IV. 



Nearctic or Sonoran ? 



DR. A. RUSSEL WALLACE'S article on the mammals and 

 birds of the Palaearctic and Nearctic Regions in last month's 

 issue of Natural Science/ will have been read with the greatest 

 interest by all students of the geographical distribution of animals. 

 The tables of genera common to the two regions, or pecuHar to one 

 of them, seem to tell strongly in favour of retaining those convenient 

 divisions of Dr. Sclater, which, by means of Dr. Wallace's own classi- 

 cal work on distribution, have become household words among 

 naturalists all over the world. Yet I venture to believe that the facts 

 may be so read as to support another view of the zoological regions 

 of the ex-tropical continents. 



The only alternative to the retention of the Palaearctic and 

 Nearctic Regions of Sclater which Dr. Wallace mentions is their 

 union into a single Holarctic Realm, as suggested by Dr. Heilprin in 

 his work on the "Distribution of Animals. "^ But in a recent memoir 

 on North American mammals 3 (already referred to in Natural 

 Science^), Dr. C. Hart Merriam advocates a different and more 

 natural view. He would unite only the "Boreal" part of Sclater's 

 Nearctic Region with the Palaearctic, leaving the rest as a separate 

 region, to which he applies Professor Cope's term " Sonoran." This 

 Sonoran Region he considers no mere borderland between the 

 Northern and Neotropical realms, but a primary division charac- 

 terised by the presence of the most distinctive North American 

 mammals. 



The Boreal division of Dr. Merriam roughly agrees with the 

 Canadian sub-region of Dr. Wallace's " Geographical Distribution of 

 Animals." He maps it, however, as extending southward along the 

 three great mountain systems of North America — the Alleghanies, 

 Rockies, and Sierra Nevada, in parts as a continuous tract, elsewhere 

 in isolated patches, some of which reach as far south as Arizona, 

 California, and Carolina. As might be expected, however, there is 

 no decided line separating the northern and Sonoran regions ; a 



1 Vol. iv., p. 433. 2 London, 1887 (Int. Sci. Series). 



^ Proc. Biol Soc. Washington, vol. vii., 1892, p. i. 

 4 Vol. iii., p. 288. 



