CRETACEOUS FORMATIONS. 61 



Both neurapophyses, fig. 3 (n), and pleurapophyses (pi) are anchylosed to the 

 centrum. The neurapophyses coalesce together, and send almost vertically upwards a 

 spinous process, which exceeds in length the whole vertical diameter of the vertebra 

 below it, and is more than twice its own antero-posterior diameter ; it is compressed 

 and gradually decreases in thickness as it rises ; it presents a rough shallow tract along 

 its fore part (fig. 1), and a wider, deeper, and smoother excavation behind (fig. 2)* 

 Two small zygapophyses are developed from both the fore-part (z) and back part 

 (z') of the neural arch. The pleurapophyses (pi) are long, sub-depressed, slightly 

 expanded as they extend downward, outwards, and backwards ; but the fractured ends 

 do not show how far they have extended forwards and backwards into a hatchet- 

 shaped extremity. They have coalesced with the lower part of the sides of the 

 centrum, an extent more than their own vertical diameter intervening between them 

 and the base of the anchylosed neurapophyses. The articulated cervical ribs in the 

 Fl. pachyomus have not quite so low a position on the centrum, and are thicker 

 vertically. 



The under part of the centrum presents two deep pits from which the vascular 

 canals ascend, divided by a moderately thick, convex, longitudinal bar (fig. 4). The 

 non-articular surface of the centrum is smooth, and the sides of the centrum are 

 slightly concave. 



A very interesting and well-marked species of the singular genus Plesiosaurus, in 

 addition to those from the older secondary strata, is thus indicated by the present 

 unusually perfect fossil vertebra. As it was discovered on one of the estates of his 

 Grace the Duke of Norfolk, I avail myself of the opportunity of fulfilling a wish of my 

 lamented friend Mr. Dixon, and of gratifying my own, by dedicating this new species 

 to the memory of Lord Bernard Howard, a young nobleman of great promise and 

 most amiable disposition, and who had given much attention to the science of geology : 

 he died suddenly in Egypt at the early age of twenty-one years, whilst pursuing his 

 travels in order to acquire a knowledge of the antiquities, the arts, and policy of 

 distant countries. 



Plesiosaurus constrictus, Owen. Tab. IX, figs. 6 and 7. 



Dixon's ' Geology and Fossils of the Tertiary and Cretaceous Formations of Sussex,' p. 3Q8. 



The species of Plesiosaurus from the Chalk-pit at Steyning, Sussex, indicated by 

 the centrum of a middle cervical vertebra, which is figured in T. IX, figs. 6 and 7, 

 differs from that of the Plesiosaurus Bernardi, (T. XVIII,) 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 unanchylosed to the 

 centrum ; it also differs from all the species of Plesiosaur hitherto defined in the degree 



