PELONEUSTES. 



49 



posterior surface of the exoccipital described above ; or possibly a pro-atlas was present 

 and rested against this anterior lobe of the arch and the facet of the exoccipital. The 

 second subvertebral wedge-bone (tv.b. 2) (hypapophysis) is small, and unites with the 

 centra of the atlas and axis. The centrum of the axis (ax.) is very similar to that of 



Text-fig. 16. 



w.b.tr 



Atlas and axis of Peloneustes philarehus : A, from side ; B, atlas from front, with the 



constituent elements separated. (R. 2439, -| nat. size.) 



at.a., arch of atlas ; ax., axis ; od., odontoid ; p.s., posterior zygapophysis ; ?'./., rib-facet ; 



w.b. 1, w.b. 2, first and second subvertebral wedge-bones. 



the succeeding cervicals, except for the small facet on its antero-ventral border for union 

 with the wedge-bone. The articular surfaces of the centra are rather wider than high, 

 and gently concave with a median pit. The length of the centrum is considerably less 



PART II. H 



