PLIOSAUEUS. 3 



smaller than in some other members of the group. The premaxillary region of the 

 snout is very slightly expanded. 



The basioccipital (b.oc.) is a very large and massive bone, bearing the whole of the 

 large occipital condyle ; this is almost hemispherical, its transverse diameter being a 

 little longer than the vertical. In the middle of the condyle there is a slight flattening 

 with a dimple-like depression, probably marking the former position of the notochord. 

 Laterally and superiorly the surface of the condyle passes without interruption into the 

 sides and top of the bone, but ventrally it is marked off by a deep groove which forms 

 a sort of short neck to the condyle in this region. In the middle ventral line there is 

 a rounded ridge which, beyond the region of the neck of the condyle, turns sharply down 

 at right angles and terminates in the ventral face of the bone which is completely 

 overlapped by the pterygoids. The lateral (pterygoid) processes are very short and 

 stout; they arise about one centimetre in front of the rim of the condyle ; their outer 

 ends are deeply concave and seem to have been covered by the pterygoids in the 

 uncrushed skull. The surfaces for union with the exoccipital-opisthotics are very 

 large and separated by a narrow interval only. The exoccipital-opisthotics themselves 

 are much crushed, especially at the upper end. It can be seen that, as usual, they are 

 almost columnar bones forming the sides of the foramen magnum. The opisthotic 

 bears a long paroccipital process (par.p.), the outer end of which is expanded and fits 

 against the hinder face of the posterior (quadrate) ramus of the pterygoid and perhaps 

 in part against the quadrate itself. 



The supraoccipital (soc.) cannot be clearly seen, owing to the crushing down upon it 

 of the parietals. The same is the case with the prootic. 



The basisphenoid is concealed by the underlying pterygoids, with the exception of a 

 small part of the anterior end ; this, as usual, is underlain by the adherent parasphenoid. 

 This bone (pas.) seems to have extended back between the basisphenoid and the 

 pterygoids ; certainly the pterygoids cannot have met between the parasphenoid and 

 the basisphenoid in the manner described by Williston in the case of Trinacromerum*. 

 The free portion of the parasphenoid in front of the basisphenoid is much broken, buc 

 it can be seen to have narrowed rapidly between the posterior interpterygoid vacuities f 

 Anteriorly where it passes between the pterygoids it widens again suddenly and then 

 naiTows gradually to a point, giving it the appearance of a very narrow spear-head ; 

 the ventral face is overlapped to some extent by the edges of the pterygoids, so that a 

 greater area is exposed on the upper than on the palatal surface : this latter is flat or 

 slightly convex from side to side. The anterior end of the bone is situated about 

 8 - 5 cm. in front of the anterior end of the posterior interpterygoid vacuities. 



* Journal of Geology, vol. xvi. (1908) p. 715. 



t It is proposed to use this term instead of " posterior palatine vacuity,'' to which some objections have 

 been pointed out by Williston and others. 



