142 
DR. MANTELL ON A PORTION OF THE LOWER JAW 
on the Iguanodon, applies with greater force to the Hylseosaurus ; it is indeed “un 
Saurien encore plus extraordinaire que tons ceux dont nous avons connaissance* * * § .” 
In the strata of Tilgate Forest I had found associated with the remains of the 
Iguanoclon, the bones of several other reptiles, namely, the Megalosaurus, one or more 
species of Plesiosaurus, of Gavial or Steneosaurus^-, and Pterodactylus, and several 
species of Chelonia, Emys, and Trionyx, besides many fishes, and one or more spe- 
cies of a bird allied to the Heron. The first specimen which led me to suspect the 
existence of a reptile belonging to a new genus, was discovered in 1832 , and described 
in a memoir read before the Geological Society of London, and subsequently pub- 
lished in the c Geology of the South-East of England to this notice I beg to refer 
for a figure and detailed description of the original^:. It will suffice for my present 
purpose to remark, that this specimen consists of part of the spinal column composed 
of seven dorsal and three or four cervical vertebrae ; eleven ribs (Plate X. fig. 6.) ; two 
coracoids and omoplates ; with numerous dermal bones and spines. From the ap- 
pearance of the block of stone in which the bones are imbedded, there can be no doubt 
that a considerable portion of the skeleton extended into the surrounding rock and 
was destroyed by the workmen. This extraordinary fossil displays osteological cha- 
racters so peculiar, as at once to establish the propriety of referring it to a new genus. 
I shall not dwell on the forms of the vertebrae, ribs, &c., but only direct attention to 
the structure of the pulmonary arch, in which a coracoid of the Lacertian type (Plate 
X. fig. 7-) is united to an omoplate resembling that of the Crocodile (Plate X. fig. 
10 .), and the presence of dermal bones and spines (Plate X. figs. 1 , 2 , 3 , 4 .) of 
enormous magnitude §. 
The second specimen of the Hylceosaurus was found imbedded in a layer of blue clay 
near Bolney in Sussex ; and, like the former, was unfortunately mutilated, and in a 
great measure destroyed, by the labourers by whom it was discovered. It appeared from 
the statement of the most intelligent of the workmen, that after removing a stratum 
of paving stone (a calciferous grit, much covered by ripple-marks), they perceived 
imbedded in the clay a great number of ribs, vertebrae, and large bones, into which 
they immediately drove their pickaxes, destroying the connexion of the bones, break- 
ing many, and preserving only some of the largest and most perfect. Although on 
* Ossemens Fossiles, tom. v. p. 351. 
f A splendid specimen of a Crocodilian reptile, with large osseous dermal scuta, probably referable to the 
Steneosaurus of Geokfroy St. Hilaire, was discovered in the Wealden strata at Swanage, by Mr. Trotter, 
and is figured and described in the ‘ Wonders of Geology,’ vol. i. (Fourth Edition) p. 402. plate iv. These 
remains are imbedded in two slabs of limestone (each four feet by three), which now occupy a case near to 
that of the Hylseosaurus in the British Museum. 
I Memoir on the Hylseosaurus, a newly-discovered fossil reptile from the strata of Tilgate Forest. Geology 
of the South-East of England, p. 289. 
§ I cannot but express my regret that this unique and most interesting fossil is, from want of space, placed 
in the Gallery of the British Museum in a situation very ill adapted to display its peculiar characters ; the frame- 
work of the case containing it intersects, and obscures many essential particulars. 
