SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 365 



union is ligamentous. Three mental foramina are present, the largest of 

 which lies beneath the anterior and median premolars. The others are 

 situated beneath the anterior root of the first molar and posterior root 

 of the second molar respectively. The condyles, unlike Thylacynus, in- 

 crease in width externally. 



Vertebral Column; Ribs and Sternum. The atlas (PI. LI 1 1, figs. 5, 

 5*2) differs from that of Borhycena, Amphiproviverra and Tliylacynus in 

 having the intercentrum firmly fused with the base of the neural arch 

 without trace of suture. The small neuro-arterial foramina are placed 

 nearer to the anterior atlanteal margin than in the other Santa Cruz 

 genera. The canal for the vertebral artery is small. It enters the neural 

 arch within the spinal canal about midway between the neuro-arterial for- 

 amen and the condyles, emerging on the lower surface (PI. LIII, fig. 5) 

 near the anterior margin of the base of the transverse process. The trans- 

 verse processes are considerably thickened ; their antero-posterior basal 

 constriction is much less than in Thylacynus. The posterior border of 

 the inferior arch supports a small median tubercle. 



i^,The axis (PI. LIT, figs. 3, 5) resembles closely that of Borhycena, dif- 

 fering from Thylacynus in the greater width of the neural spine anteriorly, 

 the more attenuated extremities of the transverse processes and the greater 

 depth of the posterior inferior keel. The posterior portion of the neural 

 spine has been broken. It was probably as long and heavy as in Bor- 

 hycena tuberata. The odontoid tapers slightly anteriorly, but less so than 

 in Thylacynus. The anterior cotyles are extended to the same degree as 

 the transverse processes. The lower surface of the centrum is almost the 

 same as in Borhycena (cf. PI. LII, figs. 5, 6). The anterior portion of 

 the inferior keel has been broken, which accounts for its apparently lower 

 elevation than in Borhycena. 



The third, fourth and fifth cervicals differ from those of Thylacynus in 

 having the diapophyses better differentiated from the inferior lamellae. 

 The centra are strongly keeled inferiorly. In the fifth cervical the pos- 

 terior portion of the keel is bifid. The upper surface of the neural arch 

 of the third cervical is perforated by a pair of large foramina. Of the 

 sixth cervical, an uncharacteristic fragment remains. Small foramina 

 pierce the lateral walls of the neural arches of the third to the sixth 

 cervicals, as in Thylacynus and Borhycena. The neural spines of the 

 posterior cervicals have not been preserved. 



