SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 351 



specimens, but they were probably as long proportionately as in Thyla- 

 cynns. The ventral surface of the centrum (PI. LII, fig. 6) has a strong 

 median keel which increases in depth posteriorly. The concavities on 

 either side are bounded externally by the inferior edges of the transverse 

 processes. Traces of the suture uniting the axial centrum with the 

 anterior cotyles and odontoid are visible in both species. 



The neural spine of the third cervical is proportionately larger and the 

 median keel of the centrum stronger than in Thylacynus. In the fourth 

 and fifth cervicals the diapophyses are well differentiated from the inferior 

 lamella, unlike Thylacynus. The inferior lamella of the sixth cervical is 

 less elongated antero-posteriorly than in the recent genus, but is much 

 deeper. The transverse process of the seventh cervical is perforated by 

 the vertebral artery. The neural spines of the cervicals increase in size 

 and probably also in height posteriorly. The inferior keels on the centra 

 decrease in depth on the fifth, sixth and seventh cervicals. The lateral 

 surface of the neural arch above the canal for the vertebral artery is per- 

 forated by a small foramen in the second to the seventh cervicals. 



The dorsal vertebrae associated with the skeleton of B. tuberata are 

 larger than in Thylacynus, with heavier neural spines. The centrum of 

 the first is keeled inferiorly, but keels are absent in the vertebrae inter- 

 preted as the seventh (PI. XLV, fig. 6) and eighth dorsals. The dorso- 

 lumbar vertebral formula was probably the same as in Thylacynus and 

 has been so represented in the restoration (PI. LXI, fig. 3). 



Three caudals are preserved with the skeleton of B. tiiberata, which are 

 interpreted as the third, fourth and fifth. The fourth caudal (PI. LI 1 1, 

 figs. 9, 9) has been selected for illustration owing to its better state of 

 preservation. It is considerably larger than the corresponding vertebra 

 in Thylacynus, but much smaller than the fourth caudal in Prothylacynus. 

 The transverse processes are broadly expanded, but are rounded at the 

 tips, in contrast with the antero-posterior extension of the tips of the trans- 

 verse processes of the proximal caudals in TJiylacynus. The presence of 

 chevrons on the fourth and fifth caudals is indicated by facets. 



The floor of the neural canal in all the cervicals, except the atlas, and 

 in the dorsal and anterior caudal vertebrae is subdivided by a median 

 ridge, on either side of which a foramen pierces the centrum. A similar 

 structure is observable in Thylacynus and also in various placental carni- 

 vores. 



