212 PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
scalene triangle ; the shortest side is turned forward, the longest side forms the cutting- 
edge, which is notched anteriorly by an oblique groove extending from near the middle 
of the outside of the crown down to the cutting-edge, then inward and forward along 
that edge to near the antero-inferior angle of the crown. The grooved part of the edge 
in its present narrow condition thus presents two trenchant borders. The fore side or 
border of the crown shows an anterior low convex ridge through the subsidence of the 
enamel between this and the mid groove ; the enamel behind this groove is again at a 
lower level, thus the antero-posterior lay of the outer enamel is undulated. The fore- 
and-aft extent of the exposed crown is 6 lines, the front border or side of the triangle 
measures 5 lines. 
The indent caused by the missing second incisor is present on both right and left 
anterior incisors ; the interspace between the first and third incisors, from which the 
second has been pushed, is greater in the left than in the right premaxillary. 
A detached fully developed third incisor of a full-grown Sthenurus Atlas is figured in 
Plate 25. fig. 8. 
In the lower jaw of this species'* the interval between the molars and procumbent 
incisor is less than in Macropus Tit an f. The present specimen shows that a similar 
character marks the upper jaw. The extent of the maxillo-premaxillary diastema is 
here 10 lines, but would be of course greater in the full-grown Kangaroo. 
The anterior molar (Plate 25. fig. 2, Plate 26. fig. 4, d 3 ), with a crown 6 lines in 
antero-posterior extent, shows a depressed middle tract of the outer surface traversed 
by two vertical ridges. The inner surface, which forms posteriorly a prominent convex 
lobe, sinks rapidly to a basal ridge as it extends forward to a low angle on the inner 
side of the anterior division of the tooth. The second molar ( cl 4 ) has a prebasal ridge 
without the fore link ; the mid link is small and low placed, in chief continuation with 
the inner angle of the fore lobe. The hind surface of the hind lobe has a triangular 
excavation. 
These characters are repeated in m 1 and m 2 ; the crown of the latter is protruding 
from the formative cell, and is unworn. The crown of the premolar, exposed in its 
formative cavity (Plate 26. fig. 4,p 3 ), is incomplete with the concomitant wide and deep 
excavation at the basal part for the unexhausted pulp. The longitudinal grooves and 
ridges of the trenchant apical border, part of which are visible in the worn premolar of 
the subject of a former Part J, are well shown in the germ of the premolar in the fossil 
now described. The fore-and-aft extent of the crown agrees with that of the fully 
developed homologue, viz. 9 lines=18 millims. 
The bony palate, so far as it is preserved, appears to have been entire. 
§ 11. Sthenurus Brehus (Restoration of dentition and part of the skull). — This species 
was founded on a maxillary portion of cranium with the left molar series, in part muti- 
lated, and with the last two molars of the right side (Phil. Trans. 1874, plate xxvii. 
figs. 5 & 6) ; also on a fragment of the left maxillary with the premolar and contiguous 
* Phil. Trans. 1874, plate xxii. fig. 5. f lb. ib. fig. 13. t lb. plate xxiv. fig. 4 3 . 
