Peculiar Genera ofWoiih Amcrlcait iVannuals 



()1 



ing tcil)k\ which l)rin<is out the iiiii)ortant fact that no less than 

 32, or 78 percent, are of Sonoran or austral origin, while only 1), 

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

 tinecl to North America, Odbox inhabited polar Eurasia in Pleis- 

 tocene times; Xearofrirhns i.s not recognized by FloAver and 

 Lydekker as more than sul)generically separable from Uratrirhiis 

 of Jaiian, and Si/naptomys is not known except from the Transi- 

 tion Zone of the United States and is here classed as Boreal l)e- 

 cause of its close relationship to the transcontinental Boreal 

 genus Ml/odes. Omitting these three. Boreal North America has 

 but 6 genera uf mammals not known from Boreal Eurasia. 



Peculiar Genera of Mammals rNHAnrn.\(; North America 



NORTH OF ^Iexico 



>hizanui 



Ovibos 



Aplodontia 



Fiber 



Synaptoinys 



Of Bumd Oriiji 



Ziipu.< 

 Erethizon 

 Neurotrichup 

 Conilvlmu 



()t Siiiionni (>ri<j'ia 



Cariacus 



Antilocapra 



( 'vnuinys 



Rc'itlu'odontouiy.'- 



Sitoiiiys 



Oryzmiiys 



(_)iiychi;)iuys 



Sigmodon 



Xeotoma 



Thomomys 



DipodomyH 



Perodipus 



Microdipodoj)8 



Perognathug 



Heteroiuvf? 



Urocyon 



Bassariscus 



Taxidea 



C'ouepatus 



IMephitis 



Spilogale 



Notiosorex 



Seal ops 



Scapauus 



Blarina 



A ntrozous 



Nycticejus 



Otopterug 



Corynor] linns 



p]ndernia 



Atalapha 



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

 ican manmials tlie following 24 genera, or 77 ])ercent, are cona- 

 nion to Boreal America and Boreal Eurasia : 



