322 BULLETIN UNITED STATES GEOLOGICAL SURVEY. 



subsistence. This is still more strikingly shown by a comparison of the 

 fauna of the middle portion of the so-called " Palsearctic Region v with 

 that of its southern border, at which point the truly tropical forms be- 

 gin to appear. The genera of a zone, say two degrees in width, at these 

 two points would be not only in large part different, but those of the 

 southern belt would be far more numerous. 



Genera of mammals of the warm-temperate portions of the eastern hemi- 

 sphere (between the isotherms of 36 and 68 to 70 F.), not occurring to 

 the northward of the 36th isotherm. 



*Macacus. \Moschus. Rhinoloplius. \Nectogalg. 



Felis. \Hydropotes. *Plecotus. Spalax. 



*Genetta. \Poephagus. *Synotus. Rhizomys. 



*Herpestes. *Addax. Scotophilus. ^Siphneus. 



* Hyaena. *Oryx. Miniopterus. Meriones. 



t Xyctereutes. Damalis. *Nyctinoraus. iCricetulus. 



t Lutronectes. ^Procapra. \Scaptochiru8. \Alactaga. 



\JEluru8. t Saiga. \Scaptonyx. *Gerbillus. 



*Equus. iPantholops. \Armsorex. *Dipus. 



tCaraelus. \Budorcas. iMygale. Muscardinus. 



\Dama. \Rupicapra. Urotrichus. Eliomys. 



^Elaphodus. Nemorhsedus. \Uropsilii8. *Hystrix. 



t Lophotragus. Capra. Crocidura. 



Summary. 



Total number 51 



Occurring in southern portions only 13 



Peculiar to the region, and generally restricted to a limited range 24 



Of rather wide range southward . 14 



A comparison of the families represented in different portions of the 

 northern hemisphere north of the isotherm of 70 F. brings into prom- 

 inence some of the points already stated, without the confusion of 

 detail incident to a comparison on the basis of genera, and gives also 

 a more convenient standard for the next stage of comparison, namely, a 

 -comparison of the fauna3 of the temperate zones with those of the tropical, 

 as well as with the fauna3 of the two great land-areas of the northern 

 hemisphere. Of thirty-three families of non-pelagicmammals found north 

 of about the isotherm of 70 F. (68 to 70), thirteen have a nearly cos- 

 mopolitan distribution, and six others are common to both the Old 

 World and the New, leaving fourteen, or about one-third, peculiar to 

 either North America or to Europe and Asia. Three of these are essen- 

 tially subtropicopolitan or tropicopolitan, having merely straggling rep- 

 resentatives north of the 68th isotherm, and five others are represented 

 each by only a single species. Seven of these fourteen families (four only 

 according to many systematistsj) are North American and seven European 



* Occurring in southern portions only ; chiefly tropical. 



t Peculiar to the region and mostly of restricted range. 



1 1 here admit to family rank Antilocapridce, Zapodidce, and Geomyidce, the two former 

 of which are treated by Mr. Wallace as subfamilies of subcosmopolitan families, while 

 the other is not commonly recognized as distinct from Saccomyidce. On the other hand, 

 I refer the Cercolabidce to the ffystritidce. 



