
636 The American Naturalist. [July, 
hypo-, and xiphiplastron of the right side. The sculpturing o 
the shell is the same as in Carettochelys. There is no trace of 
dermal scutes. The number of the peripheralia is the same as in 
Carettochelys. There is only one postneural, of the same shape as 
in this form. There is a difference in the neuralia, however. There 
are séven slender neuralia in Pseudotrionyx, which are all connected 
with each other, separating the first six pleuralia completely; the 
seventh pleuralia meet behind, and sthe eighth are entirely con- 
nected. In all the pleuralia the rib heads are well developed. If 
we now compare the plastron of Carettochelys with the portions 
preserved in Pseudotrionyx, we are struck at once by the enor- 
mous resemblance. The hyoplastra of both are nearly identical 
in shape. I may call especial attention to the border connecting 
the hyoplastron with the endo- and epiplastron. But to conclude 
from Dollo’s figure, it seems to me that the hyoplastron was not 
entirely united to these elements, but only connected with them 
by ligament, as in the Cinosternidez. The most interesting point, 
however, is that Pseudotrionyx doubtless also had a distinct meso- 
plastral element as Carettochelys. Dollo held the opinion that 
there was a small fontanelle at the outer border of the hyo- and 
hypoplastra (Echancrure naturelle, reste d'une fontanelle latérale, 
N. Fig, I., Pl. 1.) Besides, he thinks that the line of the con- 
nection between carapace and plastron was very short. There can- 
not be any doubt, however, that Pseudotrionyx showed about 
' the same conditions as Carettochelys. 
Pseudotrionyx is placed by Dollo, Zittel, and Lydekker amie 
the Chelydride. A skull originally referred by Sir R. Owen to 
Platemys is considered by Lydekker (8) as belonging to Pseudo- 
trionyx. ‘It is stated that it agrees essentially with that of 
Macrochelys ; and that this reference is confirmed by the total 
absence of the impression of horny shields, indicating that the 
skull, as in the Trionychide, was merely covered with skin. I 
think it is at least doubtful whether this skull belongs to 
Pseudotrionyx. 
We have now to consider the relations of Carettochelys. Its 
nearest relative is, as I have shown, Pseudotrionyx. There is no 
idenceev from the present material that Tranio belongs to 


