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 35
