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XI. Memoir on a Portion of the Lower Jaw of the Iguanodon, and on the Remains of 
the Hylceosaurus and other Saurians, discovered in the Strata of Tilgate Forest, 
in Sussex. 
By Gideon Algernon Mantell, Esq., LL.D., F.R.S., F.L.S., F.G.S., 8$c. 
Received February 8, — Read February 18, 1841. 
When in the year 1825 I had the honour to lay before the Royal Society a notice 
on the teeth of an herbivorous reptile found in the limestone of Tilgate Forest, in 
Sussex, I entertained the hope and expectation that the discovery of the jaws, or a 
portion of the jaw with the teeth attached, would reward my labours, and enable me 
either to confirm or modify the inferences I had ventured to deduce from an exami- 
nation of the teeth alone. And I was encouraged in this anticipation by the remarks 
of Baron Cuvier, who, in the correspondence upon this subject with which he 
honoured me, thus expressed himself : — “ N’aurions-nous pas ici les dents d’un animal 
nouveau, d’un reptile herbivore? Le temps confirmera ou infirmera cette idee, puis- 
qu’il est impossible qu’on ne trouve pas un jour une partie du squelette, reunie a des 
portions de machoire portant des dents.” But after unremitting research, and the 
collection of several hundred teeth, and bones of various parts of the skeletons of 
many individuals, even including the tympanic bone with the auditory cells, I found 
myself, at the expiration of twelve years, without any additional information respect- 
ing the maxillary organs of this colossal reptile, no trace of the jaws having come 
under my observation. 
I have, however, at length had the good fortune to discover what appears to be a 
portion of the lower jaw of a young Iguanodon, in which the fangs of many teeth, 
and the position of the germs of several of the successional teeth are preserved. 
I therefore transmit to the Royal Society a description of this interesting relic ; 
and as the Saurian remains collected by me from the Wealden strata of the South- 
east of England are now admirably arranged in the Gallery of Natural History of the 
British Museum, a notice of some of the most remarkable specimens is subjoined, 
in the hope of preserving a record of a few important particulars respecting their 
osteological characters and relations. 
Portion of the Lower Jaw of the Iguanodon. Plate V. figs. 1. 2. 5. 6. 8. and 9. 
Natural size. 
This fossil was imbedded in sandstone, and its characters were so much concealed 
by the surrounding matrix, that it almost escaped my observation in the last visit 
MDCCCXLI. t 
