436 



inner end or border of the anterior lobe. The oblique hind ridge (Plate LXXX1. 

 tig. 15, g) is, indeed, a serial repetition of the mid (r) and fore (s) links, but subside 

 with a more oblique course downward toward the base of the outer border of the hind 

 lobe, having no other division of the molar to connect with such lobe. From the fore 

 part of the base of the inner end of the hind lobe a low ridge defines the anterior surface 

 of that lobe to the inner side between it and the mid link ; this defining ridge is not 

 present in the upper molars of Macropus major, but there is a small tubercle at the inner 

 entry of the valley between the two main lobes of the upper molars in Macropus major, 

 which is not present in Macropus Titan. 



The fossil skull, with the molars agreeing in the above characters, and in size, with 

 those of more fragmentary examples of Macropus Titan (Plate LXXXI. figs. 8, 10, 15, 16 

 and Plate LXXX1I. figs. 10-12), is of a mature and somewhat aged individual. The 

 summits of both lobes of the hindmost grinder (Plate LXX1X. fig. 1) are worn so as 

 to expose a linear tract of enamel, widest of course on the anterior lobe. In the penul- 

 timate grinder a broad field of dentine is exposed on this lobe extending backward by 

 a linear tract along the base of the mid link (r), but not so far as the transverse tract 

 of dentine exposed on the hind lobe. In the antepultimate grinder both lobes are so 

 worn that the lozenge-shaped fields of exposed dentine touch and communicate at the 

 base of the worn-down link. The foremost grinder (d 4, Plate LXXVII.) is retained 

 on the right side, worn down to its base ; but this tooth has been shed on the left side, 

 and the grinding series reduced to the three true molars, as in old individuals ■ of 

 Macropus major. 



The skull of this large existing species which I have to compare with the present 

 fossil retains the last deciduous molar (d 4) 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 4, m 1, 2, 3). 



In the maxillary fossil of Macropus Titan, figured in Plate LXXXI. fig. 10, 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, Plate LXXXI., 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 (Macropus major) of which I have obtained specimens in number 

 and periods of age sufficient to exemplify these phases*. I have lately received a man- 

 dibular specimen of Macropus Titan with the molar dentition reduced to m 1 and m 3 

 (Plate LXXXIX. fig. 1 ) as in the latest observed phase in Macropus major. 



* See ' Notes,' p. 397. 



