32 



MAEINE EEPTILES OF THE OXFOED CLAT. 



below and parallel with the alveolar border is marked by a deep groove, into which 

 several foramina open ; anteriorly this groove is replaced by a number of irregularly 

 placed foramina. On the inner side the dentaries of opposite sides unite in the 

 middle line for a little more than the anterior half of the total length of the symphysis, 

 being separated in the posterior portion by the splenials. In their symphysial region 

 the dentaries unite by their flattened upper and lower borders, between which they are 

 concave from above downwards. The surface covered by the splenial seems to have 

 been nearly flat, and posteriorly, as already mentioned, the thin posterior extension of 

 the bone is wedged in between the coronoid and surangular. The upper surface of 

 the dentary bears the broad and not very deep alveolar groove, in which the presence 



Posterior portion of left ramus of mandible of Oplithahnosaurus : A, inner side ; B, outer side. 



(E. 2180, I nat. size.) 



niif/., angular bone; art., articular bone; «)•<.«., articular surface on surangular ; e., c'., coronoid-like processes 

 on surangular ; cor., coronoid bone ; cor.e., backward extension of coronoid bone beneath the articular ; 

 dent., dentary bone ; g., gi-oove on outer face of surangular ; l.p., lower process at anterior end of the 

 splenial bone ; s.ang., surangular bone ; sjil., splenial bone ; i., tuberosity on upper border of sur- 

 angular ; U.J}., upper process at anterior end of the splenial bone. 



of teeth is indicated by a number of transverse ridges, strongly marked in front but 

 becoming less distinct further back. The outer border of the groove is comparatively 

 broad and rounded, the inner thinner and sharper — particularly posteriorly, where it 

 is reinforced by the upper border of the splenial, and by which still further back it is 

 replaced. 



The splenial (spl-) is a very large bone, which, as above mentioned, extends into the 

 posterior half of the symphysis : at its thin anterior end it is divided by a large cleft 

 into an upper and lower process, the inner face of each bearing a roughened surface 

 for union with its fellow of the opposite side ; probably the posterior end of the cleft 



