224 REPORT — 1844. 



This is the only Australian fossil of the Mammiferous class which I have 

 hitherto been able to refer with certainty to an extra-Australian genus. 



A portion of a molar tooth presenting characters very like those of the 

 molars of both the Mastodon giganteus and the Dinotherium, described and 

 figured in my first memoir on the Mastodontoid femur*, I was subsequently 

 enabled to refer, in a notice of the true Mastodon's molar, to the genus Di- 

 protodon. 



The present Report is designed to give additional information of the na- 

 ture and affinities of the Diprotodon, as well as of two species of an allied 

 but distinct genus of large Pachydermoid marsupials ; such information ha- 

 ving been derived from an examination and comparison of the series of fossils 

 from the three distinct and remote localities in the continent of Australia 

 above-mentioned. 



Genus Diprotodon. 



Species D. australis. 

 The most decisive specimen of this species consists of the anterior extre- 

 mity of the right ramus of the lower jaw, exhibiting the rough articular sur- 

 face of the broad and deep symphysis, the base of the large incisive tusk, the 

 second and third molars, and the socket of the first. The third molar is 

 the most entire ; its grinding surface is produced into two high subcompressed 

 transverse ridges, placed one before the other ; there is also a ridge along both 

 the anterior and the posterior parts of the base of the crown. The exposed 

 commencement of the fangs is invested M'ith a thick coating of cement ; a 

 portion of this substance also remains in the interspace between the posterior 

 eminence and its basal ridge ; the enamel is thick and presents a rugose or 

 finely-reticulate and punctate exterior, the perforations being seen at the 

 fractured margins to lead to smooth pits extending a little way into the 

 enamel. The antero-posterior diameter of this tooth is two inches, the trans- 

 verse diameter is one inch three lines ; the extent of the three sockets of the 

 molars is four inches five lines ; they progressively diminish in size from the 

 third to the first. The second molar is much narrower than the third, but 

 its crown seems also, by the form of the broken surface, to have supported 

 two principal transverse eminences and an anterior and posterior basal ridge ; 

 its antero-posterior extent is one inch and a half, its transverse diameter at 

 the posterior division, where it is thickest, is nine lines; the coronal ridges 

 are broken off. The first or anterior molar is lost, but its socket shows that 

 it was implanted, like the other molai-s, by two fangs. The anterior part of 

 the symphysis and crown of the large incisor are broken off; the extent from 

 the first molar to the fractured end measures six inches three lines ; the upper 

 border of this tract manifests no trace of tooth or socket. The incisive tusk 

 extends forwards and slightly upwards ; it is subcompressed, measuring one 

 inch and a half in the vertical diameter and nearly one inch in transverse 

 diameter ; it has a partial coating of enamel, which extends over the inferior 

 part of the internal and the lower two-thirds of the external surface of the 

 tusk ; the enamel has the same rugose punctate outer surface as that of 

 the molar teeth. The large size of the dental canal exposed by the posterior 

 fracture of the ramus indicates the ample supply of vessels and nerves which 

 ministered to the growth and nutrition of the incisive tusk; the great depth 

 of the symphysis of the jaw gave the required strength for the operations of 

 the tusk, and space for its support and for the lodgement of its large per- 

 sistent matrix. The vertical diameter of the symphysis of the jaw anterior to 

 the molar series is four inches. The symphysial surface, contrasted with the 



* Annals of Natiual History, vol. xiii. p. 329. 



