158 



MK. R. LYDEKKER ON DINOSAURIAN VERTE3R2E 



quoted. The centrum is, however, more compressed in the English 

 specimen, while the haemal and lateral surfaces are distinctly 

 differentiated from one another, and the former surface carries a 

 pair of V-shaped ridges resembling those of T. indicus. The 

 specimen is in fact very nearly intermediate in character between 

 the figured vertebrae of T. Blanfordi and T. indicus. The abrasion 

 of the rim of the articular cup shows that the internal structure 

 of the bone is coarsely cancellous. The second specimen (No. R. 

 146 a) comprises the anterior half of the centrum of a slightly 

 smaller vertebra, and has been but little rolled. This specimen 

 shows on the ventral aspect the well-marked V-shaped ridges so 

 well displayed in the type specimen of T. indicus *, but lacks the 

 distinct chevron-facets of that form. 



We may then, I think, consider it most probable that the 

 English specimens indicate the occurrence in the Wealden of a 

 Dinosaur closely allied to Titanosaurus ; and it now remains to 

 consider whether, in the first place, they can be referred to any 

 genus already described from those beds, and, in the second place, 

 whether or not they should be regarded as generically identical with 

 one or both of the Indian forms provisionally included in the above- 

 mentioned genus. 



With regard to the first question, among the large Dinosaurs of 

 the Wealden the caudal vertebrae of Iguanodon and its allies are of 

 a totally different type from the present specimens ; while equally 

 different are those of Cetiosaurus (with which may be grouped the 

 so-called Pelorosaurus), as well as those of Megalosaurus, in both of 

 which genera the centra have either flattened or slightly hollowed 

 articular surfaces. Turning, however, to the gigantic Ornitliopsis, 

 we find that the caudal vertebrae have not been hitherto known f, 

 and there is accordingly a strong prima facie presumption that 

 the specimens under consideration may belong to that genus. 

 The nearest allies to Ornitliopsis are certain North-American 

 Dinosaurs included in Marsh's Sauropoda J, such as Brontosaurus, 

 Morosaurus, Gamarasaurus, Ampliicoelias, &c. ; in these, while' the 

 precaudal vertebrae have cavities in the centrum like those of Orni- 

 tliopsis, those of the caudal region are solid. Apparently in all the 

 American forms the centra of the caudal vertebrae are amphiccelous, 

 while those of the cervical region are opisthocoelous ; since, how- 

 ever, in some genera, such as Gamarasaurus §, the dorsal vertebrae 

 are opisthocoelous, like those of Ornitliopsis, while in others, like 

 Ampliicoelias ||, they are amphiccelous, there is apparently no 

 reason why similar variations should not also occur in the caudal 

 region of other members of the group. In Brontosaurus, where 



* Palseontologia Indica, ser. 4, vol. i. pt. 3, pi. iv. fig. 1. 



t See Hulke, Quart. Journ. Geol. Soc. vol. xxxvi. p. 36. There apparently is 

 no reason why the ainphiccelian vertebrae there mentioned should not belong 

 to Cetiosaurus, since they agree closely with the specimens from the Great 

 Oolite figured in Phillips's 1 Geology of Oxford.' 



\ See Marsh, 'Anier. Journ.' vol. xxiii. p. 83 (1882), and vol. xxvii. p. 167 

 (1884). 



§ Proc. Amer. Phil. Soc, Dec. 21, 1877, p. 237. || Ibid. p. 243. 



