﻿272 ALLEN S NATURALLSTS LIBRARY. 



more or less closely allied to living South American ones ; 

 these remains being found as low down as the Santa Cruz beds 

 of Patagonia, which probably belong to the Miocene division 

 of the Tertiary period. 



The Miocene rocks of the United States have likewise 

 yielded extinct species of Opossums, which may probably be 

 assigned to the existing genus ; unless, indeed, as has been 

 stated to be the case, they differ by the absence of any 

 inflection of the angle of the lower jaw. 



Still more numerous are the Opossum-remains from the 

 Upper Eocene, or Lower Oligocene, Tertiary beds of Europe, 

 which have been assigned to a very large number of species. 

 Although these extinct Opossums have been very generally 

 separated under the name of Feratherium^ there can be little 

 doubt that they really belong to the existing genus Didelphys, 

 which is consequently one of great antiquity. It should be 

 mentioned, however, that we are still unacquainted with the 

 number of incisor teeth in these Tertiary European Opossums. 

 Remains of the genus have been obtained from the Tertiary 

 beds of Hordwell in Hampshire, from the equivalent deposits' 

 of Debruge in Vaucluse, and of Montmartre near Paris, and 

 likewise from the so-called Phosphorites of Quercy in the' 

 South of France. 



It appears accordingly that during the middle portion of 

 the Tertiary period Opossums were widely spread over the 

 Northern Hemisphere, where they probably took origin from 

 the extinct generic types of Marsupials of the antecedent 

 Cretaceous epoch. With the development of the higher forms 

 of Mammalian life they disappeared from Europe before the 

 upper part of the Miocene, or middle division of the Tertiary 

 period, and gradually retreated to a great extent from the 

 northern half of the New World to find a secure refuge in 

 South America, It is important to notice that there are no 



