1884.] 559 (Cope. 
Pithecistes heterodon Cope. 
Oyclopidius heterodon Cope, Proceeds, American Philos. Society, 1877, 
99 
p. 22. 
In this species the fourth premolar has the same form as in P. decedens, 
but the first true molar differs much in the more prismatic shape, and the 
absence of the external vertical ribs. It is quite possible that it does not 
belong to this genus. 
Ticholeptus beds of Deep river, Montana. J. C. Isaac. 
AGRIOCHGERUS Leidy. 
Proceedings Academy, Philadelphia, 1850, p. 121. Extinct Mammals 
Dakota and Nebraska, 1869, p, 181 (as family Agriochwrida). 
Orbit not closed behind. Fourth superior premolar with two external 
Vs. Fourth inferior premolar like true molars. Otic bulla inflated. Pre 
maxillary bones distinct; no vacuities in the facial bones. 
This genus commences cotemporaneously with the genus Oreodon, and 
persists longer, viz. ; to the close of the John Day epoch. It represents : 
distinct line of succession from that which we have been considering, and 
one which contains but two known terms. Next to Agriochcerus comes, in 
this line, the genus Coloreodon Cope, which outlasted its predecessor so far 
as is yet known. It commenced with it in the John Day epoch, and con- 
tinuing into the North Fork beds, which are of later age, did not ap- 
pear later. This series Leidy regarded as a family distinct from the Oreo- 
dontide. For the present I prefer the view of Gill, that it constitutes a 
subfamily, the Agriocherine. 
This genus presents us with one of the very few cases in the suborder 
Artiodactyla, ia which the last premolar approaches (above) or accom- 
plishes (below) identity of structure with the true molars. This degree of 
complication was attained at the same period by both the equine and 
rhinocerontice lines of Perissodactyla, and all existing members of that 
order exhibit it. In the Agriocheride it made a beginning, but soon dis- 
appeared from the earth, and no Artiodactyle has developed such perma- 
nent premolars successfully since. 
In the characters of the skull this genus is less robust than the Oreodon- 
tide ; but the general skeleton remains unknown. 
Five species have been described which are referable to this genus, and 
two others are now added. One of the former is without premaxillary or su- 
perior incisor teeth, and I therefore regarded it as representing a distinct 
genus under the name of Merycopater. It, however, appears that no speci- 
mens exist in our museums which exhibit this part of the skull in other 
species of the genus, so it is absolutely uncertain whether Agriochorus 
possesses those teeth or not. The species may then be distinguished as 
follows : 
[. Otic bulle compressed, base anteroposteriorly ovoid. 
4% Foramen infraorbitale above junction of P-m. iii and iv. 
PROG. AMER. PHILOS. 800. xxt. 116. 88. PRINTED JUNE 24, 1884. 
