40 



MAEINE EEPTILES OF THE OXFOED CLAY. 



the anterior concave. At their anterior end the parietals widen out and completely 

 surround the pineal foramen (p.f). Their relation to the frontals (fr.) is difficult to 

 make out, owing to the complexity of the sutures between the two bones and the extent 

 to which they overlap. In the earlier account of the skull of this species (Ann. Mag. 

 Nat. Hist. [6] xvi. (1895) p. 252) the suture was described as passing just in front of 

 the pineal foramen, as it certainly does in the Elasmosaurs, and the bones lying 

 between the pineal foramen and the hinder ends of the facial processes of the 

 premaxilla? were therefore regarded as frontals. Further examination of other 

 specimens, particularly one which is broken across in several places, shows that in front 

 of the pineal opening (p.f.) the parietals widen out on the outer surface of the skull and 



Inner face of a portion of the skull-roof of Pehneustes philarchvs. (E. 3803, | nat. size.) 



fr., frontal ; I., lachrymal ; mx., maxilla ; o.c, olfactory canal ; par., parietals : 



p.f., pineal foramen ; po.f., postfrontal ; pr.f., prefrontal. 



overlap the frontals, extending forwards to meet the posterior ends of the premaxillae. 

 Although the frontals are thus in part concealed, they are exposed to a considerable 

 extent on the upper surface of the skull to the outer side of the parietals. Posteriorly 

 the frontals join the postfrontal (po.f.) ; in front of this they form the upper border of the 

 orbit for a short distance, then they unite externally with the prefrontal (pr.f.) and on 

 the inner side join the outer edge of the premaxillaj and appear to send forwards a 

 process between those bones and the external narial openings (nar.), of which they form 



