410 Dr. (\ W. Andrews on the 



are almost horizontal ; the anterior ant! posterior facets are 

 about in the same plane, and the processes bearing tbem 

 are separated by a well-detined rounded notch. The base 

 of the neural arch extends the whole length of the centrum, 

 and the neural arch is nearly circular in outline. 



In the three thoracic vertebrtie the rib-articulations pass 

 upwards on to the arch ; in them the zygapophysial articula- 

 tions become more oval in outline, and are more inclined to 

 tbe horizontal plane. Passing back along the dorsal series, 

 wiiich seems to have included twenty-four vertebrae in front 

 of the sacrum, the transverse processes rise rapidly on the 

 arch, at the same time the zygapophyses become more 

 inclined and relatively smaller, and towards the posterior 

 portion of the series their anterior and posterior articular 

 surfaces become concave and convex respectively. The 

 base of the neural arch is not so long from before back- 

 wards as in the cervical region. The transverse processes 

 are very massive, and terminate in a thickened convex 

 extremity, which is higher than wide and was evidently 

 capped with cartilage in life ; on the ventral surface of these 

 })rocesses close to their point of origin there is a deep pit. 

 The posterior transverse processes are more inclined back- 

 wards than those in front. Towards the hinder end of the 

 series the centra become higher than wide. In this Plesiosaur 

 the sacrum (PI. ^"II.) seems remarkably Avell developed for 

 an aquatic animal. The sacral vertebrae are four or five in 

 number: in them the transverse processes are very short, 

 forming prominences borne both on the arch and centrum ; 

 these articular surfaces for the sacral ribs are large, being 

 very considerably wider above than below — the second, third, 

 and fourth are the largest. In this region the neural spines 

 were short from betore backwards, and the small zygapo- 

 physes make an acute angle with the vertical plane. The 

 sacral ribs are remarkably strongly developed. The first is 

 a simple bar of bone, with a deepened and widened proximal 

 end for union with the vertebra: at its outer end it thins, 

 curves slightly backwards, and articulates with the anterior 

 process of the second sacral rib ; on its anterior face 

 towards the outer end it bears a strong cristiform ridge. 

 The second sacral rib is the stoutest of the series : its 

 proximal portion is compressed from before backwards, but 

 at its outer end it widens out into a massive hammer- 

 shaped head, the anterior arm of which unites with the 

 first sacral rib, while the posterior arm j(jiiis the anterior 

 limb of the similar hammer-shaped head borne by the third 

 sacral rib, which, however, is here imperfectly preserved. 



