PEOFESSOE OWEN ON THE FOSSIL MAMMALS OF ATJSTEALIA. 81 



lower jaw in the Sydney Museum also shows the socket for the minute tubercular tooth 

 (Plate IV. figs. 5 & 6, m a) behind the posterior double-rooted one (ib. m \). The " foramen 

 mentale," the anterior boundary of the depression for the insertion of the large tem- 

 poral muscle, and the form of symphysis, closely resemble all these characters as shown 

 by the cast of the mandible first described. Mr. Krefft has dotted the depth to which 

 the socket of the lower incisive tusk descends in the symphysial part of the jaw {ib. 

 fig. 6, i) : it is somewhat greater than that of the upper tusk. 



The length of the dental series of the upper jaw, in a straight line, is \ inches 3 lines ; 

 that of the lower jaw is 3 inches 3 lines. 



From present data the probable formula of Thylacoleo is : — i^, ^ ^' i* 5=3' w* J^=24. 

 Of the incisors of the upper jaw, the first is a large tusk ; of the premolars, the first is 

 small, probably two-fanged, the second a very large carnassial. The first molar is small 

 and two-fanged in both jaws, the second is restricted to the lower jaw, is still smaller, and 

 is single-rooted. The chief business of the teeth has been delegated to the tusks and 

 carnassials : development has been concentrated on these at the cost of the rest of the 

 normal or typical dental series. The foremost teeth seized, pierced, lacerated or killed, 

 the carnassials divided the nutritive fibres of the prey. 



Thylacoleo exemplifies the simplest and most effective dental machinery for predatory 

 life and carnivorous diet known in the Mammalian class. It is the extreme modifica- 

 tion, to this end, of the Diprotodont type of Marsupialia. 



Besides the full confirmation which the additional fossils, here described, give of the 

 marsupiality of Thylacoleo, its closer afiinities in that Order are shown to be, not to the 

 existing Carnivorous Marsupials, e. g., Sarcojphilus, Basyurus, Thylacinm, Didelphys, 

 but to the Diprotodons, Nototheres, Koalas, Phalangers, and Kangaroos. It may, I 

 think, be said that the skull above described is one of the most singular and interesting 

 mammalian fossils hitherto discovered. 



Admeasurements of the Skull. 



in. lin. 



Length 9 8 



Length of the facial part anterior to the orbit 3 



Breadth at the preserved posterior part of the zygoma 7 2 



Breadth at the preserved anterior root of the zygoma 6 9 



Breadth of the cranium between the temporal fossae 2 3 



Length of the bony palate, from the fore border of the palato-nares . . .2 11 



Breadth of the bony palate at the same part 3 6 



From the fore end of premaxillary to the hind border of the palato-nares . 4 9 



From the hind border of the palato-nares to that of the occipital condyles . 5 6 



Length of the temporal fossa, including the orbit 7 2 



Breadth of the interorbital space across the antero-superorbital ridges . . 3 10 

 Breadth of the interorbital space behind the antero-superorbital ridges ..30 



Least breadth of the foramen magnum . Oil 



MDCCCLXVI. jr 



