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CRETACEOUS FORMATIONS. 9 



deep scutal impression, above which the superior maxillary forms a convex promi- 

 nence at the anterior part of the orbit. The groove, which traverses the frontals, 

 is as strongly marked ; that which impresses the post-frontals is fainter. The 

 expanded trumpet-shaped portion of the tympanic bone comes nearer the upper 

 margin of the cavity than in existing Chelones. 



The palatal bones (20), have no palatal process anterior to the inner nostril, as 

 in the Chelone cuneiceps* and modern Turtles ; but are situated behind that aperture, 

 as in Bmys and Trionyx, and the vomer does not penetrate between them. The 

 palatal processes of the intermaxillary and maxillary bones form an unusually pro- 

 minent angular ridge, running nearly parallel with the trenchant margin of the jaw ; 

 the bony palate is not extended along the middle line beyond the intermaxillaries, 

 which here enter into the formation of both the inner and outer nostrils. The 

 pterygoid bones present moderately wide and deep external emarginations. 



The following are the chief dimensions of this fossil skull : 



Length of the cranium from the occipital tubercle 

 Breadth of the cranium above the tympanic cavities 

 Depth of the cranium at the parietal bones 

 Antero-posterior diameter of the orbit 

 Breadth of the interorbital space . . , 



The supracranial scutation of the Chelone pulchriceps much resembles that of the 

 Chelone Couanna. A large oval syncipital scute defending the middle region of the 

 epicranium, and being surrounded by the smaller " frontal," " superorbital," " pa- 

 rietal," and " occipital " scutes : the bones supporting the latter have, however, been 

 too much mutilated to allow of their proportions and forms being determined. The 

 fronto-nasal scutes are each bounded behind by well- defined bold curved lines, convex 

 towards the frontal scute, and deeply indenting the frontal bones. Amongst the 

 existing Chelonia, the character of the distinct nasal bones has been, hitherto, met 

 with only in an Emydian species, on which the sub-genus Hydromedusa has been 

 founded. The modifications of the bony palate in the Chelone pulchriceps afford 

 another indication of its Emydian aflSnities. 



Chelone Camperi, Oioen. (?) Tab. V. 



Large Turtle, Camper. Philosophical Transactions, vol. Ixxvi, 1786. 



I am induced provisionally to refer to the above species the two large bony plates 



or scutes figured in T. V, on account of their size, their shape, and especially their 



carinate structure. They have a smooth exterior surface, marked only by faint lines 



radiating from the median " carina" or ridge. They are thickest at this part, which 



* Monograph on the Chelonia of the London Clay, t. xv, fig. 3, 20. 



2 



