PURBECK FORMATIONS. 65 



Oolite.^ But in the present jaw, as in the type-specimen, the condyle projects backward 

 below the level of the alveolar apertures, and the lower border of the ascending ramus, 

 which it terminates behind, does not curve up to the condyle so much as in Phasco- 

 lotherium. 



It represents, in position, the angle of the jaw ; but on the inner side, in the present 

 specimen, is a fractured surface (fig. 11b, a), indicative of a part projecting inward, and 

 which would be the true homologue of the inflected angle of the Marsupial jaw. The 

 articular surface of so much of the condyle as is preserved is smoothly convex, both 

 transversely and vertically. 



A deep notch, rounded at the bottom, but narrower than in Phascolotherium, and also 

 narrower and deeper than in figs. 7 and 10, divides the condyle from the large, lofty, and 

 antero-posteriorly broad, coronoid plate. The depth of the notch gives a pedunculate 

 character to the low-placed condyle in a greater degree than in Triconodon mordax. 



The exposed (inner) surface of the coronoid (<?) is flat, with a shallow depression at its 

 fore and inner part, where it passes into the horizontal ramus. Below this depression is 

 the narrow canal, leading from a few lines in advance of the peduncle of the condyle, and 

 sinking, as the ' dental canal,' into the substance of the ramus at a vertical line dropped 

 from a little behind the last molar tooth. 



A very feeble and rather broad longitudinal impression {g) is continued from the entry 

 of the dental canal forward along the inner side of the ramus, as far as below the last 

 premolar. This condition of the mylohyoid groove repeats that in Myrmecohius. The 

 lower border of the ramus describes one uninterrupted gentle curve, convex downward 

 from the condyle to the fore end, as in Phascolotherium. The symphysis follows, with a 

 low slope upward and forward, carrying on and terminating the fore part of the curve. 

 This is markedly different from the contour of the syraphysial or fore part of the mandible 

 in the two specimens of Triconodon mordax, in which that part of the jaw is preserved (figs. 

 7 and 10). 



The inner alveolar plate projects a little from the sockets before sinking into the inner 

 surface of the ramus. The whole molar series, four premolars, and three true molars are 

 in place, with the base of the canine. 



The shape of the jaw, with the same extent of the three molars, in the subject of PI. 

 Ill, fig. 12, nat. size, leads me to refer it to the same species {Triconodon ferox) , as fig. 11. 

 It consists of a left mandibular ramus, inner side exposed, with the ascending branch in 

 part shown by an impression, and with the symphysial end crushed and mutilated. 



The portion of the bone preserved contains the last three molars, with the fore ends of 

 the upper and lower ridges of the coronoid or those bounding the pterygoid depression. 



The first molar is rather smaller than the second, and its mid cusp, being entire, shows 



' PI. I, fig. 2C ; and 'Brit. Fossil Mammals,' p. 6i, fig. 20, a. 



