X.] EXTINCT MAMMALS. 37! 



Ungulata (cont.). 



Cariacus. Greater part of America. 



DlCOTYLID^E. 



Dicotyles. Also South American. 

 Edentata. 



DASYPODID^E. 



Tatusia. South American. 



Marsupialia. 



DlDELPHYID^E. 



Didelphys. South American. 



Although the Transition zone undoubtedly forms an unsatis- 

 factory item in regard to the distinctness of the Sonoran region, 

 yet when we look at the difference of its mammalian fauna as a 

 whole from that of the Canadian sub-region of the Holarctic, and 

 the close similarity between the latter and the fauna of northern 

 Europe and Asia, there can be but little hesitation in regard to 

 the acceptance of Dr Merriam's view that the Sonoran is a valid 

 zoological region of the Arctogaeic realm. 



In a previous chapter the groups of mammals, both living and 

 extinct, confined to the eastern division of the 

 Arctogaeic realm have been already noticed, while oraupa of 

 in the present one reference has been made to such 



existing types as are restricted to the western half of Western 



, 6 /F . ., Arctogaea. 



of the same realm. It now remains to consider 

 briefly some of the leading extinct groups which are found only in 

 the latter area ; and the consideration of these comes most appro- 

 priately here, seeing that the majority of these peculiarly American 

 types are of Sonoran origin, a large number of their remains 

 having been obtained from the States of New Mexico, Kansas, 

 Nebraska, and Dakota, which lie within that region, or from 

 Colorado, Wyoming, and Montana, which are situated within the 

 Transition zone. 



Although, in common with the higher Primates, lemuroids are 

 now quite unknown in North America, they were well represented 

 there during the Puerco epoch of the lower Eocene by three 

 families. The first of these the Chriacida includes animals 



242 



