68 



A REVISION OF THE COTYLOSAURIA OF NORTH AMERICA 



outline. The articular face for the atlas is concave and there is a deep pit for the 

 continuation of the notochord; it slants downward and forward, so that if it were 

 applied to the atlas without a large preatlantal intercentrum the skull would have 

 been carried almost at right angles to the vertebral column. The foramina for 

 the exit of the posterior cranial nerves are not apparent, but deep pits on the 

 sides of the basioccipital may have led into the openings of the foramina. The 

 limits of the various bones forming the posterior plate of the skull can not be 



Fig. lo. — Skull of DiadtcUt fhastelinus. X }• No. 4839 Am. Mus. 

 A, Uteral Tiew, tbowing probable arrangement of tuturet; B, lateral view; C, posterior view; D, top Tiew; E, lower Tiew. 



made out, as the sutures can not be traced, but it is apparent that the paroccip- 

 ital bone was short, and joined, almost at once, the descending processes of the 

 squamosal and the quadrate. I have described two perforations in the posterior 

 portion of the skull in the position of posttemporal foramina and likened the con- 

 dition to that of the turtles (Case 15); in this specimen I find only two deep pits in 

 this position. 



Lateral surface of the skull: The quadrate rises almost vertically, the anterior 

 border is attached to and somewhat overlapped by the bones of the postorbital 



