188 BRITISH FOSSIL REPTILES. 



structure in these teeth as in those of the lower jaw ; but the enamel shows some 

 longitudinal striations. 



All the vertebrae of the Mosasaurm, according to Cuvier, are concave at the fore 

 part, convex at the hind part of their bodies ; the convexity and concavity being 

 greatest on the anterior vertebrae. The foremost of these are characterised by an 

 inferior process or " hypapophysis," developed from the middle of the lower surface of 

 the centrum : they have two transverse and four articular processes, and a long com- 

 pressed upper or neural spine. The centrum is longer than it is broad, and broader 

 than it is high; the terminal articular surfaces are transversely oval or reniform. 

 Such are the characters of the last cervical or first dorsal vertebrae. The middle 

 dorsal vertebrae are like these, but have no hypapophysis. Then follow vertebrae 

 which have no articular or oblique processes (zygapophyses), but have longer and 

 flatter transverse processes (diapophyses), and terminal articular surfaces of a pen- 

 tangular form, or of a triangidar form with the base downwards (see PI. 1, fig. 5). 

 Next come vertebrae with diapophyses and a pair of inferior processes (hypapophyses) 

 for the articidation of chevron-bones (haemapophyses) ; afterwards vertebras without 

 transverse processes and with large anchylosed chevron-bones (haemapophyses) ; and 

 finally vertebrae devoid of all processes whatever. 



The vertebrae discovered in the Kentish Chalk, with the jaws and teeth above 

 described, and of corresponding proportions to those parts which we observe in the 

 vertebrae of the Mosasaurus Hoffmanni, present all the generic vertebral characters of 

 that Lacertian genus, and correspond with the third and sixth kind, or with the posterior 

 dorsal and the anterior caudal vertebrae, as defined by Cuvier. But the terminal articu- 

 lations of the centrum of the dorsal vertebrae of ISLosasanrus gracilis present a full oval 

 (not elliptical) form, the long axis of which is vertical and the great end downwards 

 (PL 2, fig. 4). The length of the centrum {j,b., fig. 3), which is three centimeters 

 and a half, or one inch and five lines, exceeds the breadth ; but this is equalled by 

 the height of the centrum. The diapophyses in fig. 2, d, are broken away ; in fig. 3 

 it is uncertain whether the surface be a fractured one, or whether it is a natural 

 cavity for the rib ; the analogy of Blosasaurus Hoffmanni favours the former view of 

 it. The neural arch (fig. 3, «) is anchylosed to the centrum, as in the larger species 

 of Mosasaurus. I can perceive only a feeble indication of zygapophyses, which shows 

 that the vertebra (figs. 2 and 3) comes from the posterior region of the back. The 

 neural canal (fig. 4, «) is small and triangular ; a sharp longitudinal ridge rises from 

 the middle of its floor, and on each side of this there is a vascular canal descending 

 vertically into the substance of the centrum ; this substance presents a coarse fibro- 

 cancellous texture ; the areolae extended longitudinally, and decreasing much in size 

 at the ends of the centrum. The outer surface of the vertebra is smooth ; the margins 

 of the anterior articular concavity are sharp. 



The vertebra (fig. 2) shows, by the lower position of the diapophysis {d), that it 



