16 FOSSIL REPTILIA OF THE LONDON CLAY. 



has been established, remains of the Chelone breviceps are preserved in the Hunterian 

 Museum, and in that of my esteemed friend and coadjutor, Professor Bell, S.R.S. 

 I know no other locality of the species than that of Sheppey, in Kent. 



Chelone longiceps. Owen. Tab. Ill, IV, and V. 



Proceedings of Geological Society of London, December 1, 1841, p. 572. Report on 

 British Fossil Reptilia, Trans. British Association, 1841, p. 177. 



The second species of Chelone, from the Eocene clay at Sheppey, which I originally 

 recognised and defined by the fossil skull, Tab. Ill, differs more from those of existing 

 Chelones by the regular tapering of that part into a prolonged pointed muzzle, than 

 does the Chelone breviceps by its short and anteriorly-truncated cranium. 



The surface of the cranial bones is smoother than in the Chel. breviceps ; whilst 

 their proportions and relations prove the marine character of the present fossil as 

 strongly as in that species. 



The orbits (Tab. Ill, figs. 1 and 2, o,) are large ; the temporal fossae (ib. fig. 3, t,) 

 are covered principally by the posterior frontals (fig. 2, 12); and the osseous shield 

 completed by the parietals (7), and mastoids (8), overhangs the tympanic (28), ex- 

 occipital (2), and paroccipital (4) bones. The compressed spine (3) of the occiput is 

 the only part that projects further backwards. 



The palatal and nasal regions of the skull afford further evidence of the affinities of 

 the present Sheppey Chelonite to the true turtles. The bony palate (fig. 3) presents, 

 in an exaggerated degree, the great extent from the intermaxillary bones to the 

 posterior nasal aperture which characterises the genus Chelone ,- and it is not perforated, 

 as in the soft turtles {Trionyx), by an anterior palatal foramen. 



The extent of the bony palate is relatively greater than in the Chelone mydas, and 

 the trenchant alveolar ridge is less deep ; the groove for the reception of that of the 

 lower jaw is shallower than in the Chelone mydas, or the extinct Chel. breviceps, arising 

 from the absence of the internal alveolar ridge, in which respect the Chel. longiceps 

 resembles the Chel. caretta. 



The Chelone longiceps is distinguished from all known existing Chelones by the 

 proximity of the palatal vomer (13, fig. 3), to the basisphenoid (5), and by the depth of 

 the groove of the pterygoid bones (24), and in both these characters in a still greater 

 degree from the Trionyxes ; to which, however, it approaches in the elongated and 

 pointed form of the muzzle, and the trenchant character of the alveolar margin of 

 the jaws. 



The following are dimensions of the skull described : 



Length of the skull 



Breadth of ditto across the zygomata 



Anterc-posterior diameter of orbit . 



Inches. 



Lines. 



4 







2 



6 



1 



9 



