268 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 11, 



being but slightly convex. The upper margin slopes a little down- 

 wards from behind the premolars on to the incisive alveolus, so that, 

 if the two margins were produced, they would meet at an acute 

 angle. The diasteme is very short. The incisor (a) is comparatively 

 large and directed suddenly upwards, the point being elevated above 

 the level of the premolars, with a short blaif sheath-border. The 

 base of the incisor is impressed with a shallow longitudinal fossa, and 

 the upper edge is bevelled. The point shows no mark of abrasion. 

 The mentary foramen is small, indistinct, and situated mesially in a 

 line nearly with the middle of the diasteme. The alveolar border 

 rises in large serrate processes between the fangs. The dark -shaded de- 

 pression behind the vertical fracture {b, c) upon the matrix (o', cV, e'), 

 marks the position of the pointed gibbosity on the inner side of the 

 alveolus of the last true molar (z). It is considerably below the line 

 of implantation of the premolars, indicating that the true molars 

 were placed correspondingly low, as is seen in the jaw of the other 

 species. The longitudinal medial shade shows a deeply impressed 

 broad channel upon the outer surface of the ramus, which is most 

 pronounced under and behind the last premolar. The amount of 

 this depression is well exhibited by the vertical sections (figs. 2 & 3, 

 f&y), where (x) represents the inner surface, and (y) the outer. It is 

 seen that the inner surface is slightly concave in the vertical direction, 

 between the upper and lower margins ; and that the general con- 

 vexity of the outer surface is interrupted by a wide and deep fossa, 

 causing a mesial constriction (y). Although there is as yet no direct 

 evidence to the point available, in consequence of the outer surface 

 of the posterior portion being adherent to the matrix, still it woidd 

 appear that this channel runs back towards the depressed disk of 

 the outer surface of the ascending ramus, although it may not have 

 been continuous with it. 



The posterior fragment (c, c?, fig. 4) shows in very perfect pre- 

 servation, the whole of the inner surface of the ascending ramus and 

 condyle, with the exception of the fragile edge of the inflected lower 

 margin and angle, which are broken off and left in part imbedded in 

 the matrix-cast of the opposite slab containing the anterior fragment ; 

 it comprises also the posterior portion of the body, in which the last 

 molar is implanted. The coronoid process {e) is triangular. Its 

 anterior border slopes upwards and backwards to the apex in a gentle 

 curve, at an angle of about 45° with the alveolar border. The pos- 

 terior margin descends in a curve with little deviation from the 

 vertical into the broad sigmoid notch (c?, e), which is but slightly over- 

 arched by the apex*. Its height and width at the base are nearly 

 alike, and about equal to the depth of the body of the jaw, in a line 

 with the last molar. The apex of the process is sharp. In general 

 form the coronoid process in Plagiatdax resembles more that of the 

 predaceous marsupials, and of the Ursine Dasyurus especially, than 

 that of the herbivorous families. It differs very markedly from the 



* The artist has represented the posterior margin of the coronoid with too 

 crescentic a curve, and the point projecting too much backward over the sig- 

 n»oid notch. 



