1884.] 515 [Cope. 
above the foramen magnum to be obtuse angulate instead of broadly 
flattened as in #. jackson. The mastoid crests are roughened and are 
vertical, but do not continue directly into the paroccipital processes, but 
are separated from them by a deep excavation of the external margin, 
due to the internal position of the base of the process. 
The long diameter of the base of the paroccipital process runs outwards 
and backwards, and it is attached to the bulla at the middle of the posterior 
extremity without any intervening grooves such as are seen in the other 
species of the genus. The bulle are ovoidal in anteroposterior section, the 
regularity interrupted, however, by the presence of a ridge on the exter- 
nal side directed posteriorly, enclosing a groove which is continuous with 
the stylohyoid fossa. The ridge continues into the inferior crest of the 
tympanic bone. The sphenoid bone is regularly convex in transverse sec- 
tion, while the basioccipital is concave on each side with a narrow median 
keel, which commences opposite the anterior edge of the paroccipital pro- 
cesses. The basicranial axis is not quite in line with the basifacial, but 
does not present such an angle with it as is seen in the species of Mery- 
cochoeerus, where the skull is known to me. In this respect it agrees with 
the other species of the genus. The postglenoid processes are less promi- 
nent than in H. jacksoni, but have a base more widely extended outwards. 
The external border is very oblique, since the apex is narrowed. The 
glenoid region is more extended, both transversely and anteroposteriorly 
than in the #. jacksoni. The anterior border is continued as an alisphe- 
noid angle which becomes prominent, and overhangs the foramen ro- 
tundum, ‘The descending alisphenoid ridge commences within the anter- 
ior border of the foramen ovale. The pterygoid angle is anterior to the 
middle of the palatosphenoid wall of the nareal foramen, and in front of 
it the edge of the processus pyramidalis is marked by a shallow fossa or 
mark of insertion of the internal pterygoid muscle. The nareopalatal 
border is as far posterior to the line connecting the posterior edges of the 
maxillaries as the width of the second molar tooth. The palate is every- 
where nearly flat. The malar bones spread well away from the maxillaries 
on each side, the anterior border of the zygomatic foramen being a seg- 
ment of a circle. The squamosal part of the zygoma is more widely ex- 
panded than the malar part. In H. jacksoni the shape of the zygomatic 
foramen is quite different. Its anterior outline is interrupted by the pro- 
jection of the maxillary bone posteriorly, which gives its anterior outline 
a bilobate form. It is longer than wide in that species, and wider than 
long in the ZH. trigonocephalus. 
The infraorbital foramen is small. There are two lachrymal foramina ; 
one larger, within the preorbital border, the other smaller, below the 
tuberosity on the rim of the orbit. The frontal foramina are separated by 
& space equal to one-fourth the entire frontal width. The supraorbital 
notches are wanting. The preorbital fosse are well marked, are distinctly 
defined above, and extend as far as the anterior border of the lachrymal 
bone. The orbit is round, and looks upwards as well as outwards and 
