329 



fig. 1, d 3) it has an elliptic or ellipsoid transverse section. The outer depression (Plate 

 LII.,/) of the ramus ascendens, or " ectocrotaphyte cavity," is less deep in Phase, 

 latifrons (ib. fig. 3), and shallows more gradually forward, than in the bare-nosed recent 

 species (ib. figs. 1 & 2) ; the inflected angle (a), viewed from below as in Plate LVL, 

 has a broader base in proportion to its length, and is not produced so far or directly 

 backward in Phascolomys latifrons (fig. 3) as in Phase, platyrhinus (fig. 1). 



§ 12. Mandibular characters of extinct Wombats similar in size to the recent species. 

 — I now proceed to apply the above characters and comparisons of the mandibles of the 

 known existing kinds of Wombat in the attempt to elucidate the fossil mandibular 

 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 LIV. fig. 2 & Plate LVI. 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 

 LII. 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 Phascolomys latifrons (Plate LIV. fig. 1) than to 

 the other two existing species, and more especially to the variety, fig. 3, Plate LII. 



This affinity is more decisively shown by the form of the incisors in transverse section 

 (Plate LIV. fig. 2 a, 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, 



