265 



has been continued. 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- 

 ciable degree different from, those in the subject of Plate XXXIX. But, besides the 

 greater depth, the outer surface of the jaw is rather less convex vertically beneath the 



22 



