SCOTT: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 263 
a larger proportion of the occipital surface than in Adinotherium or Ne- 
sodon; they also are of quite a different shape, not being so broad at the 
base nor so much constricted above. The paroccipital process is longer 
than in the last named genera and differently formed : the proximal por- 
tion is almost as massive as in Nesodon, but distally it becomes much more 
slender, laterally compressed and of trihedral cross-section. The process 
has a strong inclination downward and forward, and ends distally in a 
bluntly rounded point. The supraoccipital is quite narrow at the suture 
with the exoccipitals, but widens dorsally and is alone concerned in the 
formation of the occipital crest : this dorsal portion is also extended and 
recurved, so as to overhang the occipital plane and project behind the 
condyles, but is not so thickened and heavy as it is in Nesodon. The 
broad median convexity of the exoccipitals above the foramen magnum 
becomes, on the supraoccipital, divided into two ridges by a median groove. 
The occipital crest is thin and prominent and, as has been mentioned 
before, is demarcated on each side from the dorsal border of the zygomatic 
arch by a well-defined notch, which, however, does not prevent the junction 
of the two crests. 
As a whole, the occipital surface, though constructed on the same 
peculiar plan as in the Toxodonta and Typotheria, has yet a very different 
appearance, being higher and narrower without any such broadening of 
the base, while the inferior position of the zygomatic arches and the very 
long and relatively slender paroccipital processes are important factors in 
the difference, as are also the more pronounced median convexity and 
lateral concavities, the surface in the Toxodonta and Typotheria being 
more nearly plane. As in those suborders, the occiput proper is sharply 
constricted above the foramen magnum, which is low and wide, of trans- 
versely oval shape. The constriction leaves on each side a broad space, 
which is filled by the convex, inflated, hinder surface of the post-tympanic 
process of the squamosal, which is not so large and, in particular, not so 
broad as in Nesodon , the supraoccipital expanding dorsally and extending 
somewhat over the post-tympanics. The whole structure of the occipital 
surface is rather less extremely aberrant than in the Toxodonta. 
Nothing can be determined as to the extent and relations of any of the 
sphenoidal elements, because in the Ameghino specimen they are con- 
cealed by the matrix and in the Princeton skull they are so badly crushed 
that no identification is possible. 
