272 LLOYD’S NATURAL HISTORY. 
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 /eratherium, there can be little 
doubt that they really belong to the existing genus Dyde/phys, 
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 Débruge 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 
