Peculiar Genera o North American, Mammals. 



61 



ing table, which brings out the important fact that no less than 

 ;>2. or TS percent, are of Sonoran or austral origin, while only 9, 

 or 22 percent, are of Boreal origin. Of these 9 genera now con- 

 tined to North America, Ovibos inhabited polar Eurasia in Pleis- 

 tocene times ; Neurotrickus is not recognized by Flower and 

 Lydekker as more than subgenerically separable from Urotrichus 

 of Japan, and Syndptomys is not known except from the Transi- 

 tion Zone of the United States and is here classed as Boreal be- 

 cause of its close relationship to the transcontinental Boreal 

 genus Mi/odes. Omitting these three, Boreal North America has 

 but 6 genera of mammals not known from Boreal Eurasia. 



PECULIAR GENERA OF MAMMALS INHABITING NORTH AMERICA 

 NORTH OF MEXICO 



Of Sormil Origin 



Ma/anui 

 Ovibos 

 A plodontia 

 Fiber 

 Synaptomya 



'OfS 



Antilocapra 



Cynomys 



Reithrodontoinys 



Sitoinys 



Oryzomys 



Onychomys 



Sigmodon 



Neotoina 



Thomomys 



Geomys 



Dipodomys 



Perodipus 



Microdipodops 



Perognathus 



Heteroin>> 



Zapun 

 Erethizon 

 Neurotriclms 

 Condlura 



Urocyon 



Bassariscus 



Taxidea 



Conepatus 



Mephitis 



Spilogale 



Notiosorex 



Scalops 



Scapanus 



Blarina- 



Antrozous 



Nycticejus 



Otopterus 



Corynorhimw 



Euderma 



Atalapha 



On the other hand, out of the 31 Boreal genera of North Amer 

 ican mammals the following 24 genera, or 77 percent, are com 

 mon to Boreal America and Boreal Eurasia : 



