244 Mr. C. W. Andrews on the Structure 
All the specimens described in the present paper were 
obtained by Mr. Leeds from pits in the Oxford Clay in the 
neighbourhood of Peterborough. In all cases these specimens 
are more or less crushed; but they are free from matrix, and 
supply much valuable information concerning some important 
points in the cranial anatomy of the group. The Leeds 
collection includes portions of skulls of animals referable to 
the genera Peloneustes, Pliosaurus, Murenosaurus, and Crypto- 
clidus. Only the skull of Peloneustes philarchus will be 
considered now, the other genera being reserved for a future 
occasion. 
The Skull of Peloneustes philarchus (Seeley). 
The specimens upon which the following description is 
founded consist of :—(1) a skull (Leeds coll. no. 42), of which 
the anterior portion is fairly complete and uncrushed, but the 
posterior dorsal region and the temporal arcades are greatly 
broken and distorted; the palate is in a fairly good con- 
dition (Pl. XIII. fig. 1): (2) the upper portion of a skull 
almost uncrushed in the rostral region ; the palate and a large 
part of the alveolar borders are wanting (Pl. XIII. fig. 3): 
(3) numerous crushed fragments of a skull. 
All the above are in the British Museum. 
The description of the palate is taken mainly from a speci- 
men (no. 4) in Mr. Leeds’s private collection, in which this 
region is well preserved and the sutures easily determinable 
(Pl ALU fiz. 2). 
These specimens will be referred to by the numbers affixed 
to them above. 
The general outline of the skull is that of an isosceles 
triangle, of which the apex is blunt and the height about two 
and a half times the length of the base, that is, the width of 
the hinder end. The length of specimen 1 from the tip of the 
snout to the hindermost point of the occipital condyle is 
60°5 centim., and the distance from the same point to the 
front of the pineal foramen is 46°5. In specimen 2 this latter 
measurement is about 50 centim. Specimen 4 is exactly the 
same length as 1. Other measurements will be given in the 
description of the various parts. 
The anterior portion of the snout, composed of the pre- 
maxillz, is somewhat depressed and expanded, its greatest 
width being opposite the fourth alveolus, where it measures 
about 6°5 centim. At the point where the suture between 
the premaxilla and maxilla crosses the alveolar border it is 
