432 PLAGIAULAX 



They are followed by sockets of two much, smaller teeth, 

 shown in other specimens to have subtuberculate crowns re- 

 sembling those of Microlestes. The large front tooth of Pla- 

 giaulax is formed to pierce, retain, and kill ; the succeeding 

 teeth, like the carnassials of Carnivora, are, like the blades 

 of shears, adapted to cut and divide soft substances, such as 

 flesh. As in Carnivora, also, these sectorial teeth are suc- 

 ceeded by a few small tubercular ones. The jaw conforms to 

 this character of the dentition. It is short in proportion to 

 its depth, and consequently robust, sending up a broad and 

 high coronoid process, for the adequate grasp of a large tem- 

 poral muscle ; and the condyle is placed below the level of 

 the grinding teeth — a character unknown in any herbivorous 

 or mixed -feeding Mammal : it is pedunculate, as in the pre- 

 daceous Marsupialia, whilst the lever of the coronoid process 

 is made the stronger by the condyle being carried further 

 back from it than in any known carnivorous or herbivorous 

 animal. The angle of the jaw makes no pi'ojection below the 

 condyle, but is slightly bent inward, according to the Marsu- 

 pial type.' 



' In the general shape and proportions of the large pre- 

 molars and succeeding molars, Plagiaulax most resembles 

 Tkylacoleo (fig. 173, p.m. 1 and 2), a much larger extinct 

 predaceous Marsupial from tertiary beds in Australia. But 

 the sectorial teeth in Plagiaulax are more deeply grooved ; 

 whence its name. The single compressed premolar of the 

 Kangaroo Rat is also grooved ; but it is differently shaped, 

 and is succeeded by four square-crowned, double-ridged 

 grinders, adapted for vegetable food ; and the position of the 

 condyle, the slenderness of the coronoid, and other characters 

 of the lower jaw are in conformity to that regimen. In 

 Thylacoleo the lower canine or canine-shaped incisor pro- 

 jected from the fore part of the jaw, close to the symphysis, 

 and the corresponding tooth in Plagiaulax more closely re- 

 sembles it in shape and direction than it does the procumbent 

 incisor of Rypsiprymnus. From this genus Plagiaulax differs 

 by the obliquity of the grooves on its premolars ; by having 

 only two true molars in each ramus of the jaw, instead of 

 four ; by the salient angle which the surfaces of the molar 

 and premolar teeth form, instead of presenting a uniform 

 level line ; by the broader, higher, and more vertical 

 coronoid ; and by the very low position of the articular 

 condyle. 



' The physiological deductions from the above-described 

 characteristics of the lower jaw and teeth of Plagiaulax are, 

 that it was a carnivorous Marsupial. It probably found its 

 prey in the contemporary small insectivorous Mammals and 



