22 INTRODUCTION. 
Clamatores or non-singers ;!° likewise the Turdide consists of 
the Turdine, or typical thrushes, who have a “‘ booted” tarsus, 
and the Mimine, or mocking-thrushes, who do not possess this 
feature. Combinations of less important distinctions in struct- 
ural detail characterize the genera; and therefore birds be- 
longing to the same genus have exactly the same structure. 
The difference between species is marked by coloration, and 
often size. To illustrate the foregoing, take as a subject the 
common Song Sparrow. He belongs to the Jnsessorian group, 
the order of Passeres, and the suborder Oscines. His family 
is that of the Fringillide, or finches, and his genus Melospiza. 
His specific name is melodia, but there is also a variety, M. 
fallax. ‘ Extremely similar; wings and tails slightly longer ; 
paler, grayer; the streaks not so obviously blackish in the 
centre. Whole of the Rocky Mountains and Great Basin; 
scarcely distinguishable.” (Coues.) 
§ W. The classification of birds (or other objects in nature) 
necessarily entails certain absurdities, being more or less artifi- 
cial. The method of modern classification is that of descend- 
ing from the higher to the lower groups, but sequence is too 
often insisted on among groups, which diverge (so to speak) 
from a common centre. The division of families, genera, etc., 
is more or less arbitrary, a certain degree of difference being 
necessary to separate them, whereas minor (or fractional) 
differences cause intermediate groups. Let X represent the 
degree of dissimilarity between two genera; then x represents 
the difference between two subgenera (of the same genus) ; 
1+ x between subfamilies, 2X between families, 2 -+- x be- 
16 A rather technical distinction. 
