PREFACE. vii 
well be questioned if the only wise or proper course to emphasize 
these slight variations is to bestow a name upon the specimen pos- 
sessing them. Much confusion has been created by the multiplicity 
of names that burden our nomenclature, and our difficulties are by 
no means brushed away when one is bestowed upon some specimen, 
any more than are these difficulties ignored if none is given; for 
names are often not only no panacea for scientific woes, but on the 
contrary are frequently the cause of much trouble and perplexity. 
They are useful for the recognition of specimens possessing indepen- 
dent distinctive characters, but if an example has none of these its 
appellation is of little assistance. It is the extreme to which the 
bestowal of names has been carried that is to be deprecated, not 
the announcement of differences observed, however slight, and 
against the former custom the Author has always protested, while 
advocating the latter. 
It is to be expected that countries like Mexico would contain a 
large number of animals that differ from each other in a greater or 
less degree; for that land probably possesses more varieties of climate 
within a certain number of miles square than almost any other known 
of an equal extent. The transition from a torrid to a temperate zone, 
and again to an alpine, is accomplished in a comparatively brief 
journey, and the several environments affect materially in certain 
ways the animals influenced by them. So in a small extent of 
country a number of forms allied to, but differentiated from each 
other would be expected to occur; but whether the extreme length 
to which the recognition of these variations has been carried by the 
bestowal of names is either wise or necessary, may well be doubted. 
The arrangement of the Orders and Families is the same as that 
in the ‘‘Synopsis’’; but names have in some instances been changed 
since that work was published, those heretofore employed having 
been ascertained to be either antedated by others, or previously used 
in this or some other branch of Zodlogy. Changes are continually 
occurring in Mammalian nomenclature, and it will probably be a 
long time before permanence in names is reached, as discoveries are 
being made that overturn some that are constantly employed and 
have become familiar by long use. But these changes will of neces- 
sity become less in time and a nomenclature that at least will approach 
stability may, in the distant future, be expected to be reached. By 
inserting the names of the described forms in this work the Author 
does not indorse their specific or subspecific value, and in all cases 
where an opinion is expressed, it will be found in a footnote on the 
page containing the form discussed. A critical review of all the 
species and races contained in this volume and their relations to 
