ON BRITISH FOSSIL REPTILES. 95 



One of the articular ends * is rather more concave than the other, which, from 

 the wearing away of the margins, appears slightly and unevenly convex. The 

 contracted middle part of the vertebra is concave lengthwise, and pretty regu- 

 larly convex in the direction transverse to the axis of the vertebra : the free 

 surface is finely striated, and perforated here and there by vascular foramina : 

 there is no lateral depression. The neurapophyses were broken off; their 

 bases, instead of having their long diameter corresponding with the axis of 

 the vertebra, as in Iguanodon, present it in the direction transverse to that 

 axis, as in Plesiosaurus : they do not quite meet at the middle of the upper 

 or neural surface of the centrum, but are there divided by a narrow longitu- 

 dinal tract forming the lower part of the spinal canal. 



The antero-posterior extent of the anchylosed base of the neural arch is 

 2 inches 6 lines : the transverse diameter, 5 inches. 



Two caudal vertebrae of the same species, also from Culver Cliff, present 

 the same length and unequal concavity of the articular extremities ; the an- 

 terior one, here determinable by the anterior position of the narrower hsema- 

 pophyses, being the deepest : the sides of the body are more compressed, and 

 more convergent towards the under surface ; so that, as the expanded margins 

 of the articular ends are worn away, the centrum presents rather a triangular 

 than a subcircular contour. The disproportion of its antero-posterior with its 

 transverse and vertical diameters, distinguishes it from the caudal vertebras 

 of the Iguanodon. The neurapophysis rises from the anterior three-fourths 

 of the centrum, and sends forwards a subprismatic anterior oblique process, 

 but does not develope a posterior one : it then contracts, and inclines to the 

 base of the spine, which is much shorter than in the Iguanodon. The spi- 

 nous process inclines backwards from the vertical axis of the centrum at an 

 angle of 45°. A short transverse process is developed from the junction of 

 the neurapophysis with the centrum. The haemapophysial surfaces appear 

 single on both the anterior and posterior parts of the lower surface ; they are 

 nearly flat, and slope towards each other. 



In. Lin. 



Antero-posterior diameter 3 



Transverse diameter 5 



Vertical diameter 5 



Height of vertebra to summit of spinet . 12 9 

 Antero-posterior diameter of spine ... 2 10 

 Thickness at posterior part of base ... 1 



Height of spine, 1st caudal 5 



Height of spine, 2nd caudal X . , , . . 4 



The characters and dimensions of these rolled vertebrae of Cetiosaurus 

 from the submarine beds of the Wealden formation, although somewhat ob- 

 scured by the circumstances under which they are brought to light, are suf- 

 ficiently satisfactory to establish their generic character, and to give an use- 

 ful approximative idea of their size and proportions. The corresponding 

 bones from the Wealden of Tilgate Forest supply, by their more perfect state 

 of preservation, the deficiencies of the Isle of Wight specimens, and further 

 establish the co-existence of the Cetiosaurus with the Iguanodon, Strepto- 

 spondylus, Megalosaurus and other extraordinary reptiles of that period. 

 The vertebrae of the Cetiosaurus hrevis in the Mantellian Collection are the 



* Subsequently determined by more perfect specimens to be the posterior surface. 



t This is rounded off, but seems not to have been broken. 



X The 1st and 2nd do not here refer to the place of these vertebrse in the tail ; but if the 

 vertebne were contiguous in the entire animal, the tail must be much shorter than in the 

 Jgvanodon. 



