10 MAEINE EEPTILES OP THE OXFOED CLAT. 



The splenial (spl. in PI. II. fig. 1 a) is a long thin strip of bone closely adherent to 

 the inner face of the coronoid above, and of the dentary and anterior prolongation of 

 the angular below. The posterior end cannot be made out in the specimens, though 

 probably it was as in Peloneustes (see below, text-fig. 14). Anteriorly it enters the 

 ventral side of the symphysis for a short distance. The post-coronoid portion of the 

 mandible is composed of two pieces, (1) the fused articular and surangular [art. & 

 surang.), (2) the angular (ang.). The former constitutes the upper part of the post- 

 articular process (p.a.p.), bears the articular surface, in front of which its upper border, 

 which is thickened and flattened above, slopes up to the coronoid angle ; beneath this 

 the bone unites with the coronoid on the inner, and the dentary on the outer side, 

 ventrally it unites with the angular. The articulation for the quadrate is a concave 

 kidney-shaped surface ; its concave anterior rim is strengthened by a strong prominence 

 situated rather to the inner side; the outer and posterior borders are also rather 

 prominent. On the anterior side of the outer concavity there is a deep pit, probably 

 for the attachment of a ligament. The angular is a large bone and constitutes the 

 lower border of the jaw to within a short distance of the symphysis; posteriorly it 

 unites with the surangular and articular above, and in front of the level of the 

 articular surface, probably with the posterior prolongation of the splenial. In front of 

 the coronoid angle it is prolonged forwards as a tapering process, uniting with the 

 dentary on the outer side and the splenial on the inner side. 



The teeth (PI. II. figs. 2-4) in the lower jaw are about 28 in number on either 

 side ; of these seven are in the symphysial region. The anterior pair is small, close 

 together, and directed nearly straight forwards ; the next five pairs are large and about 

 equal in size ; they are directed forwards, outwards, and upwards, but the last tooth in 

 the symphysis is smaller and does not seem to have been directed forwards. The teeth 

 in the rest of the ramus are smaller than the large symphysial teeth, and remain about 

 equal in size till the last four or five, which rapidly diminish. The structure of the 

 individual teeth is the same in the upper and lower jaws. They have been described 

 and figured by Lydekker in the Quart. Journ. Geol. Soc. vol. xlvi. (1890) p. 49, pi. v. 

 fig. 1. Each tooth, as a whole, is curved and is nearly circular in section throughout its 

 length. The root is very large, considerably larger than the enamel-clad crown, and 

 its surface is quite smooth ; the pulp-cavity is open below and is large, extending some 

 distance up into the crown. The form of the crown varies somewhat in different parts 

 of the jaw. In the smaller posterior teeth (PI. II. figs. 4, 4 a) it is smaller in 

 proportion to the root and more sharply curved than in the larger teeth. In all 

 the crown, which terminates in a sharp point, is more or less curved ; the outer 

 convex face is covered with nearly smooth enamel (PI. II. fig. 2 a), but on the 

 remainder of the surface the enamel bears numerous sharp ridges, which start from the 

 base of the crown and extend towards the apex to a varying extent : a few of the 

 stronger ridges may actually reach the tip. Towards the base of the crown some 



