FOSSIL REPTILES. 379 



of existing lizards in the Museum of the Royal College of Sur- 

 geons. The result of this comparison proved most satisfactory. 

 He found in the iguana teeth decidedly analogous to the fossil, 

 in conformation and structure. He has figured one of these 

 teeth of iguanodon, the largest and most perfect specimen 

 which he could find. The surface of the tooth is worn down 

 obliquely by piastication. The edges are serrated. The fang 

 is broken, and the hollow filled with sandstone. There is a 

 cavity or depression in the base of the fang, occasioned by the 

 absorption produced by the pressure of a secondary tooth. 



Like the teeth of the existing iguanas, the crown of the fossil 

 tooth is acuminated. The edges are strongly dentated. The 

 outer surface presents ridges, while the inner one is smooth 

 and convex. These teeth,' like most others, appear to have 

 been hollow in the young animal, and to have assumed solidity 

 with advancing age. 



From the character of the fossil remains, which more imme- 

 diately surrounded those relics of the iguanodon, it is concluded 

 that if this animal was amphibious, it was a native of the fresh 

 water, and not of the ocean. Calculating on the proportions 

 of the living animal, and supposing the same relative dimensions 

 in the fossil, as to the teeth, the individual which possessed the 

 tooth we have been describing must have been upwards of sixty 

 feet in length. A similar deduction has been made by Dr. 

 Buckland respecting the size of the iguanodon, from a femur 

 and other bones in the possession of Mr. Mantell. 



It would appear, from the researches of Mr. Mantell, that the 

 iguanodon bore on its head a remarkable horny appendage, - 

 as large, and similarly formed, as the smaller horn of the 

 rhinoceros. What he discovered of this is, externally, dark 

 brown. Some parts of the surface are smooth, and others 

 furrowed, as if for the passage of vessels. Its structure is 

 osseous, and there is no internal cavity. But it does not appear 

 to have been joined to the skull by a bony process, like some 

 horns of mammiferous animals. The horned Species are by 



