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1871.] Pelecanus having a similar upward slant ; but a closer inspection shows that the likeness is not a real one ; for in Pelecanus the free lower border of the septum, and the floor of the overlying cranial fossa are nearly parallel, the basicranial axis is bent, the front half of it making a large angle with the hinder half of it, while in this Wealden skull the floor of the cranial cavity is nearly straight in its entire extent, and the apparent inclination of the front half of the basicranial axis is caused by the great downward production of the basisphenoidal swellings behind and the bevelling off of the under surface of the basi-presphenoid in front, with a corresponding decrease of its vertical depth forward.

I have already stated my reasons for referring Mr. Fox's skull, and therefore mine, to a Dinosaur ; assuming that this opinion is accepted, it remains for me to submit the considerations which lead me to refer it to an Iguanodon. I purposely use the indefinite article, because Iguanodon is commonly spoken of as if the genus had only one representative, I. Mantelli, although the mandibles and also the vertebrae referred to this present variations which make the existence of several species very probable. I wish, however, my reference of the skull to the genus Iguanodon to be regarded rather as an attempt awaiting confirmation or correction whenever new and better material for the purpose is discovered. The jaws and teeth, either of which would have determined the reference at once, are lost ; and the circumstances of the discovery of the skull deprive us of the presumptive evidence of its nature which its association with other bones might have afforded ; so that in seeking for a clue by which to connect it with a particular Dinosaur we are limited to what inferences may be drawn from its gisement, and to what we can learn from the intrinsic features of the skull itself.

As regards the former, the bed from which it came cannot be ascertained ; but we know that the locality is rich in remains of Iguanodon : and with respect to the latter we find the clue, I think, in the obliteration of the sutures ; for these have also appeared to me to be effaced in several mandibles of Iguanodon which I have examined.

The loss of the articular end observable in all these has been occasioned by a fracture across the mandible, and not by the dissolution of a sutural union. This is plainly the case in the largest mandible figured by Prof. Owen in his ' British Fossil Reptilia and three reptilian mandibular articular bones in the Rev. Mr. Fox's collection, probably of Iguanodon, also clearly illustrate this. In other Dinosaurian skulls, or portions of skulls, examined with especial reference to this point, I have found the sutures persistent. They are so in Hypsilophodon Foxii, from which this skull is also distinguished by its large size ; they persist too in Scelidosaurus Harrisonii, of the Lias, and in the Triassic Belodon's skull. Whether they persisted or not in Megalosaurus is doubtful ; the maxilla, described last session by Prof. Huxley, is not conclusive on this point ; but a maxilla of the allied Teratosaurus, preserved in the British Museum, proves their persistence in this Saurian. The relative infrequency of Megalosaurian remains in the Isle of Wight (I state this on the

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