556 S. W. WILLISTON 



overlap of the squamosal one cannot be quite sure of the course 

 of the suture externally, but it descends no lower than I have 

 figured it. Above, the squamoso-postorbital arch is shown very 

 decisively on each side, but I cannot be sure of the suture separating 

 the two bones, and have, therefore, omitted it. I find no definite 

 evidence of a tabulare or supra-temporal in this region, though it 

 is not at all improbable that one or both are present. Posteriorly 

 the squamosal covers the quadrate broadly. The temporal open- 

 ing is moderately large and oval in form. It is bounded, it will be 

 seen, almost precisely as in Sphenodon. The parietal on each side 

 is slightly separated from the squamoso-postorbital arch, indi- 

 cating one way in which the upper temporal opening in Sphenodon 

 may have arisen. The parietal foramen is situated almost at the 

 extreme posterior end of the parietals, and very close to the 

 dermosupraoccipitals. On each side the parietals are curved 

 downward to near the top of the quadrate, but I find no evidence 

 of a suture separating the extremity of the processes. 



The occipital surface is but little injured and quite clean of 

 matrix. On the upper part of the steeper declivity, between the 

 descending processes of the parietals, there is a thin, concave bone 

 on each side, lying against the back part of the parietals, and some- 

 what separated in the middle line above by a descending process 

 of the same bones. Below, each bone diverges a little to fit into 

 a small groove on the upper external surface of the supraoccipital. 

 The suture between these bones and the supraoccipital on each side 

 is very conspicuous. The bones extend outward to the extremity 

 of the posterior parietal processes. There is a small but distinct 

 post-temporal opening on each side between the supraoccipital, 

 dermosupraoccipital, and squamosal. 



On the large surface below the dermosupraoccipitals and the 

 temporal fossae I can distinguish no sutures. In shape, the surface 

 is very much like that of Dimetrodon, as shown in the accompanying 

 figures (Figs. 3, 4) made from a viewpoint at right angles to the 

 plane of the supraoccipital. The paroccipital process is separated 

 from the upper, supraoccipital process in the same way; and their 

 union with the quadrate is very similar in both genera. I am aware 

 that this bone in Dimetrodon has been differentiated into the dermo- 



