6 • PROCEEDINGS OF THE NATIOISTAL, MUSEUM vol. 73 



nection mentioned above is a primitive one. In the great majority 

 of tortoises this connection was lost, in order to facilitate the with- 

 drawal of the head and neck into the shell or alongside of it. In 

 the seafaring turtles the articulation may have been retained as 

 a point of suspension for the head and neck. 



5. SUBORDERS OF THE TESTUDINATA. 



Tortoises must have existed already at some time during the 

 Permian, for in the Triassic they appear with all their essential 

 characters. In the Permian all the species may have belonged to 

 one famil}', but differentiations had begun. There were yet probably 

 none which could withdraw the head within the shell or hide it 

 under the edge of the carapace. No definite cervical vertebrae yet 

 existed, but in place of each a congeries of cartilaginous or bony 

 basalia. Nevertheless there were tendencies which later revealed 

 themselves in the normally bent neck of the Cryptodira and that 

 peculiar to the Pleurodira. 



Every chelonian is related to every other one of the order, but to 

 some more closely than to others. I grant that Dermochelys is con- 

 nected with the Cheloniidae more closely than with any other family 

 of the order. In the undifferentiated condition of Permian days the 

 ancestors of the Athecae and of the Cheloniidae may have been inti- 

 mately related, but when the primal athecate broke away from the 

 association, chose a life on the high seas, began to throw off the armor 

 preferred by the others of his tribe and clothed himself with another, 

 he won the right for his descendants to be regarded as a separate 

 branch of the testudinate host. 



Doctor Volker recognized the considerable differences existing be- 

 tween the Athecae and the other sea turtles, but he insisted that to 

 regard the two as belonging to distinct suborders gave a very false 

 conception of their kinship. He concluded (his page 512) that the 

 relationship was best expressed by making Dermochelys and the other 

 sea turtles a superfamily of the Cryptodira. If, however, this 

 is done the other Cryptodira must constitute another superfamily 

 and these two will, form the suborder of Cryptodira. Then the 

 Pleurodira and Trionychoidea must in their turn be given the rank 

 of suborders. The writer believes that the Emydidae, Trionychidae, 

 and the Chelyidae do not differ sufficiently from one another to be 

 representations of as many suborders. Furthermore, Doctor Volker's 

 scheme by no means brings out the great differences which have been 

 demonstrated and which he concedes as existing between Dennochelys 

 and the Cheloniidae. The writer maintains that the relationships 

 between the groups of the Testudinata are best expressed by setting 

 off the Athecae as a suborder opposed to the Thecophora. 



