THE MOSASAURIA. 229 



marine Lacertilian, wliich attained a great size. This is 

 the genvis Mosasaurus, remains of which were first obtained 

 from the Chalk near Maestricht. 



Eighty-seven vertebrae belonging to one individual of this 

 genus have been discovered, and when put together had a 

 length of thirteen-and-a-half feet. But there were certainly 

 many more vertebrae than these, as those of the end of the 

 tail are wanting, and there are gaps in the series of the 

 rest. The centres of all these vertebrae are concave in 

 front and convex behind ; but the concavities and con- 

 vexities are less marked in the posterior, than in the an- 

 terior, vertebrae. The atlas and axis are not well preserved 

 in this series of vertebrae, but the nine following all have 

 inferior spinous processes, which become shorter in the 

 posterior vertebrae, and, in the last two, are represented 

 only by a pair of low elevations. They have short trans- 

 verse processes, each terminated by a simple costal facet. 

 It is probable that these are cei"vical vertebrae. In the 

 dorsal vertebrae, of which there must have been at fewest 

 twenty-four, the transverse processes, which are strong in 

 the anterior, gradually diminish in size in the posterior, 

 vertebrae. There are no inferior processes. All the verte- 

 brae which have been mentioned hitherto have the circum- 

 ference of the centrum rounded, and are articulated to one 

 another by zygapophyses. But a series of eleven, which 

 follow them, have no zygapophyses, and the centra assume 

 a more or less triangidar prismatic form. The transverse 

 processes of these are long, thin, and bent a little downwards 

 and backwards. These seem to have been lumbar vertebrae. 

 No sacrum has been discovered, but there are numerous 

 caudal vertebrae with transverse processes, pentagonally 

 pi-ismatic centres, and chevron bones attached to the middle 

 of the under-siu-face of each. In the nine posterior of these 

 caudal vertebrae the bodies are cylindrical, the transverse 

 processes are obsolete, and the chevron bones, ankylosed to 

 the undersides of the centra, are long, inclined backwards, 

 and overlap one another. And, in the hindermost caudals, 

 the spinous processes and the chevron bones disappear. 



