7'«j0' PROP. BALDWIN SPENCER ON A [Nov. 20. 



as it is broken off at a height of 12-5 nitn. It slants slightly 

 forwards. 



\'i rtebral Column. 



Of the vertebral column there remains the broken axis and a 

 continuous series of 9 vertebrae belonging to the presacral region. 

 The axis has the odontoid process firmly attached. The articular 

 surface is elongate, its length being 10 mm. ; the anterior margin 

 of the neural arch arises at the level of the posterior end of the 

 articular surface, and is almost vertical, the under surface of the 

 overhanging end of the neural spine forming almost a right angle 

 with it. The exact extent of the spine cannot be determined as 

 the posterior part is broken. The transverse process differs from 

 that of marsupials generally (ex. Trichomrus, Dasyurus, Peru melt*, 

 Maoropus) in running out nearly at right angles to the body. 

 It is stoutly built and relatively short. The width (11 mm.) of 

 the neural cavity is decidedly greater than its height (7'5), a con- 

 dition which does not usually obtain in marsupials ; in a specimen 

 of Dendroluyus bennettianus both width and height are 9 mm. ; in 

 Trichosuru8 both are 7 mm. ; in Dasyurus viverrinus and Peramchs 

 •in, mi the height is 5 mm., the width a shade greater; in Phasco- 

 lomys the width is 15, the height 12; and in Macropus rufus the 

 width is 16 and the height 1 L*5. The ridge of bone which forms 

 the floor of the vertebrarterial canal instead of being, as in 

 recent marsupials, narrowed from before backwards so that there 

 is a distinct open space between the backwardly slanting process 

 and the centrum veutrally, is expanded so as to form a platform 

 which serves as a floor for the vertebrarterial canal. In ventral 

 view there is a low median keel ; this runs forwards to meet a ridge 

 which runs across the anterior end of the centrum and then 

 diverges outwards on each side, when it is confluent with the 

 lower edge of the articular surface, and then passes outwards on 

 to the process at the base of the vertebrarterial canal. The space 

 between this ridge on either side and the median keel is occupied 

 by a platform of bone across which runs a small ridge. This 

 platform, stretching across between the process and the centrum, 

 is a distinctive feature of the axis of the fossil form, and is not met 

 with in recent marsupials. 



The remaining vertebra are all considerably broken ; they are 

 lying on their right side, the processes of the left side being all 

 broken off. Under the four anterior ones there lie the broken 

 remains of ribs. 



The total length of this part of the vertebral columu is 191 mm. ; 

 that of a corresponding part of a Triehosurus vulpecula, of which 

 the skull is slightly smaller than that of the fossil, is 160 mm. 

 Owing to their broken state it is not possible to determine which 

 of them carried ribs. The third from the anterior end is the only 

 one in which the neural spine is preserved ; it has the form of a 

 broad plate slanting backwards, with a length of 14 mm. at its 

 base and 12 along its dorsal margin; its anterior, backwardly 



