1884.] The Tertiary Marsupialia. 687 
that division of Eocene mammals, showing that although their 
dentition is sometimes that of the carnivorous division of the 
marsupial order, they cannot be placed with them. 
The extinct marsupials belong to three types, as distinguished 
by the form of their superior molar teeth. These are tritubercu- 
late, quadrituberculate or multituberculate. To the first division 
belong the carnivorous types, or Sarcophaga of Owen; to the 
second the kangaroos and the wombats, to which Owen's name 
of Poéphaga may be applied! The third division is entirely ex- 
tinct, and is characterized by having at least three longitudinal 
series of tubercles in its superior molar teeth. To this suborder 
l apply the name of Multituberculata. The suborder Sarcophaga 
includes the opossums, and in North America the single extinct 
genus Peratherium *Aymard. This is also the genus which is 
found in the Oligo- 
cene and Miocene of 
France. It differs 
from Didelphys (the J 
true opossum) in the ASZ 
non-inflection of the Gj 
angle of the mandi- 
_ ble. Otherwise the 
two genera oe bid Fic. 1.—Peratherium fugax Cope, from the White 
the umber (esht) Stes Pier a, anterior part of Sal frm Below; A 32: 
GPU so oe t : : 
es a fn eee oo 
teeth. Five species the right side. 
_ have been found in the White River beds of Colorado. The 
a largest of these, P. fugax Cope (Fig. 1), had the skull as large as 
__ that of a mole (Scalops aquaticus). The smallest, P. huntii Cope, 
not exceed a small shrew in dimensions. 
č no extinct forms have been found in North 
— Multituberculata include three families, which differ as 
: Fourth superior premolar (at least) like true molars.,....-----++++ Tritylodontida. 
Poh » premolars (and probably others) more simple than first true mola 
_ ~~“ Premolars (and often others) developed into flat cutting blades : 
io ; 
Without suf a S the Phascolomyide in a distinct suborder, but, as it appears to me, 
oe treason. *Bulletin U, S. Geol. Survey Terrs, V, No. 1, p. 45- 
