Geological Society. 229 



Dec.jl. — A paper was read containing a " Description of the Re- 

 mains of Six Species of Marine Turtles (Chelones) from the London 

 Clay of Sheppey and Harwich." By Richard Owen, Esq., F.R.S., 

 F.G.S., Hunterian Professor in the Royal College of Surgeons. 



The author commences by quoting the generalizations given in 

 the latest works which treat of Fossil Chelonians, and examines the 

 evidence on which those from the Eocene clay of Sheppey had been 

 referred exclusively to the freshwater genus Emys by Cuvier and 

 others, and he points out the circumstances which invalidate the 

 conclusions that had been deduced from it. He then proceeds to 

 describe the fossils and to show the characters by which he has 

 established the existence of five species of marine turtles from the 

 London Clay at Sheppey, and a sixth species from the same forma- 

 tion near Harwich. 



1. Chelone breviceps. — The first species, found at Sheppey, is called 

 by the author Chelone breviceps, and its unequivocal marine nature 

 was recognised by a nearly perfect cranium, wanting only the occipital 

 spine, and presenting a strong and uninterrupted roof, extended 

 from the parietal spine on each side over the temporal openings ; the 

 roof being formed chiefly by a great development of the posterior 

 frontals. Further evidence of its marine origin exists in the large 

 size and lateral aspect of the orbits, their posterior boundary extend- 

 ing beyond the anterior margin of the parietals ; also in the absence 

 of the deep emargination which separates the superior maxillary from 

 the tympanic bone in freshwater tortoises, especially the Emys 

 expansa. 



In general form the skull resembles that of the Chelone My das, but 

 it is relatively broader, the anterior frontals are less sloping, and the 

 anterior part of the head is more vertically truncate : the median 

 frontals also enter into the formation of the orbits in rather a larger 

 proportion than in C. Mydas. In Chelone imbricata they are wholly 

 excluded from the orbits. 



The trefoil shape of the occipital tubercle is well-marked ; the 

 laterally expanded spinous plate of the parietal bones is united by a 

 straight suture to the post-frontals along three-fourths of its extent, 

 and for the remaining fourth with the temporal or zygomatic ele- 

 ment. 



These proportions are reversed in the Emys expansa, in which the 

 similarly expanded plate of the parietals is chiefly united laterally 

 with the temporal bones. In other freshwater tortoises the parietal 

 plate in question does not exist. 



The same evidence of the affinity of the Sheppey Chelonite in 

 question to the marine turtles is afforded by the base of the skull : — 

 the basi-occipital is deeply excavated ; the processes of the pterygoids 

 which extend to the tympanic pedicles are hollowed out lengthwise ; 

 the palatal processes of the superior maxillary and palatine bones are 

 continued backwards to the extent which characterizes the existing 

 Chelonise ; and the posterior or internal opening of the nasal passages 

 is, in a proportional degree, carried further back in the mouth. The 

 lower opening of the zygomatic spaces is wider in the Sheppey Che- 

 lonite than in the Emys expansa. 



