SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 4 1 I 
The mandible either has the angle moderately inflected and the inferior 
margin of the masseteric fossa widely separated from the lower mandibu- 
lar border (M. tortor , PL LXII, fig. 2 ; M. gallego sense , PI. LXII, fig. 3), 
or the angle is strongly inflected, with the masseteric fossa extending to the 
inferior border of the jaw (M. tehuelchum , PL LXII, fig. 4). The chin 
is either heavy, with prominent tubercle ( M . tortor ) or shallow (M. tehuel- 
chum). The inferior mandibular border is much less convex than in 
Didelphys. The rami are unfused, as in that genus. The mental foram- 
ina are fairly constant in number and position. A large foramen is sit- 
uated either beneath the anterior premolar, or beneath adjacent roots of 
the anterior and median teeth in species with unspaced premolars. A 
second foramen is placed below the anterior root of the first molar. 
Some specimens show two foramina beneath this tooth (No. 9595 Amer- 
ican Museum). A minute foramen piercing the anterior portion of the 
masseteric fossa is present in M. gallego sense, but does not occur in the 
other species. 
Skeleton (PL LXII, figs. 8-12). — Parts of the right scapula and ulna, 
an incomplete right humerus, and the first to the sixth cervicals, lacking 
the neural arches, are associated with the left half of a lower jaw and 
two upper molars of M. tehuelchum. 
The body of the scapula (PL LXII, fig. 11) has been almost entirely 
destroyed. The spine is prominent, but has been broken in the region 
of the acromion. The neck is short. The coracoid process is large, with 
inflected anterior margin. 
The humeral head (PL LXII, fig. 12) has been somewhat damaged. 
In general, it resembles that of Prothylacynus and Cladosictis , but does 
not overhang posteriorly to so great an extent. The greater tuberosity 
has been broken off ; the lesser tuberosity is prominent and is separated 
from the head by a wide, shallow groove. The distal end is broad, with 
powerful supinator ridge and enormously developed inner epicondyle. 
The margin of the supinator ridge has been fractured and the character 
of its proximal end cannot be determined. A large internal epicondylar 
foramen is present. 
The posterior border of the ulna (PL LXII, fig. 10) is strongly convex. 
The shaft is flattened laterally and deeply excavated on either side of the 
sigmoid cavity. 
The atlas and axis (PL LXII, fig. 9) are imperfectly preserved, but the 
