262 BRITISH FOSSIL REPTILES. 



remarked, in reference to this discovery of the Iguanodon, that it " shows that the 

 duration of this animal did not cease with the completion of the Wealden series. The 

 individual from which this skeleton was derived had probably been drifted to sea, as 

 those which afforded the bones found in the fresh-water deposits subjacent to this 

 marine formation had been drifted into an estuary."* 



One of the chief advantages of Mr. Bensted's remarkable discovery, is the demon- 

 stration which it affords of the vertebral characters of the Iguanodon, — an important 

 evidence of organisation, the difficulty of obtaining which will be appreciated by 

 reference to my ' Report on British Fossil Reptiles/f in which descriptions of the 

 various vertebrae that had been found in the Wealden up to the year 1841 are given. 



In the point of view in which I have had this remarkable and unique collection of 

 the remains of one and the same animal figured, there are four vertebrae with their 

 bodies in natural juxtaposition at the upper corner opposite the right hand, and the 

 same number a little dislocated at the lower corner of the specimen. The latter show 

 the characteristic neural arch in the best state of preservation, and the second of 

 these vertebrae is represented of the natural size in PI. 3. 



In neither of these series, nor, indeed, in any part of the specimen, is there a 

 vertebra with a parapophysis, or articular tubercle or impression for a rib, upon the 

 centrum, — a character indicative of one from the neck or anterior part of the thorax. 

 The whole of the exposed outer surface of the centrum, save the two extremities, is 

 smooth or " non-articular," as in the middle and hinder parts of the trunk in the 

 Crocodilia. Both the terminal or articular surfaces of the centrum are slightly concave, 

 and with a nearly circular contour, with the vertical diameter slightly predominating 

 (PI. 4) ; the sides of the centrum rapidly contract as they recede from the articular 

 ends towards the middle of the vertebra, and are chiefly remarkable for the almost 

 plane surface which they form as they converge towards the lower surface of the 

 centrum, the middle part of which is thus somewhat wedge-shaped, but with the lower 

 border obtuse, and slightly concave lengthwise, as shown in PI. 3. 



The converging sides are, however, slightly convex vertically, more concave 

 transversely ; the free surface is traversed by fine longitudinal linear impressions. The 

 neurapophyses have coalesced with each other and with the neural spine ( /w) above, 

 forming a remarkably broad and lofty neural arch, the base of which {n n) is still 

 articulated by suture in this young Iguanodon to the centrum. In a few of the 

 vertebrae this persistent suture has permitted a dislocation of the arch. The base of the 

 neurapophysis is coextensive with the centrum lengthwise, and is developed inwards, 

 transversely, so as almost to meet its fellow and circumscribe the neural canal. As the 

 neurapophysis ascends it diminishes at first, in both diameters, and then again increases 



* Bridgwater Treatise, vol. i, p. 241. 



t Transactions of the 'British Association,' 1844, pp. S4 — \3:i. 



