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130 ZOOLOGICAL GEOGRAPHY. [part hi.
themselves on little mounds and gaze on intruders, is noticed by-
all travellers. On the left, in the foreground, is one of the
extraordinary pouched rats of America (Cfeomys hursarins).
These are burrowing animals, feeding on roots; and the mouth is,
as it were, double, the outer portion very wide and hairy, behind
which is the small inner mouth. Its use may be to keep out the
earth from the mouth while the .animal is gnawing roots.
A mouth so constructed is found in no other animals but in
these North American rats. In the distance is a herd of
bisons {Bison americanus), the typical beast of the prairies.
Birds.—This sub-region has many peculiar forms of birds,
both residents, and migrants' from the south or north. Among
the peculiar resident species we may probably reckon a dipper,
(Cinclus) ; Salpindes, one of the wrens ; Poospiza, Calamospiza,
genera of finches; Picicorviis, Gymnoldtta, genera of the crow
family; Centrocercus and Pedioccetes, genera of grouse. As
winter migrants from the north it has LeucosticU and Pledro-
jphanes, genera of finches ; Perisoreus, a genus of the crow
family ; Picoides, the Arctic woodpecker ; and Lagopus, ptar-
migan. Its summer migrants, many of which may be resident
in the warmer districts, are more numerous. Such are, Oreos-
coptes, a genus of thrushes ; Campylorhynchus and Cathcvpes,
wrens ; Paroides, one of the tits ; Phcenopepla, allied to the
waxwing ; Erribernagra and Spermophila, genera of finches
Pyrocephalus, one of the tyrant shrikes ;
Callipepla and Cyrtonyx,
American partridges. Besides these, the more widely spread
genera, Harporhynchus, Lopliophanes, Carpodacus, Spizella, and
Gyanocitta, are characteristic of the central district, and two genera
of humming-birds
—
Atthis and Selasphorus—only occur here and
in California. Prof. Baird notes 40 genera of birds which are re-
presented by distinct allied species in the western, central, and
eastern divisions of the United States, corresponding to our
sub-regions.
It is a curious fact that the birds of this sub-region should
oxtend across the Gulf of California, and that Cape St. Lucas,
at the southern extremity of the peninsula, should be decidedly
more " Central " than " Californian " in its ornithology. Prof.
;