558 (Jan, 18, 
Cope.] 
those of the lower jaw, I suspect that the former were absolutely wanting 
in this genus. If s0, we have in the Oreodont line the same process of re- 
duction above, as has taken place in other lines of Artiodactyla at the 
latest or modern stage of their history. 
In Pithecistes the inferior canine is caniniform, and masticated in con- 
tact with the superior canine, owing to the great abbreviation of the sym- 
physeal region. 
The diagnosis of the genus is as follows : 
Inferior premolars three ; incisors one. Canine caniniform, masticating 
with the superior canine. No diastema, Symphysis codssified. 
Two species are referred to this genus without conclusive evidence as to 
the number of their premolars. It is probable that they have but three, 
since their superior fourth premolars are of reduced size and incomplete 
type of form, 
Pithecistes brevifacies Cope. 
Proceedings American Philosophical Society, 1877, p. 219. 
Ticholeptus beds of Deep river, Montana, Discovered by J. OC. Isaac. 
Pithecistes decedens Cope, sp. nov. 
Established on a right maxillary bone, which contains the fourth pre- 
molar, the first and second true molars, and part of the alveolus of the 
third true molar. The last named tooth was not probably entirely pro- 
truded. This, with the moderate wear of the fourth premolar, indicates that 
the animal was fully grown, though young. 
The species differs from all the members of the family whose dentition 
is known to me in the small size and simplicity of structure of the fourth 
premolar, The internal crescent of this tooth bounds only the posterior 
three-fourths of the external wall, and therefore leaves the anterior edge 
of the latter free. It is, moreover, not very convex, and its edge is not so 
elevated asis that of theexternal wall. The latter is flat on the external side, 
and its anterior marginal angle corresponds with the point of junction of 
the anterior extremity of the internal crescent. The true molars have the 
anterior horns of their crescents prominent, being sections of well-de- 
veloped vertical columns. In this they differ from those of the P. hetero- 
don, where these ridges are very weak. 
The malar process of the maxillary bone is robust and prominent, and 
begins to expand opposite the first true molar. It presents a tuberosity 
downwards. The infraorbital foramen issues above the front part of the 
fourth premolar. 
Measurements. M. 
Tylana reel chen de POMOTODOSLEPI OL v.yiy- breve sew «6 vine eG 
UPAR EV GTO), Jus tiik dai v4 90 diet 0 elena: vac OU 
Tiiimater anny anteroposterior .....+... eee nigeyS ah 6 OORT 
C ATANBVEIBO. ce ees ene Hine viuds even ACO Ie 
aie teieva: Pe i Ganteroposterlor. weveceieveneserens 0115 
CAPONS POLES) Vv celal vinrenlih-Chcinne aed . 008 
Ticholeptus beds, Deep river, Montana. J. C. Isaac. 
