CHELONIDJB. 61 



important as showing the variation which occurs in the contour of 

 the mandible of different individuals. 



This species attains large dimensions, but the skull is considerably 

 larger in proportion to the shell and limb -bones than in existing 

 Cheloniclce. The undermentioned specimens exhibit the alteration 

 in the characters of the skull with age ; and also prove the cor- 

 rectness of Owen's association of the skull with the shell. 



Eab. Europe (England and Belgium). 



37205. The nearly entire adult skull ; from the London Clay (Lower 

 {Fig.) Eocene) of Harwich, Essex. Noticed by Owen in the 

 Rep. Brit. Assoc, for 1841, p. 178, as Ghehne planimen- 

 tum ; and described and -figured by him in his ' Eeptilia of 

 the London Clay, &c.' vol. i. pt. i. pi. xi., as G. crassicostata, 

 at which date the palatal and occipital regions were con- 

 cealed by matrix. Noticed by Seeley in the ' Ann. Mag. 

 Nat. Hist.' ser. 4, vol. viii. p. 232, where it is considered 

 to be inseparable from the next species. Described aud 

 figured by the present writer in the ' Proc. Zool. Soc' 

 1889, p. 60, pis. vi. & vii. The bones of the frontal aspect 

 are mostly wanting, and there is no justification for the 

 separation of the nasals from the prefrontals, as represented 

 in Owen's figure. The bones of the occipital region and 

 the posterior portion of the palate are entire. The depth 

 of the masseteric fossa of the mandible, noticed in Cope's 

 description of the type species, is very clearly shown. 



Bell Collection. Purchased, 1863. 



37205 a. Part of the shaft of the right humerus, associated with 

 (Fig.) the preceding. Figured by Owen (op. cit. pi. xi. fig. 1) in 

 connection with the skull, to which it was originally 

 attached ; and also by the present writer, oj>. cit. pi. vii. 

 fig. 2. In the extreme constriction of the middle of the 

 shaft and its sharp postaxial border this specimen agrees 

 with the humerus of the Belgian example figured by 

 Dollo in the ' Geol. Mag.' dec. iii. vol. v. p. 266, fig. 2, 

 and reproduced in fig. 6. It is of small size in com- 

 parison with the skull. Same history. 



R. 918. Nodule containing the imperfect skull and shell of a half- 

 grown individual ; from Harwich. The skull is inter- 

 mediate in point of size between the preceding and following 

 specimens, and shows the frontal aspect nearly entire ; it 

 agrees precisely in characters with No. 37205. The 



