FOSSIL REPTILIA OF THE WEALDEN FORMATIONS. 21 



Certain vertebrae of the " anteriorly convex" system were further distinguished by 

 the origin of the transverse process from saHent ridges converging so as to form a 

 pyramidal base of such process, and by a deep depression behind tlie costal facet. 

 These characters are peculiar to the anterior dorsal vertebrce. In the posterior dorsal 

 and lumbar vertebrae, recognised by Cuvier as belonging to the same " seconde Gavial 

 de Honfieur" by the character of the pyramidal base of the transverse process, the 

 anterior convexity had subsided: even in a dorsal vertebra, in which the articular 

 surface for the head of the rib is still distinct, only a little higher placed, the terminal 

 articular surfaces of the centrum are nearly equal and flat, " a pen pres egales et 

 planes."* 



Upon the discovery of " opisthocoelian" vertebrae, or those of the " systeme 

 convexe en avant" in the Wealden formations,! I threw out the suggestion | that, as 

 in the second Honfieur Gavial, they might be the anterior vertebrae of a large Wealden 

 Saurian, having vertebrae wiih flattened terminal surfaces in a more posterior part of 

 the spine. Observing, also, that such vertebrae, in the Cetiosaurus breeds, were slightly 

 concave behind, though fiat in front, it seemed to me that this genus might have the 

 best claim to them. But, after pointing out the difference in the antero-posterior 

 diameter of the large convexo-concave and plano-concave vertebrae, I remarked that 

 "additional evidence of a very decisive character must be obtained before the great 

 Cetiosaur can ba admitted to have resembled the Pterodactyle in such disproportionate 

 length of the cervical vertebrae. "§ 



No discovery of the long convexo-concave or opisthocoelian vertebrae, so associated 

 with short plano-concave or bi-concave vertebrae, as to have belonged to the same 

 animal, has yet been made, though nearly twenty years of quest and collection of 

 Wealden fossils have passed since the importance of that additional evidence was 

 pointed out. I, therefore, still feel myself without the requisite grounds for a decisive 

 settlement of the question of the genus of the long and large opisthocoelian vertebrae 

 of the Wealden, and continue to refer them, provisionally, as in my ' Report/ to a 

 species of Streptospondylus.\\ 



* ' Ossemens Fossiles,' toni. cit., p. 311. 



t Previous to my Report on British Fossil Reptiles, 'Trans. British Association,' 1841, these vertebrae 

 had been deemed " proccElian ;" and, in the question of which of the various-shaped Wealden vertebrae 

 might belong to the Iguanodon, Dr. Mantell thought that " the concavo-convex vertebrje which correspond 

 so entirely to those of the Iguana and Monitor, would seem to offer a more probable approximation" 

 (' Geology of the South-east of England') ; only their extreme rarity opposed the hypothesis. 



X ' Report on Brit. Fossil Reptilia,' ib., p. 96. 



^ Ib. 



II Report on Britisli Fossil Reptiles, 'Trans. Brit. Association,' 1841, p. 91. The futility of subsequent 

 speculations on this subject, in the ' Philosophical Transactions' of 1849, p. 286, has been shown by the 

 discovery of the true cervical vertebrae of the Iguanodon, described in my ' Monograph' of 1855. 



