12i G. P. Wieland — On Marine Turtles. 



The hyo- and hyjtoplastra exhibit no very unusual features, 

 except a great number of peripheral spines. The curved or 

 somewhat boomerang-shaped xiphiplastra are of course more 

 primitive than are the long and straight forms common to the 

 Cheloniidse. 



That the plastral fontanelles appear to be of less area than 

 is shown in figures of Protostega, is due more to the fact that 

 the plastron under consideration is the best and most complete 

 example known in the Protostegidse than to any marked vari- 

 ance in proportions. The plastral resemblance in Protostega 

 and Archelon is very striking, in view of other differences 

 separating these genera. 



The Shoulder Girdle and Manus. — The marked feature of 

 the huge shoulder girdle is the projection of the coracoid all 

 the way back to the pubis, a feature also present in Protostega 

 and common to the existing Eretmochelys. The most charac- 

 teristic element in the shoulder girdle of Archelon is the 

 humerus because of its distinctly thalassic type. 



The testimony as to the organization of the manus is reason- 

 ably complete and aside from minor differences exhibits general 

 agreement with that of Protostega. The centrale in the latter 

 is, for instance, more distinctly angled. While all the carpal 

 elements of either a right or a left flipper are present, only the 

 principal bones of the carpus have been found in position or 

 approximately so. It is only in the left flipper that bones 

 from another specimen have been introduced, namely, carpale 

 I, the intermedium, and the pisiform, which fortunately were 

 found together in this supplementary specimen. The only 

 element in doubt was the centrale, but this seems to have been 

 of a rounder form than in Protostega. 



Of the metacarpals and phalanges, the majority are present 

 and the proportions of the fingers are essentially those adopted 

 in the restoration, although when a specimen is once found with 

 these elements in place, as in the case of the Pittsburg Museum 

 specimen, some slight modification of the present restoration 

 may prove necessary. 



The important anatomical features of the front flipper then 

 are: (a) Agreement with Protostega y. (b) general agreement 

 with the Cheloniidae, the centrale exhibiting strong contact 

 with metacarpal I, instead of exclusion from contact with this 

 element by junction of the intermedium and carpale II ; 

 (c) the comparatively slight modification and elongation of the 

 phalanges for pelagic life, as contrasted with the much 

 modified thalassic humerus. Although the latter is thus mod- 

 ified, it lacks much of the strength exhibited by the paratha- 

 lassic Dermochelan humerus ; for while the radial crest has 

 shifted toward the middle region of the shaft, it has failed to 



