2G MAEIJNTE EEPTILES OF THE OXFOED CLAT. 



Skull (PI. III. figs. 1 , 1 a). — The skull is unfortunately too much crushed and 

 imperfect for it to be possible to give a complete account of its structure, since not 

 only are portions wanting altogether, but the sutures in the parts preserved are very 

 obscure. 



The basioccipital {hoc.) bears the whole of the very large, sessile, and nearly hemi- 

 spherical occipital condyle. Beneath the condyle the body of the bone is covered and 

 concealed by the underlying pterygoids {ft.), which meet beneath it in the middle line; 

 large lateral (pterygoid) processes are present, the obliquely truncated ends of which 

 united with the posterior rami of the pterygoids. The exoccipital and opisthotic 

 seem to have been closely similar to the same elements in the other members of the 

 family, e. g. Peloneustes (see p. 35). 



The quadrate (q.) is a large and very stout bone, its articular surface for the mandible 

 being very wide ; in fact, the whole jaw-apparatus seems to have been exceptionally 

 strong. The squamosal (sq.) is of the usual triradiate form ; the inferior ramus unites 

 with the quadrate, the upper runs up to the parietal, but owing to crushing the 

 relations between the two bones are obscure ; the anterior (zygomatic) ramus is 

 comparatively slender. 



The parietals {par.) form a high narrow sagittal crest between the temporal fossa?. 

 They seem to surround the relatively small pineal foramen {pf.), but their relations 

 to the frontals cannot be made out. In the Plesiosaurs, the fronto-parietal suture is 

 usually opposite the anterior end of the pineal foramen, so that the frontals take part 

 in the formation of that opening, or just in front of it, so that they are excluded. Here 

 it seems possible that the foramen is entirely enclosed by the parietals, which may 

 extend some distance in front of it, meeting in front the hinder extremities of the long 

 facial processes of the premaxillse, as Williston describes in the skull of Bolicho- 

 rhyncops*. If this is the true interpretation, then the frontals (fr.) are overlaid to a 

 great extent by the parietals and only appear laterally on the outer surface of the 

 skull ; they unite anteriorly with the facial processes of the premaxillag ; external 

 to the frontals there seems to be a separate bone, which is probably the prefrontal. 

 The postorbital bar is missing on both sides, so that no trace of the postfrontal or 

 postorbital can be seen. 



The anterior part of the snout is relatively shorter than in Plesiosaurus and Pelo- 

 neustes; on their enlarged dentigerous portion, the premaxillce {pmx.) each carry 5 or 6 

 teeth, the anterior pair being the smallest and in close apposition on the middle line. 

 The facial processes are prolonged back as far as the level of the anterior border of 

 the orbit, where they meet the parietals. The maxillae {mx.) are very incomplete on 

 both sides in the specimen described, and it is not known how many teeth they each 

 bore. They extend back some distance along the facial processes of the premaxillae 



* " North American Plesiosaurs, Pt. I.," Field Columbian Museum, Geological Series, vol. ii. no. 1 (1903), 

 p. 16, pi. iv. fig. 1. 



