8 BRITISH FOSSIL REPTILES. 



Sheppey, described and figured in the last edition of Cuvier's ' Ossemens Fossiles,' for 

 example, are referred to the fresh-water genus Emys ; and the statement in tlie earlier 

 edition of the ' Ossemens Fossiles,' that the greater part of the remains of Chelonian 

 reptiles belong to the fresh-water or terrestrial genera, is repeated. 



The aim of the Memoir, communicated to the Geological Society in December, 

 1841, was to show that the conclusion deduced by Cuvier, from an imperfect carapace 

 from Sheppey, which might probably have belonged to a species of Emys, had been 

 unduly extended to other Chelonites, which undoubtedly belonged to the marine genus 

 Chelone ; and that this genus was represented, in the Eocene strata, by at least six 

 species ; the remains of five of which were from the London Clay at Sheppey, and 

 those of a sixth were tolerably abundant in the cliffs near Harwich. 



In the carapace of the fossil Chelonian from Sheppey, communicated by Mr. Crowe, 

 of Faversham, to Cuvier, and figured in the ' Ossemens Fossiles' (torn, v, part 2, pi. xv, 

 fig. 12), the author of that great work conceived that all the characters of the genus 

 Emys were perfectly recognisable. 



He points out the proportions of the neural plates, which are as long as they are 

 large ; and in the figure they are represented of nearly a quadrate form, and not 

 rhomboidal. 



The fifth neural plate in the fragment figured (probably the eighth) is separated 

 from the sixth (ninth) by a point, which is made by the mesial ends of the fifth 

 (probably the seventh) pair of costal plates ; a structure which Cuvier says slightly 

 recalls what he had observed in the Jura Emys of Solcure.* 



But Cuvier admits that the neural plates {jihufirs vert eb rales) are narrower than 

 those of existing Emydes ; and that the equal breadth of the ribs is a character common 

 to the Cliehnes with the Emydes. 



Now, in reference to the carapace figured by Cuvier, it is to be observed, that the 

 margins are wanting ; and that the broad conjoined portions of the costal plates are 

 not longer than they might have been, had the fossil belonged to a turtle {Chelone) ; 

 and, consequently, that there is no proof that they were united together by suture 

 throughout their whole extent, as in the Emydes ; but that they might have terminated 

 in narrow tooth-like processes, as in the Chehnes. 



The narrowness of the neural plates is a character which, with their smoothness, 

 undoubtedly approximates the fossil to the Chehnes ; and, without intending to affirm 

 that the fossil in question does not belong to the family ^wyt/iVfe, which unquestionably 

 existed at the time of the deposition of the Sheppey clay, its determination appears to 

 me to be much less decisive than mio-ht be inferred from the remarks in the ' Ossemens 

 Fossiles.' 



* Tom. cit., p. 2.34. This structure is not, however, peculiar to the geiuis Emtjs ; in the carapace of 

 the Chelone caouaniin, iu the Museum of the Royal College of Surgeons, the seventh neural plate is separated 

 from the eighth by the junction of the expanded extremity of the seventh rib on one side -with that of the 

 opposite rib, and the eighth neural plate from the ninth by the same modification of the eighth pair of 

 rib ;. A similar modification may also be seen in the carapace of the Trionyx Henrici, PI. 6. 



