22 CHELONIA. 



desert. This specimen belonged to a large and very old 

 individual; the costal bone having far outgrown the 

 extremity of the rib. 



Presented by Sir R. Owen, K.C.B. 



Genus AULACOCHELYS, Lydekker \ 



Distinguished by the deep groove traversing the thickened distal 

 extremity of the costals and the outer border of the hypoplastral. 



Aulacochelys circumsulcata (Owen 2 ). 

 Syn. Trionyx cireumsulcatus, Owen 3 . 



The type and only described species. 

 Hab. Europe (England). 



30404. A costal bone ; from the Upper Eocene (Lower Oligocene) 

 {Fig.) of Hordwell, Hampshire. The type specimen ; described 



and figured by Owen in his ' Reptilia of the London Clay, 



&c.' pt. i. p. 59, pi. xix. b. figs. 1-3. 



Hastings Collection. Purchased, 1855. 



33198 a. The postero-external extremity of a right hypoplastral 



probably belonging to this or an allied form ; (?) from 



Hordwell. There is a deep groove in this specimen on 



the outer border, corresponding with the one in the costal. 



Dixon Collection. Purchased, 1851. 



Subfamily Emydin^. 



Hyoplastral welded with hypoplastral : outer extremity of nuchal 

 underlying first costal ; pterygoid sending an upward process to join 

 the opisthotic, and thus dividing the posterior aperture of the 

 labyrinth into two foramina ; marginals present or absent ; sculpture 

 tuberculate ; neurals sometimes absent. 



Genus EMYDA, Gray \ 



A prenuchal marginal bone ; neurals usually 7 ; 7th and 6th 

 costals uniting in the middle line, the latter pair being very large ; 

 a series of posterior marginals ; plastron with seven callosities. 



1 Ann. Mag. Nat. Hist. ser. 6, vol. iii. p. 53 (1889). On p. 273 of the same 

 volume Baur states that the character on which this genus is founded is merely 

 individual. 



2 Eeptilia of the London Clay, &c. (Mon. Pal. Soc), vol. i. pt. i. p. 59 

 (1849).— Trionyx. 3 Loc. tit. 



4 Synopsis Eeptilium, p. 49 (1831) ; also Catalogue of Tortoises in British 

 Museum., p. 46 (1844). 



