TOXOCHELYID&. I8I 
plastron (except the epiplastra and the entoplastron) and the right humerus. From the portion 
of the carapace present the whole has been restored, as seen in Professor Williston’s original 
description. The figures presented in the present work have been redrawn, with slight modi- 
fications, from Williston’s paper. 
The skull (figs. 231, 232) is remarkable for its breadth and the massiveness of the jaws. 
As shown bythe figures, the posterior breadth is maintained with slight diminution far forward, 
so that the head appears very blunt, altho the snout is somewhat produced. The narial 
opening is broader than high, and its upper boundary is furnisht mostly by a pair of small 
nasals. The orbits are rather large and directed rather strongly upward. The interorbital 
space is 19 mm. wide. The bones covering the temporal region are so much damaged that the 
Fics. 231 AND 232.—Porthochelys laticeps. Skull of type. x3. 
231. Upper surface. 232. Palatal surface. 
extent of the roof can not be determined; but it was probably as extensive as in Toxochelys. 
The bones of the upper surface of the skull are much roughened, as in Chelydra. : 
The palatal surface of the skull is shown in fig. 232. The cutting-edge of the maxilla is 
deeper than in Toxochelys latiremis, and its depth increases toward the jugal bone. The palatal 
surface of the bone, 10 mm. wide in front, increases to 20 mm. at the hinder end. The masti- 
catory surface extends over on the palatine and is markt internally by a rough ridge. “Trans- 
versely the surface is slightly concave. The choane are not encroached on by plates from the 
vomer and palatines, as they are in the Chelontida, but lie well forward in a shallow fossa. 
They are separated by the vomer, which is wide anteriorly, narrow between the choanz, and 
develops a sharp ridge on its palatal surface. As in Chelydra, each pterygoid developt a strong 
lateral process, against which the inner surface of the 
dentary workt. The width of the pterygoids, where 
narrowest, is 30 mm. The quadrates are notcht behind 
for the passage of the columella, as in 7 oxochelys. 
Of the mandibles only the united dentaries are pres- 
ent (fig. 233). They are very heavy and strong bones. 
The masticatory surface is somewhat concave both trans- 
versely and longitudinally, and is bounded internally 
along the anterior half by a rough ridge. At the sym- 
physis the two ridges unite and run to the front of the 
jaw. This masticatory surface is, in front, only about 
half as wide as is the symphysis itself; but it widens 
backward and overhangs the inner lower border of the 
jaw. The coronoid process is considerably elevated. 
The carapace (plate 31, fig. 2; text-fig. 234) is now very flat. How deprest it was during 
life it is impossible now to say; but it probably had no great elevation. It is nearly circular, 
Fic. 233.—Porthochelys laticeps. Den- 
tary bones of type. 4. Redrawn 
from Williston’s figure. Shows grind- 
ing-surfaces. 
