XIII. 



PLEIOSAURUS NITIDUS. 361 



on the upper face, the spoon-shaped base of the neural canal, which 

 from nearly parallel edges in the anterior half expands to two 



Diagram CLVII. Dorsal vertebra of Pleiosaurus nitidus. Scale one-eighth of nature. 

 Seen in front, with the neurapophysis and diapophysis in place. 



and even three times the width in the posterior part, approaches 

 the structure of P. gamma, where the middle of the canal is very 

 narrow, or actually reduced to a line. 



Looked at in front, the neural canal is not circular, but widest 

 above : the neurapophysis has a lanceolate section and a longitudinal 

 vertical notch or groove : the diapophyses are oval in section. The 

 articulating face is nearly plane, but pitted in the middle ; something 

 more than a half ellipse in outline, with two edges sloping upwards 

 to the neural canal (Diagram CLVII.). 



Seen sideways or from below, it differs little from that of P. 

 gamma. 



Length, 1-9 inch; breadth, 3*00; height, 2'6o (270). 



The caudal vertebra (anterior), somewhat larger than the others, 



I 2 



Diagram CLVII I. Caudal vertebra of Pleiosaurus nitidus. Scale one-fifth of nature. 

 i. Seen laterally. 2. Viewed from below. 



agrees in general character with them; having a similar neural 

 canal, and articulating faces similarly pitted and bordered. The 

 cicatrix for the transverse process, nearer to the anterior side, is 

 sharply bordered. The lower surface, rather plane, is bordered by 

 the loops of the hsemapophysial attachments. 



Length, 1-9 inch; breadth, 2'9 ; height, 2*4 (2*5). 



