PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AUSTEALIA. 311 
Th.e upper sectorial tooth of the fossil (^Plate XI. figs. 1 and is larger than 
that of the largest Lion or Tiger which I have seen, and than that of the great extinct 
Lion {Fehs spelcea, Plate XIV. fig. 4, 4 ). Its antero-posterior extent is 2 inches 
o lines, that in Felis s'pelcBa being I inch 7 lines. The greatest diameter of the upper 
tubercular tooth (Plate XI. fig. 2, ^), which is at right angles to that of the sectorial 
one, is '1\ lines, that of the Lion (Plate XIV. fig. 4, m 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 lest of the socket. A portion of the fossil tooth has been broken away at 
this part (Plate XI. fig. 2, p 4), 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, yi 4): the crown of the sectorial in Thyla- 
colco is thicker heie 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 Thylacoleo consists exclusively of the ‘blade.’ The trenchant edge of this is not 
notched as in the Felines where it is trilobate (Plate XII. fig. I,y) 4 ^, but is even and 
uniform, describing a very feeble concaVty lengthwise (Plate XI. fig. 1, p a). 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, wa'vy 
lengthwise, being in this direction gently concave at the mid-part, convex at each end, 
with minor undulations 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 shght convexity downward and backward, in vertical extent I 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 of Sarcophilus {Dasyurus) ursinus (Plate XIV. fig. 2 ). In this 
tooth the ‘ blade ’ forms the chief part of the croAvn ; 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 {ih. fig. I, m, Plate XI. fig. 2, h) 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 
2 T 2 
