ON THE EXTINCT MAMMALS OF AUSTRALIA. 2'Ji> 



molar teetli, seems enormous, much exceeding that of any Rhinoceros, and 

 almost equalling the same part in the deep-jawed Hippopotamus ; its antero- 

 posterior extent to the fractured end of the jaw is six inches, its vertical dia- 

 meter three inches, its direction is obliquely from below upwards and forwards, 

 its Aipper or posterior margin nearly straight, its lower or anterior one convex ; 

 it stands out a very little way from the vertical plane of the inner surface of 

 the ramus. The thickest part of the symphysis of the jaw does not exceed 

 three inches, that is, at its lower part, which is convex in every direction. 

 The surface of the bone seems to have been naturally roughened by minute 

 vascular grooves and ridges ; it has been crushed and cracked. The ridge, 

 which doubtless formed the anterior part of the base of the coronoid process, 

 begins to stand out below the socket of the third grinder ; the smooth abraded 

 surface at the back of the posterior talon of that tooth indicates the pressure 

 against a contiguous tooth in the portion of jaw which has been broken away. 

 The symphysial portion of jaw differs in a striking degree from the corre- 

 sponding part in the known existing or extinct Pachyderms, which have, like 

 the Australian extinct Mammal, a single incisor tusk in each ramus of the 

 lower jaw. In the young Mastodon the tusk is situated in a less deep, more 

 suddenly contracted, and more produced symphysis ; the symphysis of the jaw 

 in the existing Sumatran Rhinoceros, and in the extinct Rhin. incisivus, is 

 much less deep and is broader in proportion ; the peculiar deflection of the 

 symphysis in the Dinotherium makes it differ still more strikingly from the 

 Diprotodon, in which the incisive tusks of the lower jaw extended obliquely 

 upwards. The sudden slope of the toothless margin of the jaw anterior to 

 the molares distinguishes the existing Proboscidians, which have, besides, a 

 smaller anchylosed symphysis and no lower tusks. 



In the proportion of the symphysial articulation to the molar teeth, I know 

 of no quadruped that so nearly resembles the present large Australian fossil 

 as the Wombat ; but in this Marsupial that part of the ramus of the jaw is 

 broader in proportion to its depth ; in this dimension, viz. the proportion of 

 breadth to depth of the jaw supporting the anterior molares, the Kangaroo 

 more resembles the Diprotodon ; and the molars of the Kangaroo in their 

 double-ridged crowns are those amongst the Marsupials which most closely 

 correspond with the molars in the present gigantic fossil. 



In the general size of the tusk and jaw, in the extent of the symphysis, in 

 the subquadrate form of the incisive tusk, and the partial disposition of ena- 

 mel, the agreement between the present fossil, which was obtained from the 

 bed of the Condamine river, west of Moreton Bay, and the corresponding 

 fragment of jaw and tooth above-cited*, from the Wellington Valley cavern, 

 is so close as to leave no doubt as to their generic identity. The tusk in the 

 cavern specimen appears to be a trifle broader in proportion to its depth or 

 vertical diameter, and a difference is indicated in the shape of the symphysial 

 articulation ; but these may be individual or sexual varieties, and at all events 

 they do not afford decisive ground for specific separation. The original con- 

 dition of the fossil from the stratum forming the bed of the Condamine river 

 is much altered and it is heavily impregnated with mineral matter. 



The next specimen, obtained by Sir T. Mitchell from the same locality and 

 deposit as the fore-part of the jaw above described, yields an interesting indi- 

 cation of the affinity of the Diprotodon to the peculiar Order which almost 

 exclusively represents the Mammalian class in Australia. It is a portion of 

 the left ramus of the lower jaw of apparently the same individual Diprotodon 

 australis ; it includes the two fangs of the last molar teeth and the angle of 



* Mitchell, loc. cit., pi. 31, figs. 1 and 2. 

 I84;4f. o 



