Cope.) 390 [April 15, 
species does not belong to Hyrachyus. The anterior cross-crest of the 
molar preserved, is lobate, resembling the same ridge in the species of An- 
chitherium. The posterior cross-crest is uninterrupted. If this species 
possesses affinity with Anchitherium, it will perhaps possess three digits of 
the manus, in which case it will be reterred to the Triplopide, in harmony 
with the indication furnished by the ear structure. 
The Triplopus amarorum is much larger than the 7’. cud¢tal’s, equalling 
the Hyracodon nebrascensis. It differs from the 7. cwbztalés in the stronger 
temporal ridges, and more elevated sagittal crest ; also, in the shorter post- 
tympanic process. The internal lobes of the last superior molar are con- 
nected by a basal ledge, not found in the 7. cubitalis. 
The interorbital space is wide and flat, and is most expanded at the post- 
orbital angles. 
From this point the face contracts rapidly forwards, From the same 
angle it contracts abruptly posteriorly to the rather narrow brain-case. 
The anterior temporal ridges are nearly transverse near the postorbital 
processes, and then converge more gradually, uniting opposite the posterior 
inferior border of the zygomatic fossa. The elevated sagittal crest diverges 
into two lateral supraoccipital crests, which contract as they descend, and 
continue to the extremities of the posttympanic processes. Although the 
postorbital angles are prominent, they cannot be called processes. The 
paroccipital processes are large, and are directed vertically downwards. 
They are separated by the usual concavity from the occipital condyles. 
The posttympanics are very short, forming only an angle projecting 
downwards at the anterior base of the paroccipitals, from which they 
are only separated by a notch. The inferior side of the tympanic bone 
is flat near the meatus, but opposite the stylomastoid fossa its posterior 
border is turned forwards, and is produced into a well marked process. It 
encloses a groove in front of it, which is continuous with the pterygoid 
fossa. The petrous bone is not inflated, and its inferior surface is divided 
into two longitudinal ridges. The inner is the less prominent, and is in 
close contact with the basioccipital. The postglenoid processes are robust 
and obtuse. The basioccipital is excavated in front of each of the con- 
dyles. The inferior surface is nearly flat, with a slight median keel. The 
pterygoid fossa is well defined, and is long and narrow. The posterior nareal 
trough is elongate, the descending pterygoid processes of the sphenoid 
originating as far back as the apex of the os petrosum. This species is es- 
pecially characterized by the presence of an acute keel-like ridge, which 
extends horizontally above the foramina sphenodrbitale and opticum, and 
turns upwards anterior to the latter, terminating a half inch below the in- 
ferior base of the postorbital process. All the foramina are below it, but 
there is a fossa above it, opposite the interspace between the f. opticum and 
f. sphenoorbitale. : 
A supraorbital foramen pierces the frontal bone, a quarter of an inch 
within the superciliary border. There are five or six postparietal foramina, 
two of which are nearly on the squamosal suture. There is a postsqua- 
