374 University of Kansas Geological Survey. 



this process is perforated by a large foramen. Between the 

 posterior end of the pterygoids there is a small triangular 

 space into which is wedged the basisphenoid ; this, as in all the 

 sea turtles, appears very slightly on the lower surface of the 

 skull. This triangular surface of the basisphenoid is very rugose. 



The basioccipital presents a broad, slightly concave, lower 

 surface, on a somewhat higher plane than that of the basisphe- 

 noid, so that there is a sharp offset of about a half a centimeter 

 at the junction of the two. Near the posterior end, the bone 

 turns sharply upward. Near the center of the bone, two small 

 tuberosities are seen on the angle thus formed, on each side of 

 a slight concavity in the median line. The occipital condyle 

 is distinctly tripartite ; the lower portion is formed by the basi- 

 occipital and has an antero-posterior length of about one centi- 

 meter. 



The exoccipitals form the lateral thirds of the occipital condyle. 

 They extend for some distance laterally and apparently separate 

 the basioccipital from any contact with the opisthotic. They 

 form the sides of the foramen magnum, which is completed 

 above by the supraoccipital. Each bone is pierced on the lower 

 side by a large foramen. 



The opisthotic joins the supraoccipital and petrosal in front, 

 the exoccipital behind, and runs outwardly to join the posterior 

 border of the quadrate. Near the posterior edge, a strong, 

 sharp ridge extends the full length of the bone. At the distal 

 extremity there is developed on the posterior margin a promi- 

 nent rugosity just before the bone unites with the quadrate. 

 This gives to each side of the cranial region a concave posterior 

 outline, corresponding somewhat to that of the temporal roof. 



The quadrates have the sides of the stapedial notch closely ap- 

 proximated, but not so much so as in T. serrifer. The whole 

 bone is inclined somewhat backwards, so that the lower ex- 

 tremity was the most posterior. The articular face is rather 

 broad, and is divided into two parts, an outer and an inner, 

 by a deep notch. The alse are short, and show articular sur- 

 faces all around the convex edges for the squamosal and quad- 

 rato-jugal. From the outer extremity of the articular face a 



