16 BRITISH FOSSIL REPTILES. 



has been established, remams of the Chelone hreviccps are preserved in the Hunteriau 

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



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



Chelone longiceps. Owen. PI. 12 and 13. 



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

 British Fosiil ReptUia, 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 (PI. 1 2) differs more from those of existing 

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

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



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

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

 strongly as in that species. 



The orbits (PI. 12, figs. 1 and 2, o,) are large ; the temporal fossae (ib. fig. 3) 

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

 completed by the parietals (7), and mastoids (s), 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 {Trioni/x), by an anterior palatal foramen. 



The extent of the bony palate is relatively greater than in the Chelone mt/clas, 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 lonjjiceps 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 followinsr are dimensions of the skull described: 



Length of the skull ....... 



Breadth of ditto across the zygomata .... 



Antero-posterior diameter of orbit ..... 



* The smaller figures are placed on the parts in Pis. 11 and 17^, by comparison with which the tor- 

 responding bones of the present skull will be readily discerned. 



