1884. | 567 [Cope. 
muzzle has three distinct fosse. The largest of these is above the position 
of the fundus of the superior canine alveolus; the second is below the 
fundus; and the third is behind the position of the infraorbital foramen, 
and above the third and fourth premolars, and the first true molar. The 
lachrymal region is plane, and the nasals are flat. ‘The frontal bone is 
nearly flat in section between the posterior borders of the orbits, but each 
is decurved to the lachrymal opposite the anterior border of the orbit. 
There is no indication of the three planes of the infraorbital region charac- 
teristic of the A. trifrons, nor of the median convexity of the A. guyotianus, 
The anterior temporal ridges commence about the middle of the width of 
each frontal bone, and unite after a shorter independent course than they 
have in A. guyotianus into a long, narrow saggital crest. This bifurcates 
posteriorly into two prominent lateral crests, which are directed down- 
wards and soon terminate, but which send forwards and downwards a 
delicate posttemporal crest. This passes without interruption into the supe- 
rior edge of the zygomatic arch. This arch is not expanded either upwards 
or laterally, and is rather weak. The external face of the malar bone is 
gently concave, and the inferior edge is rather wide, is truncate, and 
grooved along the middle. The occiput is deeply concave between the 
crests, and below them is gently convex. The superior edge of the fora- 
men is deeply notched at the middle, much as in MZ. guyotianus. 
The occipital condyles are large, and their inferoanterior angles are pro- 
duced horizontally for a short distance, forming short processes which are 
separated by a concavity of the basioccipital bone. The latter is plane be- 
low, but anteriorly develops a low meridian angle, which, widening on the 
sphenoid, causes its inferior face to be convex. The posttympanic element 
is distinguishable from the mastoid by a superficial groove, and a slightly 
free apex, and the mastoid from the paroccipital by a slight groove. The 
external base of the paroccipital extends but 5 mm. external to the line of 
the external border of the occipital condyles, and is therefore much less 
prominent than in the majority of species of Oreodontinse. The base of the 
paroccipital has a posterior and an anterior face, nearly at right angles 
with each other. The latter is continued into the pinched posterior promi- 
nence of the auditory bulla, and encloses on its external side, with the 
apex of the posttympanic, the deep stylohyoid fossa. The tympanic bone 
is represented by a tuberosity below the meatus, and a laminar expansion 
on the posterior face of the postglenoid process. The otic bulla’s long axis 
is inwards, and a little posterior from the internal side of the postglenoid 
process, from which it is separated by a narrow interval. The bulla is con- 
stricted at right angles to its long axis, in two parts. The external part 
is subglobular with the side next the postglenoid process flattened. The 
internal part is roughened, displays a flat side posterointernally, and has 
an apical keel which extends posteriorly and a little externally into the 
base of the paroccipital processes. This form is not known in any other 
Species of the family. The postglenoid process is more robust than in 
either M. guyotianus or M. trifrons. Its width and thickness are equal, 
PROG. AMER. PHILOS. 800. xxi. 116. 87. PRINTED JuLy 1, 1884. 
