70 ON THE GEOGRAPHY OF ANIMALS. 
caterpillar-catchers (Ceblepyring) : two species have 
been detected, in both of which the males differ mate- 
rially from the females.* Interesting, therefore, as is 
the ornithology of Mexico, in demonstrating the transi- 
tion from the zoological tribes of Northern America 
to those of the Southern, nature has not, as it were, 
paused on her route, and given animal forms to this 
region, which she has withheld from the adjoining. 
There is no distinction between the geographic groups of 
Mexico, and those of the countries to which it is united: 
the genera are common to both; the peculiarity con- 
sists in finding these genera intermixed in one and the 
same spot; and exhibited in the form of species, which 
appear, for the most part, restricted to the American 
isthmus. The following table of the genera of birds 
hitherto discovered in Mexico, will better illustrate 
our meaning. 
(98.) The genera of birds characteristic of South 
America, found in Mexico, but either unknown, or 
only represented by one species (*) in North America, 
are as follows : — 
Prionites 777. Motmot. Macrocercus Veil. Mackaws. 
Trogon L. Trogon. Xiphorhynchus Sw. Creepers, 
Harpya Cuv. Harpy Eagles. Crotophaga LZ. Ano-bird. 
Polyborus Ved. Carracara Eagles. | Tiaris Sw. Crestfinches. 
Cassicus D. Hangnest. Cynanthus Sw. Fork-tailed Hum- 
Tanagra Sw. True Tanagers. ing-Birds. 
Pyranga Vier. Red Tanagers. Lampornis Sw. Even.tailed Hum- 
Psittacus L. True Parrots. ming- Birds. 
* Psittacarus Sw. Parrakeets. 
(99.) The genera more peculiar to North America, 
found also in Mexico, but which, with few exceptions — 
(marked *), are unknown in South America, are the 
following : — 
Setophaga Sw. Fantailed Warblers. | Pipilo Viéei/. Groundfinch. 
Seiurus Sw. Wagtail Warblers. * Ammodramus Sw. Sandfinch. 
Sialia Sw. Blue Robins. Sturnella Véezd. Crescent Starling. 
Sylvicola Sw. Titmice Warblers. Colaptes Sw. Ground Woodpecker. 
Vermivora Sw. Worm - eating 
Warblers, 
(100.) To state the result in a more popular form, 
* See Zool. Illus. 2. pl. 62. 102. 
