188 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. XXXIV. 
from corresponding ones of the other. In general, those of the log- 
gerhead are thicker and have a greater angle between the upper and 
the lower faces, when these faces are distinguishable. A fair com- 
parison may be made between those of the large specimen of the 
bastard-turtle and the large loggerhead, No. 29013. The latter is a 
disarticulated skeleton, the carapace of which is about 855 mm. long 
and 810 mm. wide. The bastard-turtle has therefore about four-fifths 
the length of the loggerhead. The second peripheral of the logger- 
head is 18 mm. thick; that of the bastard-turtle is 12.5 mm. In both 
species there is, from the fourth peripheral backward, a sharp edge 
which separates the upper face of each peripheral from the lower 
face. The rib-pits are in the inner, or visceral, face. Let us com- 
pare the sixth peripheral of each species, that one which receives 
the rib of the third costal bone. In the loggerhead (Plate XI, fig. 1) 
the upper face is shghtly convex. The lower face, here more prop- 
erly the outer, makes a right angle with the upper and is only 27 
mm. wide. In the bastard-turtle (Plate XI, fig. 2) the upper face is 
concave, the angle between the two faces is about 45°, and the width 
of the lower face is as much as 45 mm. The eighth peripheral of the 
loggerhead has the upper face nearly plane, the angle between the 
two faces is about 75°, and the width of the lower face is about 27 
mm. In the bastard-turtle the upper face 1s somewhat concave, the 
angle between the two faces is less than 30°, and the width of the 
lower is 60 mm. The upper face of the eleventh peripheral of the 
loggerhead is convex above, the lower more strongly so, the angle 
between the two about 45° at the border, still less at some distance 
from it, and the lower is about 50 mm. wide. In the bastard-turtle 
the upper face is decidedly concave, the lower convex, the angle 
between the two about 40°, and the lower is 68 mm. wide. 
There appear to be in all specimens of the bastard-turtle two supra- 
pygal bones. In the large individuals the anterior is bifurcate, as 
in most species of Zestudo, receiving the hinder suprapygal and 
sending a branch on each side to the eleventh peripheral. The hinder 
suprapygal becomes suturally jomed to the pygal in the smallest 
known specimens, and it is crossed near the middle of its length by 
the sulcus between the fifth vertebral scute and the two hindermost 
marginals. 
The second suprapygal of the loggerhead does not so early join 
the pygal. However, in the large loggerhead mentioned, it has be- 
come as completely sutured to the pygal and twelfth peripherals as 
it is in the bastard-turtle. The posterior hump mentioned by Gar- 
man is on this bone. The first suprapygal is bifureate, as in the 
bastard-turtle, but it has not contracted sutural union with any 
peripheral. If later it should do so, it would be with the twelfth 
peripheral, not with the eleventh, as in the bastard-turtle. The pygal 
