of the Skull in Peloneustes philarchus. 243 
rare occurrence of that portion of the skeleton, and partly by 
the crushed condition of most of the existing specimens. 
The first account of the cranial osteology of these animals 
is that given by Conybeare in his description of a Plesiosaur 
from the Lias of Street * ; and it is with the skulls of several 
species from deposits of that age that most of the more 
important papers on this subject deal, those of Plestosaurus 
rostratus, P. homalospondylus, and P. dolichodirus having 
been described by Owen f, that of P. Hthertdget by Huxley f, 
and that of P. Conybeart and P. megacephalus by Sollas §. 
An important note on the structure of the palate in P. dolicho- 
dirus has recently been published by Lydekker 
Of the post-hassic forms, portions of the skull of Murcno- 
saurus Leedsi have been described by Seeley {], an imperfect 
specimen of that of Pliosaurus macromerus ** by Owen, who 
has also given an account of an incomplete cranium referred 
by him to a member of the genus Polyptychodon tf. 
Recently Williston ¢{ has ‘given an account of a skull of 
Cimoliosaurus, and the same specimen is the subject of a 
paper by Cope §§. The upper surface and the single tem- 
poral arcade are described; these appear to differ in several 
points from the same regions in the skull which is the subject 
of the present paper. The more important of these differences 
will be referred to below. 
The relation of the Sauropterygia to other reptiles has been 
discussed by Baur |||; and Koken 4/4], in an important paper on 
some remains of Nothosaurus, has given a valuable summary 
of our present knowledge of the Plesiosaurian skull, which 
renders any detailed account of the earlier papers unnecessary 
here. 
* “ Additional Notices on the Fossil Genera Ichthyosaurus and Plesio- 
saurus,” Trans. Geol. Soe. ser. 2, vol. i. p. 119. 
+ “Fossil Reptilia of the Liassic Formations,” pt. 3 (Mon. Pal. Soe. 
1865). 
t Quart. Journ. Geol. Soe. vol. xiv. (1858) p. 281. 
p- 20, pl. iv. 
tt} Trans. Kansas Acad. Sci. vol. xii. (1890) pp. 174-178. 
§§ Proc. Amer. Phil. Soc. vol. xxxiii. no. 144, Jan, 1894, pp. 109-118, 
alae 
\||| “On the Phylogenetic Arrangement of the Sauropsida,” Journal of 
Morphology, vol. i. (1887) p. 97. 
4/4] “ Beitriige zur Kentnisse der Gattung Nothosaurus,” Zeitschrift d. 
deutschen geol. Gesellschaft, 1893, Bd. xlv. Heft 3, p. 887. 
