52 



MAEINE EEPTILES OF THE OXEOED CLAY. 



curves sharply back, iu the fourth and fifth there is an increase in length and they also 

 curve backwards. Behind these to about the tenth (text-fig. 18) there is a gradual 

 increase in height, the spines being nearly straight and sloping a little backwards. 

 Behind this, again, the height of the spine remains about the same to the eighteenth, 

 then in the posterior two or three members of the series (text-fig. 19) there is a 

 decrease in height and increase of width, passing into the form found in the dorsal 

 region. 



In addition to the two or three vertebra? in which the rib-articulation is partly on 

 the arch and partly on the centrum ( pectorals), there are about twenty dorsals. The 



Text-fig. 19. 



Posterior cervical vertebras of Peloneustes joJiilarclius, from left side. (B. 3318, if nat. size.) 

 cue., anterior zygapophysis ; «.«., neural spine ; p.z., posterior zygapophysis ; r.f., facets for ribs. 



centra of these are longer than in the cervicals, and their lateral and ventral faces are 

 deeply concave from before backwards. The articular faces are higher than in the 

 cervicals, the height in some cases exceeding the width ; the surface is very slightly 

 concave and there is a central pit which, in some cases, is situated at the summit of a 

 slight elevation. The neural arches are not well preserved in any specimen. The 



