NO. 1101. PROCEEDINGS OF THE NATIONAL MUSEUM. 9 



place, while Dr. Alleii views the eiiects of moisture as of a higher 

 importance, in some cases surpassing those of temperature. A brief 

 quotation from these two authors will reveal their respective attitudes. 

 In this latest jiaper Dr. Merriam remarks : 



Humidity and other secondary causes determine tlie presence or absence of partic- 

 ular species in particular localities within their appropriate zones, but temperature 

 predetermines the possibilities of distribution; it fixes the limits beyond which 

 species can not pass, it defines broad transcontinental belts within which certain 

 forms may thrive if other conditions permit, but outside of which they can not 

 exist, be the other conditions never so favorable. ' 



Dr. Allen remarks: 



Of strictly climatic iulluences, temperature is by far the most important, although 

 moisture plays an influential part. 



Moisture alone may determine tht^ character of life over extensive regions, regard- 

 less of temperature, which, under ordinary conditions, is the ascendant controlling 

 influence. - 



The terminology employed by Dr Allen is the more precise, and as 

 he pays more attention to moisture in his faunal map than does Dr. 

 Merriam, his system will receive the larger share of attention in the 

 present connection. 



It will be impossible to describe here in detail the regions laid down 

 by Dr. Allen, and the reader is referred to his original maps and to 

 those of Dr. Merriam. 



The territory of the United States, with the exception of the princi- 

 pal mountain ranges and the addition of the Mexican i^lateau, is j)rac- 

 tically coextensive with the faunal area called by Dr. Allen the "Warm 

 temperate subregiou." This territory is divided by a north and south 

 line, rniiniiig a little east of the one hundredth meridian, into two 

 "provinces" — the "humid" of the east and the "arid" of the west. 

 The dividing line between these two provinces is a natural one, and one 

 of much importance in connection with the group of animals we are 

 now studying. As Dr. Allen remarks in regard to his two provinces, 

 "they are not separated by isothermal lines, trending in an east and 

 west direction, but by a north and south line, determined by the amount 

 of rainfall. Thus, in the present instance, temperature as a climatic 

 intinence governing the distribution of animals and plants is subordi- 

 nated to the other climatic intluence, humidity, which varies greatly in 

 these two contrasting regions, in consequence of the long continued 

 peculiar physiographic and geographic conditions of the two regicms."^ 



Xorth of the warm temperate region extends the cold temperate, 

 stretching away northward to the limit of trees and southward along the 

 principal mountain chains of the United States ; also including the larger 

 part of Maine, Xew Hampshire, and Vermont, together with northern 

 Michigan, Wisconsin, Minnesota, and Dakota. 



iNat. Geog. Mag., VI, p. 238. 



2 Bull. Amer. Mus. Nat. Hist., IV, pp. \m, 200. 



3 Bull. Amer. Mus. Nat. Hist., IV, p. 230. 



