106 G. R. Wieland — On Marine Turtles. 



Presumably the evidence in favor of Baiir's view is increas- 

 ing. The writer so regards it. The fact that the cervicals of 

 Toxochelys and Archelon agree in general, and at the same 

 time differ most widely from tlie cervicals of Dermochelys and 

 of the Cheloninge, is, however, rather unexpected. Did the 

 vertebrse of tliese Cretaceous forms tend to simplify, or has 

 there been a more or less remote homoplastic parallelism in 

 the course of com|)lication in the case of the sixth, seventh 

 and eighth vertebrae of the modern sea turtles, and such widely 

 different forms, for instance, as the Testudinidse ? 



The question at once arises, what is to be regarded as a very 

 primitive Testudinate cervical, and what was the form in the 

 species, genus, or group which made its way into the sea and 

 gave rise to the marine group ? We may most reasonably 

 suggest as ar very primitive cervical type, that of a turtle like 

 the Pleurodiran Eryinnochelys^ in which there is a well-nigh 

 complete agreement with the modern Crocodilia, the second, 

 and not the fourth, centrum being biconvex. vVnd we assume 

 that some descendant of such a primitive type, with double 

 convexity moved back to the fourth cervical centrum, the 

 hfth-eighth centra remahiing simply procoelous, stood in some 

 common ancestral relationship to the sea turtles and most other 

 existing Cryptodirans. It would at present, therefore, seem 

 that even since the sea turtles split off from their littoral an- 

 cestry there has been a certain parallelism in the secondary 

 cervical modifications undergone by them and the most nearly 

 related land forms. This may hence prove, once we know the 

 record more completely, to be another example of the fact 

 that a course of evolution and change once established in a 

 persistent group, may long continue, after the invasion of wholly 

 new environments. There is in biologic, as in physical evolu- 

 tion, inertia. 



As to the carpus of Archelon. It will certainly be very 

 interesting if my surmise that there is no union between car- 

 pale 1 and the centrale should prove correct. This, although 

 to be regarded as a secondarily acquired character, would in- 

 deed go far toward narrowing the gap between the extreme 

 ends of the marine group. I may point out that the greatly 

 accentuated bow of the radius of Archelon would make it 

 probable, even in the absence of more direct evidence, that 

 there was present some marked change in the order of the 

 carpals. 



Systematic Position of Archelon. While the data given in 

 the preceding notes go far towards showing that Protostega 

 and Archelon present more osteological resemblances to Der- 

 mochelys than any other turtles whatsoever, living or extinct, 

 their structure is essentially that of the Chelonidae, of which 



