Description of a New Plesiosaur. 313 



middle line probably with the anterior ends of the pterygoids, though 

 this is not quite clear. 



The premaxillcB (pmx.) which form the narrow muzzle, each 

 bear alveoli for five teeth. Of these the anterior one is small and 

 close to the middle line ; the second is rather larger ; both these 

 teeth seem to have been directed forward. The third and fourth 

 teeth are large, the fifth again smaller. Immediately behind the 

 last there is a short diastema crossed by the maxillo-premaxillary 

 suture. Within the row of alveoli and separated from them by a 

 flattened area there is a row of pits which mark the points at 

 which the replacing teeth appear. Internal to the two posterior 

 pits the surface of the premaxilla is raised into a ridge on a level 

 with the vomer against which it abuts. The facial surface of the 

 premaxillae consists of a broad anterior region, convex from side to 

 side with a median groove marking the line of union of the two 

 bones, and a backwardly prolonged narrow facial process, the two 

 bones uniting in this region to form a prominent ridge with concave 

 sides which extends back between the orbits ; how far back the 

 facial processes of the premaxillae extend cannot be determined from 

 this specimen, but probably, judging from what occurs in some of 

 the Oxford Clay genera, they joined the f rentals a little in front 

 of the level of the posterior border of the orbits. It is possible that 

 these backward prolongations of the premaxillse may, as suggested 

 by Williston, include some other element, possibly the nasal, though 

 I have never seen any evidence of this. The upper surface of the 

 anterior part of the premaxillaB is much roughened and bears a 

 number of vascular foramina. 



The maxilla (mx.) is not completely preserved on either side of the 

 skull, and it is not possible to say how many teeth it bore ; it can 

 be seen, however, that the first tooth was small, while the suc- 

 ceeding three were greatly enlarged, the third being the largest. 

 The palatine portion of the bone is in contact with the premaxilla 

 in front ; behind this it forms the outer border of the internal nares ; 

 behind this again it joins the palatine for some distance, but pos- 

 teriorly is separated from it by the narrow sub-orbital vacuity (s.o.v.). 

 Behind this it unites with the transverse bone and posteriorly prob- 

 ably with the jugal. The facial surface is imperfectly preserved : 

 the maxillo-premaxillary suture runs from the alveolar border 

 upwards and backwards, then backwards nearly parallel with the 

 middle line as far as the external nares which form deep notches 

 in the border of the bones, their inner edge being formed by the facial 

 processes of the premaxillae. The relations of the facial region of 



