Description of a Nciv Plesiosaur. 315 



front of the articular surface the upper border, formed by the united 

 surangular and articular, rises to a blunt coronoid angle where it 

 meets the dentary on its outer side and the coronoid (cor.) on the 

 inner ; the anterior limits of the coronoid are not known, but it 

 seems to have extended as a thin plate, closely adherent to the 

 inner face of the dentary, forwards to about the level of the middle 

 of the dental series. The greater part of the dentigerous part of 

 the mandible is formed, as usual, by the dentary, which is the only 

 element visible on the outer side of this part of the jaw. On its 

 inner face the upper part of the posterior end is covered by the closely 

 adherent coronoid, while beneath this is the thin plate-like splenial 

 (spl.) which closes Meckel's groove, and probably extended forward 

 to the symphysis into the formation of which it perhaps entered : 

 posteriorly it is prolonged back some distance behind the level 

 of the coronoid angle, forming the lower (inner) edge of the 

 opening of the dental (Meckel's) canal. Beneath the splenial and 

 on the inner side of the dentary the angular sends forward a 

 long tapering process, the anterior end of which is concealed 

 by the overlap of the splenial upon the dentary. In the neigh- 

 bourhood of the symphysis the dentary widens out and bears 

 at least three greatly enlarged teeth : behind these the teeth are 

 smaller and continue about equal in size for the first six or seven : 

 behind these again there is a gradual reduction in size to the end 

 of the series. The outer face of the dentary is marked by numerous 

 vascular grooves and foramina. 



Several teeth (PI. XVIII., Fig. 4) are preserved, differing much in 

 size and to some extent in shape. The larger ones have long 

 conical, slightly curved crowns, circular in section and probably 

 terminating in a sharp point. On the inner (concave) side of the 

 crown the enamel is raised into numerous fine longitudinal ridges 

 which tend to unite with one another in pairs as they are followed 

 towards the tip of the crown; similar ridges occur to a less extent on 

 the anterior and posterior faces of the crown, but on the outer (convex) 

 face the enamel is almost smooth, only a very faint ridging being 

 visible. The roots of the teeth are very large, smooth and circular in 

 section. In the smaller teeth (PI. XVIII., Fig. 4) the crown is more 

 strongly curved. The enamel ridges are relatively larger and fewer 

 in number, but their arrangement is the same as in the large teeth. 



Of the vertebral column (PI. XVIII., Figs. 5, 6 ; text-Figs. 2, 3) a 

 considerable portion is preserved. Twenty-one or twenty-two 

 cervicals are present, of which eleven are anterior, the remainder 

 posterior and forming a continuous series with the fifteen pectorals 



