PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
217 
shown in the subject of Plate hi., Philosophical Transactions, 1866. (I may add that 
photographs, and specimens of this tooth (m 1 ) from the breccia-cave, illustrate the con- 
stancy of character in the solitary spelaean example of the true or tubercular molar series 
from the upper jaw of Tliylacoleo.) 
Of the first incisor ( i 1 ), nearly one inch projects from the outer wall of the socket in 
the subject of fig. 1, Plate XI. ; the inner wall (fig. 2, ib.) extends two lines lower down 
the tooth. The dimensions of the outlet of the socket give those of the corresponding 
part of the tooth, which very closely fits and adheres to the socket. The anterior 
border of the exposed part of the incisor shows a moderate curve convex forward ; the 
posterior border, three lines below the socket, shows, after a slight basal convexity, the 
beginning of a curve concave backward. The exposed base of the tooth retains for four 
or five lines below the socket a coating of cement beneath which the enamel emerges. 
This is thicker toward the back than at the fore part of the crown, but nowhere exceeds 
half a line. Much of it is broken away from the base of the crown here preserved ; and 
at the outer and back part of the base of the crown the enamel presents a free rounded 
edge, for two lines vertically, as if it were there interrupted. The dentine is extremely 
dense ; the diameters of the broken part of the crown, which I take to be about halfway 
from the pointed end of the crown, are 7 lines by 5-| lines; the dentine here presents, 
in transverse section, a narrow oval form, broader before than behind, and more convex 
outwardly than on the inner side. 
Of the second incisor (i 2 ) one can infer from its socket that it had a root about 5 lines 
in length, tapering to an obtuse point, and a crown measuring 4 lines in diameter at its 
base. 
The third tooth which has been displaced from the somewhat larger socket opening 
upon the premaxillo-maxillary suture, and which makes a slight prominence on the out- 
side of the alveolar tract, at a short distance from the second, I conclude to have been a 
canine (c ) ; the fang, or implanted part, has been 9 lines in length, slightly curved, taper- 
ing to the end. 
The tooth remaining in the socket (Plate XI. figs. 2 & 3, p 1 ) on the inner side of the 
hind part of the canine ( c ) has the summit of the enamelled crown broken away ; the 
diameters of the base of the crown are 4 lines and 3 lines. The root is firmly fixed in 
the socket: I regard tbys as the first premolar (p 1 ). Its internal position, its implanta- 
tion in the maxillary at some distance from the suture with the premaxillary, and its 
continuation of the oblique line of the succeeding premolars, weigh with me against re- 
garding it as a canine, according to the hypothesis of the tooth (c, Plate XL figs. 1-3) 
being a third incisor, as in some hypothetical restorations referred to in the sequel. 
The second premolar (p 2 ) in situ in the specimen (Plate XI. figs. 1, 2, 3) is somewhat 
smaller than p 1 , with a very short enamelled crown, forming a low ridge extending 
from the outer side to nearly the inner side, and there meeting and blending with a 
second low ridge at right angles, close to the inner border of the crown. The enamel is 
limited to forming the low-ridged cap or summit of the tooth ; the rest of the tooth 
