PEOFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 



311 



The upper sectorial tooth of the fossil (Plate XI. figs. 1 and 2, is larger than 

 that of the largest Lion or Tiger which I have seen, and than that of the great extinct 

 Lion {Felis spelcea, Plate XIV. fig. 4, 4). Its antero-posterior extent is 2 inches 

 3 lines, that in Felis spelwa being 1 inch 7 lines. The greatest diameter of the upper 

 tubercular tooth (Plate XI. fig. 2, h), which is at right angles to that of the sectorial 

 one, is 7-| lines, that of the Lion (Plate XIV. fig. 4, m 1) averaging 6 lines. 



The upper sectorial tooth of the Felines is divided into a ' blade ' and ' tubercle,' the 

 latter being developed from the inner side of the base of the fore-part of the crown, and 

 being supported by a fang which makes an extension of the socket inwards at right 

 angles to the rest of the socket. A portion of the fossil tooth has been broken away at 

 this part (Plate XL fig. 2,^j4), but apparently little more than the enamel; and the 

 socket certainly shows no inward extension indicative of a ' tubercle ' so large and 

 distinct as in the Felines (Plate XIV. fig. 4, p *) : the crown of the sectorial in Thyla- 

 coleo is thicker here than in the rest of its extent, and has been slightly convex on the 

 inside as on the outside of this part of the tooth ; but there appears to have been no 

 distinct lobe or tubercle, and I conclude that the crown of the upper great sectorial in 

 the ThylacoJeo consists exclusively of the ' blade.' The trenchant edge of this is not 

 notched as in the Felines where it is trilobate (Plate XII. fig. 1, ^ 4), but is even and 

 uniform, describing a very feeble concavity lengthwise (Plate XL fig. 1, p 4). In the 

 specimen it has been worn to a sharp edge by the play of the blade of a similar sectorial 

 obliquely upon its inner side. The outer side of the crown is convex vertically, wavy 

 lengthwise, being in this direction gently concave at the mid-part, convex at each end, 

 with minor rmdulations of the surface near the base. The inner side of the crown is 

 gently concave vertically at its mid-part, slightly undulated, but mainly convex length- 

 wise. The anterior border of the crown is formed by a subdentate ridge, sloping 

 with a slight convexity downward and backward, in vertical extent 1 inch : the crown 

 gradually decreases in this diameter to its back part, which ends in the form of a low 

 protuberance. The tooth is strongly implanted by, apparently, an undivided base 

 coextensive with the crown. I have not thought fit to mutilate the unique fossil to 

 determine the depth and precise character of this implantation. The thickest part of 

 the tooth is 8 lines. 



The tooth which most nearly corresponds with the sectorial of Thylacoleo is the 

 penultimate upper molar oi SarcopMlus {Dasyurus) ursinus (Plate XIV. fig. 2). In this 

 tooth the ' blade ' forms the chief part of the crown ; it is concave externally, convex 

 internally lengthwise ; its edge is entire, slightly concave ; but it is associated with an 

 anterior lobe and antero-internal tubercle, wanting in the fossil. 



The tubercular tooth {ib. fig. 1, m, Plate XL fig. 2, b) in Thylacoleo is on the inner side 

 of, and at right angles with the sectorial tooth, but is almost half an inch in advance of 

 the hind end of that tooth : in Felis (Plate XIV. fig. 4, m) it is close to that end. In 

 Thylacoleo this tooth consists of a principal portion next the sectorial, and a small lobe 

 (Plate XI. fig. 2, b) forming the inner or ' mesial ' end of the crown : the principal part 



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