10 ON THE MANDIBLE OF ZVaOMATTJRUS, ETC. 



an interval of 15 mm. in breadth The whole tooth is abbreviated 

 in correspondence with the shortness of the intermaxillary and 

 its armature ; the length of the diastoma being 60 mm., while 

 that of the longer faced Nototherium is 98-5. 



There are now two crania of Zygomaturns in this Museum, 

 besides two pieces of other crania, and two editions of a cast of 

 the type skull preserved in the Australian Museum. As a 

 passing thought it may appear somewhat strange that of Noto- 

 therium, of which so many maxillary and mandibular remains 

 are extant, the upper deck of the skull should be unknown, 

 while the single jaw of Zygomaturus now brought to light should 

 have been preceded by several cranial relics. The difficulty 

 would hardly be worth notice were it wholly true ; but as a 

 matter of fact the Xototherium skull is by no means absent from 

 our collections. We have here the greater portion of one skull, 

 the facial and maxillary parts of another, the nasals with the 

 intermaxillary of a third and numerous fragments of the brain 

 case ; no doubt others exist elsewhere but have escaped recogni- 

 tion owdng to their unlikeness to corresponding parts of the 

 Zyqomaturus skull. I do not propose to describe the skull of 

 Nototherium in this place, but will merely say that in general 

 form it resembles that of Diprotodon, as indeed we might have 

 expected from the likeness between the mandibles. The facial 

 region is elongate, the nasals small and but little expanded, the 

 post-nasal depression long and shallow, the brain case narrow in 

 front with well marked parietal crests, the zygomas flat and com- 

 paratively feeble, the occipital region sloping backwards ; all fea- 

 tures in forcible contrast with those of Zygoviaturus. The upper 

 incisors may be known from those of Zygomaturus by their 

 retaining nearly the same breadth and thickness throughout 

 and consequently exhibiting a much greater surface of wear. 



In sum, the massiveness of the articular region, its expan- 

 sion at a different angle to that made by the horizontal limbs, 

 the form of the incisors, with the shape and size of their 

 sockets, the small size of the molars and shortness of the 

 symphysis, are likely, one would fain think, to be convincing 

 proofs that the mandible of Zygomaturus has no generic affinity 

 with that of Nototherium. 



