50 CHELONIA. 



nearly obliterated in the adult 1 ; epiplastrals narrower than in 

 Chelone ; entoplastral shorter and T-shaped ; and the xiphiplastrals 

 still narrow, but uniting rather more fully. Coracoid shorter and 

 stouter, with a greater distal expansion than in Chelone. Humerus 

 with the head placed rather more obliquely to the shaft, the latter 

 more constricted, and the radial process nearer to the head than in 

 the type genus. 



The skull is larger in proportion to the shell than in Chelone. 

 The position of the posterior nares tends to become more backward 

 and the relative length of the mandibular symphysis to increase 

 with age. In old individuals the length of the postsymphysial 

 portion of the mandible is only slightly longer than that of the 

 symphysis itself. 



Thalassochelys eocsenica, Lydekker 2 . 



Known only by the humerus ; .attains dimensions equal to 

 T. caretta. 



Hob. Europe (England). 



R. 1557. Cast of the imperfect left humerus. The original was 

 obtained from the Middle Eocene of Bracklesham, Sussex ; 

 and is in the collection of J. B. Ogle, Esq. It is the type 

 of the species, and is described and figured by the writer 

 in the ' Proc. Geol. Assoc' vol. xi. p. 177, fig. 1. The 

 distal extremity is wanting, and the head has been 

 considerably eroded. The strongly marked coustriction 

 of the shaft affords the ground of the generic reference. 



Made in the Museum, 1889. 



Thalassochelys, sp. 



Very imperfectly known ; fully as large as T. caretta, from which 

 it is distinguished by the form of the mandibular symphysis. 

 Perhaps specifically identical with T. eocamica. 



Hah. Europe (England). 



38995. The left half of the mandibular symphysis ; from the 

 London Clay (Lower Eocene) of the Isle of Sheppey. 

 Noticed by the writer in the ' Proc. GeoL Assoc' vol. xi. 

 p. 177. The edge of the alveolar border is worn away. 

 This large specimen comes much nearer to the mandible 



1 The costals may completely unite with the marginals. 

 J Proc. Geo]. Assoc, vol. xi. p. 177 (1889). 



