PLAGIAULAX. 353 



boid form, the upper border being less curved ; it affords a 

 more extensive surface of attachment to the principal biting 

 muscles than in most predatory extinct or recent quadrupeds. 

 This character, with the depth and strength of the jaw, sug- 

 gested the specific name. From the shape of the exposed part 

 of the ramus, we may conclude that the part answering to the 

 angle is bent inwards, and that Triconodon was a genus of the 

 marsupial order. The specimen was discovered by Mr. Beccles 

 in the same " dirt-bed " at Purbeck as that in which Spalaco- 

 therium was found. 



Genus Plagiaulax,* Fr. — The most remarkable of Mr. 

 Beccles' discoveries in the above formation are the mammalian 

 jaws indicative of the genus above named, of which two species 

 have been determined by Dr. Falconer. 



Sp. Plagiaulax Becclesii, Fr. — -Two specimens exemplified 

 the shape and pro- 

 portions of the entire 

 jaw of this species 

 (fig. 119). The fore- 

 most tooth (i) is a 

 very large one, 

 shaped like a canine, 

 but implanted by a 

 thick root in the 

 fore part of the jaw, like the large lower incisor of a shrew or 

 wombat. The three anterior teeth in place have compressed 

 trenchant crowns, and rapidly augment in size from the first 

 (2) to the third (4). They are followed by sockets of two 

 much smaller teeth, shewn in other specimens to have sub- 

 tuberculate crowns resembling those of Microlestes. The large 

 front tooth of Plagiaulax is formed to pierce, retain, and kill ; 



* An abbreviation for Plagiaulacoclon, from TXaytc;, oblique, and «vXh%, 

 groove ; having reference to the diagonal grooving of the premolar teeth. " Pro- 

 ceedings of the Geological Society," March 1857, p. 261. 



2 A 



Fig. 119. 

 Plagiaulax Becclesii (twice nat. size), Purbeck. 



