Dr. C. W. Andrews — Skull and Jaw of Peloneustes. 161 



pineal opening is much greater than' the Elasmosaurs, and indeed 

 is carried to such a degree that their anterior angle reaches the 

 posterior ends of the facial processes of theprenaaxillse, thus excluding 

 the frontals from the middle line on the outer surface of the skull. 

 On the cranial face (Fig 1) it can he seen that the parietals meet in 

 front of the pineal foramen {pf.) and run forwards in the form of 

 a wedge {par.) between the frontals, which, though excluded from the 

 pineal foramen, run back as far as about the middle of that opening. 

 In front of the ventral wedge-like prolongation of the parietals the 

 frontals {fr.) appear to meet at least for a short distance in the 

 middle line beneath them. The posterior region of the frontal unites 

 extensively with the post-frontal (po.f), which extends back to the 



Fig. 1. Inner face of the middle portion of the skull roof of Peloneustes 

 philarchus. (About one-third nat. size.) fr. frontals ; I. lachrymal ; 

 mx. maxilla ; o.c. channel enclosed by the downgrowths of the frontals ; 

 par. parietals ; p.f. pineal foramen ; po.f. post-frontal ; pr.f. pre-frontal. 



level of the middle of the pineal foramen, and has a short contact 

 with the parietal ; externally the post-frontal unites with the post- 

 orbital. In front of the post-frontals the ventral surface of each 

 frontal is raised into a high cristiform ridge, which curves downwards 

 and inwards towards the middle line, where it just meets its fellow 

 of the opposite side for a short distance, thus enclosing a deep 

 channel {o.c), probably for the olfactory nerves. Anteriorly these 

 ridges die away a little in front of the anterior angle of the orbit. 

 Antero-laterally the frontal unites with the pre-frontal {pr.f.), and 

 these again on their outer side join the element which is here regarded 

 as the lachrymal {I.). 



Professor Williston, 1 in his account of the structure of the skull in 



1 North American Plesiosaurs, pt. i (Field Columbian Museum, Geological 

 Series, vol. ii,No. 2 (1903), pi. iv, fig. 1). Also Proc. U.S. Nat. Mus., vol. xxxii 

 (1907), p v 478, pi. xxxvii. 



DECADE V. — VOL. Vm. — NO. IV. 11 



