Principle in Palceontology. 179 



true carnivorous type is always the same, whether we consider 

 the placental or the marsupial orders. There is no more dif- 

 ference between a small marten cat and a tiger than there is 

 between the minute Antechinus and the largest Thylacine ; 

 teeth and jaw are constructed on the same principle ; and no 

 teacher knows this better than Professor Owen. 



But the Thylacoleo stands not isolated. I can prove several 

 distinct species ; and I have already discovered a much smaller 

 allied form, described under the generic term of Plectodon. Of 

 this genus I can also demonstrate three species at least. 



On the 2nd April, 1870, I dispatched, by direction of the 

 Trustees, two cases of specimens (2100 in number) to Profes- 

 sor Owen, no. 846 of which was the right lower incisor of a 

 Plectodon. Professor Owen never mentions this, the most 

 interesting specimen in the whole series, though it bears con- 

 siderably on the question at issue, and I doubt not we shall 

 hear of it at some future time. I kept photographs of it to 

 prove its identity with my duly established genus Plectodon ; 

 whenever this becomes necessary. 



I must bring my remarks to a close, however, though there 

 are numerous errors yet to be corrected. 



Making every allowance for Professor Owen's want of spe- 

 cimens, I am surprised to read the following sentence (p. 243) : 

 — " In the Bettongia jjenicillata^ with such worn incisors, and 

 with all the molars in place and showing an habitual use, the 

 trenchant premolar retains its vertical groovings to the cutting- 

 edge of both the outer and inner sides. They have been used 

 to divide the grass-blades and leaf-stalk or other tough part 

 or fibre of the vegetable food; but the more important and 

 continuous work of mastication has had grinders in number, 

 size, massiveness, and complexity of horizontal area fitted to 

 perform it. Old age is attended with seeming exceptions to 

 this rule in both human incisors and hypsiprymnal premolars, 

 which then show the wear or work of life." 



I draw the attention of Australians to table case A, section 

 4, in the new wing of the Museum, where "hypsiprymnal" and 

 " bettongial " (fossil and recent) premolars may be seen, in 

 which not only the premolars, hut the following three molars^ 

 are worn " Thylacoleo fashion," leaving not a vestige of the 

 vertical grooves. 



Much-worn human incisors are by no means rare in the 

 skulls of our collection ; and in a particular one, found at 

 Bondi, all the teeth are ground down to the roots. This re- 

 markable wear is caused by the chewing of certain reed or 

 bulrush-roots {Typha Shtittleworthii) ^ for the purpose of get- 

 ting at the starch between the fibres and to obtain the fibre 



