188 
PEOFESSOE OWEN ON THE EOSSIL MAMMALS OF ALSTfi ALIA . 
evidences of similar-sized Wombats, of which I have received or worked out twelve spe- 
cimens from the breccia-masses transmitted to the British Museum by the Trustees of the 
Australian Museum, Sydney, New South Wales, in conformity with the desire of the 
Colonial Legislature, and in connexion with their liberal vote in aid of further explorations 
of the bone-caves discovered by Sir Thomas Mitchell, C.B., Wellington Valley. Four 
other and more complete specimens are from the freshwater deposits of Queensland. The 
first of the cave specimens which I shall describe consists of the almost entire symphysis 
(Plate XX. fig. 2 & Plate XXIII. fig. 4), and it is the only specimen from the breccia 
which shows this instructive part of the lower jaw. With the bone are included the 
implanted bases of the incisors (?'), the three anterior molars of the right side ( d 3, d 4, m 1 ), 
and parts of the first and second molars of the left side. The upper surface of the dia- 
stemal part of the symphysis (/, s) is concave transversely, divided by sharp margins from 
the sides, and has a mesial longitudinal channel at the anterior third, without the pair of 
such channels. Lengthwise the upper contour of the diastema is slightly concave (Plate 
XXII. fig. 7, l, s'). From the fore part of the anterior molary alveolus to the broken end 
of the symphysis is 1 inch 6 lines ; the breadth of the symphysis midway is 9 lines. So 
far the fossil shows a closer affinity to Phascolomys Icttifrons (Plate XX. fig. 1) than to 
the other two existing species, and more especially to the variety, fig. 3, Plate XXII. 
This affinity is more decisively shown by the form of the incisors in transverse section 
(Plate XX. fig. 2, i, i) and of the anterior molars (ib. d 3 ). The enamel covers and 
defines the lower broad flattened side of the incisor, bending up a little way upon both 
outer and inner sides, which converge toward the upper, narrower surface, but unequally ; 
the outer surface descending therefrom, at first more vertically, toward the base, while 
the inner surface slopes to the mid line of the symphysis as it descends. 
Thus there is a greater interval between the upper than the lower sides of the two 
incisors ; the vertical exceeds the transverse diameter of the transverse section of the 
tooth. In these characters the lower incisors of the fossil agree with those of Phasco- 
lomys latifrons. 
In the Platyrhine and Tasmanian Wombats the transverse prevails over the vertical 
diameter of the exposed end of the incisors, and the enamel bends up from the lower along 
the outer surface nearly to the upper one, describing a uniform convexity, transversely. 
The fossil adheres also to the latifront type in the shape of the first molar, d 3 (fig. 2, 
Plate XX.), and resembles the Hairy-nosed Wombat in the size of its molars, which is less 
than in Phascolomys platyrhinus (Plate XIX. fig. 2, d 3, d 4 , m 1 ). But the following 
differences present themselves in the comparison of the present fossil with the corre- 
sponding part of the mandible of Phascolomys latifrons. I 11 that species the upper 
transversely concave intermolar part or surface of the symphysis does not extend back- 
ward beyond the alveolus of the second molar ; at the third molar the inner wall of the 
jaw soon changes its concavity for a convexity bending down to the back part of the 
symphysis. In Phascolomys platyrhinus the concave upper surface of the symphysis 
extends further back, and this character is exaggerated in the fossil ; for the inner wall 
