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e daii 
1891.] On the Relations of Carettochelys, Ramsay. 637 
a different family from Carettochelys. I do not hesitate, therefore, 
to place both genera in one family, Carettochelyidæ Boulenger, 
1887, which name has the priority before Pseudotrionychidæ 
Boulenger, a family established in the Encyclopedia Britannica, 
(Vol. XXIII), p. 457, to contain Pseudotrionyx Dollo and 
Anostira Leidy. 
This family may be characterized in the following way : 
CARETTOCHELYIDÆ. 
Shell without epidermal shields. Plastron composed of eleven 
elements, two small mesoplastra being present, which are sepa- 
rated from each other. Only ten peripherals on each side, be- 
sides the single nuchal and pygal. (Carettochelys, Pseudotrionyx.) 
Upper surface of skull covered with small, round, raised 
rugosities exactly as the shell, with three posterior processes, as in 
Trionychia; skull resembling in shape that of the Cinosternidæ, 
but snout more projecting. Limbs paddle-shaped ; digits much 
elongate, only the two inner clawed. (Carettochelys.) 
How far Pseudotrionyx agrees with Carettochelys in the latter 
characters, new finds have yet to determine. 
The question now is, To which group of tortoises does this 
family belong? In a former paper I distinguished four - 
groups of tortoises: the Amphichelydia, Cryptodira, Pleurodira, 
and Trionychia. Of one thing we are sure: it does not belong to 
the Pleurodira. Unfortunately we do not know the structure of 
the cervicals, which is so characteristic of the three remaining 
groups. From all that is at present known, it appears to me that 
the Carettochelyidæ are nearest to the Trionychia, but show at 
the same time characters of a group of Cryptodira, composed of 
the families Staurotypidæ and Cinosternide. I expressed 
a few years ago the opinion that the Trionychia did come from 
forms which had the peripherals complete, and carapace and 
plastron closed; that the Trionychia are not*an original, but a 
highly specialized group. Carettochelys shows i in the structure of | 
the skull, especially of the pos n, Tri 
I nee that the anceste 

