WEALDEN FORMATIONS. 27 



rare occurrence, associated 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 have been parts of the same species. 



We now know, however, that certain of the cup-and-ball vertebree are of a kind 

 more nearly resembling those of an extinct CrocodiHan, with teeth very different from 

 either those of Iguanodon or of the modern diminutive IguanoB. The elimination of 

 these, otherwise perplexing ball and socket-jointed vertebrae, forms, therefore, an 

 essential step in the appropriation to the Iguanodon of its proper vertebral type. 



Genus — Cetiosaurus, Owen. Tabs. VIII, IX, and X. 



In the notices of the various forms or types of vertebrae from the Wealden strata, 

 pubUshed by their persevering investigator. Dr. Mantell, prior to 1841, he states* 

 that " his first step was, with the able assistance of the Rev. W. D. Conybeare, to 

 separate those that belonged to the Crocodile, Plesiosaur and Megalosaur, or at least 

 the vertebrae which most resembled those from Stonesfield." 



Many enormous vertebrae remained, which are referred, in the Mantellian 

 Catalogue of the collection subsequently puVchased for the British Museum, to the 

 Iguanodon. From these residuary specimens I separated, in my ' Report on British 

 Fossil Reptiles,' of 1841, the vertebrae characteristic pf the genera PoiJcilopleuron, 

 Deslong., Streptospondylus, v. Meyer, and Cetiosaurus, which latter genus had 

 previously been characterised by vertebral peculiarities observed in specimens obtained 

 from older Oolitic strata. 



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

 acquainted by the examination of the late Mr. Saull'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 presented the well-marked generic characters of those of 

 the dorsal region in the Cetiosaurus longus of the middle Oolite, as, e.g., 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 

 neurapophyses and their anchylosis to the anterior part of the upper surface of the 

 centrum : but they differed from the vertebrae on which the characters of the present 

 genus were first founded + by the shortness of their antero-posterior diameter as 



* 'Illustrations of the Geology of Sussex,' 4to, 182", p. 76 ; 'Geology of the South-east of England,' 

 8vo, 1833, p. 278. 



f See ' Proceedings of the Geological Society' for June, 1841. 



