169 



their dentition and shape of mandible than they do any other family of diprotodont 

 Marsupials*. From the characteristic reduction in size and number of the molar teeth 

 I have associated them as members of a " paucidentate " family or section. 



To which of the existing families of Diprotodonts is the paucidentate one most 

 nearly allied \ Thjlaeoleo best lends itself to the solution of this question, its maxillary 

 as well as mandibular dentition being now, I may affirm, accurately determined. It 

 is highly probable, from the close conformity of Plagiaulax to Thylacoleo in the pecu- 

 liarly and extremely modified dentition of the lower jaw, that the maxillary teeth also 

 resembled those of the larger diprotodont carnivore. Of this the dental formula is : — 



*S ^JP-^ m -B- =30. 



No existing Diprotodont offers a like formula. That of the Poephogaf departs further 

 than in most other diprotodont families, because there is no tooth interposed between 

 the incisor and sectorial in the lower jaw, and in most Kangaroos not more than two 

 are developed between the front incisor and sectorial in the upper jaw on each side, the 

 two intervening teeth being incisors — both projecting anterior to the maxillo-premaxillary 

 suture. Hypsiprymnus and Bettongia have a small canine in that suture, and two incisors 

 between the larger front incisor and the sectorial in the upper jaw, but no teeth in that 

 interspace in the lower jaw (figs. 17, 18). Of the more important true molar teeth 

 (id. ib. m 1-4), the first three have " a quadrate form, presenting four equidistant blunt 

 tubercles which are joined in pairs by transverse ridges, but with these ridges less ele- 

 vated than the points of the tubercles ; there is a slight trace of the band of the tooth " 

 ('cingulum' of my 'Odontography') "on the front and back part of each molar as in 

 Macropus. The hindermost" (fourth) "molar is generally small, almost round. Cases 

 occur in which the last molar tooth is absent ; and, what is more extraordinary, I have 

 observed an extra tooth on each side of the upper jaw in a species of Hypsiprymnus"$. 



Thus in these mixed feeders, but with the vegetable diet predominating, the molar 

 teeth adapted to such diet are never fewer and commonly more in number than in the 

 most typical placental Herbivora. In relation, apparently, with the drier and tougher 

 vegetable fibres of Australia, the premolar is trenchant and strengthened by vertical 

 grooves and ridges. In one of the New Guinea. Tree-Kangaroos (Dendrolagus dorco- 

 cephalus) this trenchant tooth (p, fig. 1G) is proportionally larger than in the Australian 

 Potoroos and Bettongs, but the light-giving teeth (the true molars) "are conformable 

 with the Macropus type"§. 



* Dr. Falcoxer asserts, " TJnjlacoIeo and Plagiaulax may be regarded as being as wide apart among the Mar- 

 supials as the two former (Machairodus and MoscJm.s) are among placental Mammals." — X. p. 358 ; XL p. 442. 



t I hold by this term, preferring it to the subsequently propounded one, Macropoda, of Vax der Hoevex, 

 because the latter is equally applicable in its descriptive sense to the long-legged, saltatory Polyprotodonts. 



t Waterhouse, ' A Xatural History of the Mammalia ' (Marsupial ia), 8vo, 1845, p. 194. 



§ Ibid. p. 182, pi. 10. fig. 3. In my ' Odontography' I showed that the " maximum of development of the 

 trenchant premolar was attained in the arboreal Potoroos of Xew Guinea (Hypsiprymnus ursinus and Hyps, 

 dorcocephalus), in the latler of which its antcro-posterior extent nearly equals that of the three succeeding molar 



