188 PEOFESSOK 0^\YN OX THE FOSSIL MAMMALS OF ArSTEALIA. 



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., AVellington 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. AVith the bone are included the 

 implanted bases of the incisors (/), the three anterior molars of the right side (d s, d 4, m i), 

 and parts of the first and second molars of the left side. The upper surface of the dia- 

 stemal part of the symphysis (I, 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, I, 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 Pliascolomys latifrons (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) and of the anterior molars (ib. d a). 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 Pliasco- 

 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 Ilairy-nosed Wombat in the size of its molars, which is less 

 than in Pliascolomys plafyrhiiius (Plate XIX. fig. 2, da, d 4, mi). But the following- 

 differences present themselves in the comparison of the present fossil with the corre- 

 sponding part of the mandible of Pliascolomys latifrons. In tliat species the upper 

 transversely concave intermolar part or surface of the symphysis does not extend back- 

 ward beyond the ah colus 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 Pliascolomys platyrliinus the concave upper surface of the symphysis 

 extends further back, and this character is exaggerated in the fossil ; for the inner wall 



