PHYLOGENY OF SHELL OF TESTUDINATA 425 



Versluys (p. 326) holds the view that, since the Cryptodira 

 possess the thecophore shell inherited from the Amphichelydia, 

 the primitive ancestor of Dermochelys must also have possessed 

 such a shell, and by this there appears to be meant a practically 

 complete shell such as that of the Cheloniidae. The present 

 writer holds, however, that Dermochelys was not derived from 

 the Amphichelydia and has therefore nothing to do with the 

 cryptodires. The common progenitor of the Athecae and the 

 Thecophora possessed the elements of the armor found now in 

 Dermochelys; likewise, perhaps in a rudimentary form, the ele- 

 ments which constitute the carapace and the plastron of the 

 other existing turtles. Proceeding from this common condition, 

 the Thecophora lost the superficial skeleton, but developed the 

 deeper-seated one, while in the Athecae the inner one became 

 more and more reduced. 



Versluys appears to be in doubt whether or not the epithecal 

 armor of Dermochelys was secondarily developed. He is in- 

 cUned to regard it as composed partly of new elements, partly of 

 old. The median and costal rows of enlarged scutes of the leather- 

 back may, he thinks, be new structures, and he refers to those 

 epithecal bones found alternating with the neurals in Toxochelys 

 and the more numerous ones of Archelon. He thinks it possible 

 that new epithecal bones might arise under the horny scutes 

 at their center of growth. This appears to be a reasonable 

 proposition. It would provide for rows of four or five bones; 

 but how would Doctor Versluys account for the approximately 

 fifty bones in each of the seven rows of the carapace of Dermo- 

 chelys? Where did all the little plates of bone originate that fill 

 the spaces between the rows? If it be assumed that the species 

 of Toxochelys were developing a new epithecal shell, two ques- 

 tions may be asked: 1) Why should they have been providing 

 for themselves a new armor whilst the old one was yet in good 

 order? 2) Those epithecal^ neural bones had a tendency to 

 coossify with the underlying neurals. How could a new shell 

 be produced under such circumstances? As old useless elements 



1 These have been called by Wieland epineurals, but the term had long before 

 been applied to very different bones in the fishes. 



