PELONEUSTES. 



53 



neural spines seem to have been broader and lower than in the cervicals. The 

 transverse processes are stout and slightly curved, the concavity being downwards ; 

 they enlarge a little at their outer end, which terminates in a nearly flat surface for 

 union with the rib. In the posterior part of the back the centra seem to decrease in 

 height, and in the sacrals they are considerably wider than high. The caudal centra 

 are likewise wider than high, and at the same time are shorter than the dorsals. The 

 caudal ribs articulate with deeply concave surfaces, the rims of which form well- 

 marked projections on the sides of the centrum. Beneath the rib-facets the sides of 

 the centrum are gently concave in all directions ; they pass into the nearly flat ventral 

 surface in rounded ventro-lateral angles, which are truncated both anteriorly and 

 posteriorly by oblique chevron-facets. The last few caudal centra decrease in size very 

 rapidly ; in the last preserved, the neural arch was present and the chevron-facets 



Text-fig. 20. 



Cervical ribs of Peloneustes philarchus : A, B, anterior ; C, middle ; D, posterior ribs. 



(R. 3318, § nat. size.) 

 l.f., lower (parapophysial) facet ; it./., upper (diapophysial) facet. 



were relatively much larger than in the more anterior caudals ; this may indicate that 

 there was a small vertical fin-like expansion at the end of the tail. Unfortunately, no 

 chevrons are preserved. 



In the cervical region, as noted above, all the ribs (text-fig. 20), with the exception 

 of one or two at the hinder end of the series, are double-headed ; the upper (u.f.) 

 and lower (l.f.) facets are separated by a notch or groove ; towards their distal end, at 

 least in the anterior part of neck, they are strongly compressed from above downwards, 

 and widen out so that their outer end is produced a little forwards into a slight 

 angle and backwards into a much more prominent one ; in the posterior members 



