156 MAEINE EEPTILES OF THE OXFOED CLAY. 



straight border above it, is a clearly defined sutural surface for union with the lower 

 ramus of the squamosal (sq.). 



There seem to be two possible explanations of this peculiar structure of the quadrate 

 region : one, as already mentioned, that the two quadrates have been fractured in an 

 exactly similar way, the other that there are really two distinct elements. In the latter 

 case the smaller inner bone (qJ) uniting with the pterj'goid would be the true quadrate, 

 while the larger outer one overlapped by the squamosal would be a quadrato-jugal. 

 This latter would bear the greater part of the articular surface for the mandible, a 

 condition which, so far as I am aware, is never found in other reptiles, though in 

 Sphenodon the quadrato-jugal does seem to enter into the formation of the outer border 

 of the articulation. The absence of the division in any specimens, some quite young, 

 of other species, favours the idea that a symmetrical fracture has occurred, but. never- 

 theless, it seems well to suggest the other explanation also. 



The squamosal (text-fig. 75) is a large triradiate bone as in Murcenosaurus, but there 

 are some differences of detail. The dorsal bar {sq.') running up to meet the squamosal 

 process of the parietal is comparatively slender ; at its upper end it is slightly enlarged 

 and bears a deeply pitted suiface for union with the parietal. In this genus tlie dorsal 

 rami of the two squamosals do not seem to have met in the middle line over the 

 parietals. Ventrally the bar widens out and the ridge forming its upper border 

 bifurcates, the anterior arm becoming continuous with the upper edge of the anterior 

 ramus. This is thin and broad, its upper margin being convex, the ventral concave, 

 and passing posteriorly into the anterior edge of the broad ventral (quadrate) ramus. 

 Tlie posterior border of this latter has on its inner face an extensive sutural surface 

 for union with the quadrate (or quadrato-jugal), which it overlaps to a considerable 

 extent. The anterior end of the zygomatic process {sq.) probably united both with 

 the jugal below and the lower edge of the postorbital above. 



The remainder of the skull is represented by mere fragments, which it has not been 

 found possible to piece together. 



The mandible (PI. VUI. figs. 1, 1 a) is very well preserved in the type specimen. 

 In its general structure it is closely similar to that of Murcenosaurus, the same fusion 

 between the constituent bones having occurred. It is rather stouter in proportion to 

 its length than in Murcenosaurus, at least in the tooth-bearing region ; the coronoid 

 angle, which seems to be formed by the hinder end of the splenial, is very little 

 developed ; the symphysis is short. 



The teeth (PL VIII. figs. 1, 2) in both the upper and lower jaws are long, 

 slender, curved, and terminating in very sharp points. The enamel at the lower part 

 of the crown is raised into fine nearly parallel ridges ; these mostly die away towards 

 the point, only one or two continuing to the actual tip. 



Vertebral Column (PI. VIII. figs. 5-8). — In the length of the neck and in the structure 

 of the individual vertebrae this genus approaches Crijptocleidus and diflfers widely from 



