94 REPORT— 1841. 



epoch, removes one of the chief difficulties attending the determination of 

 the true vertebral cliaracters of the Iguanodon. For if gigantic vertebrae, 

 agreeing in the important character of their articular surfaces with the ex- 

 isting Iguana, had actually been discovered, though of rare occurrence, asso- 

 ciated with teeth of corresponding dimensions, but similar in form to those 

 of the Iguana, there would have been strong ground for suspicion, that such 

 vertebrae and teeth might be parts of the same species * 



The elimination of these, otherwise perplexing, ball and socket-jointed 

 vertebra?, and their identification with the peculiar Crocodilian genus of Hon- 

 fleur, on which M. H. von Meyer has imposed the name of Streptospondylus, 

 forms, therefore, an essential step in the appropriation to the Iguanodon of 

 its true vertebral characters. 



Cetiosaurus. 



Cetiosaurus brevis, nob. — The attempt to reduce to order the various forms 

 and types of vertebrae, which the Wealden strata have yielded to test the saga- 

 city of the interpreters of its organized treasures, was one of Dr. Mantell's 

 earliest labours, and he states f that his first step was, with the able assist- 

 ance of the Rev. W. D. Conybeare, to separate those that belonged to the 

 Crocodile, Plesiosaurus and Megalosaurus, or rather which resembled those 

 from Stonesfield. Many enormous vertebrae then remained, from which those 

 belonging to the Iguanodon were to be chosen ; from these residuary speci- 

 mens the characteristic ones of the PoiMlopleuron and Streptospondylus have 

 already been eliminated, and I next proceed to remove from them the verte- 

 brae which characterize the genus Cetiosaurus. 



Of the existence of vertebrae of this genus in the Wealden strata, I first 

 became acquainted by the examination of Mr. SauU's collection of sea-rolled 

 fossils washed out of the submerged Wealden beds, and deposited on the 

 shores of the Isle of Wight, at Sandover Bay. 



The vertebrae in question present the well-marked generic characters of 

 those of the dorsal region in the Cetiosaurus. as the breadth of the centrum, 

 its subcircular contour, its median contraction and unequal concavity of the 

 articular extremities ; as, also, the short antero-posterior extent of the neura- 

 pophysis, and their anchylosis to the anterior part of the upper surface of the 

 centrum : but they differ from the vertebrae on which the characters of the 

 present genus were first founded J by the shortness of their antero-posterior 

 diameters as compared with their breadth and depth, whence I propose to de- 

 signate the species by the name of Cetiosaurus brevis. 



The centrum of a dorsal vertebra of this species from Culver Cliff mea- 

 sures. In. Lines. 



in antero-posterior diameter 3 6 



transverse diameter 6 4 



vertical diameter 6 



* This suspicion is expressed, but with due caution, by Dr. Mantell in his ' Geology of 

 the South-east of England.' " The somewhat angular vertebrae, described as appearing to 

 constitute a Second System, I should be disposed, from their number, and from their so 

 commonly occurring in the localities where the teeth of the Iguanodon most abound, to refer 

 to that animal ; it must, however, be mentioned, that the concavo-convex vertebrae which 

 correspond so entirely with those of the Iguana and Monitor, would seem to offer a more 

 probable approximation ; yet the extreme rarity of the latter renders it questionable, since 

 there appears no reason why the vertebrae shoiild not have been preserved in as consider- 

 able numbers as the teeth." — p. 306. The vertebrae of the Iguanodon discovered by Mr. Ben- 

 stead in the greensand quarries near Maidstone, are so crushed or so imbedded, as to prevent 

 a satisfactory determination of both articular extremities. 



t Illustrations of the Geology of Sussex, 4to, 1827, p. 76. Geology of the South-east of 

 England, 8vo, 1833, p. 278. 



X See Proceedings of the Geological Society for June 1841. 



