THE MOSASA0RIA. I97 



described by Prof. Owen under the name of Dolichosanrus. 

 It possesses an exceedingly elongated bodj', but is provided 

 with limbs and with a distinct sacrum, consisting of two ver- 

 tebrae. Its most remarkable peculiarity, however, lies in the 

 number of its cervical vertebrae, which were not fewer than 

 seveuteen. 



11. The Mosasauria. — The cretaceous rocks of Europe 

 and America have yielded another remarkable long-bodied 

 marine Lacertilian, which attained a great size. This is the 

 genus Mosasaimis, remains of which were first obtained from 

 the Chalk near Maostricht. 



Eighty-seven vertebrce 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 vertebree are concave in front and 

 convex behind ; but the concavities and convexities are less 

 marked in the posterior, than in the anterior, vertebrte. Tiie 

 atlas and axis are not well preserved in this series of vertebras, 

 but the nine following all have inferior spinous processes, 

 which become shorter in the posterior vertebrce, and, in the 

 last two, are represented only by a pair of low elevations. 

 They have short transverse processes, each terminated by a 

 simple costal facet. It is probable that these are cervical 

 verlebrte. 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 

 vertebrae which have been mentioned hitherto have the circum- 

 ference of the centrum rounded, and are articulated to one 

 another by zygapophj'ses. But a series of eleven, which fol- 

 low them, have no zygapophyses, and the centra assume a 

 more or less triangular prismatic form. The transverse pro- 

 cesses of these are long, thin, and bent a little downward and 

 backward. These seem to have been lumbar vertebrae. No 

 sacrum has been discovered, but there are numerous caudal 

 vertebrae with transverse processes, pentagonally prismatic 

 centres, and chevron-bones attached to the middle of the 

 under-surface of each. In the nine posterior of these caudal 

 vertebrae the bodies are cylindrical, the transverse processes 

 are obsolete, and the chevron-bones, anchylosed to the under- 

 sides of the centra, are long, inclined backward, and overlap 



