319 
PAL.EOSYOPS LEIDY, AND ITS ALLIES. 
in this subfamily of having no median junction of the premaxillaries while in all 
other species these bones have a broad symphysial attachment. 
rile anterior border of the orbit is placed over the posterior third of the first 
molar. The floor of the orbit is rather elongated and the orbital process of the 
frontal is large. The zj^gomatic arch is very heavy, and its scpiamosal division 
presents a broad external fiice. The arch is strongly descending, and the zygo- 
matic portion has a very long horizontal connection with the malar. The malar 
arises abrujitly from the cheek, jiresenting outwardly a sharp external ridge, and 
inferiorly a broad horizontal surface. The malar insertion resembles very closely 
that of L. laticeps. The infraorbital foramen is large and not exposed. Most of the 
cranial portion of this skull is wanting, but enough remains of the auditory region 
to show that the postglenoid was short and heavy, being more like the form of this 
process in P. inegai'himis. 
Pal,t:osyoi>s- bore.vlis. 
This species has been described by Prof. Cope' from a portion of a right maxil- 
lary bone containing the last three true molars and also one premolar. Other por- 
tions of the skeleton have also been described by him i]i his “ Tertiary Vertebrata ”. 
As this is the earliest species of the genus in its geological horizon and as it is asso- 
ciated with such forms as Lambdotherium popoagicum, both from the Wind River 
Eocene of W3u)ming, we should expect to find some interesting primitive characters 
more closely connecting it with Lambdotherumi than with the higher .species of 
Palceosyops. In my opinion, however, such is not the case, and I find in the 
molars of P. borealis advanced dental characters which relate it much more closely 
to Palceosyops than to Lambdotherium. Perhaps this may indicate that Lanibdo- 
therium is not the direct ancestor of the Palseosyops line, and that we must look to 
an earlier geological period for the common ancestor of both Lambdotherium and 
Palceosyops. 
Dentition. — The last sujjerior premolar, the only one of this series pre- 
served, is smaller transversely than the first true molar. Its external face is straight 
and shows no median buttress. Its anterior lobe is provided with a slightly marked 
vertical fold. The paracone is larger than the metacone. Its internal lobe is 
large, low and blunt, and the tooth is provided with a Avell developed protoconnle. 
In Lambdotherium a large protoconnle is present upon the last superior premolar, 
and this conule is much larger than that of P. borealis. The absence of this conule 
from the premolar series of the higher genera of this subfamily is to be remarked ; so 
that this character in P. borealis must be considered a primitive one. The last 
superior premolar of P. borealis is provided with an incomplete basal cingulum, and 
its anterior and posterior cingula are very conspicuous. 
In the true molars we have much more highly differentiated teeth than in 
Lambdotherium, the external Y’s being more strongly expressed than in that genus. 
The external lobes of the molars have not those Cbnspicuous vertical folds between 
'American Xaturalist, 1880, page 746. 
