76 



The dorsal vertebra arc remarkable from tlie fact that the diapophyscs 

 disappear on the anterior part of the series, and gradually diminish in length 

 from behind forward to the point of disappearance. On the median and 

 posterior parts of the series, they are very elongate, and rise for a short dis- 

 tance from the basis of the neural arch. Anteriorly, they descend and shorten, 

 and finally remain only as the slightly-elevated borders of rib-pits. Through- 

 out the whole of the anterior portion of the column to the cervicals, the neural 

 spines are of great elevation, and of such antero-posterior extent as to be 

 nearly continuous. 



The cervical vertebrm are not only more numerous, but become anteri- 

 orly much smaller and more attenuated than in its allies of the same family. 

 They are remarkably compressed, the centra much longer than deep, and 

 deeper than wide, and with smooth concave sides. 



The ribs of the anterior cervico-dorsal region are inserted directly in the 

 vertically-oval pits of the centrum. Immediately at the point where these 

 cease, thin traverse processes appear to arise from the lower edges of the rib- 

 pits. They form a continuous series with the ribs, and soon rise from the 

 plane of the lower face of the centrum, and are directed obliquely downward. 

 At the end of the cervical series, they are directed nearly vertically down- 

 ward. The number of these vertebrae is very great; the anterior diminishing 

 to a very small size ; the whole measuring a little more than half the total 

 length. Most of the cervicals possess two venous foramina below, the dorsals 

 two, and most of the caudals one. 



The resemblance of the caudals to the usual type of Plesiosaurus is seen 

 in the fact that each bears near its posterior articular aspect, on the inferior 

 face, a pair of articular surfaces for chevron-bones. Similar vertebrae had 

 been described by Leidy as the caudals of a genus he called Discosaurus. 

 The study of the present genus shows that they are really of the caudals of the 

 allied genus Chnoliasaurus, the support caudals of the latter being the cervicals. 



The ribs are simple-headed ; the abdominal ribs seen in Plesiosaurus are 

 possibly wanting, as none were found by the discoverer of the fossil, after a 

 careful search. 



The end of the muzzle, with symphysis mandibuli, was preserved. This 

 is flat, the symphysis co-osified and rather short, tlie premaxillary grooved at 

 the intervals between the dental alveoli. The teeth are deeply implante<I, 

 with small pulp-cavity, are cylindric, and furnished with nearly straight elon- 



