TOXOCHELYID7E. 



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 by the 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 ot 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 



232. 



FIGS. 231 AND 2^2.Porthochclys laticeps. Skull of type. Xj. 



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 choanz are not encroached on by plates from the 

 vomer and palatines, as they are in the Cheloniidae, but lie well forward in a shallow fossa. 

 They are separated by the vomer, which is wide anteriorly, narrow between the choanae, 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 Toxochelys. 



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 c 



FIG. 233. Porthochelys laticeps. Den- 

 tary bones of type. Xi- Redrawn 

 from Williston's figure. Showsgrind- 

 ing-surfaces. 



