DESCRIPTION OF REPTILES. 219 
of the bony symphysis of the lower jaw. Both the Chelone wmbricata and the 
Chelone caouana have this part deeper and more pointed than the Ch. mydas, but 
neither species has the symphysis so depressed or so slightly convex below as it 
is in the Bracklesham Chelonites. 
These fossils also differ amongst themselves in this respect. The symphysis 
which is here referred to the Chelone trigoniceps is the broadest and flattest : the 
figures 5 & 6, Tab. XIII. illustrate this character, and more especially the back 
view, fig. 7, showing the deep and broad genio-hyoid groove g: this is reduced 
to a transversely oblong foramen in Chelone mydas. 
The second species indicated by the maxillary symphysis is that figured in 
Tab. XIII. figs. 1’ & 1": its sides meet at a more acute angle, and it is narrower 
in proportion to its length ; is more convex below and more concave above, with 
the alveolar borders a little more raised, and the middle line less raised than in 
Chelone trigoniceps. In this respect it is intermediate between the Chelone imbri- 
cata, where the upper surface of the symphysis is more concave, and the Chelone 
caouana, where it is flatter than in the Chelone trigoniceps. The fossil symphysis 
under notice has also a smooth transverse genio-hyoid groove at its back-part. 
It accords so closely in form with the end of the upper jaw of the Chelone convexa 
(fig. 1) from Sheppey, that I refer it provisionally to that species. 
Two other specimens of the symphysis of the lower jaw (figs. 8 & 9), of rather 
larger size, appear to belong to the same species as that referred to the Chel. 
longiceps *, by the characters of the concavity of the upper surface, the convexity 
of the lower surface, and the degree of convergence of the sides or borders of the 
symphysis. The larger of the two shows the genio-hyoid groove, and the nearly 
vertical outer side of the jaw (fig. 10) opposite the back part of the symphysis, 
and this shows no impression of the smooth fossa receiving the insertion of the 
biting muscles ; whereas in the Chelone trigoniceps (fig. 11) that fossa extends to 
the same transverse line or parallel with the back-part of the symphysis. 
The very rare and interesting Chelonite in Mr. Coombe’s museum, figured in 
Tab. XIII. fig. 4, was the first portion of the cranium of a reptile of this order 
that I had seen from the eocene deposits at Bracklesham. It includes the bones 
forming the roof of the mouth and portions of the bony nostrils and orbits, and 
the tympanic pedicles. 
The extremity of the upper jaw is broken off, but the straight converging 
alveolar borders clearly indicate the muzzle to have been pointed, as in the 
* Report on British Fossil Reptiles, p. 177. 
