144 
DR. MANTELL ON A PORTION OF THE LOWER JAW 
No certain examples of the skull, jaws, or teeth of the Hylseosaurus have been met 
with ; but in the stratum of sandstone which contained the first specimen, a few 
teeth, decidedly of a lacertian structure, and of a very peculiar form, were disco- 
vered*; fifteen only have been noticed, of which ten are deposited in the British 
Museum. These teeth are about 1^ inch in length, and commence at the base with 
a cylindrical fang or shank, which gradually enlarges into a crown of a clavated 
form, terminating in an obtuse angular apex ; the lateral margins of which are more 
or less worn, as if from attrition with the teeth in the opposite jaw. The surface of 
the enamel, as shown in the figures, is covered with faint longitudinal strise. The 
crown is solid, but the fang is hollow, and in every specimen appears as if broken off 
close to the jaw. This character may, however, have originated from necrosis, oc- 
casioned by the pressure of a successional tooth. The example figured (the only one 
which remained in my possession,) has unfortunately been destroyed by the lapidary 
in attempting to make a section for microscopical examination. From the portions 
preserved, I have, however, been able to ascertain that the tooth possessed the struc- 
ture which Mr. Owen describes as characteristic of the teeth of the Monitor and 
of most reptiles. It has a central medullary canal, with very fine calcigerous tubes 
radiating from the centre, at right angles to the periphery of the tooth, which has a 
thin coat of enamel, in which no vessels or tubes can be detected ; the extremely 
dense structure of this fossil presents a striking contrast to the plexus of medullary 
canals and calcigerous tubes and cells observable in the tooth of the Iguanodon. 
The reference of this tooth to the Hylseosaurus must not, however, be considered as 
decisive, till confirmed by the discovery of teeth attached to the jaw in connexion 
with other parts of the skeleton of this extraordinary reptile. 
In this imperfect sketch, I have only attempted a slight outline of the osteological 
characters of some of the extinct reptiles whose remains I have discovered in the 
Wealden formation of the South-East of England, and I leave to those who have 
more leisure and ability for the task, the complete restoration of the Fauna of the 
country of the Iguanodon and Hylseosaurus. For this purpose I have presented to my 
distinguished friend, Professor Owen, drawings by M. Dinkel, of the principal spe- 
cimens in my collection, which I had employed that eminent artist to execute some 
years since, with the view of laying before the Royal Society a full description of the 
originals. Unavoidable circumstances have compelled me to abandon that intention, 
but which I no longer regret, since the subject will be elucidated by one far more 
competent to do it justice. 
Removed from the field of my former labours, having disposed of my collection, 
the fruit of twenty-five years assiduous research, and being engaged in the duties of 
* Wonders of Geology, vol. i. p. 403. In the Geology of the South-East of England (p. 293.) these teeth, 
on the authority of M. Boue, were referred to the Phytosaurus or Cylindricodon of Dr. Jager; an opinion 
which subsequent observations have proved to be untenable. 
