ALLEN ON GEOGRAPHICAL DISTRIBUTION OF MAMMALS. 335 



Die Yergieichung der Thierwelt beider Contiuente zeigt namlich, dass 

 die circumpolare Fauna in beiden dieselbe ist, dass in der Hocbgebirgs- 

 fauna nocb bedeutendeUebereinstimmung herrscht, dass in der iibrigen 

 palao- und neoborealen Tbierbevolkeruug sowohl identische Arten als 

 gemeinsam eigenthiimliche Gattungen sich linden, endlich dass selbst 

 jene Typen, welche jedem Continente eigentbiimlicb sind, doch eine ge- 

 wisse Uebereinstimmung hinsichtlich des Oharakters der Fauna an sich 

 tragen, so dass sie einander naher stehen als Angehorigen anderer Ee- 

 gionen. In der neuen Welt ist eine Modification der Fauna auch durch 

 das Eindringen neotropischer Formen gegeben."* He further also calls 

 attention to the similarity of life which prevailed throughout this cir- 

 cumpolar region during the Quaternary period. 



It is unnecessary to cite further, from the abundant material at hand, 

 the opinions of specialists in reference to the propriety of recognizing a 

 North Temperate Eealm, as distinguished from the tropical regions of 

 the globe, and in contradistinction from a north and south line of divi- 

 sion of the North Temperate Zone into two primary ("Palsearctic" and 

 "Nearctic") regions. 



The chief differences between Dr. Sclater's division of the northern 

 hemisphere and the present consist in setting off at the northward an 

 Arctic Realm, the union of the so-called Nearctic and Palsearctic Regions 

 into one circumpolar belt, and in the adoption for the same of a more 

 northern limit than that proposed as the boundary of the two above- 

 named Sclaterian regions. As will be shown later, the subdivisions of 

 the North Temperate Realm or {'■'•Arctogcea'''') as here defined agree in 

 the main with the "subregions" of Sclater and Wallace. The more 

 northward location of the southern boundary of the North Temperate 

 Realm in North America results in the elimination of several character- 

 istic tropical types, which extend a short way only into Dr. Sclater's 

 Nearctic and Palsearctic Regions, and which, when considered as mem- 

 bers of these regions, give false or misleading results when the two re- 

 gions are contrasted on a numerical basis, grounded on the proportion 

 of peculiar types, — numerous forms being thus reckoned as components 

 of the Nearctic and Pali3earctic regions which are properly tropical. 



In North America, the division between characteristic temperate and 

 tropical forms of life approximately coincides with the isotherm of 68^ 

 F,, or somewhere between 68° and 70"^ F. This line begins on the At- 

 lantic coast a little below the northern boundary of Florida, and runs 

 thence westward along the Gulf coast to Southern Texas, and thence 

 farther westward to the Pacific, not far from the international bound- 

 ary between the United States and Mexico, swerving more or less north- 

 ward or southward in accordance with the configuration and elevation 

 of the land-surface. It thus leaves the greater part of the peninsula of 

 Florida within the American Tropical Realm, to which the fauna of its 



* Verhaadl. der K. K. Zool.-Bot. Gesell. in Wien, Bd. xxv, 1876, pp. 50, 51; see also 

 p. G2. 



