MAMMALS OF THE MEXICAN BOUNDARY. 71 



each possesses a wholly distinct flora and fauna gives them biological 

 importance out of proportion l<> their extent. Before proceeding to 

 a discussion of the composition of their fauna] ard floral elements, 

 it will be well to take up the subject of subdivisions of the primary 

 regions, which may he classified ;i> below : 



Primary regions. Secondary life zones. 



i 1. Arctic or Arctic-Alpine /one. 



1. Boreal Region ■< 2. HudsOnian /one. 



( .*'.. Canadian Zone. 



i t. Transition /one. 



l'. Austral Region J 5. Upper Austral Zone. 



/ 6. Lower Austral Zone. 



.".. Tropical Region __7. Tropical Areas. 



The Boreal and Austral regions are each naturally divided into 

 three subsidiary transcontinental zones, their boundaries being irregu- 

 larly sinuous in conformity to the governing isotherms, just as in the 

 case of the primary region.-." 



"A knowledge of the life areas, and of the so-called faunas and floras is 

 indispensable to the student of biology whose held has an uneven surface, 

 or occupies a large extent of country. The time spent in mastering the life 

 zones of his held will save the expenditure of a vast amount of speculative 

 energy — in wondering, for instance, why it is that he rinds as many forms of a 

 certain group at a certain point on the Pacific slope of the Sierra Nevada of 

 California as are found between those mountains and the Atlantic, the answer to 

 which is that the same life areas fall within each held, one in a belt only 10 

 miles in width, the other more than 2nd times as wide. The Historical 

 Synopsis of Faunal and Floral Divisions Proposed for North America, by 

 Dr. C. Hart Merriam (Proc. Biol. Soc. Wash., VIII. pp. 6 to 20), L'ives the 

 principal authorities on distribution and life areas in America: while, for work- 

 ing purposes, the following will suffice: 



By Dr. J. A. Allen: On the Mammals and Winter Birds of East Florida, 

 with * * * a Sketch of the Bird-Faunae of Eastern North America. Bull. 

 Mus. Comp. Zoo].. II. No. :;. April, 1871. 



The Geographical Distribution of North American Mammals. Hull. Amer. 

 Mus. Nat. Hist.. XIV, Art. XIV, December 29, 1892, pp. 199 to 243, with 4 

 colored maps. 



By Dr. ('. Hart Merriam: Results of a Biological Survey of the San Francisco 

 Mountain Region and Desert of the Little Colorado. Arizona. North American 

 Fauna. No. ::. September 11. 1890, pp. L36+vii, with numerous colored maps and 

 charts. 



The Geographic Distribution of Life in North America, with Special Refer- 

 ence to the Mammalia. Proc. Biol. Soc. Wash.. VII, pp. 1 to 64, with colored 

 map. 



Laws of Temperature Control of the Geographic Distribution of Terrestrial 

 Animals and Plants. The National Geographic Magazine, VI, December 29, 1894, 

 pp. L'L".t to 238, with four colored maps. 



The Geographic Distribution of Animals and Plants in North America. 

 Yearbook of the I'. S. Department of Agriculture for 1894, pp. 203 to 211, with 

 map showing life zones of the United states. 



