437 



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 2 inches of the diastemal tract is, however, preserved in 

 advance of d « 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 LXXIX., fortunately 

 gives the extent of the diastema between the molars and incisors (Plate LXXXVI. 

 Jig. 11), and, guided by the proportion which this part bears to the upper diastema in 

 Macropus major, I have restored, in outline, in Plates LXXVL, LXXVII. & LXXIX., 

 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 dia- 

 stema 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 different patterns of the outer surface 

 of the crown, of which I give two in examples indicative of species as large as Macropus 

 Titan and Sthenurus Atlas. 



In one type (Plate LXXVI. fig. 4, Plate LXXVII. fig. 2) the anterior half of the crown 

 is divided into three unequal convex tracts by two oblique grooves, of which the hinder 

 one extends nearest to the base or root of the tooth ; in the other type (Plate LXXVI. 

 fig. 3, Plate LXXVII. fig. 5) a deeper oblique fissure subequally bisects the crown ; 

 it marks off a more prominent fore part of the outer surface from a lower and vertically 

 shorter, but rather more longitudinally extended, hind tract. As the first of these 

 patterns is repeated in the third upper incisor of Kangaroos with a small premolar 

 (Macropus major, Plate LXXVII. fig. 3), and the second pattern is found in Kangaroos 

 with a large trenchant premolar (Halmaturus ualabatus, Plate LXXX. tig. 20, Halm, 

 rujicollis, ib. fig. 21), I refer the fossils of the second pattern to Sthenurus Atlas, and 

 those of the first pattern to Macropus Titan. 



Macropus Titan has the triangular form of occiput (Plate LXXVIII. fig. 2) as in 

 Macropus major (ib. fig. 3), the apex of which at the summit of the superoccipital ridge 

 (3) is somewhat rounded off. 



In like manner a second inner ridge from the base of the paroccipital (4) converges 

 towards its fellow as it rises, parallel with the outer ridge from the mastoid, but subsides 

 at 2, before attaining the summit of the exterior ridge, 3. 



The crown of the superoccipital arch projects rather more backward in the fossil than 

 in Macropus major ; it is not on a vertical plane with, or sloping forward from, the 

 occipital foramen. The surface below the arch is traversed by a less prominent medial 

 vertical ridge in Macropus Titan than in Macropus major. 



45* 



