DEKMATEMYD1D.E. 129 



R. 425. A somewhat smaller right femur ; from Bach. 



Purchased, ] 884. 



R. 423. A tibia ; from Bach. This specimen indicates a larger in- 

 dividual than either of the preceding specimens. 



Purchased, 1884. 



Family DERMATEMYDIDiE. 



This family, in which the nuchal bone has a long costiform pro- 

 cess, appears to connect the Chelydridce with the Cinostemidce, the 

 recent forms having the entoplastral bone and obturator notch of 

 the former, and the proccelous caudal vertebrae, open temporal 

 fossse, and convex nuchal of the latter. The plastron may be united 

 with the carapace either by suture, with the development of 

 large buttresses (Dermatemys), or by a straight ligamentous suture 

 (Claudius). 



The occurrence of proccelous caudal vertebras in one extinct 

 genus (Toxochelys), which has been referred to the Chelydridce, is 

 suggestive of a transition between that and the present family, and 

 auy palaeontologieal definition of the latter would therefore be pre- 

 mature. 



The undermentioned genus is provisionally referred to the Der- 

 matemydidce on account, of the resemblance of its long and narrow 

 vertebral shields to those of the Eocene Baptemys and the existing 

 Dermatemys, and also from the resemblance of its vermiculated shell 

 to that of the latter. The so-called Adocida of Cope J are probably 

 also referable to the Dermatemydidce, the abortion of the heads of 

 the ribs not being a character of family value. In the Cretaceous 

 Adocus there are traces of vermi dilation, which are more distinct in 

 the Eocene Agomphus (with which Amphiemys is stated by Baur 2 

 to be identical) ; and it has yet to be proved that the latter is really 

 distinct from the undermentioned genus. 'While Agomphus was 

 placed by Cope (I. c.) in the Emydidce next Dermatemys, Amphiemys 

 was referred to the Adocidoi. 



Genus TRACHYASPIS, Meyer 3 . 



Shell with vermiculated sculpture. Neural bones 8 in number, 

 hexagonal, and mostly elongated, with short anterolateral surfaces. 

 Vertebral shields long and narrow. Plastron unknown. 



1 Yertebrata of Tertiary Formations of the West — Eep. U.S. Geol. Surv. 

 Terrs, vol. iii. p. 113 (1884). 



2 Zool. Anz. toI. ii. p. 525 (1888). 



3 Neues Jahrb. 1843, p. 699. 



PARI III. K 



