G. JR. Wieland — On Marine Turtles. 



121 



dermal elements is lacking, although, an agreement with the 

 five plastral keels of the leatherback may be conjectured. 



The Plastron (figure 8). — The nearly perfect plastron of the 

 type has suffered somewhat during collection, by its removal 

 from an exceedingly hard marl matrix into which the numer- 

 ous and often interlocking spines of the mid-plastral region 

 penetrated. Nevertheless, as finally mounted, the plastron 

 may be said to be in splendid condition. All the central 



Fig. 11. 



Figure 11. — Archelon ischyros. Left eighth or ninth marginal as found 

 in conjunction with an additional element in a supra-marginal position. 

 Shown % natural size. If the anomalous element is not a supra-marginal 

 it must be referred to the supra-neural series just anterior to the pygal. A 

 .slight asymmetry does not prevent, although it makes such a position less 

 probable. It is easier to consider this element as having been found in a 

 natural position, and as perforce thus accounting for the supra-marginal 

 keel of the carapace of Dermochelys. 



portions of the large plates are present, with most of the spines, 

 so that neither their size, form, length, or number, is ever in 

 doubt. More important still, all the elements are but little 

 crushed and, save the epiplastra, are present in their normally 

 articulated position, just as they were figured in 1898. 9 In 



