1852. ] OF THE ROYAL INSTITUTION. . 141 
WEEKLY EVENING MEETING, 
Friday, March 5. 
W. R. Hamitron, Esq. F.R.S., F.S.A., Vice-President, 
in the Chair. 
Gipron ALGERNON Manrett, Esq., LL.D., F.R.S., 
President of the West London Medical Society, &c. 
On the Structure of the Iguanodon, and on the Fauna and Flora of the 
Wealden Formation. 
Tue geological phenomena of the South-East of England, com- 
prising the lithological characters and organic remains of the 
Diluvial, Tertiary, Cretaceous, Wealden, and Oolitic deposits, were 
described in two Lectures delivered to the Members of the Royal 
Institution by Dr. Mantell in 1836 and 1849. In those dis- 
courses the Fauna and Flora of the Wealden were cursorily noticed, 
and the Iguanodon and other gigantic terrestrial reptiles, whose 
fossil remains have invested the strata of Tilgate Forest with a high 
degree of interest, were briefly alluded to. The present Lecture 
was restricted to a consideration of the Fauna and Flora of the 
countries whence the deposits constituting the Wealden districts 
were derived ; and the osteological characters of the most remarkable 
fossil Saurians peculiar to this geological epoch, were especially 
illustrated. 
After a concise exposition of the characters of the various 
formations which have succeeded, and now overlie, or in other 
words, are of more recent origin than the Wealden, — namely, the 
Drift or Diluvium, containing bones of large mammalia, as_ the 
Mammoth, Mastodon, Rhinoceros, Horse, Deer, &c;—the Hocene, 
or ancient tertiary strata of the London basin, abounding in marine 
exuvie of special and for the most part extinct types;—and the 
Cretaceous or Chalk-Formation, comprising the White-Chalk of the 
North and South Downs, and the Chalk-marl, Galt, and Greensand, 
of Surrey, Kent, and Sussex, the whole characterized by innumerable 
marine shells, zoophytes, fishes, reptiles, &c. of extinct species and 
genera;— Dr. Mantell proceeded to illustrate the structure of the 
Iguanodon as exemplified by the isolated parts of the skeleton hitherto 
discovered, and of which numerous examples were exhibited on the 
tables of the Institution. 
The perfect germ, and the unused tooth, of the Iguanodon, are 
characterised by the prismatic form of the crown, which is traversed 
on the thick enamelled face by three or four longitudinal ridges, and 
has the lateral margins denticulated, and the summit finely crenated ; 
in this state the teeth resemble those of the living Iguana of the 
West Indies, —a resemblance which suggested the generic name of 
Iguanodon. [But the fossil teeth are of enormous size in comparison 
with their recent prototypes; for the tecth of the Iguana are as 
