STENEOSAUEUS. 91 



unite in median suture ; anteriorly they may be separated by a small notch, while 

 posteriorly the splenials are thrust in the form of a wedge between them to a varying 

 degree. Their buccal surface is more or less convex from side to side — this is especially 

 well seen in the mandible of St. leedsi (PI. V. fig. 4). The alveolar borders are 

 straight, and bear a varying number of teeth which seem to have been directed upwards, 

 forwards, and outwards. At the level of the third and fourth teeth, which are enlarged 

 and close together, there is an expansion, behind which the jaw is much narrowed ; 

 behind this point again there is a gradual widening towards the hinder end of the 

 jaw, varying in extent in the different species. The ventral face of the symphysial 

 region is convex from side to side, aud marked by a number of irregular longitudinal 

 grooves. Behind the symphysis the dentaries are overlapped on the upper surface by 

 the narrow coronoids, which for some distance run in between them and the splenials. 

 At its posterior end the dentary bifurcates, the bottom of the fork forming the anterior 

 angle of the elongated lateral vacuity ; the ventral ramus unites in overlapping suture 

 with the anterior end of the angular, while the dorsal ramus is overlapped by the 

 anterior prolongation of the surangular. 



The splenials (spl.), as above noted, unite in median symphysis anteriorly, and are 

 thrust like a wedge between the dentaries. The angle at which they meet is marked 

 by a deep pocket-like fossa, their ventral union extending further back than the dorsal 

 and thus forming a floor to the fossa. In the posterior portion of their symphysial 

 region, and behind this, they are separated above from the dentaries by the narrow 

 coronoid. Posteriorly the splenial overlaps the inner face of the anterior end of the 

 angular aud surangular ; it is here thin and forms an inner wall to the anterior part 

 of the lateral vacuity. 



The coronoid (cor.) differs considerably in form and position from the bone usually 

 so called in recent Crocodiles. In these it is a small splint of bone on the inner side 

 of the jaw at the anterior end of the lateral fossa. In Steneosaurus, on the other hand, 

 as has been described by Deslongchamps ('Notes Paleontologiques,' pp. 226—7), it is a 

 narrow ribbon of bone on the upper surface of the jaw; its anterior portion being 

 interposed between the dentary and splenial, while posteriorly it overlaps the surangular. 

 Deslongchamps states that it helps to form the border of the lateral vacuity, but this 

 does not seem to be the case in any of the specimens examined. The arrangement 

 and form of the other bones of the mandible are much as in recent Crocodiles. 

 The surangular (s.ang.) at its narrow anterior end unites with the splenial and 

 dentary, and is overlapped by the hinder end of the coronoid ; behind this it forms the 

 upper boundary of the elongated lateral vacuity. Posterior to this again, it supports 

 the articular as in recent species. The angular (ang.) forms the whole of the lower 

 portion of the hinder part of the jaw : in front it joins the dentary ; behind this it 

 forms the lower boundary of the lateral vacuity, and behind this again its upper 

 edge joins the surangular. The articular (art.) bears the whole of the articular 



N 2 



