PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF AU STEALIA. 
213 
molar entire (ib. figs. 7, 8, & 9) from a younger individual. Both fossils were from 
Mitchell’s Breccia-cave in Wellington Valley, New South Wales, and formed the first 
evidence of this extinct species which came to my hands. 
Since the publication of the paper ( loc . cit.) illustrative of these fossils I have been 
favoured, through the persevering and successful quest of George F. Bennett, Esq., 
with portions of the skull and lower jaw of older and younger individuals of the same 
species from the freshwater drift at Clifton, Queensland. One of these specimens 
exhibits the entire molar series, left side upper jaw, with that of the right side, less the 
last molar ; another fossil includes the premaxillaries and upper incisors ; and a third 
consists of the fore part of the mandible with the lower incisor and with the first three 
molars of the right side. AJi4 hree specimens are parts of the same skull. 
A fourth lot consisted of four portions of the upper jaw of a mature but younger 
individual than the subject of plate xxvii. loc. cit., and included the incisors and pre- 
molars of both sides, and the entire molar series of the right side. 
A fifth specimen consisted of the fore part of the upper jaw of an aged individual 
with much of the crowns of the incisors worn away, and the smaller ridges on the inner 
side of the premolars rubbed smoothly down. 
These specimens instructively exemplify the constancy of the maxillary molar 
characters of the genus and species as shown in the type specimen, and add those of 
the mandible and the characters of both upper and lower incisors. 
Of the upper incisors the first or foremost (Plate 28. figs. 1, 2, & 3, i i) has a greater 
relative superiority of size over the second and third than in any existing species of 
Kangaroo that has come under my observation ; in this character Sthenurus approaches 
the Koalas and Potoroos among existing, and the colossal Diprotodonts among extinct 
Marsupials. 
The transverse diameter of the crown of i i is 8 lines (17 millims.) ; it nearly equals 
that of the two following incisors, of which the third (i 3) is broadest, viz. 5 lines 
(10 millims.) along the oblique trenchant or working border ; the thicker, triturant 
surface of the second incisor is 4 lines (8 millims.) in longest diameter. The crowns 
of the six incisors describe a semicircle (ib. fig. 3) ; those of the anterior pair, separated 
by a line’s breadth in the fossil, evidently touched each other in the living animal at 
their median angles, which show the effects of mutual pressure. 
Each incisor is curved lengthwise, with a strong outward or forward convexity ; 
the exposed enamelled crown of the first measures in a straight line 1 inch 1 line 
(27 millims.), that of the second incisor 7^ lines (15 millims.), that of the third 
incisor the same ; this, as usual, expands to the working surface ; its outer enamel is 
bisected by a feeble linear longitudinal groove. The transverse interval between the 
two incisors of the third pair is 1^ inch. 
The outer half of the fore surface of the crown of the second incisor (i 2) is prominent, 
and is pressed into a corresponding channel of the hind surface of the first incisor ; 
the channelled part of the contiguous surface of the second incisor reciprocally receives 
