i894. NEARCTIC OR SONORAN ? 57 



While admitting the great convenience of the Six Regions of 

 Dr. Sclater, it seems that the above-mentioned facts yield strong 

 support to the suggested revision of their boundaries. The addition 

 of the Boreal tract of North America to the Palaearctic Region will 

 render that great division of the earth's surface more natural than it 

 is at present, as the elements of the Northern American fauna are 

 seen to be chiefly Palaearctic in their affinities. To this great realm 

 Dr. Heilprin's name of Holarctic might be applied, or it might 

 perhaps be better known as the Great Northern Region. I need 

 hardly remind students of Geographical Distribution that such a 

 region was mapped thirty years ago in Murray's work'^ on Mammalian 

 Distribution. The Sonoran Region will, indeed, be somewhat less rich 

 than the old Nearctic in peculiar forms of life, but it will retain its most 

 distinctive characteristics and comprise a more natural fauna than did 

 the larger tract. The objection to the new arrangement, which I 

 cannot but feel to be considerable, is that, even outside the broad 

 transition tract of Dr. Merriam, overlapping of the two faunas 

 takes place, especially in the extension of peculiarly American 

 birds to the Arctic Ocean. Still, I cannot think that this overlapping 

 should deter us from adopting the more natural division. No 

 zoological region can be mapped with the hard and fast line of a 

 political frontier, and the zoologist must always think more of faunas 

 than of geographical boundaries. That two distinct faunas exist in 

 North America seems abundantly clear, although the nature of the 

 country has allowed considerable overlapping. It is well to 

 remember that in parts of the Mediterranean sub-region there is a 

 decided Ethiopian colouring to the fauna, in spite of the barrier of the 

 Sahara. Were Africa without that barrier to the northern spread of 

 Ethiopian forms, we should have such a mingling of two faunas as 

 would necessitate a wide transition tract on our own side of the 

 Atlantic. 



Geo. H. Carpenter. 



I'^The "Geographical Distribution of Mammals." By A. Murray. London, 

 1866. 



