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, PI. LXII, fig. 2 ; M. gallegosense, PI. LXII, fig. 3), 

 or the angle is strongly inflected, with the masseteric fossa extending to the 

 inferior border of the jaw (M. tehuelchum, PI. 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. gallegosense, but does not occur in the 

 other species. 



Skeleton (PI. 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 (PI. 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 (PI. 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 (PI. 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 (PI. LXII, fig. 9) are imperfectly preserved, but the 



