Geological Society. 235 



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 fossae, and 

 the share contributed to that roof by the post-frontals, distinguish 

 the present, equally with the foregoing Chelonites, from the fresh- 

 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 

 Essex, 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- 

 ficiently entire to yield good specific characters, but it demonstrates 

 unequivocally its title to rank with the marine turtles. It is figured 

 in Mr. Kcenig's ' Icones Sectiles,' pi. 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- 



