122 G. B. Wieland—On Marine Turtles. 



commenting on this figure, Dr. Hay states that a length of 

 2100 millimeters is thus indicated for the plastron, making it 

 larger than the carapace, which he considers impossible. 

 Neglecting my measurement of the plastron, which was given 

 as 2000+ millimeters, as well as the fact that the entoplastron 

 is very plainly shown a little anterior to its true position, he 

 also fails to note that the exact length of the carapace with, 

 the nuchal in position had not been determined by anyone. 

 His first premise is therefore unfounded and his conclusion a 

 pure assumption. 



The important point, however, is that in the restoration, 

 where the length of both carapace and plastron is definitely 

 determined, the two are found to be nearly equal. In the 

 dorsal view, the plastron appears a little shorter than the cara- 

 pace, while in the ventral view, the enormous expanse of the 

 plastron, greater by far than in Protostega Gopei and greater 

 than in any other sea-turtle, entirely cuts out the carapace. 

 Archelon ischyros was certainly a very singular marine form ; 

 with its enormous size, huge plastron, and small femoral notch 

 set far back, it had need of the great humerus, which by reason 

 of form and musculature represents a powerful sea-type. 



The unique T-shaped entoplastron of the Protostegidse has 

 had an interesting history. First called a nuchal by Hay in a 

 Kansas specimen, it was left for Wieland 8 to determine con- 

 clusively and figure both these elements in A. iehyros, although 

 there was uncertainty whether epiplastra were present at all. 

 For reasons that now appear trivial, being merely an imper- 

 fectly indicated condition of overlap seen in the field, the excel- 

 lent point of view developed in the paper just mentioned was 

 abandoned for a time. 14 



Meanwhile the specimen of 1902 w T as obtained and was 

 found to include still another puzzling bone, — the element 

 that must be regarded as an anomalous epiplastron ; and still 

 later the fine type of Protostega Gopei, here described, was 

 discovered by Sternberg and acquired for the Yale collections. 

 Thus was I enabled to determine finally that the nuchal and 

 entoplastron noted in the paper of 1898- 8 were truly such. 

 This correction appeared in the Annals of the Carnegie 

 Museum of Pittsburg for 1906. 16 



That scarcely one of the naturalists interested in the Pro- 

 tostegidse escaped from wrong conclusions as to the nuchal and 

 entoplastron, is after all not surprising. Both elements are of 

 a form not before observed, this being especially true of the 

 entoplastron, which except in P. potens Hay shows no indica- 

 tion of any ordinary type of epiplastral superposition or 

 junction. 



