392 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 23, 



where, at 7*5 inches from the postarticular ridge, it makes a coro- 

 noid eminence, which is less elevated than that of lizards, but which 

 rises more than that of crocodiles. From this onwards the border 

 sinks at first in a rather steep curve, and then runs forwards nearly 

 horizontally to the straight dentary part. 



The lower border of the ramus sweeps downwards and forwards 

 from the posterior extremity in a nearly uniform curve to about 6 

 inches behind the hindermost tooth, from which point onwards it is 

 nearly straight. Six inches from the posterior extremity, and 4 

 inches behind the coronoid process, the curve is broken by a distinct 

 angle. 



The form of the toothed part may be roughly compared to a three- 

 sided prism. The upper surface is nearly flat, and its inner border 

 rises slightly higher than its outer border, which is pierced by the 

 alveoli at short intervals. The inner surface is vertical. It is scored 

 by furrows and striae, which begin a little distance in front of the 

 angle which the straight part makes with the curved part of the 

 jaw, and which mark, I think, the beginning of the symphysial 

 suture. The outer and under surface, much defaced, is transversely 

 convex. Behind the straight dentary part, the ramus loses in thick- 

 ness, and at about 6 inches from the last visible tooth it begins to 

 gain in depth, while the inner and outer surfaces becoming par- 

 allel, the transverse section has here an oblong figure. From this 

 backwards the depth of the ramus increases till it attains its maxi- 

 mum in the coronoid eminence, behind which it declines to the pos- 

 terior extremity. 



The large vacuity in the outer surface, between the angular, sur- 

 angular, and dentary bone, present in all living crocodiles, and, as 

 far as I can learn, in all extinct ones of the Tertiary period, is 

 entirely absent from this Kimmeridge jaw, in which the component 

 bones meet closely. For about 16 inches from the posterior ex- 

 tremity, the outer surface is nearly equally shared by the angular 

 bone below, and an upper splint comprising, I suppose, the dentary 

 and surangular, with a small portion of the articular bone. About 

 1| inch in front of the postarticular ridge, and therefore just at 

 the front of the articular surface, on the upper border, there is a 

 fissure filled with stone, which may be the suture between the arti- 

 cular and surangular bones ; but I cannot trace any suture marking 

 the respective shares of the surangular and dentary bones, unless a 

 fissure running along the bottom of a groove which indents the 

 surface of the jaw, parallel vrith its upper border, for 7 inches 

 forwards from the coronoid eminence, be part of it, of which I feel 

 very doubtful. This composite surangular and dentary splint, with 

 the articular, forms the upper border and the greatest part of the 

 posterior extremity of the ramus. From this latter to a short 

 distance in front of the articulation, the natural surface of the bone 

 has suffered from chipping, and is quite destroyed here ; but it re- 

 appears in front of the articulation, and it exhibits, for about 12 

 inches, a fine longitudinal striation ; the striae spread from a point 

 in the lower border of the splint, below the articulation, in a fan- 



