DERMATEMYDID^. 



225 



Geological Distribution of the Genera of 

 Dermatemydida. 



crowded the humerals against the intergulars into the place of the supprest gulars. Then 

 the pectorals and the abdominals have coalesct. 



In Anosteira apparently the plastral scutes were so delicate that they left no impressions 

 of the sulci on the bones. 



Usually there are no striking modifications of the scutes of the carapace; but attention 

 may be called to those of Xenochelys, and more especially to those of Anosteira. 



As regards the geological continuance of the family, we find the earliest form, Basilemys, 

 in the Judith River beds and three genera exist to-day. All together sixteen genera are here 

 recognized, and these have the geological distribution presented in the accompanying table. 



Pseudotrionyx has been described from the 

 Bruxellian of Belgium by Dr. Louis Dollo. 

 There can be no doubt that it is related to Anos- 

 teira of America. The Bruxellian beds are equiv- 

 alents of our Wind River deposits. Anosteira 

 anglica has been described from the Lower Oli- 

 gocene of Hordwell, England. The character of 

 the sculpture and the straightness of the hypo- 

 xiphiplastral suture suggest a closer relationship 

 with Pseudotrionyx than with Anosteira. Like 

 Anosteira, Pseudotrionyx probably had only 10 

 pairs of peripherals. 



We know nothing about the history of the 

 Dermatemydidae prior to the Upper Cretaceous. 

 Tretosternon Owen, of the Wealden, suggests 

 strongly the genus Adocus; but the skull is said 

 by Dollo (Peltochelys duchastelii, Bull. Mus. roy. 

 d'hist. nat., Belgique, in, 1884, p. 79) to have 



the temporal region protected by a bony roof. It is easy to conjecture that some form similar 

 to Tretosternon was the Jurassic ancestor of the Dermatemydidae, which during the Upper 

 Cretaceous times evolved into so many genera and species. 



As already stated, Pseudotrionyx of the Middle Eocene is evidently related to the Derma- 

 temydidae. It is believed to be related also to Carettochelys insculpta, a species living in the 

 Fly River, New Guinea. Happily, our knowledge of this species has been increast by the 

 description of a better specimen than either of those previously known. This description is 

 given by Mr. Edgar R. Waite in the Records of the Australian Museum, vi, 1905, pp. 1 10-1 18, 

 and is illustrated by four plates and three text-figures. Baur regarded this turtle as belonging 

 among the Trionychidae, but as being closely akin to Pseudotrionyx and exhibiting connections 

 with the Dermatemydidae. Waite shows that the turtle is a true Cryptodiran nearest to the 

 Dermatemydidae, but also as connecting the Cryptodira with the Trionychidae. The animal 

 is certainly a Cryptodire, but not a dermatemyd. It belongs to a family near the Derma- 

 temydidae. Probably Pseudotrionyx belonged to the same family; and a comparison of the 

 figures of the shell with those of Dollo's Peltochelys duchastellii (Bull. Mus. roy. Hist. Nat., 

 Belgique, in, 1884, p. 78, plate II) shows many striking resemblances. Waite states that 

 the quadrate is not completely closed behind, but that there is a posterior notch, wide but not 

 deeply cleft. On the other hand his figure (op. cit., plate xxvi, fig. 3) appears to show dis- 

 tinctly that the stapes entered the tympanic cavity by a hole in the quadrate, just as it does 

 in Trionyx. If this conclusion is correct, this differentiates the family from the Derma- 

 temydidae; as does also the wide separation of the pterygoids by the palatines and the basi- 



sphenoid. , 



It seems not unreasonable to suppose that from the Dermatemydidae there sprang the 

 Emydidae and the Chelydridae. From the least differentiated Dermatemydidae, as Adocus, 

 the Emydidae differ especially in the lack of intergulars and inframargmals; but both these 

 series of scutes might cease to be developt. In one of the earliest of the Dermatemydidae 

 there are no inframarginals, except at the axillary and inguinal notches. Were it not for the 

 intergulars and the extraordinary sculpture of Basilemys we might regard it as an Emyd. 



