272 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
of the younger individual (Plate XXII. figs. 5, 6, 8) is well within the limits of indi- 
vidual and sexual range of variety. 
The outer surface of the portion of mandible of Sthenurus Atlas (Plate XXIV. fig. 7) 
shows a longitudinal sinuous shallow channel, extending from below the fore part of p 3 
to m 1 , at a distance varying from 2 lines to 5 lines below the alveolar border. Below 
the channel the ramus swells to greater thickness than in the largest of the mandibular 
fossils of Macropus Titan. The lower border has been broken away ; and in the longi- 
tudinal extent of mandible here preserved, the fractured surface shows a pretty uniform 
breadth or thickness of 9 lines. 
The increase of the fossil (Plate XXIV. fig. 7) over the younger Sthenurus (Plate 
XXII. fig. 5) is shown by the bone more than by the teeth. But even in the smaller 
specimen (ib. figs. 5, 6) the mandible is relatively stronger and deeper than in Macropus 
Titan (ib. figs. 13, 15). In this species the last four molars ( d 4 and m 3) occupy a longi- 
tudinal extent of 2 inches 4 lines, but in Sthenurus Atlas of 2 inches. These differential 
mandibular and dental characters come well out in comparing figs. 5 & 13, and figs. 
8 & 14, in Plate XXII. 
§ 8. Sthenurus Brehus, Ow. — This species is represented by two fossils from the 
Breccia-cave of Wellington Valley, presented to the British Museum by the Trustees of 
the Natural-History Museum of Sydney, New South Wales, and forming part of the 
results of the exploration by Prof. Thomson and Gerard Krefft, Esq., carried out 
with the aid of the legislative grant*. 
The specimens formed part of a series of duplicates, thickly encrusted, like those of 
Thylacoleo and Phascolomysf, with the reddish stalagmite of the cave. 
The most acceptable and instructive results of the clearance of the fossils from their 
matrix were the subjects of figs. 5-9 of Plate XXVII. The largest specimen (figs. 5 & 6) 
consists of a portion of cranium including a great part of both maxillaries, with the 
intervening palatal plates and both palatine bones ; the zygomatic masseteric process 
came out entire on both sides of the skull. The molar series of the left maxillary 
( p 3 to m 3) had undergone fracture of the crowns of the two anterior teeth ; the portion 
of the right maxillary included the two posterior molars. 
The pattern of the molar crowns closely accords with that of Sthenurus Atlas, and 
the narrow but well-defined prebasal ridge (ib. fig. 6, m 2 , f) was without the link ; the 
mid link (ib. ib. r) was represented by a rudiment at the bottom of the valley between 
the two transverse lobes, a, b ; the postbasal ridge (g) was represented by the crescentic 
border of a depression on the hind surface of the hind lobe ; the main ridges were 
rather narrow antero-posteriorly in proportion to their breadth and vertical extent. 
The superiority of size of Sthenurus Brehus over Sthenurus Atlas may be estimated 
by comparing figs. 5-9, Plate XXVII., with figs. 4-6, Plate XXIV. The base of the 
broken premolar (Plate XXVII. fig. 6, p 3 ) shows similar proportions of that tooth, 
although, as the crown swells out beyond the part retained, this does not yield the whole 
* Phil. Trans. 1870, p. 570. f Ib 1871 and 1872. 
