62 FOSSIL REPTILIA OF THE 



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 (^j^ are elliptic, situated at the middle of the ridge dividing the under 

 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, interrupted by a trans- 

 verse 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 Plesiosaurus, T. IX, figs. 8 and 9, belong, 

 by reason of their size, to the Plesiosaurus Bernardi. 



A much-fractured tooth, (Tab. IX, fig. 10,) as thick as those of figs. 9 and 18, 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 Steneosauroid Crocodilian. It was obtained from the same chalk-pit, at 

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



The teeth, figs. 7 and 8, T. XX, 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 end 

 than in the typical Plesiosaurian teeth. These specimens were found in the lowest 

 bed of the Lower Green-sand beneath Shanklin Chine, Isle of Wight ; I am indebted 

 for the drawings of them to John Edward Lee, Esq., of the Priory, Caerleon, Mon- 

 mouthshire. 



Inches. 



Lines, 



2 



4 



2 



2 



1 



7i 



1 







