THE STRUCTURE AND RELATIONSHIPS OF ANCODUS. 
491 
while in the American species it is generally less than in the European. The 
longest-faced of the White River forms is A. americanus, in which the relative 
length of the muzzle is nearly the same as in A. velaums, the shortest of the Euro- 
pean species. The facial elongation is increased by a shifting of the orbits. In 
Protoreodon, Oreodon and Agriochoerus the anterior rim of the orbit is above the in- 
terval between “i and while in Ancodus, as also in Merycochosrus, it has re- 
treated so as to be above As regards the length of the face, Agriochcerus is 
intermediate between Oreodon and Ancodus, and it seems altogether probable that 
in this respect it has been conservative, and represents very nearly the common 
starting point whence the three lines diverged. As would naturally be expected, 
Protoreodon is decidedly nearer to this type than is Oreodon, and it is a suggestive 
fact that the anthracotherioids from the Titanotherium-beds, as yet but little known, 
have the facial proportions, length of diasteinata, etc., very much as in Agriochcerus. 
The mandible displays corresponding differences in the three diverging lines. 
The condyle and angle are much alike in all, but Ancodus is peculiar for the re- 
markable production of the angle below the level of the horizontal ramus, while the 
angle is more thickened and the condyle more elevated in Oreodon. The develop- 
ment of the coronoid process varies much within the limits ol the separate families, 
in the American species of Ancodus it is high and recurved, with deep sigmoid notch, 
while in the European species it is rather feebly differentiated, low and of triangular 
shape. In Oreodon it is intermediate between these two extremes, and in Protore- 
odon and Agriochoerus it resembles the shape found in the American species d An- 
codus. Doubtless in this respect also Agriochcerus and Protoreodon represent nearly 
the original condition. In all of these genera the masseteric fossa is ratlin small, 
and situated high up on the ascending ramus, and is in most of the species quite 
deeply impressed, least so in the European representatives of Ancodus. Ihe de- 
velunmonl of the horizontal ramus varies in accordance with the e on gat. on of the 
face in Oreodon it is short and deep, with abruptly trancated ohm and steeply 
inclined symphysis; in Arou’.r it is very long and quite shallow (though m th s 
latter respect there is much difference to be noted between the various sjKCiesh 
AgHocl2rt,s is intermediate between the two 
Butiposed Anihracotherium of the Titanothenmn-beds, as well 
^ ^ The three lines display very striking divergences in the character of the den 
1 • .1 of itiP sknll-structure, Agriochcerus, in some degree, com- 
tition, and as in t le case ■ Protoreodon also have an inter- 
bines the features of the other two. The teeth ot ^ 
mediate chameter between J '' 
different sense. I" „„„ has assumed the form and functions of 
upper canine is trihedral and 1 premolor. The premolars 
irs:^rerLiy,hutLm^^^^^^^^ 
^he's: » 
ingly like those of the existing brachyodont ruminant . 
64 JOURX. A. N. S. PHILA., VOL. IX. 
