218 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
projecting from the socket is covered by cement. The length of the cement-clad root is 
given in the figure of, I believe, the homologous tooth in Plate XI. fig. 14. 
The third premolar (p 3 ), also preserved in the specimen (Plate XI. figs. 1-3), is rather 
larger in size, has a similar extremely low and slightly prominent crown, with the same 
ridge running from the outer to the inner side, crossed by the shorter ridge at right angles 
near the inner side of the crown, to which the longer ridge extends, leaving the shorter 
ridge chiefly conspicuous behind it. The vertical extent of the cement-covered and 
enamelled part of the second and third premolars projecting beyond their sockets does 
not exceed 3 lines. This specimen resolves the doubt expressed with regard to their 
empty sockets in the specimen figured in Plate hi. of the ‘ Philosophical Transactions ’ for 
1866, p. 78*, and demonstrates that each socket contains its own small simply implanted 
tooth, and was not a division of a socket lodging a larger two-fanged premolar. 
Beyond the third premolar the fore part of the crown of the maximized carnassial f 
(Plate XI. figs. 1 & 2, p 4 ) extends downward 10 lines. The shape, structure, vertical 
grooving, and dimensions of this tooth agree with those in the specimens described in 
the previous Memoirs. 
The trenchant margin of the upper carnassia.l is worn, as usual, obliquely from with- 
out upward and inward, the cutting-edge of the enamel being external (Plate XL fig. 2, 
p 4). This edge does not run straight, but sinks to form a low angle at the end of a well- 
marked external vertical groove (ib. 0 ), marking off rather more than one-third of the hind 
part of the crown, which answers to the similarly but better defined hind lobe of the 
feline upper carnassial. The smoothly worn surface is thus divided into two parts, the 
anterior one being broadest anteriorly at the thickest part of the tooth, while the pos- 
terior gains breadth as it recedes toward the hind end of the crown. But the indica- 
tions of resemblance to the feline carnassial, especially to that of Machairodus (Plate XL 
figs. 15, 16), do not end here. The inner surface of the crown, about one-fourtli of the 
way from the fore to the hind margin, projects and terminates in a ridge (v, figs. 2 & 3, 
Plate XI.), which expands to the base of the crown, representing the more developed ridge 
or vertical swelling of that part of the carnassial in Machairodus (fig. 15, v), from the 
broadening base (d) of which the tubercle of the upper carnassial, wanting in Machairodus 
as in Tliylacoleo , is developed in Felis. An opposite vertical ridge on the outer side of 
the crown in Tliylacoleo (fig. 1, p 4, u ) represents the most prominent part of the middle 
lobe of the carnassial in Felines (fig. 16, u), whence the outer surface bends inward to 
the angle or groove dividing that lobe from the hind one. The outer surface in Thyla- 
coleo bends in the same direction to the corresponding angle or groove ( 0 , figs. 1 & 3), 
then curves outward to the hind end of the crown. This is very low and subobtuse, as is 
the corresponding end of the carnassial in Felines. But the fore part of the crown, in 
* “ At the fore part of the carnassial socket the alveolar border is excavated by either a similar socket for a 
two-rooted tooth, or by two contiguous sockets for two small single-rooted teeth.” 
t No evidence has yet been had that this or the antecedent permanent teeth had displaced deciduous prede- 
cessors ; the adopted symbol p is to he taken with this reservation. 
