16 FOSSIL REPTILIA OF THE 



and the neurapophysial surface. The terminal articular surface (ib., fig. 3) is very 

 little concave, sububundulating, with a transversely elliptical, very shallow, central 

 depression. The sides of the centrum are slightly concave, the under surface more 

 feebly so, and it is not longitudinally ridged. The venous foramina are divided 

 by a transversely convex tract of 6 lines extent (Tab. VII, fig. 2). The whole of the 

 non-articular surface is smooth. The costal surfaces (fig. I, pi) are almost wholly 

 situated in the posterior half of the centrum. The neural arch and spine, by rare 

 fortune, are preserved in the present instance (fig. 1) in natural articulation with 

 the centrum. The sutural line describes a subangular convexity downwards, and 

 with the lowest part (np) nearer the anterior surface of the centrum. The neurapo- 

 physis, as it rises, has its fore-and-aft extent decreased by emarginations, of which 

 the posterior one is the longest ; this extent then increases by the development of 

 the zygapophyses, of which the posterior (?) is most raised ; but the anterior ( z ) most 

 produced. The spinous process (m) is remarkable for its antero-posterior extent, 

 preserving the same width to its truncated summit ; it thus presents a subquadrate 

 figure, and is inclined rather forward ; it arises from the entire fore-and-aft extent 

 of the median line of the neural arch. The total height of the vertebra, from the 

 under part of the centrum to the summit of the spine, is 9 inches ; the height of 

 the spine itself is 4 £ inches ; the antero-posterior diameter is 2\ inches. The 

 articular surfaces of the prezygapophyses (z) look upward and a little inward ; 

 those of the postzygapophyses ( z ) look in the opposite direction. 



Two other cervical vertebrae, with the characters above defined, are preserved in 

 the slabs of stone exhibiting the parts of the skeleton of the same individual Plesiosaur. 

 In the last cervical vertebra (Tab. VIII, figs. 1 and 2) the costal surface is of large size, 

 especially in the vertical direction, and is supported in its lower third upon a parapo- 

 physis ( p ), which has now risen to the middle of the side of the centrum, and has come 

 in contact with a diapophysial development (d) of the side of the neural arch, support- 

 ing the upper two thirds of the costal surface. Together they form a thick and deep 

 outstanding process, 2 inches in vertical by 1 inch 3 lines in transverse extent, with 

 the articular surface for the expanded head of the rib looking outward and rather 

 downward, fig. 2. The terminal articular surface of the centrum (fig. 2, c ) presents 

 a sharper or better defined border than that of the normal cervical vertebra 

 (Tab. VII, fig. 3) ; it is 3 inches 6 lines in transverse, and 2 inches 8 lines in vertical 

 diameter, almost an ellipse in figure, but with the lower curve greater or deeper 

 than the upper one ; the central shallow depression is continued in the present 

 vertebra, of similar proportions and contour as in the foregoing normal cervical 

 vertebra. The neural arch has become anchylosed to the centrum, but the 

 greater part is broken away. The neural canal (n) is subcircular, 8 lines in 

 diameter. 



