172 



The rest of the outer surface is feebly undulated, and that more toward the base than the 

 upper part of the crown. On the inner side, the basal undulation, through vertical risings 

 and sinkings of the enamel, is more feebly marked*. The chief vertical indent on the 

 outer side of the crown of the Thylacoleonine upper carnassial is near the posterior 

 third (Plate VII. figs. 1, 3, o), and answers to the deeper vertical notch in Machairodus 

 (ib. fig. 15, o) and Fclis which defines the posterior lobe of their upper carnassial. It is 

 interesting to note that this notch is less marked in Machairodus than in Felis, and also 

 that the concavity of the outer side of the carnassial from before backward (i. e. from 

 the outer ridge representing the second or middle lobe in Machairodus and the hind 

 end of the crown) represents the more angular concavity due to the deeply vertical 

 groove on the outer part of the carnassial in the above placental Camivora. 



Professor Flower (XII. p. 309) states that " the resemblance of the great premolar of 

 Thijlacolco to the " carnassial " of the true Camivora is merely superficial ;" and he speci- 

 fies among the differences, " especially the absence of any distinct inner lobe or tubercle" 

 (in the upper molar) "supported by a third fang" (ib. p. 310). He was, probably, not 

 cognizant of the example afforded by one of the extinct true Camivora of the absence 

 of the inner lobe or tubercle, or, rather, its reduction to a ridge, the lower swollen 

 base of which (Plate VII. fig. 15, v') may be compared to " a less developed homologue 

 of the inner tubercle in the normal species of Felis" f. 



Dr. Falconer, indeed, repudiates this partial homology, and affirms " of the upper car- 

 nassial of his Sewalik Machairodus" that " neither the anterior lobe nor the middle one 

 bears the slightest indication of bearing an internal tubercle" (XL p. 456) ; and this 

 further evidence of transitional structure between the Feline and Thylacoleonine carnas- 

 sials will probably be acceptable to Professor Flower, though it is enunciated, as I think, 

 in exaggerated terms. 



The well-defined vertical ridges and intervening grooves on both outer and inner sur- 

 faces of the crown of the sectorial premolar of the Potoroos vary in number in different 

 species, but are countable and pretty constant in such species, rising from four to eight 

 or more ; they are best marked on, and sometimes limited to, the apical half of the crown, 

 the enamel at the base being smooth and even. The fore part of the Potoroo's sectorial 

 is not broader (is usually narrower) than the hind part, and the cutting-edge runs straight 

 or nearly so. 



The transverse expansion of the fore part of the lower carnassial of Thylacoleo, repre- 

 senting the thicker anterior lobe of the carnassial of the Felines, the fore-and-aft con- 

 vexity of the outer surface of the crown, and the concavity of the inner surface answer- 

 ing to that which defines the two lobes of the blade in Felines are better marked than 



* Dr. Falconer, quoting my original description of the carnassial in llujlacoleo as being " slightly grooved 

 vertically on the inner side," correctly proceeds : " these indentations disappear about halfway up towards the 

 edge, where the surface becomes reticulately rugose, being precisely the reverse of what occurs in the last pre- 

 molar of IIlJps^l>r1Jmnus , '' (X. p. 350, XI. p. 440). 



t Owex, British Fossil Mammals, 4to, 184G, p. 178. 



