1893.] Fossil Mammalia of Southern Patagonia. 445 
internal border, and not on their upper face as is the case 
among rodents and all other known mammals which have 
chisel-like incisors the. mandibular branches of the same 
animals have no symphyseal suture, the surface of the bone, 
at this point, being nearly as smooth as the rest of the jaw. 
It thus results that the two mandibular rami of the Epanorthide 
were susceptible of lateral movements, and the singular 
incisors could perform, up to a certain point, the function of 
horizontal pincers. 
Also, although I am quite convinced that the Plagiaulaci- 
dæ and the allied fossil forms have been derived from the 
Didelphian Diprotodontia, the relation with the living 
Diprotodontia is not so close as I had thought. The discov- 
ery I made showing that the large furrowed tooth of the man- 
dible of the Plagiaulacide is not the last premolar, as had 
been believed, but is the first true molar, separates the latter 
from the living Diprotodontide. This character justifies a 
sub-order in the Diprotodontia, to which can be given the 
name Plagiaulacoidea, a name which is as appropriate for the 
northern forms known as Multituberculata as it is for those of 
the Eocene of Patagonia. 
The recent studies that I have made of the Microbiotheriide 
have confirmed me in my opinion that they represent the 
direct ancestors of the living Didelphyide. The latter have 
certainly originated in South America, and although their 
remains have not yet been found in the Parana formations, 
they will be found there some day. 
One of the fossil groups of Patagonia which presents the 
greatest interest is that of the primitive Carnivora, allied both 
to the Dasyuride and to the Creodonts. It seems to me impos- 
sible to find a line of demarcation between them. Instudying 
the material in my possession, I arrive at the following conclu- 
sions: The Dasyuride are descended from the Microbiotheriidz 
and are then modified into Creodonts; these, in their turn, are 
transformed into the more modern Carnivores. The dental 
formule of these primitive carnivora are varied—take, for 
example, the superior incisors, of which the Microbiotheride 
have five pairs like the Didelphyde ; the Dasyuride have 
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