I. Introduction. This very fine fossil was obtained from the débris of Wealden Shales, after a fall of the cliff near Atherfield (Isle of Wight). The complete skeleton was probably present when in situ, and the missing portions were carried away by the heavy seas, which scoured the foot of the talus for several days, preventing all search for the bones except at low tide. When its discovery was announced in 1917, the disarticulated bones of the skull were lying scattered among the bones of the body and limbs in many blocks of the matrix. The unfused condition of the elements of the skull proved the skeleton to be that of a young individual, and as, notwithstanding this fact, there were six anchylosed vertebræ in the sacrum, it was identified as a specimen of Iguanodon bernissartensis, and the portion of the integument found was described as belonging to that species. The study of the bones, after they had been cleared of the matrix and restored, has, however, proved the fossil to belong to a new species, and hereafter it will be designated Iguanodon atherfieldensis. The estimated length of the skeleton is 6·3 metres (about 21·6 feet). The elongation of the facial part of the skull, the transverse expansion of the edentulous portion, the great constriction between that and the frontal area, the broad and square cranial region, and the heavy mandible agree with I. mantelli and I. bernissartensis. The skull is intermediate in build between the graceful skull of the