• 2 MAEINE EEPTILES OF THE OXEOED CLAT. 



to the present species, which he at the same time included in his genus Peloneustes. 

 Recently Mr. Leeds has collected the greater part of the skeleton of a large Pliosaur, 

 including the skull and mandible. The latter, though crushed in the opposite 

 direction, agrees closely in structure with the jaw figured by Phillips ; and the vertebra? 

 also resemble those of the type specimen of P. evansi, so that it appears that this 

 skeleton may be referred to that species, and from it very large additions to our 

 knowledge can be made. One consequence of this additional information about the 

 species is, that it is found to differ very considerably from the typical species of 

 Peloneustes, and, since some of the points of difference are of considerable importance, 

 it is doubtful whether a new genus, in some respects intermediate between Peloneustes 

 and Pliosaurus, should not be established for its reception. For the present, however, 

 this species will be referred to Peloneustes and the differences between it and 

 P. philarchus pointed out. 



In addition to the specimens referred to above, some other imperfect skeletons, in 

 which the skull and mandible are not preserved, have been referred to this species. 



The skull is known only from specimen E. 3891 recently obtained by Mr. Leeds. 

 It differs from that of Peloneustes philarchus in possessing a broader snout, the borders 

 of which are straight, there being practically no constriction at the point where the 

 maxillo-premaxillary suture crosses the alveolar border. The premaxillary teeth are 

 six in number and are not greatly enlarged ; the diastema betweeen the premaxillary 

 and maxillary teeth is very short indeed, a character which distinguishes this skull 

 from that of Pliosaurus. The number of maxillary teeth is smaller than in Pelo- 

 neustes philarchus, there being only about 22 on either side. The palate is without 

 any anterior interpterygoid vacuity, and the suborbital vacuity, if present at all, must 

 have been A r ery small. 



The symphysis of the mandible (text-fig. 27, B) differs from that of P. philarchus in 

 being shorter, in carrying only 11-12 teeth on each side, and in not being at all 

 expanded; in the number of teeth in the symphysis, the jaw is thus intermediate 

 between those of P. philarchus and Pliosaurus. The total number of teeth on either 

 side of the lower jaw is 32-36. 



The teeth (text-fig. 28) differ from those of both Pliosaurus and Peloneustes 

 philarchus in possessing smoother enamel, the ridges being fewer and in nearly all 

 cases confined to the inner (concave) side of the crown. Another peculiarity of the 

 teeth of this reptile is, that they undergo wear to an extent not observed in any other 

 Plesiosaurian ; in some cases they are worn down to a blunt stump (iv.s.). This 

 peculiarity probably indicates that this species lived on some animal protected by a 

 hard shell or armour, for it does not seem possible that the wear can have been 

 brought about by the grinding of the teeth against one another. A similar though 

 much less marked state of wear is sometimes to be seen in teeth of Pliosaurus and 

 of Polyptychodon. In spite of this extreme tooth-wear, the presence of tooth-germs on 



