ON DITROTODON MINOR, IIUX. 



43 



process more gradually and with a distinct backward slope, which 

 is continued along the edge of the coronoid plate — this in D. aus- 

 tralis is verticil. The ascending ramus is relatively narrow, its 

 external fossa very concave — below the condylar process its posterior 

 wall is reduced to exf-reme thinness, where in 1). australis the bone 

 retains nearly an inch of thickness. The neck of the condyle is at 

 its narrowest considerably broader — its articulating surface, not 

 quite perfect in the specimen, also broader at its inner end. On 

 the inner side of the jaw the post molar platform which in D, australis 

 forms with the inner side of the ascending ramus a continuous 

 surface expanding transversely, and produced backwards and 

 upwards from the angle so that its edge overhangs the posterior 

 dental foramen, in D. minor forms a narrow short and convex 

 surface, with a low obtuse angle distant from the foramen by much 

 more than the length of the last molar. The difference in age between 

 these two jaws being entirely insufficient to account for the struc- 

 tural difference here shown, it must be due either to sex or species. 

 The nnlar teeth are those of I), australis, reduced in dimensions. 

 The premolar has been shed — its loss at this early age can hardly 

 be other than an individuality, yet it may be observed that in the 

 cast of a mandible of the species, the original of which is unknown 

 to the writer, the appearances indicate a similarly early shed ling 

 of the premolar. 



DIMENSIONS. 



D. MINOR 



D. AUSTRALIS 



Length from anterior edge 



of dental 



mm. 



mn?. 



orifice to back of coronoid 



process... 



402 



404 



Height at sigmoid notch 





254 



204 



• ,. condyle 





290 



309 



m 3 





100 



115 



d* 





129 



147 



Width of ascending ramus at 



the cond- 







lar process 





149 



172 



Length of condyle 





120 



121 



Breadth (mesial) 





38 



36 



Length of molar series d 4 — m 3 





181 



215 



