G. R. Wieland — On Marine Turtles. 



113 



find indispensable. It may, however, be stated that in the res- 

 toration, Plate IV, the skull undoubtedly shows the exact 

 proportions of the supra-occipital, this being an improve- 

 ment upon the earlier figures. 



The Vertebral Column. — The fact that the vertebral column 

 of Archelon is so nearly complete and uncrushed, with nearly 

 all the elements in undisturbed natural position, gives to the 

 restoration high value. Only the four proximal cervicals and 

 a few of the smaller caudals from near the tip of the tail are 

 missing, while from the eighth cervical to the fifth caudal, 



Fig. 6. 



Figure 6. — Archelon ischyros. Skull of cotype shown about 1/8 natural 

 size. The bounding sutures of all the exterior elements may readily be 

 distinguished. [The restored supra-occipital crest, perhaps, is shown. too 

 slender.] The low set squamosal is, in comparison with P. Copei and P. gigas, 

 seen to be a family character of the Protostegidee. 



inclusive, all the vertebrae are complete and in natural contact. 

 Further, in the large specimen collected in 1902, the fourth 

 cervical is present and of the normal or cyrtean form common 

 to all marine Testudinata. 



In Archelon, the cervicals succeeding the fourth are coelo- 

 cyrtean, with the inferior sides of the centra heavily double- 

 keeled. The valley between the keels is broad and shallow, 

 Neither in form nor size is there much variation in the distal 

 cervical centra. Aside from strength and great size, the dorso- 



