120 REPORT — 1841. 



crown. The complicated and expanded crown of the Iguanodon's tooth is 

 supported on a narrower stem ; and the stems or fangs, if the crowns were 

 in contact without overlapping, must have been separated by interspaces of 

 proportional breadth, viz. twice their own breadth ; but the thickness of the 

 crown of the tooth of the Iguanodon renders it very unlikely that they did 

 overlap each other. Now the crowns of the teeth of the Hylaeosaur are ex- 

 panded to such an extent, as, if in contact to require an interspace of the fangs, 

 not broader than the fangs themselves; and the interspaces of the fangs in 

 the fragment of jaw under consideration correspond with crowns of this 

 breadth. The fangs of the teeth in the Iguanodon are conical, and more or 

 less angular ; in the teeth presumed to belong to the Hyleeosaur the fangs are 

 cylindrical ; the sockets in the present fragment correspond with the latter 

 form. 



In my Odontography*, I adopted the opinion of Dr. Mantellf respecting 

 the present fossil ; but subsequent examination and consideration of its cha- 

 racters have led me to a different conclusion. It might, nevertheless, be 

 urged that the teeth of the young Iguanodon may exhibit such modifications 

 as would affect the validity of the objections here offered ; but these, I think, 

 establish the greater probability that the jaw in question originally contained 

 teeth of the form of those that I have referred to the HyloEosaurus. 



The remains of the Hylaosaurus have been discovered in the Wealden 

 formation in the following localities : Tilgate Forest, Bolney and Battle. 



Iguanodon Mantelli, Cuv. 



The bones of an enormous reptile, successively discovered in tho Wealden 

 strata by Dr. Mantell, interpreted by their discoverer with the aid of Cuvier 

 and CliftJ, named Iguanodon by Conybeare§, lastly found in juxtaposition 

 to the extent of nearly half the skeleton, in the green-sand quarries of Mr. 

 Benstead, offer not the least marvellous or significant evidences of the inha- 

 bitants of the now temperate latitudes during the earlier oolitic periods of the 

 formation of the earth's crust. 



With vertebrae subconcave at both articular extremities, having, in the 

 dorsal region, lofty and expanded neural arches, and doubly articulated ribs, 

 and characterized in the sacral region by their unusual number and compli- 

 cation of structure ; with a Lacertian pectoral arch and unusually large bones 

 of the extremities excavated by large medullary cavities and adapted for ter- 

 restrial progression ; — the Iguanodon was also distinguished by teeth, resem- 

 bling in shape those of the Iguana, but in structure difiering from the teeth of 

 every other known Reptile, and unequivocally indicating the former existence, 

 in the Dinosaurian Order, of a gigantic representative of the small group of 

 living lizards which subsist on vegetable substances. 



Of this remarkable Reptile, the results of personal examination of almost 

 a'l the recognisable remains that have hitherto been collected in public or pri- 

 vate museums, are here given. 



Teeth. — The value of the ordinary external characters of the teeth of the 

 oviparous Vertebrata has never perhaps been placed in so striking a point of 

 view as in the leading steps to the discovery of the Iguanodon, which cannot 

 be better recounted than in the words of Dr. Mantell. 



* Part ii. p. 24S. f Wonders of Geology, vol. i. p. 393. 



% See Philosophical Transactions, 1825, "Notice on the Iguanodon, by Gideon Mantell, 

 F.L.S." 



§ " The name Iguanodon, derived from the form of the teeth (and which I have adopted 

 at the suggestion of the Rev. VV. Conybeare), will not, it is presumed, be deemed objection- 

 able." — Loc. cit. 



