236 Geological Society. 



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 Prof. Bell, 

 which exhibits well the character of the broad and flattened symphysis. 



A carapace of a smaller individual of Chelone planimentum from the 

 Harwich coast, with the character of the inwardly projecting ribs 

 strongly marked, is likewise preserved in the choice collection of the 

 same excellent naturalist. One of the hyosternal bones enclosed in 

 the same nodule of clay testifies to the partial ossification of the 

 plastron in this species. 



In the summary of the foregoing details the author observes, that 

 they lead to conclusions of much greater interest than the previous 

 opinions respecting the Chelonites of the London basin could have 

 originated. Whilst these were supposed to have belonged to a fresh- 

 water genus, the difference between the present fauna and that of 

 the Eocene period, in reference to the Chelonian order, was not very 

 great ; since the Emys or Cistudo Europaa still abounds on the Con- 

 tinent, and lives long in our own island in suitable localities : but 

 the case assumes a very different aspect when we come to the con- 

 viction, that the majority of the Sheppey Chelonites belong to the 

 true marine genus Chelone ; and that the number of species of the 

 Eocene extinct turtles already obtained from so limited a space as 

 the isle of Sheppey exceeds that of the species of existing Chelone. 



Notwithstanding the assiduous search of naturalists, and the attrac- 

 tions to the commercial voyager which the shell and the flesh of the 

 turtles offer, all the tropical seas of the world have hitherto yielded 

 no more than five well-defined species of Chelone, and of these only 

 two, as the C. Mydas and C. caretta, are known to frequent the same 

 locality. 



The indications which the Sheppey turtles afford of the warmer 

 climate of the latitude in which they lived, as compared with that 

 which prevails there in the present day, accord with those which all 

 the organic remains of the same depositary have hitherto yielded in 

 reference to this interesting point. 



That abundance of food must have been produced under such in- 

 fluences cannot, Mr. Owen states, be doubted ; and he infers, that to 



