419 



Jagus erubescens), or with vacuities, as in most species of HalmaUirus ; but part of the 

 border opposite the interval between di and m 1 (Plate LXXXIV. fig. 6) is so smoothly 

 rounded off as to suggest that it is a natural, not a broken, tract. 



The premolar has the middle two fourths of its outer surface slightly depressed and 

 feebly concave lengthwise (ib. figs. 4 & 6, a), with two chief vertical ridges and others 

 faintly indicated. The fore and hind ends of the outer surface are smooth and 

 convex, or bulging; the free margin is subtrenchant, with the ends of the terminal 

 bulges obtuse. The inner surface or division of the crown (ib. fig. 5, b) is much lower 

 than the outer one, yet having more of the character of a part of the crown than of a 

 developed " cingulum ;" it increases in height as it recedes, the hind part swelling into 

 an inner lobe, continued at the back part of the crown into the postexternal tubercle 

 and abutting against the inner side of that part by a second transverse ridge. The 

 lower and less developed fore part of the inner division of the crown is similarly con- 

 nected with the antexternal tubercle, viz. by a low ridge forming the fore part of the 

 crown, and by a buttress-like production against the inner surface of that tubercle. 

 The intermediate part of the inner division is connected with the outer division by three 

 transverse ridges (ib. fig. 6,p> s). A premolar of the size shown in the figures, and with 

 the structure above described, would be held, according to its proportions to the molars 

 behind, as indicative of a subgeneric section of Macropodidoe, for which I propose the 

 term Stheuurus, suggested by the form and proportions of a vertebra of the very powerful 

 tail of this great extinct Kangaroo*. I shall presently be able to show that the modi- 

 fications of the mandible and mandibular incisor support this distinction. 



The bilophodont upper molars of Sthenurus are characterized by a narrow prebasal 

 ridge (ib. fig. 6,/) without a fore-link ; by a still narrower and shorter postbasal ridge, 

 represented by that, g (fig. 4 a), which curves from the outer part of the base to the 

 inner angle of the hind lobe, along the back part of the crown, that surface sinking a 

 little above the part of the ridge nearest the base of the tooth. The mid-link (Plate 

 LXXXIV. fig. 6, to 3, r) is thin, low, or rudimental, yet still traceable from the back part 

 of the inner angle of the anterior lobe to the middle of the base of the fore part of the 

 hind lobe. The contour of the working-surface of the molars is more subquadrate 

 than in Macropus Titan, the fore-and-aft diameter being not so much greater than the 

 transverse. The series describes a feeble curve convex outward, but changes anteriorly 

 to a slight concavity through the modification of the premolar at a, as above described. 

 The abraded state of d 4 contrasts with the almost untouched crown of p 3, showing the 

 earlier development of the hinder tooth. The dentine is just exposed on the inner 

 halves of the lobes of to i. The enamel only shows abrasion at the summits of the lobes 

 of to 2 ; the edges of those of to 3 are slightly polished by wear anteriorly. This fossil 

 has come from an individual that perished in the prime of life. 



In existing Kangaroos the upper premolar of Macropus ualabatus, Lesson (Plate 

 LXXXIV. figs. 1-3, p 3), bears the nearest resemblance to that of Sthenurus Atlas, and is 



* Gr. a-diroi, strength: oiph, tail. 



