SINCLAIR: MARSUPIALIA OF THE SANTA CRUZ BEDS. 381 



In the remaining cervicals the neural spines increase regularly in 

 robustness and probably also in height, although this can not be deter- 

 mined, owing to the fracturing of their extremities. The inferior lamellae 

 of the transverse processes are more wedge-shaped than in Thylacynus, 

 resembling rather this region in Borhycena, and, as in that genus, the dia- 

 pophyses are fully differentiated on the fourth cervical. The transverse 

 processes of the seventh cervical are perforated by the arterial canal. The 

 centra are all heavily keeled inferiorly, but, owing to imperfect preserva- 

 tion, it can not be determined whether the keels decrease in depth in the 

 posterior cervicals, as in Prothylacynus and Thylacynus. The upper sur- 

 face of the neural arch of the third cervical is perforated on the left side 

 by a rather large foramen. A smaller corresponding foramen occurs 

 somewhat farther back on the right side. Small foramina may occupy 

 similar positions in some of the other cervicals. The foramina piercing 

 the lateral walls of the neural arches of the second to the seventh cer- 

 vicals, which are so prominent in Thylacynus (text-fig. 5, d], are present 

 in some of the cervicals of Cladosictis and absent in others. 



The dorso-lumbar formula is apparently nineteen, although this can 

 not be accurately determined, owing to the incomplete state of preserva- 

 tion of the column. The neural spines of the anterior dorsals are high 

 and broad, but gradually decrease in both dimensions to the tenth, or anti- 

 clinal vertebra. Beyond this point, the strong backward slope of the 

 spines changes abruptly to a forward direction. Metapophyses are devel- 

 oped on the tenth dorsal, and are prominent as far posteriorly as the sec- 

 ond lumbar, beyond which they begin to decrease in height. Ana- 

 pophyses also appear on the tenth dorsal and increase in size posteriorly 

 until the fifth lumbar is reached, when they become smaller. 



The lumbars (Plate LVII, fig. 6) are six in number. They have heavy 

 neural spines strongly inclined forward, with broad tips flattened superiorly, 

 and wide, thin transverse processes, with a forward and downward curva- 

 ture. The long, keeled centra increase regularly in size posteriorly. In 

 the first, second and third lumbars, the keels are bifid posteriorly, inclos- 

 ing a more or less flattened, wedge-shaped area. The prezygapophyses 

 overlap the outer margin of the postzygapophyses, producing an inter- 

 locking articulation. This applies also to the anterior zygapophyses of 

 the thirteenth dorsal. 



The sacrum (Pis. LVII, figs i, \a\ LVIII, figs, i, 7, fa) is composed 



