DESCRIPTIONS OF FOSSIL LIZARDS GILMORE 



17 



/Skull. — Both skulls lack their premaxillaries, but otherwise the 

 crania are fairly complete. Since the skulls have much of their outer 

 surfaces covered with tuberculated scuta, there is but little of the 

 structure, aside from the palate, to be observed. The skull of this 

 species is blocklike, broad across the parietals, and gradually nar- 

 rowing from the back of the orbits forward. In profile there is a 

 sag in the forward parietal region, but from a point above the center 

 of the orbit the superior surface curves regularly downward to the 

 nose. The central part of the frontonasal region of the skull is trans- 

 versely hollowed out. 



The entire external surface of the skull, except for a narrow strip 

 paralleling the dental border of the maxillae, is covered by tubercu- 

 lated osseous scuta. From a study of both skulls it has been possible 

 to work out the extent and arrangement of nearly the entire scutel- 

 lation, as shown in figure 4. 



Figure 4. — Skull and lower jaw of Olyptosaurus giganteus Gilmore : Lateral view of 

 U.S.N.M. no. 13869 ; scutellation restored from opposite side and from specimen U.S.N.M. 

 no. 13861. ar, articular; ang, angular; c, coronoid ; d, dentary ; mx, maxillary; na, 

 nasal ; o, orbit ; sa, surangular ; sq, squamosal. Natural size. 



Comparison of the scutellation of the top of the two skulls shows 

 considerable variation in the sizes of the scutes, though their general 

 arrangement is much the same in both specimens. Those of U.S.N.M. 

 no. 13861 are the coarser and in that respect approach nearest to the 

 type specimen with which it has been directly compared. On the 

 dorsal side the scutes are arranged in irregular longitudinal rows, 

 becoming more regular in their arrangement above the orbits. In 

 this species the scutes have angularly convex upper surfaces, which 



