248 
PROEESSOR OWEN ON THE EOSSIL MAMMALS OE AUSTRALIA. 
with rather less transverse extent ; and the two succeeding teeth diminish, chiefly in 
transverse thickness. The grinding-surface of the last molar (m 3) has a fore-and-aft 
extent of 64 lines, with a transverse diameter at the hind lobe of but 3 lines. In shape, 
implantation, and structure, showing interruption of the enamel coating at the outer side, 
these upper molars closely adhere to the generic character of Phascolomys. The exposed 
implanted ends show the widely open persistent pulp-cavities. The section of the base 
of the right incisor has a transverse diameter of 6 lines, a vertical one of 5 4 lines. The 
upper, which would become the front surface, is transversely convex ; the under surface 
is transversely concave, but irregularly so, from the greater production downward of the 
inner angle. The upper incisor appears, from the present remnant of it, to differ in 
shape as well as size from that of Phascolomys medius. The inner interspace between 
the pair at the place of fracture (Plate XXXV. fig. 5) is 7 lines ; they no doubt converged 
as they descended to come into contact at their exposed and working ends. 
The above-described fossil is from a full-grown and seemingly old individual. 
I am glad, however, to have another example of the size of teeth which typifies 
Phascolomys magnus. It is afforded by a fragment of the right maxillary, with 
the second, third, and fourth molars in situ , and portions of the sockets of the first 
and fifth. 
The antero-posterior extent of the grinding-surfaces of the three teeth in place is 
2 inches 4 lines, according in all dimensions and in relative size with those in the sub- 
ject of figs. 1--4, Plate XXXV. The outer surface of the bone shows the same relative 
position of the malar process of the maxillary, the same shape and course of the prezygo- 
matic ridge, so far as it is preserved. Part of the malar bone contributing to the fore 
part of the orbit is also here preserved ; but the fragment has been much rolled and 
worn, and is incrusted with the petrified lacustrine deposit. 
In both specimens the enamel has a finely reticulate surface, with a tendency to longi- 
tudinal striation. This surface aids the attachment of the cement. 
Amongst the detached teeth worked out of the portions of breccia from the Wellington- 
Valley bone-caves transmitted to the British Museum was one entire molar tooth 
and the halves of two others (Plate XXXV. fig. 6), of the size of those of Phascolomys 
magnus. The entire molar corresponds closely with the third, upper jaw, left side, in the 
specimen last described from Darling Downs (ib. fig. 1, m 1 ). We thus get evidence of 
the former range of Phascolomys magnus over some hundreds of miles of the Australian 
continent. 
§ 3. Phascolomys gigas , Ow.* — Of the lower jaws of Wombats exceeding in size that 
of Phascolomys medius (Plate XXXIV.), I have seen none with a molar series having 
the same relative size to the upper one in Phascolomys magnus (Plate XXXV.) which 
the teeth of the lower jaw bear to those of the upper one in existing Wombats, and 
in all the extinct species of which I possess means of comparing those teeth. 
A series of lower molars with an extent of grinding-surface of 4 inches 3 lines (Plate 
* Art. “ Palaeontology,” Encyclopaedia Britannica, 1858, vol. xvii. p. 175. fig. 114. 
