DOUGLASS: THE TERTIARY OF MONTANA 215 
long muzzle. Zygomatic arches deep — broad as seen from the side. Post-glenoid process 
long and inclining forward toward the lower end. Squwamosal extending downward in 
a broad mastoid process outside of the external auditory meatus. Depression at anterior 
portion of zygomatic arch rather deep. Anterior cusp of P* small and low. 
GENERAL DESCRIPTION. 
Dentrtion. —In this specimen the incisors and canines are not preserved ; the 
premolars and molars on the right side are well preserved, also the last five teeth on 
the left side. 
P* is a small, simple, laterally compressed, one-rooted tooth, slightly curving 
backward toward the point. The diastema behind this tooth is about three times 
the length of the tooth. 
P* is a little larger, is two-rooted, has a sharply-pointed protocone and a minute 
posterior cusp. 
P# is three-rooted, has a minute anterior cusp, a protocone larger than that in 
P2, and a well developed posterior cusp which is, except at its point, connate with 
the higher protocone. This tooth has a well developed but not very large conical 
deuterocone. ‘There is a trace of a cingulum on the exterior and posterior portions. 
On all the teeth posterior to P*, the antero-external is higher than the postero- 
external cusp. 
P+ is nearly like the molars, is smaller than M* and M® but slightly larger than 
M*. It hasasmall, low, anterior basal cusp which is only shghtly above the alveolar 
border. The tritocone is separated from the protocone little if any more than in P#, 
but is much nearer equal to it in size. The posterior cusp on the deuterocone is 
minute. | 
M+ differs from P* in having a lower antero-external cusp, which is more 
separated from the postero-external one, in having a cingulum with minute outer 
anterior and posterior basal cusps, and in having a somewhat larger, yet small, 
postero-internal cusp. The tooth is also wider transversely than P+. 
M differs very little from M+. 
M®# is smaller, has a reduced postero-external cusp, and has no postero-internal 
one. 
DrscRIPTION OF SKULL. 
The occiput is broad, medially vertical, and sub-semicircular as seen from 
behind. The height is about four fifths the width—the exact proportions being 
18: 22 millimeters. The foramen magnum is large and has a heart-shaped 
outline. It is about one third the width of the occiput, and nearly half the 
