130 
ZOOLOGICAL GEOGRAPHY. 
[part III. 
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 ( G-eomys bur sarins). 
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 he 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, 
(i Ginclus ) ; Salpinctes , one of the wrens ; Poospiza , Calamospiza, 
genera of finches; Picicorvus, Gymnolcitta, genera of the crow 
family; Centrocercus and Pedioccetes, genera of grouse. As 
winter migrants from the north it has Zeucosticte and Pledro - 
phanes, genera of finches ; Perisnreus, a genus of the crow 
family; Picoides, the Arctic woodpecker; and Zagopus, 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 ; Campylorhynckus and Catherpes , 
wrens; Paroides, one of the tits; Phamopepla, allied to the 
waxwing; Embernagm and Spermophila , genera of finches; 
Pyrocephalus, one of the tyrant shrikes ; Callipepla and Cyrtonyx, 
American partridges. Besides these, the more widely spread 
genera, Harporhynchus, Lophophanes, Carpodacus, Spizella, , and 
Cyanocitta , 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 
extend 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. 
