1*0 • FOSSIL CHELONIAN REPTILES OF THE 



these fossils is represented, of half the natural size, in Tab. I. This specimen is now 

 preserved in the Museum of the Philosophical and Natural History Society of 

 Dorchester. 



Chelone costata. Owen. Tab. VIII. 



From the Wealden Clays of Tilgate Forest have been obtained many fragmentary 

 Chelonites, indicative of species representing two of the actual families of the order, 

 viz. Paludinosa and Marina ; and such, therefore, as might be expected to be met with 

 in the deposits of a large estuary. I propose to commence the description of these 

 Wealden Chelonites by those which indicate a species of the marine family. 



Portions of the carapace and plastron, and bones of the extremities of a large 

 species of Turtle, some of them indicating individuals with a carapace nearly three feet 

 in length, form part of the Mantellian collection, purchased by the British Museum : 

 a few of these Chelonites have been figured in Dr. Mantell's ' Illustrations of the 

 Geology of Sussex,' 4to, 1822. 



The author of that work has not deduced any specific characters from these fossils, 

 and the nature of most of the specimens hardly allowed their determination to be car- 

 ried closer than to the marine family of Chelonia. 



With regard to one of the specimens (PI. VI, fig. 2), however, Mr. Clift's authority 

 is quoted for its resemblance with the corresponding part of the Chelone imbricata, and 

 Dr. Mantell acknowledges that " as Cuvier had referred the turtles of Melsbrock to the 

 Emydes, we at first entertained doubts whether our approximation of this specimen to 

 the Clielonice were correct. Mr. Clift's remark, however, tends to confirm the opinion 

 that it belongs to a marine turtle." (Op. cit., p. 62.) 



After a careful comparison of the specimens in the British Museum, I have come 

 to the conclusion that the Wealden species differs from the Chelone imbricata, Chelone 

 carinata, and other recent species, in as great a degree as do most of the extinct 

 Chelones, in the greater extent of ossification of the costal interspaces and of the 

 plastron. 



A characteristic portion of the great Wealden Turtle is represented, of the natural 

 size, in Tab. VIII of the present Monograph. It includes the second and third 

 marginal plates, and considerable portions of the first and second costal plates, with 

 the connate portions of the pleurapophyses, or vertebral ribs. These are remarkable 

 for their breadth and prominence, and have suggested the name proposed for the 

 present species of Wealden Chelone. 



In the same plate are represented a mutilated right iliac bone, fig. 3, and the right 

 femur of, probably, the same species of Turtle. These, also, are from the Wealden 

 formations of Tilgate Forest, and form part of the Mantellian Collection now in the 

 British Museum. 



