2G8 



In the removal of the part of the outer wall of the ramus in quest of a possible 

 germ of a premolar or vertically replacing tooth, the base of the socket of the incisive 

 tusk (Plate XL. fig. 5, ?'*) was shown to extend beneath the first molar (d 3, I) as far as 

 the septum, dividing the socket of that tooth from the next, lodging d *. 



The base of the incisive socket makes a feeble prominence at its upper and inner side 

 at the hind third of the plate, sloping to the symphysial articular surface. The direction 

 of the socket and of its contained incisor is that of the long axis of the symphysis. 



The outlet of the socket (figs. 1 & 4, d), 1 inch in advance of that of the foremost 

 ■molar, is subquadrate, 7 lines in vertical and 6 lines in transverse diameter. The ante- 

 rior outlet of the dental canal (fig. 1, 32) holds the same relative position as in the first 

 described jaw of Nototherium Mitchelli. 



The general depth of the present young jaw is of course much less, relatively to the 

 crowns of the teeth in place, than in the adult. 



I have been favoured by the Trustees of the Australian Museum, Sydney, with pho- 

 tographs and a plaster cast of the left ramus and back part of the symphysis of the 

 mandible of a mature Nototherium from the freshwater deposits of Darling Downs. 



It includes the series of five alveoli of its side, the last three of which support their 

 teeth, which are rather more worn than in Mr. Hughes's specimen, and rather less so 

 than in the mandible figured in Plate XXXVIII. 



The longitudinal extent of the five alveoli is 6 inches 9 lines, as in Mr. Hughes's 

 specimen ; that of the last three molars is 4 inches 6 lines, but the hind talon of the last 

 molar seems to have been broken away ; were it entire, as in the first-described mandible, 

 the three teeth would occupy an extent of 5 inches. The inner wall of the crown in 

 each of the three molars has been broken away ; but they appear to have equalled in 

 breadth those teeth in the subject of Plate XXXIX., or the female mandibular specimen. 



The inflection of the lower border of the jaw begins, as usual in the adult, on the 

 vertical parallel with the socket of the last molar ; the hind part of the symphysis extends 

 to the vertical parallel with the fore part of the third molar (m 3). 



The vertical diameter of the jaw below the last molar (m 3), taken at the outer wall of 

 its alveolus, is 3 inches 2 lines ; that taken at the third molar (m 1) is 3 inches 1 line. 



At the fractured fore part of the cast is plainly shown part of the bottom of the socket 

 of the left incisor, with its longitudinally striate and finely rugous surface. There is not 

 enough of the cavity preserved to show that the missing part (almost the whole) of the 

 socket and incisor differed in shape or direction from those in the subject of Plate 

 XXXVIII. fig. 1, i. 



Agreeing, to the extent to which this cast does, with that of the more complete man- 

 dible of the inferred female of Nototherium Mitchelli, in every particular in which the 

 comparison can be instituted, I am unable to point out any character whereby it can be 

 referred to a different species ; and I doubt whether a scrutiny of the original specimen 

 would have supplied indications of such distinction. 



