ON BRITISH FOSSIL REPTILES. 99 



of the arch. The finely wrinkled or fibrous character of the free surface is 

 more strongly marked in these caudal than in the dorsal vertebrae. 



In the three succeeding vei'tebrae the neural arch diminishes in height, the 

 anterior articular processes diminish in length, and the posterior articular im- 

 pressions in depth. The upper and lower parts of the sides of the body be- 

 come somewhat more concave; the posterior articular surface grows flatter. 



A detached chevron bone, eight inches in length, consisting of two haema- 

 pophyses, anchylosed only at their distal or inferior extremities, and with their 

 distinct proximal ends more divaricated than are the confluent ones in the 

 Iguanodon, corresponds with the caudal vertebrae here described, and doubt- 

 less belongs to the Cetiosaurus brevis. 



The following are dimensions taken from the four caudal vertebrae above 

 described : — 



Antero-posterior diameter of centrum . 

 Transverse diameter of centrum . . 

 Vertical diameter of centrum . . . 



Of the present species of Cetiosaurus, I have examined specimens of the 

 bodies of one dorsal and three posterior caudal vertebrae in the collection of 

 Gilpin Gorst, Esq., which were obtained from the central strata of the Weal- 

 den, near Battle Abbey, commonly called the ' Hastings beds.' 



The dorsal centrum closely agrees with those in the Mantellian Collection : 

 its anterior surface is, as in them, nearly flat, or slightly convex ; the poste- 

 rior surface is concave. 



In. Lines. 



The antero-posterior diameter 3 2 



The transverse diameter of the anterior surface ... 5 3 

 The vertical diameter of the anterior surface .... .5 2 

 A fracture of this centrum through its middle shows it to consist throughout 

 of a coarse cellular texture. The neurapophyses, with an antero-posterior ex- 

 tent of base of two inches three lines, are continuously anchylosed with the 

 centrum, as in Mammalia, and leave about three quarters of an inch of the 

 posterior part of the centrum free. The lower part of the spinal canal is 

 horizontal ; its transverse diameter one inch three lines. 



The posterior caudal vertebrae present an antero-posterior diameter of nearly 

 four inches, with a breadth of three and a half inches, and a depth of four 

 inches, measuring to the lower part of the posterior haemapophysial surface. 

 The antero-posterior length of the base of the neurapophysis is two inches 

 two lines ; and it does not begin so close to the anterior part of the cen- 

 trum as in the dorsal vertebra. The upper and lower portions of the side 

 of the centrum are more distinctly separated by the comparative projection 

 of the middle part, which gives the obscurely hexagonal form to these ver- 

 tebrae. The inferior parts are most concave, and converge to form the sides 

 of the longitudinal sulcus, to which the inferior surface of the centrum is re- 

 duced at this part of the tail. It is plain, from these modifications of the ver- 

 tebrae, that the tail must here have presented the compressed Crocodilian 

 type ; and it is satisfactory to have these indications of the Saurian affinities 

 of the present gigantic fossil, in consequence of the very close approximation 

 of the larger vertebrae to the Cetaceous type. The vertical extent of the 

 osseous basis of the tail was here augmented by strong haemapophyses, which 

 have left more prominent articular facets on the under part of the centrum 

 than in the larger anterior caudal vertebra; : these facets, instead of being in 

 pairs, are confluent at the anterior, and at the posterior ends of the loAver sur- 



II 2 



