104 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



surface for the lower jaw. Furthermore, there has been a deep notch 

 in the upper and posterior part of the quadrate. This suggests that 

 the tympanic cavity has been supplemented by a cavity in the 

 squamosal. In Chelonia there is no such notch, but the quadrate is 

 deeply scooped out in that direction. In Chelydra the squamosal is 

 much enlarged backward and excavated to a thin shell of bone and 

 forms a large bulla, into which the cavity in the quadrate freely 

 opens. Most living turtles, outside of the Dermochelyidce and Chelo- 

 niidce, possess more or less developed squamosal bullse. While that 

 of Toxochelys was probably not greatly developed, there was a beginn- 

 ing of the structure. 



12. The quadrate bears an open stapedial notch, as it does in 

 the Cheloniidce but not in the Chelydridce. 



13. The parietals are mostly wanting in my specimen. On the 

 left side there is a portion of the bone which entered into the side 

 wall of the brain-case. From the upper outer edge of this piece 

 there jutted out the plate which helped to roof over the temporal 

 fossa. How far backward this roof extended, and whether or not 

 there was produced a parieto-squamosal arch, cannot be determined; 

 but, at any rate, at the hinder end of the piece which remains, the 

 horizontal plate is quite thick. Professor Cope (Proc. Amer. Phil. 

 Soc. 1877, P- X 7^) states that the temporal fossae, as shown in his 

 skulls, were extensively roofed over. We are therefore justified in 

 concluding that the arrangement was quite like that in the 

 Cheloniidce. 



In front of the piece of the parietal referred to, there are seen on 

 each side the lower ends of the descending processes of the parietals. 



14. The frontals of my specimen are wholly missing. Pro- 

 fessor Cope in describing T. serrifer (Cret. Vert., p. 300) indicates 

 that they entered into the rim of the orbits. This is most probable, 

 judging from the shortness of the prefrontals of my specimen. In 

 the Chelydridce the frontals are widely excluded from the orbital rims. 



15. A portion of the jugal is still present, bounding the left 

 orbit. It has been deeply excavated on the lower border, while the 

 bone between this excavation and the rim of the orbit is very 

 narrow. 



1 6. From the above examination of the skull of Toxochelys it is 

 seen that in general the anterior portion resembles more or less 

 closely that of Chelydra, the posterior portion that of the Cheloniidce. 

 In the anterior portion the most important deviation from the 

 Chelydrine pattern consists in the extension of the palatine around 

 the outside of the choanae. In the hinder portion there is no essential 

 deviation from the Chelonian type, unless it shall prove to be in the 



