We are indebted to the researches of Mr. Mantell* for our knowledge of the existence of that curious and most gigantic herbivorous reptile the Iguanodon†. The localities in which he discovered it are limited to the Hastings sand, or Wealden formation in Tilgate Forest, at the west extremity of which district are the quarries of Headfold Wood Common, where was found the enormous femur described by Mr. Murchison in the Geological Transactions‡, as being three feet seven inches long, and probably derived from this animal. In the course of this year, 1829, I have ascertained its presence in three other localities, which are important, not only in relation to the history of this singular reptile, but as tending still further to connect the geological structure of those parts of the Isle of Wight and Isle of Purbeck wherein it occurs, with the Hastings sand, i. e. the iron sand of the Weald of Sussex and Kent. 1. Iguanodon at two new localities in the Isle of Wight. The first of these new localities is on the south coast of the Isle of Wight, in the iron sand which forms the shore, a little east of Sandown Fort, between high and low water. The most remarkable specimen I possess from thence is the gigantic metacarpal bone about to be described. The form of this bone nearly resembles one in the collection of Mr. Mantell, which Cuvier saw, and pronounced to be the metacarpal bone of the thumb of a reptile; but