GILBERT: ON THE SKULL OF XEROBATES UNDATA COPE. 147 
inner, almost vertical surface, and takes no part in the formation 
of a false roof. 
The occipital condyle is triangular, broadest above, with a 
slight depression on the posterior surface. Back of the basi- 
sphenoid there is a well-marked concavity, the anterior and lateral 
margins of which coincide with those of the bone itself. The 
basioccipital processes are strong. 
The exoccipital fossa is a shallow, round pit, with its ventral 
wall quite low. Immediately above this concavity, and over the 
sutural union betweeen the exoccipital and the opisthotic, there is 
a long, shallow concavity. 
The epiotic is only partially fused with the supraoccipital. The 
external carotid foramen is midway between the tympanic rim and 
the zygomatic arch; there is a shallow crease curving upward and 
forward from this foramen. On the posterior margin of the tem- 
poral fossa and in front and exterior to the carotid foramen there 
is a large, stout, dorsally concave tuberosity, the suture between 
the prootic and the squamosal passing through its middle and 
through the carotid foramen. A broad, shallow groove separates 
the tuberosity from the zygoma, and there is another on the inner 
side. The external auditory meatus is oval; it looks downwards, 
backwards and slightly outwards. 
The basisphenoid is triangular, with its base posterior; the 
surface is in a plane of about twenty-six degrees with that of the 
base of the skull. 
The parietals form no portion of a false roof; they are rounded 
above, and there is a perceptible ridge arising from each antero- 
lateral process and fusing with its mate a little in front of the 
occipital crest. The antero-lateral margin is at an angle of forty- 
five degrees with the horizontal. There is a broad, shallow de- 
pression on the upper surface. 
The frontals are much wider than long, with a broad, median 
depression, a continuation of that from the parietals. The antero- 
lateral ridges of the parietals continue on the frontals. The 
rhinencephalic groove below is not bridged over. 
The prefrontals are strongly convex forward and laterally. The 
compressed top and flattened sides give to this region a decidedly 
quadrilateralshape. Theanterior margin is concave antero-poste- 
riorly and convex vertically. On the inner side and from the 
posterior part, a strong triangular process extends inward and 
backward to meet the upward and forward process of the vomer. 
The anterior ventral part of this process has an angular ridge, 
