; 
| 
Sr aa aS en i ont ap OS ee ae a N ee Rae ee een Se a Se eee ae ae es 
1884.] The Tertiary Marsupialia. 689 
Cope, is intermediate in dimensions, and the dentition has some 
well-marked peculiarities. The characters of the skeleton, so far 
as known, are derived from the P. taoénsis (Figs. 3 and 4). 
The angle of the lower jaw is inflected, and the dental foramen 
is at the anterior apex of a large fossa,'as in most marsupials. 
There are but two true molars in each jaw, and a single simple 
premolar, below. The condyle of the humerus presents characters 
shared by Meniscoéssus of the Laramie, which are found in lizards, 
There is a strong and thick intertrochlear ridge in front, which is so 
swollen at one side of the middle line as to resemble the condyle 
Fic, 3.— Pol, SEPET a : i ; sizes fi th Lowes 
‘ymastodon taoénsis Cope, jaws, two-thirds nat: size; rom the 
ere beds of New Mexico. (ae Tight mandibular ramus right side; 4, do., 
S al side; c, do., from above; d, from below. Original, from Report U. S. Geol. 
€y Terrs., F, V, Hayden in charge, Vol. 111. 
femur. The trochlea for the coronoid process of the ulna, on 
x Posterior side, is narrowed so as to suggest a rotular groove 
(Fig. 427 ). The humeral cotylus of the ulna is adapted to this con- 
dyle by a flare on each side (Fig. 4c). The astragalus is without 
trochlea, as in most Puerco Mammalia, and the trochlear portion 
S gently convex anteroposteriorly. The head is much narrowed, 
ju -aSa Narrow navicular face which is convex in only one, the 
vertical, direction, On its outer side it bears a large flat facet for 
ie cuboid bone (Fig. 4a’). This form is much like that of the 
kangar oos. It shows that the peculiar structure of the posterior 
fi ; 
Aof the Macropodidæ already existed at this early day, though 
