 
more at length. 
The present report, therefore, is the first of the series of general reports referred to, to be fol¬ 
lowed as soon as practicable by the remainder of the Yertebrata. The special reports on the 
zoology of each line of survey will be found in. connexion with the other reports belonging to 
their respective parties, and, in their full notices of the life of our western animals, possess 
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