PALAEONTOLOGY ^^^.-.^^-^ 



occur the remains of four species, namely, A. antiqua, A. cunekeps, A. 

 convexa, and A. subcristata. These turtles appear to have been related to 

 the existing loggerhead [Thalassochelys), but were of comparatively small 

 size. The genus thalassochelys itself is also recorded from Sheppey, 

 although the specimens in the British Museum on which the determina- 

 tion rests are scarcely sufficient to afford specific characters. A second 

 extinct genus of the family is represented in the London Clay of 

 Sheppey by Lytoloma crasskostatum and L. planimentum, although both 

 these species were originally described upon the evidence of Essex 

 specimens. The turtles of this genus, which were of large size, differ 

 from their modern cousins, among other characters, by the great extent 

 of the union between the two branches of the lower jaw, and the 

 backward position in the skull of the inner apertures of the nasal 

 passage. 



Passing on to the typical tortoises and terrapins [Testudinidce) it may 

 first of all be mentioned that a tortoise-shell from Sheppey originally 

 described as Emys comptoni has been assigned to the existing African 

 genus Homopus^ the members of which are terrestrial in their habits. 

 Two species of terrapin from the same locality and formation, to which the 

 names Emys testudiniformis and £. bkarmata were given by their describers, 

 are now known to be members of the existing American genus Chrysetnys. 

 Of special interest are two other freshwater tortoises from the London 

 Clay of Sheppey, since they belong to the family Pelomedusidce, the exist- 

 ing members of which, like all the tortoises which move their heads and 

 necks sideways {Pleurodira), are confined to the southern hemisphere. 

 One of these, Podocnemis bowerbanki, belongs to a genus now living in 

 South America and Madagascar, the typical Amazonian P. expansa being 

 the largest of existing freshwater tortoises. The second, Dacochelys 

 delabechei, has been made the type of a genus by itself, but might per- 

 haps be better included in Podocnemis. It was as large as the existing 

 Amazonian species mentioned above. 



The list of chelonians from the London Clay of Sheppey closes 

 with the huge Eosphargis gigas, a species at first referred to the true 

 turtles, but now known to represent an extinct genus of leathery turtles 

 {Dermochelyidce), which differ from the former, among other characters, 

 by the upper shell being formed typically of a number of small bones 

 arranged so as to form a mosaic-like pavement. Some idea of the size 

 of the Sheppey species may be gathered when it is stated that the skull 

 measures 1 3 inches in diameter. There are numerous remains of this 

 huge turtle in the British Museum, all from Sheppey. 



The numerous fishes from the London Clay of Sheppey are for the 

 most part of great interest, several of them being the sole representatives 

 of their genera. Some have been quite recently named by Dr. Smith 

 Woodward in the fourth part of the British Museum Catalogue of Fossil 

 Fishes ; to which work the reader may be referred for full descriptions of 

 the fossil fishes from all the formations of the county. 



Commencing with the sharks and rays, we find two species of 

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