125 
is 38 mm. both at their anterior and posterior ends. An 
apparently nearly perfect isolated tooth from the same locality 
has the very similardimensions of 182 mm. and 39mm. foritslength 
and breadth, respectively, and in this it can be seen that the 
width is preserved, with almost absolute uniformity, throughout 
its whole extent. The thickness in the mid-longitudinal line of 
the tooth, just posterior to the bevel of the cutting edge, is 8 mm. 
which, at the somewhat thickened lateral borders, is increased to 
10 mm. These measurements, also, apply along the whole length 
of the tooth. 
Thus it will be seen that the Callabonna teeth are somewhat 
larger than those that came under the notice of Owen. No other 
incisors exist in the upper jaw. 
The restoration of the skull has not been completed, but the 
large fragment which contains the pair of upper incisors contains 
also on each side a complete molar series of phascolomydian type. 
Of this the antero-posterior length, measured along the grinding 
surfaces, is 114mm. In an old Phascolomys mitchelli and a 
young adult P. latifrons the corresponding lengths are 53 mm. 
and 49 mm. respectively. 
In Phascolomys mitchelli the section of the upper premolar is 
sub-triangular and its inner side is indented by a distinct longi- 
tudinal groove which imperfectly defines a small anterior lobe 
from a larger posterior ; in P. latifrons scarcely a trace of such a 
groove exists and the section approximates to a quadrate figure. 
In Phascolonus gigas the bilobate character of this tooth is 
more distinctly evident both by the sharper definition of the 
groove and by the greater relative size of the anterior lobe, the 
transverse width of which, however, still falls considerably short 
of that of the posterior. On the outer side of the tooth there is 
a barely evident longitudinal depression which can barely be 
called a groove. The antero-posterior length of the premolar 
grinding surface is to the succeeding molar as 19 to 24. 
Of the true molars J/. ] and JW. 2 are the largest of the series 
and approximately equal in size; J. 3 is distinctly smaller both 
in length and breadth and in all three the lobes are approxi- 
mately equal. The posterior, or fourth, molar is unequally 
bilobed and is still more reduced in size—it is in fact smaller than 
the premolar. The reduction chiefly affects the posterior lobe 
but it is also shared by the anterior. The inferiority of size of 
the last molar is, also, a character in both Phascolomys mitchelli 
and P. latifrons, but in the latter the two lobes are more nearly 
of equal size than in the former, where the anterior division has 
remained relatively larger. 
Of the two specimens of lower jaw which are included amongst 
the remains one comprises the united horizontal rami with the 
