220 DESCRIPTION OF REPTILES. 
Chelone longiceps of Sheppey ; and the muzzle being shorter, the form of the skull 
has more nearly approached that of a right-angled triangle. The whole cranium 
is broader and shorter, and the tympanic pedicles wider apart. The middle line 
of the palate developes a somewhat stronger ridge: the orbits were relatively 
larger and advanced nearer to the muzzle than in Chelone longiceps: the malar 
bones are more protuberant behind the orbits, and their external surface inclines 
inwards as it descends from behind and below the orbit to form the lower border 
of the zygoma, which it does not do in the Chelone longiceps. 
The upper surface of the fossil shows the palatines rising to join the vomer at 
the middle line, and the two small subcircular vacuities (occupied by membrane 
in the recent skull) between the palatines and prefrontals and maxillaries ; the 
anterior border of the temporal fossa formed by the malar and pterygoid is entire 
on one side, and shows that that vacuity was as broad as it is long. The olfac- 
tory excavations in the maxillaries are deep. The articular surface of the tym- 
panic pedicles closely accords with those of recent Chelonians. 
The very regular triangular form of the skull indicated by this fragment has 
induced me to propose the name of Chelone trigoniceps for the species. 
Chelone convera, Owen*. 
The cranium of the Chelonite from the London clay of Sheppey, which was 
kindly presented by the Earl of Enniskillen to Mr. Dixon, figured in Tab. XIII. 
figs. 1,2 & 3, differs from the Chelone breviceps + in the more pointed form of the 
muzzle, and the less rugose character of the outer surface of the bones; and 
from the Chelone longiceps { in the less produced and less acute muzzle, and the 
more rugose surface of the bones. In its general proportions and triangular form 
it approaches nearer to the Chelone trigoniceps, but differs from this species in 
the contour of the lower border of the orbits, in the configuration of the surface 
of the bony palate, and in the minor expansion of the malar regions. ‘The palate 
is traversed longitudinally by a deep median groove, between which and the 
shallower grooves on the inner sides of the alveolar borders are two well-marked 
longitudinal convexities. 
The frontal bones enter into the formation of the upper borders of the orbits, 
which are nearly circular in form, as in Chelone longiceps ; not subrhomboidal 
with the angles rounded off, as in Chelone breviceps. 
* Proceedings of the Geological Society of London, December 1, 1841, p. 575. 
+ Report on Brit. Foss. Reptiles, p. 178. { Ibid. p. 177. 
