576 
The true marine character of the present Sheppey Chelonite is 
likewise satisfactorily shown in the small relative size of the entire 
femur which is preserved on the left side, attached by the matrix to 
the left xiphisternal. It presents the usual form, a slight sigmoid 
flexure, characteristic of the Chelones; it measures one inch in 
length. In an Emys of the same size, the femur, besides its greater 
bend, is 14 inch in length. 
5. Chelone subcristata.—The fifth species of Chelone from Sheppey, 
distinguishable by the characters of its carapace, approaches more 
nearly to the Chelone Mydas in the form of the vertebral scutes, 
which are narrow in proportion to their length, than in any of the 
previously described species; but is more conspicuously distinct by 
the form of the 6th and 8th vertebral plates, which support a short, 
sharp, longitudinal crest. The middle and posterior part of the first 
vertebral plate is raised into a convexity, as in the Chel. longiceps, 
but not into a crest. 
The keeled structure of the sixth and eighth plates is more marked 
than in the fourth and sixth plates of Chelone Mydas, which are 
raised into a longitudinal ridge. 
The characters of the carapace are then minutely described. 
Sufficient of the sternum is exposed in the present fossil to show, 
by its narrow elongated xiphisternals, and the wide and deep notch 
in the outer margin of the conjoined hyo- and hyposternals, that it 
belongs to the marine Chelones. 
The xiphisternals are articulated to the hyposternals by the usual 
notch or gomphosis; they are straighter and more approximated 
than in the Chel. Mydas; the external emargination of the plastron 
differs from that of the Chel. Mydas in being semicircular instead 
of angular, the Chel. subcristata approaching, in this respect, to the 
Chel. breviceps. . 
The shortest antero-posterior diameter of the conjoined hyo- and 
hyposternals is two inches seven lines. The length of the xiphi- 
sternal two inches six lines. The breadth of both, across their 
middle part, one inch three lines. 
The name proposed for this species indicates its chief distinguish- 
ing character, viz. the median interrupted carina of the carapace, 
which may be presumed to have been more conspicuous in the horny 
plates of the living animal than in the supporting bones of the fos- 
silized carapace. 
6. Chelone planimentum.—This species is founded on an almost 
entire specimen of skull and carapace of the same individual, in the 
museum of Prof. Sedgwick; on a skull and carapace belonging to 
different individuals, in the museum of Prof. Bell; and on a carapace 
in the British Museum; all of which specimens are from the London 
clay at Harwich. 
The skull resembles, in the pointed form of the muzzle, the Chel. 
longiceps of Sheppey, but differs in the greater convexity and breadth 
of the cranium, and the great declivity of its anterior contour. 
The great expansion of the osseous roof of the temporal fossz, and 
the share contributed to that roof by the post-frontals, distinguish 
the present, equally with the foregoing Chelonites, from the fresh- 
