6i6 



NA TURE 



\_April 28, 1887 



Two other caudal vertebra;, liaving the same structural fea- 

 tures, occur among the detached remains, and belong, like the 

 first, to the second fourth of the tail. Another tolerably com- 

 plete vertebra, with a considerably longer centrum, corresponds 

 very closely with a caudal vertebra of Gypochelys from the third 

 fourth of the tail. In this, as in one of the foregoing vertebrae, 

 the chevron bones are anchylosed with the centrum. I conceive, 

 then, that there can be no doubt that the pelvic bones and these 

 caudal vertebr.-e belonged to a Chelydroid Chelonian, of about 

 the size of the largest " snapping turtles " which are met with in 

 North .\merica at the present day. 



Prima facie, the skull found in the same block might also be 

 expected to be that of a Chelydroid ; and, in fact, it is so. I 

 <lo not base this interpretation on the Chelonian character of the 



upper jaw, as there are various extinct Saurian reptiles which 

 closely approximate to Chelonia in this part of their structure. 

 The diagnostic characters lie in the back part of the skull ; and 

 especially in the auditory region, which is altogether Chelonian. 

 Not only so, but when this fragmentary skull is compared with 

 that of Chelydra, the correspondence between the two is singu- 

 larly exact (Figs. 3 and 4). In two respects, however, the fossil 

 differs from Chelydra and Gypoclielys. 



(i) The roof over the temporal fossa formed by the parietal, 

 post-frontal, and other bones, which leaves the auditory region 

 uncovered in the recent genera,' extends back, beyond the 

 occiput, in the fossil, and sends down a broad vertical rim from 

 its margin. 



(2) The upper surface of the cranial shield is, at most, rugo e 



JV 



-■P5 



Fig. I.— Caudal vertebra of Ceratockelys, N, 

 platform on the neural arch ; /c, pre zygapo- 

 physis mutilated ; tr. broken transverse pro- 

 cess ; Chv\ processes for the chevron bone ; Chvy 



y^j 



f Chelydra. Letters 



Figs. 3, i.—SknWs oS Ceratoc/ielys {F\%. 3) andC/w/yi^m (Fig. 4); the latter of the naturals 

 the former much reduced. The portion of the skull of Chelydra which corresponds « 

 the fossil is shaded. 



in the recent C/ielyd rider ; in the fossil, three strong conical pro- 

 cesses, like horn-cores, of which the middle is the longest, are 

 developed from its posterior and lateral region.' 



This skull is described and figured in the Philosophical Trans- 

 actions for 1886 (Plate 30, Fig. I) by Sir R. Owen, under the 

 generic or sub-generic name o( Meiolania, and is said to belong 

 to a Saurian reptile closely allied to the " Megalania prisca" 

 described in earlier communications. But the skull is assuredly 

 that of the Chelydroid Chelonian to which the pelvis and caudal 

 vertebra belong. What Megalania prisca may be I do not pre- 

 tend to say ; but the remains which I have described can have 

 nothing to do with any Saurian reptiles ; and I propose to confer 



' It is possible thiit these may be dermal bones coherent-uith the proper 



on the genus of Chelonia to which ^they belong the name of 

 Ceratockelys. 



The singular osseous caudal sheaths described by Sir R. 

 Owen, in the same memoir, also appertain to Ceralochelys. They 

 formed part of the series of remains sent to the British Museum 

 along with the foregoing, in which none but Chelonian bones 

 have yet been discovered ; and the remains of vertebrae left in 

 these sheaths are similar to the caudal vertebra; of the terminal 

 fourth of the tail in the Chclydrida. The snapping turtles are 

 noted for the length and strength of the tail and for the strong, 

 laterally-compressed, acuminated " scales " which form a crest 

 along the median dorsal line, while others, less strongly keeled, 

 lie at the sides of the tail. In m.any Chelonia, the extremity of 



' The "roof" extends much further back in riatystor.um. 



