158 E. C. CASE 



the Diadectidae indicates that it may well be the parasphenoid detached 

 from the basisphenoid and- placed in an interior position, retaining 

 its connection with the basisphenoid by extension of the cartilaginous 

 basicranial axis, if at all. Perhaps the median ossified plate described 

 as descending from the anterior part of the skull roof is an ossification 

 of the ethmoid complex, and aids in the support of the vomer. The 

 list given above shows that the parasphenoid rostrum of the basi- 

 sphenoid is not a constant feature even in well-defined Cotylosaurians. 



6. The method of entrance of the internal carotid arteries into 

 the brain cavity. In the Rhynchocephalia and Squamata the carotid 

 arteries divide beneath the skull floor, and the internal carotids pass 

 through the basisphenoid from below, leaving a pair of foramina 

 which are very constant and noticeable features. In many of the 

 turtles the carotids pass into the skull through a foramen posterior 

 to the quadrate, and then divide into an internal and external carotid. 

 The internal carotids enter the basisphenoid through the side of the 

 bone, and then pass out of the top, leaving no foramina on the lower 

 surface. This character is not constant for all turtles. In some the 

 internal carotids enter the pterygoid, or the foramen is in the suture 

 between the basisphenoid and pterygoid. 



I find foramina on the lower surface of the basisphenoid in the 

 Rhynchocephalia, Squamata, and probably Dinosauria. In the Testu- 

 dinata (partim), Chelydosauria, Crocodilia, there are no foramina 

 on the lower side of the basisphenoid. 



7. The presence of paired descending plates from the skull roof 

 anterior to the brain cavity. As no trace of an epi-pterygoid was 

 found, the paired plates descending from the lower surface of the 

 parietals is strongly prophetic of the plates in the turtles. They 

 have the same position and, apparently, the same relation to the 

 pterygoids below and the foramen for the fifth nerve. 



Opposed to the Testudinate affinities is the absence of any plastral 

 elements, even abdominal ribs, and proscapular process of the 

 shoulder girdle. 



In just the characters in which the Chelydosauria (Otocoelidae, 

 Diadectidae) approach the turtles they are distinct from the Cotylo- 

 sauria {Pareiasauridae and Pariotichidae), and so it seems very 

 probable that we have in the Diadectidae forms very closely related 



