WIELAND: THE OSTEOLOGY OF PROTOSTEGA 289 
but of rounder and more regular contour. The nearly ovate pisiform is distinctly 
intermediate in development between that of the existing Dermochelys and the 
Cretaceous congener Toxochelys in which the pisiform is smaller than in any other 
distinctly marine turtle. 
The first metacarpal is broad, and the first finger short and robust asin Towochelys 
(see Fig. 8) and other members of the Cheloniide. Finger disparity is pronounced, 
the second finger being little elongate as in Toxochelys, with the third and fourth 
fingers of medium and nearly equal elongation, and the fifth fully as elongate as the 
second. ‘The first to third fingers bore free claws, but not the fourth and fifth. 
In its general features the front flipper of Protosteya agrees much more closely with 
that of Toxochelys (Fig. 8) than with that of other forms, as one might well expect. 
The existing Cheloninee do not present so close a likeness, because of the peculiar 
elongation of the radius and dependent carpal variations, although the boundaries 
are much the same, the centrale in particular being in contact with carpale 1 in both 
cases. With Dermochelys, in which carpale 1 is small and excluded from contact 
with the centrale, the points of likeness are more obscure, although there is no dis- 
tinct suggestion in the carpal organization, that the former belongs to an utterly dif- 
ferent race. Pisiform development is also more like that of the primitive forms 
than in Dermochel Ys. 
The relative size of the front flippers as compared with the carapace is great, 
since they are not only robust, but have a spread equal to about 33 times the length 
of the dorso-sacral series of vertebree. In the existing carnivore Thalassochelys this 
ratio is nearly as great, being equal to about three, but falls to two to one in the 
algaphagous Chelone. In the carnivore Dermochelys the ratio is about 23 to 1, a 
result of comparison rather unexpected in view of the very great length of fingers in 
the latter, and accounted for by the great length of the clipper-built Dermochelan 
body. There is in the comparison just made the very strongest suggestion that Pro- 
tostega, more distinctly than any marine turtle thus far known, hunted prey, which 
swam actively, and, bearing in mind other features, was perhaps even powerful. 
In my deseription of the front flippers of Toxochelys™ I presented an interesting 
tabular comparison of the relative percentages of length of the several elements of 
the front flipper and humerus of various Testudinates, which exhibited the general 
trend of change since the Jurassic in the development and variation of flippers from 
amore generalized limb-type. I now include Protostega in this comparison. The 
humerus is in each case considered as having a length of 100, and the finger lengths 
as reduced to the same ratio, but including arbitrarily for convenience the meta- 
carpals, as follows : 
14See Footnote 8. 
