ACICHELYID^E. 147 



R. 1445. Part of an anterior marginal bone ; from the London 

 Clay of Sheppey. The outer border and one suture are 

 entire. The inner surface is smooth, the whole bone is 

 much more massive than the anterior marginals of Ano- 

 stira, and also differs by the regularly elliptical form of 

 the surface for sutural union with the adjacent marginal. 



Purchased, 1847. 



38971. An imperfect right humerus, which may be referable to this 

 form ; from the Middle Eocene of Bracklesham, Sussex. 

 This specimen, which wants the head and the extremity 

 of the ulnar process, differs from the humerus of all ex- 

 isting Chelonians in the great development of the radial 

 condyle, which resembles that of Lizards. The ectepi- 

 Condylar foramen, of which the outer bar is broken away, 

 pierces the bone at a considerable distance above the 

 ectepicondyle and is thereby peculiar. The contour of 

 the proximal extremity of the bone is not unlike that of 

 Macroclemmys. If this specimen does not belong to the 

 present genus, it must indicate a new type. 



BowerbanJe Collection. Purchased, 1865. 



Family ACICHELYID M \ 



Shell cordiform, more or less incompletely ossified, the plastron 

 having a vacuity which persists for a long period, if not throughout 

 life; nuchal without costiform process. Plastron connected with 

 carapace by axillary and inguinal buttresses 2 . Nature of caudal 

 vertebrae unknown. Temporal fossae of skull partially roofed. 

 Humerus (fig. 1, A) with the head imperfectly developed, the shaft 

 but little curved, and the radial and ulnar processes small; the 

 former placed on the level of the head. All the phalangeals clawed. 



As already mentioned {supra p. 27), it is probable that this 

 family may be regarded as including the ancestors of the Chelonidce. 

 Prom their common occurrence in the marine deposits of the Kime- 

 ridge Clay, and their apparent rarity in the freshwater beds of the 

 Wealden, it is probable that the Acichelyidce were mainly of marine 

 habits. 



1 =Eurysternid<e, Dollo (1880) = Tkalassemydes, Kiitimeyer (1873). 



2 See Uiitirneyer, N. Denkschr. schw. Gres. Nat. vol. xxv. art. 2, p. 38. 



l2 



