No. 1.] RELATIONSHIPS OF PROTOSTEGA. 41 
breadth of the plastron to the breadth of the lower surface of 
the turtle is as 5 to 6. The distance across the plastron in 
this specimen of Pvotostega in its widest place is 1.029 meters; 
and this, according to the ratio stated, would make the lower 
surface of the turtle 1.235 meters wide. The widest part of 
the carapace in Chelonia does not correspond with the widest 
part of the plastron, but is broader somewhat behind it, so the 
general form of the carapace was not long and narrow, but 
almost round. 
As shown in Pl. V, Fig. 6, the quadrate, pterygoid, and pala- 
tine of the smaller specimen are all united and very slightly 
distorted by pressure, especially in a linear direction. The 
measurements of these bones, including length of quadrate, 
length of condylar face of quadrate, and length from posterior 
end of quadrate to anterior end of palatine, are almost exactly 
the same as that of a skull of Chelonia mydas, which measures 
.197 meters from snout to occipital condyle. The humerus of 
the smaller specimen is six-elevenths as large as the same bone 
in the larger specimen, both being in excellent condition. If it 
is assumed that the same ratio applies to the head, the larger 
specimen would have a skull measuring .363 meters from snout 
to occipital condyle. 
No material is at hand to give exact measurements of the 
neck, but assuming with Hay that the neck extended in front 
of the carapace a distance equal to one-sixth of the carapace, it 
would have a length of .278 meters. 
The exact figures are: 
Plastron, from xiphiplastra to anterior end, hyoplastra . . . 1.15 meters 
Breadth of fontanelle at suture between hyo- and hypo-plastra. .525 “ 
Breadth of plastron at widest part of hyoplastra. . . . . . 1.029 “ 
The estimated figures are: 
iengta of carapace = =’. . .' “1.640 meters 
enpthvotbeady) Siete te fh 6 gOgt 
Wength Gh mechs. Mies ve Weel a) Ue lp 27 Ou Ne 
Ota mee usar Cer Viele au ffl t21-p' 20977 3th ace 
Widthtof carapacelnn ts. <6 <i) <0 Te23i5y ice 
In both Cope’s and Hay’s specimens the animal was a very 
little larger than in the present one. 
