> 
1884.) , 563 [Cope. 
Agriocheerus guyotianus Cope. 
Hyopotamus guyotianus Cope, Proceedings American Philosophical So- 
ciety, 1878, p. 77. Merycopater guyotianus Cope, American Naturalist, 
1879, p. 197, Proceeds. Amer. Philos. Soc., 1879, 375. 
Three crania, one with nearly entire mandible, and numerous fragments 
with mandibles, represent this species in my collection. It is the most 
abundant species of this genus in the John Day beds of Oregon. 
The cranium is of peculiar form. It is elongate from the orbits back- 
wards. The muzzle is elevated and compressed, so that the profile is hori- 
zontal, with subordinate irregularities. The occiput is therefore low as 
compared with the muzzle. The zygomata are rather slender, and are not 
expanded. The side of the muzzle is concave just below the superior 
border of the maxillary bone and above the fundus of the canine alveolus. 
The inferior part of the maxillary is concave from below the anterior 
border of the orbit to the line of the canine alveolus, The region above 
and anterior to the lachrymal bone is convex, leaving the flat nasal bones 
a little depressed. The frontal has a convex swelling on the middle line 
just posterior to the frontal foramina, from which point the surface slopes 
gradually and evenly to the supraorbital borders, and not in two planes, 
as in A. trifrons. At. the front of the orbit the section of the frontal bone 
is convex at the sides and a little so at the middle. The supraorbital 
border is short and concave, not long and straight as in A. trifrons, and 
the postfrontal process is moderately prominent, and is not decurved. The 
anterior temporal ridges do not reach them. The former converge in 
nearly straight lines at an acute angle to a long sagittal crest. This in turn 
bifurcates into two very prominent posterior temporal crests, which over- 
hang the occipital condyles. The brain-case is an elongate-oval, and the 
olfactory portion is long and narrow, but not especially constricted at any 
one point. There is a prominent small tuberosity at the inferior part of 
the lachrymal bone ; above it the preorbital border is not defined as far as 
the beginning of the supraorbital. The postfrontal process originates be- 
low the anterior temporal surface which is continued along its posterior 
edge. The malar bone is concave on its external face. The zygoma is 
compressed, and has a long low superior convexity behind. Its crest con- 
tinues into a fine, low, posttemporal crest, which turns posteriorly above 
to its prominent posterior expansion above mentioned, The latter turn 
outwards at the apices, and send a low ridge downwards towards the occi- 
pital condyle. Below, the latter form a low angle on each side, which sep- 
arates a median from a lateral plane. Above, the occiput is deeply con- 
cave, and has a trace only of median keel. 
The basicranial axis is flat and rather wide between the otic bullte. 
The occipital condyles have distinct inferior boundaries which are sepa- 
rated by a flat interval. The posttympanic region is wide, and is bounded 
inferiorly by the deep styloid fossa. This is surrounded internally and pos- 
teriorly by the funnel-shaped base of the paroccipital process, which ex- 
tends first posteriorly as a longitudinal lamina, and then outwardly. Its 
