28 MARINE EEPTILES OF THE OXFOED CLAY. 



a slight convexity : it is very wide. The postarticular process is relatively very 

 small. 



The five or six teeth (PL III. figs. 2 & 3) in the symphysial region are greatly 

 enlarged ; behind these are about twenty closely-crowded teeth, the first five or six 

 small, then about ten of moderate size, and behind these a gradual decrease in size to 

 the end of the series. The crowns are sharply pointed, curved and circular in section, 

 and without marked carinse, the enamel being marked by a series of fine longitudinal 

 ridges, only a few of which extend to the tip ; these ridges are most numerous on the 

 inner (concave) side of the crown. The upper teeth are of a similar character. 



Vertebral Column (PL III. fig. 4). — All the vertebrae in the type specimen are much 

 crushed and no other skeleton in which they are preserved is at present known. The 

 result of the crushing is that the vertebrae are distorted in various ways, so that little 

 can be made out as to their exact form and proportions. The cervical region consists 

 of about twenty vertebra?, including the atlas and axis, which are fused with one 

 another. The atlantal cup can be seen to be completed below by a large wedge-bone 

 in the usual manner. The succeeding cervicals (PL III. figs. 4, 4 a, 4 b) have short 

 broad centra, the length of which in the mid-ventral line is about half the width ; the 

 height of the uncrushed centrum seems to be about the same as the width. The 

 articular ends are gently concave. The double rib-facet (r.f.) is raised on a 

 prominence projecting downwards and outwards ; the upper and lower surfaces, which 

 are deeply concave, are separated by a well-marked ridge. In the neural arch the 

 pedicles are long and their bases unite with the whole length of the centrum ; in the 

 type specimen the neuro-central suture is still open. The zygapophyses (a.z., p.z.) are 

 very large and project very considerably both in advance of and behind the centrum ; 

 their articular facets are oval and nearly fiat. The neural spines (n.sp.) seem to have 

 been very short in the front of the neck, but increased in height posteriorly, though 

 possibly those at the extreme hinder part of the neck were a little shorter than those 

 anterior to them. 



There appear to have been about thirty dorsals, but they are all so distorted that no 

 description is possible ; the same may be said of the caudals, the centra of which seem 

 to have been rather deeply concave with a central pit. 



Shoulder-girdle (text-fig. 8). — This, so far as known, is typically Pliosaurian. The 

 scapula (sc.) is of the usual triradiate form, the ventral ramus (v.sc.) being much 

 expanded and very thin ; its inner end is broadly convex. A strong ridge separates 

 the ventral surface from the outer face of the dorsal ramus (d.sc). 



The coracoid (cor.) is a large plate of bone, very thin posteriorly but thickened at 

 the level of the glenoid cavity, the thickening forming a convexity on the dorsal 

 (visceral) surface which extends to the middle line, where it bears the deepened part of 

 the symphysial surface (sym.) which is convex above and concave below (cf. text-fig. 21). 

 In front of this thickened region the bone again becomes thin and is prolonged 



