1884, | 571 [Cope 
GENERAL CONCLUSIONS. 
From what is now known of the history of the Oreodontide, the following 
conclusions may be drawn, These are especially instructive as far as 
they go, since they involve the causes of the rise, great development, de- 
cadence and extinction of one of the best-marked types of Mammalia the 
world has seen. The history of this type involves more or less the history 
of the life of the North American continent during the Miocene epoch of 
Tertiary time. It moreover involves the laws which regulate the vital 
success of all types of life, and which express the causes of multiplication, 
of energy, of weakness, and of sterility. 
Two lines of the family, the Oreodontine and the Agriocherine, come to 
light simultaneously in geological time, the White River epoch, or the 
Oligocene. The latter is a higher type than the former in its more com- 
plex fourth premolars, while it is inferior in the non-closure of the orbits 
posteriorly. It may then be regarded as a parallel line. It has but two 
generic types, while the Oreodontine present us with seven. So far as yet 
known, the Agriocherinse did not continue as long as the Oreodontine, 
as will be shown in tabular form below. 
In the progressive.modifications of the Oreodontini series, the first step 
was the inflation of the otic bulla (genus Eucrotaphus). This was suc- 
ceeded by the codssification of the premaxillary bones (genus Mery- 
cochorus). These changes were accompanied by a regular increase in 
dimensions. The species of Merycochcerus are all of the largest size, and 
there are no small ones. The smallest species of Eucrotaphus are equal to 
the largest ones of Oreodon. The fourth genus Merychyus, while it loses 
none of the points already gained, shows a deficiency in its facial walls 
where vacuities appear, There is the greatest range of size here : with one 
species (Mf. major), as large as any of the Merycocheri, we have another 
as large as the usual Eucrotaphi (JZ eygomaticus), and several one degree 
smaller, or as large as the largest Oreodons. In the next genus the facial 
vacuities have attained to an enormous size. The premolar teeth become 
smaller, and the weakness of the narrow symphysis of the lower jaw is 
made up for by its codéssification. The size is reduced from equal to the 
smallest Merychyi, to that of the smallest Oreodons (genus Leptau- 
chenia). In the next stage (genus Cyclopidius) the superior incisors dis- 
appear. Finally, the lower jaw is so reduced in front that it loses both 
incisors and premolars, in spite of its symphyseal codssification (genus 
Pithecistes), 
The species may be thus arranged in accordance with their distribution 
in time, 
White River Hpoch. Oreodon gracilis; O. affinis; O. culbertsoni. Eu- 
crotaphus jacksoni; E, major. Agriochcwrus antiquus; A. major; A. 
latifrons. 
John Day Epoch. ucrotaphus jacksoni; E. major. Merycochwrus 
superbus; M. leidyi; M. chelydra, sp. nov. ; M. macrostegus, sp. nov 
