216 BRITISH FOSSIL REPTILES. 



and 7, differs from that of the Flesiosaurus Bernardi, {' Enaliosauria,' PI. 26,) in its great 

 length, as compared with the height and breadth of the articular surfaces of the centrum, 

 and in the small size of the costal articulation (pi), the pleurapophyses having been 

 unanchyloscd to the centrum ; it also differs from all the species of Plesiosaur hitherto 

 defined in the degree of lateral constriction of the centrum between those surfaces, if 

 this be natural. The free or non-articular surface of the centrum is rugose, showing the 

 coarsely fibrous texture of the bone. The under surface (fig. 6) is slightly concave, both 

 transversely and longitudinally, is subquadrate and oblong, with two approximated 

 vascular orifices at its centre, separated by a slight rising, which is not developed into 

 a ridge. The small costal surfaces (pi) are elliptic, situated at the middle of the ridge 

 dividing the vinder from the lateral surfaces of the centrum, twice their own vertical 

 diameter below the neurapophysial surfaces, and equidistant from the two ends of the 

 centrum. The articular surfaces here are convex at their circumference, slightly 

 concave in the rest of their extent, with a feeble longitudinal rising at the centre, in- 

 terrupted by a transverse linear groove. The neurapophyses terminated below in a 

 very open angle. The vertebra appears to have been subject to pressure, and is slightly 

 distorted ; but it is difficult to conceive how this could have operated so partially as to 

 have produced the compressed character of the middle of the centrum and have left 

 the two articular ends of their natural form. 

 The following are its principal dimensions. 



Antero-posterior diameter of centrum .... 



Transverse diameter of articular surface of ditto 



Vertical diameter of ditto ...... 



Distance between the neurapophysial and costal pits 

 Transverse diameter of middle of centrum above the costal 



pits .......... 1 7 



It is most probable that the teeth of the Plesiosaiirus, PI. 2, figs. 8 and 9, belong, 

 by reason of their size, to the Plesiosaurus Bernardi. 



A much-fractured tooth, (PL 2, fig. 15,) as thick as those of figs. 8 and 9, but 

 diminishing more rapidly to the apex, shows similar unequal but more numerous 

 ridges all round the enamelled surface ; its crown is composed of the same kind of 

 hard dentine as in the Crocodiles and Plesiosaurs, with a moderately thick covering 

 of enamel. The tooth may be a variety of the Plesiosaurian type, or it may have 

 belonged to a Stencosauroid Crocodilian. It was obtained from the same chalk-pit, at 

 Houghton, near Arundel, as the vertebra of the Plesiosaurus Bernardi. 



The teeth, ' Enaliosauria,' PI. 28, figs. 7 and 8, present more slender proportions, and 

 so far, are more strictly Plesiosauroid. The fang is round, smooth, and deeply excavated 

 by the pulp-cavity, which is indicated by the dotted line at p; the enamelled crown 

 supports numerous fine longitudinal ridges: it is rather more compressed at its fractured 



