572 
being wanting. The eight pairs of expanded ribs are also present, 
with sufficient of the narrower tooth-like extremities of the six an- 
terior pairs to determine the marine character of the fossil, which is 
indicated by its general form. Other minute characters are detailed ; 
and a comparison with the Chelonite from the tertiary beds near 
Brussels, figured by Cuvier, is instituted. : th 
The sternum of the Chelone breviceps, although more ossified than 
in existing Cheloniz, yet presents all the essential characters of that 
genus. ‘There is a central vacuity left between the hyosternals and 
hyposternals ; but these bones differ from those of the young Emys 
in the long pointed processes which radiate from the two anterior 
angles of the hyosternals, and the two posterior angles of the hy- 
posternals. 
The xiphisternals have the slender elongated form and oblique 
union by reciprocal gomphosis with the hyposternals, which is cha- 
racteristic of the genus Chelone. 
The posterior extremity of the right episternal presents the equally 
characteristic slender pointed form. 
With these proofs of the sternum of the present fossil being modi- 
fied according to the peculiar type of the marine Chelones, there is 
evidence, however, that it differs from the known existing species in 
the more extensive ossification of the component pieces: thus, the 
pointed rays of bone extend from a greater proportion of the margins 
of the hyo- and hyposternals, and the intervening margins do not 
present the straight line at right angles to the radiated processes. 
In the Chelone Mydas, for example, one half of the external margin 
of the hyo- and hyposternals, where they are contiguous, are straight, 
and intervene between the radiated processes, which are developed 
trom the remaining halves; while in the Chelone breviceps about a 
sixth part only of the corresponding external margins are similarly 
free, and there form the bottom, not of an angular, but a semicircular 
interspace. 
The radiated processes from the inner margins of the hyo- and hy- 
posternals are characterized in the Chelone breviceps by similar mo-" 
difications, but their origin is rather less extensive ; they terminate 
in eight or nine rays, shorter and with intervening angles more equal 
than in existing Chelones. The xiphisternal piece receives in a notch 
the outermost ray or spine of the inner radiated process of the hy- 
posternal, as in the Chelones, and is not joined by a transverse 
suture, as in. the Emydes, whether young or old. * 
The characters thus afforded by the cranium, carapace, plastron, 
and some of the bones of the extremity, prove the present Sheppey 
fossil to belong to a true sea-turtle; and at the same time most 
clearly establish its distinction from the known existing species of 
Chelone ; from the shortness of the skull, especially of the facial part 
as compared with its breadth, the author proposes to name this extinct 
species Chelone breviceps. : 
2. Chelone longiceps.—The second species of Sheppey turtle, called 
Chelone longiceps, is founded upon the characters of the cranium, ca- 
rapace, and plastron. The cranium differs more from those of exist- 
