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 Thy lacy nus , in- 
crease in width externally. 
Vertebral Column; Ribs and Sternum . — The atlas (PL LIII, figs. 5, 
5#) differs from that of Borhycena , A mphiproviverra and Thylacynus 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 a) 
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. 
S The axis (PI. LII, 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. PL 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. 
