196 CHELONIA. 



1st and 2nd marginals, and portions of the 1st and 2nd 

 costals. The figure is totally incorrect in regard to the 

 boundaries of the bones and horny shields. The area 

 occupied by the first vertebral shield is very similar in 

 contour to that obtaining in PlesiocJielys, its lateral boun- 

 dary joining the sulcus between the 1st and 2nd marginal 

 shields. (In Idiochelys this boundary joins the sulcus 

 between the 2nd and 3rd marginal shields.) The nuchal 

 shield consists of a median and two lateral portions, as in 

 the carapace of PlesiocJielys figured by Riitimeyer, op. tit, 

 pi. vi. The crenulated anterior boundary of the 2nd ver- 

 tebral shield is seen on the inner side of the specimen. 

 The fragments of the plastron show no distinctive features. 



42888 a. Part of the same slab, showing the right scapulo-precora- 



(Fig.) coid and humerus. Figured by Meyer, op. cit. figs. 2-4. 



The humerus closely resembles that of Chelys, and differs 



entirely from the specimens referred to the Acichelyidce 



(p. 157). 



42888 b. The associated right coracoid. Figured by Meyer, op. cit. 

 (Fig.) fig. 5. 



42888 C. Part of the same slab, showing the dorsal aspect of the 

 (Fig.) right manus. Figured by Meyer, op. cit. fig. 6. The 

 metacarpals and phalangeals are beautifully shown. In 

 the reduction of the number of phalangeals of the second 

 digit this specimen indicates a step towards the existing 

 Pelomedusa, in which alone among aquatic forms the 

 number of phalangeals in all the digits of the manus is 2 ; 

 the number in the pes being 2, 2, 3, 3, 3, or the same as 

 in the present specimen. 



42888 d. Part of the same slab, showing the distal extremity of 

 the left humerus, part of the manus of the same side, the 

 centra of four cervical vertebras, and fragments of the 

 shell. Two of the vertebras clearly show the bases of 

 transverse processes, while in the others, which were pro- 

 bably later in the series, these appear to be wanting. 



Genus PLESIOCHELYS, Eiitimeyer \ 



Syn. Stylemys, Maack 2 (in parte) . 



Shell with the nucha] more or less emarginate ; neurals generally 



1 N. Denkschr. schw. Ges. Nat. vol. xxv. art. 2, p. 28 (1873). 



2 Palocontograpkica, vol. xviii. p. 320 (1869). Preoccupied by Leidy, 1851, 

 vide supra, p. 93. 





