24 MAEIXE EEPTILES OE THE OXFOED CLAY. 



the corresponding surface on the lower edge of the nasal. The anterior end of the 

 bone runs out into a pointed process, the outer face of which is overlapped by the 

 pointed posterior prolongation of the premaxilla. Looked at from above (text-fig. 13, B), 

 the boue is seen to widen out considerably towards its middle, forming a palatine plate 

 which is concave from side to side: possibly this concavity, anteriorly at least, received 

 a posterior process of the premaxilla. The upper edge of the inner border of the palatine 

 plate is peculiarly irregular, being produced into a series of elongated processes which 

 lie almost parallel with the long axis of the bone ; possibly these were connected with 

 the bones of the palate, but their use is obscure. Beneath the palatine expansion {pl.p.) 

 the inner face of the bone is deeply concave from above downwards, and anteriorly 

 forms the postcricu' portion of the dental gi'oove {d.g.), in which, however, no trace of 

 the presence of teeth can be observed. 



The 2)remaxill(v are greatly enlarged and elongated bones, forming the greater part 

 of the rostrum. Anteriorly they terminate in a blunt point, from which they gradually 

 increase in depth backwards : their outer surface is convex from above downwards, 

 and a little above the alveolar border bears a strongly-marked longitudinal groove, into 

 which numerous foramina, probably vascular, open ; this groove begins a little in front 

 of the narial opening and dies away a few centimetres from the end of the snout, 

 though the foramina are continued right to the end. The palatal face of the bone 

 bears the broad alveolar groove continuous posteriorly with that of the maxilla. On 

 the outer side of the anterior portion of the groove is a series of regular indentations 

 separated by rounded ridges and marking the points of insertion of the relatively small 

 and apparently very loosely attached teeth. The inner side of the groove is formed by 

 a thickened rounded border, which, in the anterior region at least, was in contact with 

 its fellow of the opposite side, but posterioiiy the two were probably separated by the 

 vomers, though the structure of this part of the skull is not well shown in any 

 specimen. The inner face of the premaxilla is concave from above downwards, forming 

 a long channel-like groove deepening from before backwards. For some distance 

 this groove receives the anterior end of the nasals, as noticed above, and for a long 

 distance the premaxilla; meet above those bones. For the greater part of their 

 junction in the mid-dorsal line the premaxilliie seem to have been merely in contact, 

 but just before they diverge they were united by a strong ligamentous connection, 

 the remains of which are seen in the elongated roughened surface occurring at this 

 point. Behind this the superior border slopes away towards the inferior, the two 

 meeting at the end of the long pointed posterior prolongation which overlaps the outer 

 face of the maxilla. This posterior prolongation may have been slightly notched by 

 the anterior angle of the narial opening, as in Ichthyosaurus acutirostris (see Fraas, 

 ' Die Ichthyosaurier,' pi. ii. fig. 1). 



Ihe parietal (text-fig. 14) is a boue of very peculiar shape. It consists of a body 

 ■which formed the posterior part of the roof and part of the side-wall of the cranium, 



