PHYLOGENY OF SHELL OF TESTUDINATA 439 



there were, however, in all probability not more than eleven 

 peripheral bones on each side. 



Fraas (op. cit., p. 409, fig. 1; reproduced by Jaekel) has indi- 

 cated the presence of twenty or more marginal scutes in Pro- 

 ganochelys; but if there were really present lines which marked 

 out the boundaries between these areas, some of them were 

 probably bone sutures; others sulci between the marginal scutes. 



The results sought after in this paper may be summed up as 

 follows : 



1. The neck of the leatherback has not been inherited from 

 the cryptodires, but has been independently developed. 



2. The evidences relied on to connect the leatherback with 

 the chelonioid sea-turtles, living or extinct, are by no means 

 compelling. 



3. Vestigial bones have been discovered in the Thecophora 

 which correspond to those of the following keels in Dermochelys: 

 the upper median (Toxochelys, Archelon, Chelys); the costal 

 (Chelys); the supramarginal (Archelon), the marginal (Chelys), 

 and the first lateral of the plastron (Chelys) . The supramarginal 

 keels are represented in many species by scute areas also. The 

 inframarginal keels are known to us only from scute areas on 

 the bridges. The lower median keel may be retained in the 

 unpaired intergular of the Pleurodira, the intercaudal (Abel 

 op. cit. p. 410, fig. 319) and occasional unpaired scutes in other 

 turtles. 



4. By the presence of vestigial bones on the peripherals at 

 the points whence the marginal scutes expand it is shown that 

 these peripherals are not to be homologized with the marginal 

 bones of Dermochelys, but that they belong to the thecal armor. 



5. The occurrence of the various elements representing the 

 epithecal armor in species scattered about in nearly all the large 

 groups of turtles, and most of them provided with good solid 

 shells, appears to show that these elements are vestiges of an 

 armor of a common ancestor and not the beginnings of a new 

 epithecal one. 



6. The retention of the epithecal covering by Dermochelys, 

 the loss of most of the thecal shell, and the possession of many 



