178 REPORT — 1841. 



than they are long ; the xiphisternals are unusually broad. The tooth-like 

 processes from the mesial margins of the hyo- and hyposternals are more 

 numerous and smaller than in existing species, and interlock with each other, 

 so that two margins of each of these bones are joined by suture, instead of 

 one, as in almost all other turtles. Yet in the largest specimens of this species 

 which I have seen, the centre of the sternum remains unossified, its sides un- 

 united by bone with the. carapace, and the external and part of the internal 

 margins of its constituent bones preserve their separated tooth-like rays. 



The small specimen of which the plastron is figured by Parkinson and by 

 Cuvier, belongs to the present species of Chelone ; it is now preserved in the 

 rich collection of Prof. Bell. In the same collection there is preserved a 

 specimen of Chelone longiceps, the plastron of which is 8 inches in length 

 and nearly 8 inches in breadth ; in this specimen, which is the largest of the 

 present species that I have seen, the central vacuity of the plastron and the 

 toothed margins of many of the constituent bones remain. Three of the Che- 

 lonites in the museum of Sir P. Egerton, two in that of Mr. Bowerbank, one 

 in that of Mr. Dixon, and one in the Hunterian Collection, belong to the 

 Chelone longiceps. All these specimens are from the Isle of Sheppey. 



Chelone planimenttim, nob. — The species which, in the number of indi- 

 viduals representing it comes next in order after the Chelone longiceps, is 

 characterized by a flat and unusually long symphysis of the lower jaw, but 

 this is associated with a broad, high, and convex cranium, and with a muzzle 

 not longer than in ordinary Chelones. The carapace is characterized by the 

 strength of the ribs which traverse the whole of the under part of the ex- 

 panded plates in the form of thick convex ridges. 



All the specimens of this species that I have hitherto seen are from the 

 Eocene clay of the eastern coast of Essex. A carapace in the British Mu- 

 seum measures 13 inches in length and 12 inches across the fourth pair of 

 expanded ribs. A skull in the museum of Prof. Sedgwick, associated with a 

 carapace and other parts of the skeleton of the same individual, and another 

 skull in that of Prof. Bell, indicate that the head was relatiA'ely as large in 

 the Chelone planimentum as in the Chelone imhricata. 



Chelone breviceps, nob. — This species, in the narrow, ovate, and posteriorly 

 pointed carapace, and in the less extensive ossification of the sternum, re- 

 sembles more the recent Chelones than does the Chelone longiceps. Its cra- 

 nium also preserves the ordinary form in its depth and in the shortness of its 

 muzzle. The external surface of the cranium and osseous buckler is rugous. 

 The angles by which the expanded ribs are wedged into the interspaces of the 

 vertebral plates have equal or nearly equal sides. It appears to have exceeded 

 the Chelone longiceps in size : a portion of the osseous buckler of a Chelone 

 breviceps, with a carapace 16 inches in length, is preserved in the museum of 

 Mr. Robertson, surgeon, at Chatham. 



Smaller specimens of the Chelone breviceps, all from the Isle of Sheppey 

 are preserved in the Hunterian Collection, in the museum of Prof. Bell, and 

 in that of Mr. Bowerbank. Mr. Bowerbank's specimen exhibits the head in 

 connection with the carapace and plastron, and is the most beautiful Chelo- 

 nite, perhaps, that has yet been obtained from any formation. 



Chelone convexa, nob The surface of the bony buckler of this species, 



like that of the Chelone longiceps, is smooth, but the forms of the constituent 

 bones of the carapace and their degree of ossification differ considerably from 

 those of a Chelone longiceps of the same size, and resemble those of Chelone 

 mydas. The carapace is more convex than in the preceding species from 

 Sheppey, and than in the existing Chelones, whence the specific name of the 

 present extinct species. It is from the Isle of Sheppey. 



i 



