130 ZOOLOGICAL GEOGRAPHY. [PART in. 



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 bursarius). 

 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) ; Salpinctes, one of the wrens; Poospiza, Calamospiza, 

 genera of finches; Picicorvus, Gymnoldita, genera of the crow 

 family; Centrocercus and Pedif&fates, genera of grouse. As 

 winter migrants from the north it has Leucostide and Plectro- 

 phanes, 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 Catherpes, 

 wrens ; Paroides, one of the tits ; Phcenopepla, allied to the 

 waxwing ; Embernagra 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. 



