573 
ing species, by its regular tapering into a prolonged pointed muzzle, 
than does that of the Chelone breviceps by-its short and truncated jaws. 
The surface of the cranial bones is smoother ; and their other mo- 
difications prove the marine character of the fossil as strongly as in 
the Chelone breviceps. 
The orbits are large, the temporal fossee are covered principally 
by the posterior frontals, and the exterior osseous shield completely 
overhangs the tympanic and ex-occipital bones. The compressed 
spine of the occiput is the only part that projects further backwards. 
The palatal and nasal regions of the skull afford further evidence 
of the affinities of the present Sheppey Chelonite to the Turtles. 
The bony palate presents in an exaggerated degree its great extent 
from the intermaxillary bones to the posterior nasal aperture, and it 
is not perforated, as in the Trionyxes, by an anterior palatal fora- 
men. 
The extent of the bony palate is relatively greater than in the 
Chelone Mydas ; the trenchant alveolar ridge is less developed than 
in the Chel. Mydas ; the groove for the reception of that of the lower 
jaw is shallower than in the existing Cheloniz, or the extinct Chel. 
breviceps, arising from the absence of the internal alveolar ridge. 
The present species is distinguished by. the narrowness of the 
sphenoid at the base of the skull, and by the form and groove of the 
pterygoid bones, from the existing Chelonie, and @ fortiori from the 
Trionyxes; to which, however, it approaches in the elongated and 
pointed form of the muzzle, and the trenchant character of the alve- 
olar margin of the jaws. 
The general characters of the carapace are next given, and a spe- 
cimen from Mr. Bowerbank’s collection is more particularly described. 
This carapace, as compared with that of the C. breviceps in the 
same collection, presents the following differences : it is much broader 
and flatter; the vertebral plates are relatively broader ; the lateral 
angle, from which the intercostal suture is continued, is much nearer 
the anterior margin of the plate; the C. longiceps in this respect re- 
sembling the existing species: the expanded portions of the ribs are 
relatively longer; they are slightly concave transversely to their axis 
on their upper surface, while in C. breviceps they are flat. The ex- 
ternal surface of the whole carapace is smoother, and although as 
depressed as in most turtles, it is more regularly convex, and sloping 
away by two nearly plane surfaces from the median longitudinal ridge 
of the carapace. 
Among the minor differences of the two Sheppey fossils the author 
states, that the first vertebral plate of C. longiceps is more convex at 
its middle part, and sends backwards a short process to join the 
second vertebral plate, in which it resembles the C. Mydas. The 
second plate is six-sided, the two posterior lateral short sides being 
attached to the second pair of ribs, in which the present species differs 
from both C. Mydas and C. breviceps. The third vertebral plate is 
quadrangular instead of the second, as in C. breviceps and C. Mydas. 
The impressions of the epidermal scutes are deeper, and the lines 
which bound the sides of the vertebral scutes meet at a more open 
