116 



G. M. Wieland — On Marine Turtles. 



which are evidently small posteriorly. Immediately back of. 

 the nuchal, however, there does not appear to be an underly- 

 ing neural, and one may say with certainty that all the anterior 

 neurals at least are very greatly reduced. It is, too, equally 

 clear that these mere thin sheets of underlying bones that 

 can be referred to neurals, so far as they were seen in 

 fracture sections, have had their function taken over by the 



Fig. 8. 



Figure 8. — Archelon ischyros, x 1/36. Ventral view of type. Compare 

 legend of the preceding figure. Note that all the elements of the plastron 

 here shown occupied their normal position as originally recovered. Only 

 the doubtful position of the omitted epiplastra prevents final accuracy. 

 Note also the great length, of the plastron ; it is nearly as long as the cara- 

 pace. Observe the small size of the femoral notches. The rib pair passing 

 beneath the hyo-hypoplastral suture is the fifth. 



outer dermal series, which is continuous from nuchal to pygal 

 and thus corresponds to the neural keel of Dermochelys. 



On the nuchal itself no additional elements were observed, 

 but, as just stated, one may suppose from the great reduction 

 in thickness such may well have been present. Indeed, it is 

 not impossible that the posterior end of the nuchal extended 

 beneath the first of the median supra-neural elements, and 



