577 
water genera Emys and Trionyx. In the oblique position of the 
orbits, and the diminished breadth of the interorbital space, the pre- 
sent Chelonite, however, approaches nearer to Trionyx and Emys than 
the previously described species. 
- Its most marked and characteristic difference from all existing or 
extinct Chelones is shown by the greater antero-posterior extent and 
flatness of the under part of the symphysis of the lower jaw, whence 
the specific name here given to the species. 
Since at present there is no means of identifying the well-marked 
species of which the skull is here described with the Chelonite figured 
in the frontispiece to Woodward’s ‘ Synoptical Table of British 
Organic Remains,’ and alluded to without additional description or 
characters as the ‘ Chelonia Harvicensis’ in the additions to Mr, 
Gray’s ‘ Synopsis Reptilium,’ p. 78, 1831; and since it is highly 
probable that the extensive deposit of Eocene clay along the coast of 
Kssex, like that at the mouth of the Thames, may contain the relics 
of more than one species of our ancient British turtles, the author 
prefers indicating the species here described by a name having refer- 
ence to its peculiarly distinguishing character, to arbitrarily associa- 
ting the skull with any carapace to which the vague name of Harvi- 
censis has been applied. 
Besides the specimen of Chelonite from Harwich, in the museum 
of Norwich, figured by Woodward, there is a mutilated carapace of 
a young Chelone from the same locality in the British Museum. 
This specimen exhibits the inner side of the carapace, with the heads 
and part of the expanded bodies of four pairs of ribs. It is not suf- 
ficently entire to yield good specific characters, but it demonstrates 
unequivocally its title to rank with the marine turtles. It is figured 
in Mr. Keenig’s ‘ Icones Sectiles,’ pl. xvi. fig. 192, under the name 
of Testudo plana. 
The carapace of a larger specimen of Chelone, from the coast of 
Harwich, was purchased, by the British Museum, of Mr. Charles- 
worth, by whom a lithograph of the inner surface of this Chelonite, of 
the natural size, has been privately distributed, without description. 
The carapace in the museum of Prof. Sedgwick, forming part of 
the same individual (Chelone planimentum) as the skull above described, 
exhibits many points of anatomical structure more clearly than the 
last-mentioned Chelonite in the British Museum ; it also displays the 
characteristic coracoid bone of the right side in its natural relative 
position. The resemblance of this carapace in general form to that 
of the Chelone caretta is pretty close; it differs from that and other 
known existing turtles, and likewise from most of the fossil species, 
in the thickness and prominence of the true costal portions of the 
expanded vertebral ribs, which stand out from the under surface of 
the plate through their entire length, and present a somewhat angular 
obtuse ridge towards the cavity of the abdomen. 
In the large proportional size of the head, the Chelone planimentum 
corresponds with the existing turtles; and that the extinct species 
here described attained larger dimensions than those given above, is 
proved by a fossil skull from the Harwich clay, in the collection of 
