206 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
the grinding series reduced to the three true molars, as in old individuals of Macropus 
major. 
The skull of this large existing species of Kangaroo which I have to compare with 
the present fossil retains the last deciduous molar ( d f) on both sides of the upper jaw, 
without any trace of the socket of the premolar which had worked in advance of the 
four retained grinders (d 1 , m 1 , 2 , 3 ). In the maxillary fossil of Macropus Titan (figured 
in plate xxi. fig. 10, Phil. Trans. 1874) the two roots of p 3 are retained, the crown 
having been accidentally broken away. That of the last molar (m 3) had not come into 
place, although the front lobe had pushed its way out of the formative cell. The two 
lobes of m 2 in the same fossil show attrition of the enamel ridge, but not so as to reach 
the dentine. 
In the younger subject of figs. 6, 7, 8 of the same plate and volume, the four teeth 
in place are d 3, d 4, m 1 , and m 2 ; above the first of these is exposed the crown of p 3 in 
its formative cell, and part of that of m 3 is shown behind m 2 . 
The series of changes of the upper molar dentition of the extinct Macropus Titan are 
thus as instructively and almost as completely displayed in petrified specimens as in the 
existing species ( Macr . major), of which I have obtained specimens in number and 
periods of age sufficient to exemplify these phases *. I have previously described a 
mandibular specimen of Macropus Titan , with the molar dentition reduced to m 2 and 
m 3 f , as in the latest phase hitherto observed in Macropus major. 
The cranial specimen exemplifying the reduction of molars to three on the left and 
four on the right side, lacks, unfortunately, the part of the upper jaw which supported 
the incisor teeth. Nearly two inches of the diastemal tract, however, is preserved in 
advance of d 4 on the right side. A fossil mandible of another individual of Macropus 
Titan , with a similar stage of dentition as the right side in Plate 26, fortunately gives 
the extent of the diastema between the molars and incisors $ ; and guided by the pro- 
portion which this part bears to the upper diastema in Macropus major , I have restored 
in outline in Plates 25 and 26 what is wanting in the present fossil, together with an 
outline of the mandible and mandibular teeth. 
The length of the mandibular diastema in Macropus major is 1 inch 9 lines, that of 
the maxillo-premaxillary one is 2 inches 6 lines. The length of the mandibular 
diastema in Macropus Titan being 2 inches 6 lines, that of the maxillo-premaxillary 
diastema, according to the pattern of the recent species, should be 3 inches 6 lines. 
There are indications, however, that the muzzle was relatively rather shorter in the 
larger extinct Kangaroo, and I have restored it with an interval of 3 inches 3 lines 
between the foremost molar and hindmost incisor. 
Of this characteristic tooth fossil specimens reveal two patterns of the outer surface 
of the crown in examples indicative of species as large as Macropus Titan and Sthenurus 
Atlas. 
In one type (Plate 25. fig. 4) the outer surface of the crown is divided into three 
* See notes, p. 245, Phil. Trans. 1874. f Tom. cit. plate Lxxvi. fig. 3. i Tom. ext. plate xxyi. fig 11. 
