Mr. Owen on the Phascolotherium. 63 



The base of the inwardly-bent angle of the lower jaw progressively increases in 

 Didelphys, Dasyurus and Thylacinus ; and, judging from the fractured surface of 

 the corresponding part in the fossil, it also resembles most nearly, in this respect, 

 the Thylacinus. 



The condyle of the jaw is nearer the plane of the inferior margin of the ramus 

 in the Thylacine than in the Dasyures or Opossums ; and consequently, when the 

 inflected angle is broken off, the curve of the line continued from the condyle 

 along the lower margin of the jaw in the Thylacine is least : in this particular 

 again the Phascolothere resembles the Thylacine. In the position of the dental 

 foramen, the Phascolothere, like the Thylacothere, differs from all the zoophagous 

 Marsupials already cited, and also from the placental Fer(B ; but in the Potoroo 

 {Hypsiprymnus) , a marsupial Herbivore, the orifice of the dental canal is situated, 

 as in the Stonesfield Marsupials, very near the vertical line, dropped from the last 

 molar tooth. (See letter e, PI. V. figs. 1, 2 and 3, and PI. VI. figs. 1 and 2.) 



A portion of the inner wall of the jaw, near its anterior margin, in the Phasco- 

 lothere, has been violently broken off, so that the form of the symphysis cannot be 

 precisely determined ; but in the gentle curve by which the lower margin of the 

 jaw is continued along the line of the symphysis to the anterior extremity of the 

 jaw, the Phascolotherium resembles Didelphys more than Dasyurus or Thylacinus. 



It is interesting to find that this analogy is associated with a correspondence in 

 the condition of the teeth at the anterior part of the jaw. In examming the fossil 

 we can scarcely refuse our assent to Mr. Broderip's opinion, that there were origi- 

 nally four incisors in each ramus of the jaw of Phascolotherium, as in Didelphys. 

 Of the three incisors which are actually present in the fossil, only the internal and 

 posterior surfaces are displayed, and not the whole breadth of the tooth ; so that in 

 the enlarged figure of the jaw detached from its matrix, the incisors appear both 

 narrower and further apart than they really are. The incisors in the Thylacinus 

 are of a prismatic form ; and the surface, corresponding to that which is exposed 

 on the fossil, forms one of the angles, from which the tooth increases in breadth to 

 its anterior part, which forms one of the three facets. 



Allowing for this circumstance, which must be borne in mind in an endeavour 

 to arrive at the true affinities of the Phascolothere, the incisors in that fossil are 



land of Marsupial animals. Our specimen," continues Mr. Broderip, " lies imbedded with a number of 

 fossil shells of that genus. The individuals are of the same species so frequently found at Stonesfield." 

 — Loc. cit. p. 4. May we be permitted to conjecture that Australia, in its marsupial inhabitants, its 

 AraucaricB and Cycadeous plants, with the living Clavagella, Terebratulcb and TrigonicE of its coasts, 

 presents us with the picture, as it were, of the last remains of an old and worn-out world, — of one that 

 has long been superseded in this hemisphere by other strata and a higher type of mammiferous organ- 

 ization ? 



