PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
57 
The commencement, an inch above the anterior angular inflection, of the posterior 
inflected margin (Plate V. figs. 1 & 5, a) and the corresponding outswelling at the outer 
part of the ascending ramus (ib. fig. 5, h) indicate more definitely than in the first 
described mandible the part from which the neck of the condyloid process has been con- 
tinued. The breadth of the back part of the jaw here is 2 inches 2 lines. 
The anterior outlet of the dental canal is, as in the former mandible, on the same 
vertical line as the fore part of the first molar ; but it is placed rather lower down : it 
is of similar size and shape. 
A third example yielding Nototherian mandibular characters is also from the fresh- 
water deposits of Darling Downs; it was discovered at Eton Vale by Edward S. Hill, 
Esq., and was presented to the British Museum by Sir Daniel Cooper, Bart. It is part of 
the left ramus of an adult and seemingly male jaw, and includes the sockets of the last 
three molars with the penultimate and last of these teeth in place, but mutilated. It 
retains a similar proportion of the ascending ramus to that in the two preceding jaws, 
but with more of the fore part of the base of the coronoid process. The vertical dia- 
meter of the ramus behind the last molar socket is 3 inches 9 lines ; the thickness of 
the jaw below that socket is 2 inches 7 lines. 
From the hindmost socket to the orifice of the dental canal is 2 inches 8 lines. The 
postalveolar process with the base in the Nototherian position is, as usual, broken away, 
like most projecting parts in these rolled and transported drift-fossils. The fore part 
of the coronoid rises to 1 inch and 9 lines above the dental orifice, but at that height 
has been fractured. The antero-posterior extent of the two last sockets is 3 inches 
6 lines, as in the first described mandible, with which all the other characters of the 
present specimen correspond so far as they are shown. I refer it, therefore, to a large 
old male of Nototherium Mitchelli. The marks of torrential action are very plain in this 
water-worn fossil : it is massive and heavy from some mineral infiltration. 
A fourth rolled and mutilated specimen from the same locality, contributed by the 
same liberal donor, retains the last three molars and the socket of the second, with 
the hind part of the symphysis, showing the same vertical relative position to their 
molar (m i) as in the former specimens of Nototherium Mitchelli. The teeth, so far as 
they are preserved, agree in size, shape, and proportion with those of that species. The 
ascending ramus has been broken away behind the last alveolus and the beginning of 
the base of the coronoid process. The dental canal is here exposed an inch below that 
part of the process, and half an inch from its outer side. 
The fore-and-aft extent of the three last sockets is 5 inches 5 lines. The depth of 
the ramus at the interspace between the last two sockets is 4 inches 2 lines in a 
straight line; below the interval between the penultimate and the antepenultimate 
molars it is 4 inches 3 lines. In the first described mandible the same admeasurement 
is here 3 inches 9 lines; in the type jaw it is 3 inches 7 lines; in the second and sup- 
posed female jaw it is 2 inches 10 lines. Between this and the mandibular fragment 
under description the difference of depth of the horizontal ramus seems too great for 
mere sexual variety ; yet the three last molars are not at all larger than, or in any appre- 
mdccclxxii. i 
