8 FOSSIL REPTILIA OF THE LONDON CLAY. 



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

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

 species ; the remains oi 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 Soleure.* 



But Cuvier admits that the neural plates (plaques vertebrates) are narrower than 

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

 to the Chelones 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 (Clielone) ; 

 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 Chelones. 



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



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



that the fossil in question does not belong to the family Emydidce, which unquestionably 



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



me to be much less decisive than might be inferred from the remarks in the ' Ossemens 



Fossiles.' 



* Tom. cit., p. 234. This structure is not, however, peculiar to the genus Emys ; in the carapace of 

 the Chelone caouanna, in the Museum of the Royal College of Surgeons, the seventh neural plate is separated 

 from the eighth hy 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 

 ribs. A similar modification may also be seen in the carapace of the Trionyx Henrici, T. XVI. 



