No. I.] RELATIONSHIPS OF PROTOSTEGA. 45 
second digits have claws; in Evetmochelys the first and some- 
times the second; and in Dermochelys there are no claws. 
4. The plastron of Dermochelys is reduced, not primitive. In 
the cretaceous Pvotostega and Protosphargis the plastron is 
much more strongly developed than in Dermochelys. These 
forms also lack the entoplastron, which is present in the Che/o- 
nizdae. The remaining elements of the plastron are directly 
referable to that of the Che/onizdae, though the hyo- and hypo- 
plastron are not united by suture. 
5. In addition to the mosaic-like carapace of Dermochelys 
there is present a nuchal plate which is comparable to that of 
the Chelonitdae and to it alone. 
His conclusion was that the only difference between the 
Athecae and Thecophora is in the form of the carapace and its 
complete separation from the inner skeleton, that the ancestors 
of the A¢hecae had the carapace united with the inner skeleton, 
and that the peculiar carapace was formed by the breaking up 
into small pieces of the original carapace; giving as evidence of 
this process the case of a specimen of Evetmochelys, in which 
he observed that the costal plates from the third to the sixth 
had separate ossicles of bone on their edges. He also cited the 
reduction of the peripherals of Evetmochelys and their complete 
disappearance in Dermochelys, and the peculiar anterior rib in 
both forms. 
To this paper Dollo (9 and 10) replied in detail, maintaining 
the natural value of the group Athecae. 
I. He considered that if Dermochelys was descended from 
the Cheloniidae, in which there are always fontanelles in the 
carapace, that there should be some in the carapace of Dermo- 
chelys. He regarded a supposition that such fontanelles existed, 
but had been filled up by the dermal ossifications as improbable. 
He says (9), p. 165, “Or préfére-t-on supposer que les ancétres 
des Chélonées avaient une carapace sans fontanelles et que, de 
cette souche, se seraient dévélloppés par delamination, les 
Atheques, et, par formation de fontanelles, les Chélonées 
actuelles ?’”’; however, he considered this as improbable, as both 
the embryological evidence of living forms and the paleonto- 
logical evidence of the earliest known turtle (T7halassemys 
