254 
PROFESSOR OWEN ON THE FOSSIL MAMMALS OF AUSTRALIA. 
The superficial resemblance in the comparative views given in XII. pp. 312, 313, figs. 2 &4, 
of the skulls of the Koala and of the Thylacoleo (as restored by Professor Flower)^ 
vanishes when they are turned from the front to the side view, as in figs. 6 & 8, p. 233. 
The sectorial of Phascolarctos forms one fifth of the molary series, and mainly through 
“ the greater relative size than in other vegetable-feeding Diprotodonts of the four fol- 
lowing molar teeth”'*. The incisor formula differs by excess, as the premolar formula 
does by defect, compared with the dentition of Thylacoleo , and this in the same way and 
degree as in Kangaroos and Potoroos. 
We must pass to another family of Diprotodonts to find the two minute (I termed 
them “functionless”) premolars f in advance of the last which retains its sectorial use 
and equality of length with the succeeding molar. In Phalangista ursina , Ph. maculata , 
and Ph. chrysorrhoa the functional premolar is preceded by two rudimental premolars as 
in Thylacoleo. In Phalangista. Coolcii (fig. 19), where the 
upper canine is minute and protrudes at the maxillo- 
premaxillary suture, two small premolars intervene 
between it and the homologue of the upper carnassial 
of Thylacoleo : the same degree of correspondence in 
numerical formula is represented by some Petaurists J ; 
but I have failed to find any species of “ Carpophaga ” § 
in which three premolars appear between the functional 
one and the canine, or any species in which the upper 
incisors are reduced to two on each side. That a ten- 
dency to deviate by such reduction was amongst the inconstant characters of organization 
of diprotodont Marsupialia is exemplified by the Wombats, in which no incisors are 
developed behind the large upper anterior pair. Thylacoleo shows an interesting inter- 
mediate stage of the incisive formula, viz. i. between the i.~ °f Phizopliaga || and 
the i. of all other existing families of Diprotodonts. 
Of all known Marsupialia , recent or fossil, Plagiaulax , so far as its dentition is accu- 
rately determined, is most closely allied to Thylacoleo. In the lower jaw the true 
molars are similarly reduced to two of small size and tubercular form. One cannot 
suppose that they were opposed by more tuberculate molars above ; the analogy of Thy- 
lacoleo (Plate XIV.) would point to fewer. A character, indeed, of the first of the inferior 
molars of Plagiaulax , overlooked by Dr. Falconer, would indicate that it worked secto- 
rial-wise, like the fore part of the anterior lower molar of Thylacoleo , upon the back 
part of the blade of a large upper carnassial ; I allude to the smooth vertical wall-like 
surface of the inner side of the outer half of the crown of m 1, in Plagiaulax 
* Owen, “ Classification of Marsupialia ,” Trans. Zool. Soc. (1839 ) p. 326. f Loc. cit. p. 323. 
X E. g. Petaurus (Belideus) Jlaviventer, Cycl. of Anat. Art. Marsupialia, tom. cit. p. 264, f. 89. 
§ Owen, “ Classification of Marsupialia ,” ut supra, p. 322. 
|| Ibid. p. 329. 
% Owen, Monograph on Mesozoic Mammals, tom. cit. t. iv. fig’s. 9, 12. 
Fig. 19. 
Mandible and teeth, Phalangista 
Coolcii, nat. size. 
