INTRODUCTION 



superficial characters given in this field book are not exclusively 

 diagnostic, but under the circumstances they must suffice, and 

 they will be found serviceable when taken in conjunction with 

 the known geographical range. Apart from making the book 

 too technical, the inclusion of skull characters for every form 

 would require a work of not one but several volumes. Upon 

 rare occasions, when a species has been so dependent upon 

 cranial characters that superficial characters were too obvi- 

 ously inadequate, it has become necessary to employ these 

 internal data. Many lovers of mammals see their specimens 

 in the flesh and a description of external features is what is 

 wanted. The more technical reader is referred to the con- 

 stantly cited revisions which are given in the text and most of 

 which are to be found in well-stocked libraries throughout 

 the country. For anyone wishing to go beyond the handbook 

 stage in his study of mammals, these revisions are not only 

 helpful but an absolute essential. 



Standard List of Species and Subspecies 



Descriptions of new species and subspecies are continually 

 being published. Since work on this field book began,- quite 

 a few such papers have appeared and it has become necessary 

 to revise manuscript to include changes. For the purposes 

 of the field book it has seemed advisable to draw a dividing 

 line somewhere; otherwise the manuscript would have been 

 unduly delayed by going back over copy to bring it up to 

 date. Miller's List of North American Recent Mammals offered 

 a satisfactory solution for this problem and the 1923 edition 

 was chosen as the basis for this field book. However, I have 

 used all subsequent papers for data other than new names and 

 have attempted to consult every source up to the time of going 

 to press; also the new names and changes of nomenclature in 

 important revisions since 1923 have been used. 



Sources of Data Used 



Wherever possible, I have compiled the data for the synopses 

 from the different revisions or monographs which have been 

 written on North American mammals. These monographs 

 are the published results of years of study and are based upon 



