iv PREFACE TO THE SECOND EDITION. 
For those who are already familiar with the use of analytical keys in 
works on natural history such instructions would of course be quite 
superfluous; but as some who possess the book may not have had pre- 
vious experience with such “keys,” the following directions are given 
for their benefit : 
In the first place, it may be stated that the principle upon which 
the keys are constructed is that of dichotomous antithesis. That is, 
each character tested must conform to one or another phrase, there 
being only one alternative. Therefore, if the characters mentioned 
after a do not fit the bird in hand, everything following must be 
ignored until a? is reached. Having found that the bird belongs to a! 
or a’, as the case may be, then the immediately following &' is to be 
tested, and so on until the ultimate division is reached and the bird 
identified. 
The method may be more fully explained by selecting some par- 
ticular species for identification; and for better illustration we will 
select one belonging to a mainly extralimital family, and therefore less 
familiar to the student of North American birds. The bird is from 
the State of Tamaulipas, Mexico, somewhat resembles a medium-sized, 
thick-set flycatcher, but is evidently not a member of the Tyrannide. 
We will suppose that the person is a beginner, and does not,even know 
the Order to which the bird belongs. In this case it is necessary to 
commence with the “Key to the Higher Groups,” on page 1, which 
begins as follows: “a'. Hind toe connected by web or membrane with 
the inner toe.” 
The bird in hand has the hind toe quite free from the inner toe; 
therefore it must be sought for under “a. Hind toe, if present, not 
connected with inner toe,” in regard to which character it agrees. 
Then 4 must be tested. “d” says, “Nostrils tubular and feet 
webbed.” It has not tubular nostrils nor webbed feet, and therefore 
it must belong to 0’, which says, “Nostrils not tubular, or else feet 
not webbed,” both of which alternatives fit the bird in question. Pro- 
ceeding to “c'. Cutting-edges of bill more or less distinctly fringed 
