CHAP. XVIII.] 
BIRDS. 
301 
3, the Oriental 1, the Ethiopian 1, and the other regions have 
no peculiar families. 
The distribution of the Passeres may be advantageously 
considered as divided into the five series of Turdoid, Tanaeroid, 
Sturnoid, Formicarioid, and Anomalous Passeres. The Turdoid 
Passeres, consisting of the first 23 families, are especially 
characteristic of the Old World, none being found exclusively 
in America, and only two or three being at all abundant there. 
The Tanagroid Passeres (Families 24-33) are very characteristic 
of the New World, five beiDg confined to it, and three others 
being quite as abundant there as in the Old World ; while there 
is not a single exclusively Old World family in the series, 
except the Drepanididse confined to the Sandwich Islands. 
The Sturnoid Passeres (Families 34-38) are all exclusively Old 
World, except that two larks inhabit parts of North America, 
and a few pipits South America. The Formicarioid Passeres 
(Families 39-48) are strikingly characteristic of the New World, 
to which seven of the families exclusively belong; the two 
Old World groups being small, and with a very restricted 
distribution. The Anomalous Passeres (Families 49-50) are 
confined to Australia. 
The most remarkable feature in the geographical distribution 
of the Passeres is the richness of the American continent, and 
the large development of characteristic types that occurs there. 
The fact that America possesses 14 altogether peculiar families, 
while no less than 23 Old- World families are entirely absent from 
it, plainly indicates, that, if this division does not represent the 
most ancient and radical separation of the land surface of the 
globe, it must still be one of very great antiquity, and have 
modified in a very marked way the distribution of all living 
things. Not less remarkable is the richness in specific forms 
of the 13 peculiar American families. These contain no less 
than 1,570 species, leaving only about 500 American species in 
the 13 other Passerine families represented in the New World. 
If we make a deduction for those Nearctic species which occur 
only north of Panama, we may estimate the truly Neotropical 
species of Passerine birds at 1,900, which is almost exactly 
