10 FOSSIL REPTILIA OF THE LONDON CLAY. 



But the figure in Parkinson's work gives clearly the latter character ; whence also 

 we may infer that it agreed more with the Chelones also in the size of the postfrontals ; 

 although the anatomy of the skull is too obscurely delineated to demonstrate this 

 fact. 



The following important affinities are, however, unquestionably indicated in 

 Parkinson's figure : — -first, the large size of the orbits, which are nearly six times 

 greater than those of the Emys expansa ,• secondly, their more posterior and lateral 

 position ; and thirdly, the greater breadth of the interorbital space : in all which 

 characters the Sheppey fossil closely resembles the true Chelones, and differs from the 

 only known species of Emys (Podocnemys) expansa, in which the temporal openings 

 are protected by a bony roof. 



That fresh-water tortoises have left their bony cuirasses in the Sheppey clay, will 

 be subsequently shown ; but the evidence of the genus Emys, adduced by Cuvier, is 

 incompetent to prove their existence ; and, it may be affirmed, that of the fossils 

 cited by the founder of Palaeontology, some, with great probability, and others with 

 certainty, are referable to the marine genus, Chelone. 



Without further discussing the question as regards these evidences, I shall proceed 

 to describe the specimens from Sheppey which I have myself had the opportunity 

 of examining ; and shall commence with those which belong undoubtedly to the 

 marine family. 



Chelone breviceps. Owen. Tabulae I and II. 



Proceedings of the Geological Society, December 1, 1841; Report on British Fossil 



Reptiles, Trans. British Association, 1841, p. 178. 

 Syn. Emys Parkinsonii. J. E. Gh-ay. 



— de Sheppey. M. v. Meyer (?). 

 Chelone antiq.ua. Kcenig (?). 



The first of the Chelonites, which led me to the recognition of this species, was a 

 nearly perfect cranium from Sheppey (Tab. I, figs. 1 — 4), wanting only the occipital 

 spine, and presenting a strong and uninterrupted roof, extended posteriorly from the 

 parietal spine on each side (7, 7), over the temporal openings to the mastoids (8, 8) ; 

 and formed anteriorly by a great development of the posterior frontals (22). 



This unequivocal testimony of the marine genus of the fossil, is accompanied by 

 similar evidence afforded by the large size and lateral aspect of the orbits, the 

 posterior boundary of which extends be} r ond the anterior margin of the parietals ; and 

 by the absence of the deep emargination which separates the superior maxillary from 

 the tympanic bone in the fresh-water tortoises, and especially in the Podocnemys 

 expatim. 



In general forrn, the skull of the present species of Sheppey Chelone resembles that 

 of the Chelone mydas, Brongn. : but it is relatively broader ; the prefrontals (14) are 



