1 
: 
1847.] OWEN ON EXTINCT ANTHRACOTHERIOID QUADRUPEDS. 115 
joint obliterated ; its upper concavity deepens as it recedes, but with- 
out contracting transversely, as in the Hog. The depth of the sym- 
physis is more suddenly gained than in the Hog or Peccary. Viewed 
from below (fig. 4) there is a very slight expansion at the alveoli of 
the canines (c); but this is not attended with any widening of the 
upper channel of the symphysis. The posterior third of the under 
surface of the symphysis is excavated by two wide and shallow chan- 
nels, one on each side of a slight median ridge. 
The upper border of the diastema, before and behind the first 
insulated premolar, p 1, fig. 3, is flat and rough, as if the edge had 
been rubbed down on a plane surface; but I believe it to be a natural 
feature of the fossil. The posterior limit of the symphysis is just 
behind the socket of the first premolar. The outer buttress of the 
anterior base of the coronoid process begins to swell out below the 
hind lobe of the last molar tooth. The first or anterior outlet of the 
dental canal is a little im advance of the socket of the second pre- 
molar: the second outlet is beneath the third premolar. The outer 
wall of the jaw does not swell out so much as in Cheropotamus Cu- 
vieri, and the inner surface is flatter than in that species. 
According to the value of the characters which determine and 
distinguish genera and subgenera in the present accepted systems 
of Mammalogy, I estimate those differences which have just been 
pointed out in the upper and lower true molars, and in the propor- 
tions and relative positions of the lower premolars and canines of the 
fossils figured in Pl. VII. figs. 1-5, and in Pl. VIII. figs. 1-5, as of 
themselves equivalent to establish at least the subgeneric distinction 
of the pachyderm to which they belonged from the Anthracotherium 
of Cuvier. 
With those fossils, however, Lady Hastings was fortunate enough 
to discover, in the same stratum and locality, a series of upper molar 
and premolar teeth of a smaller species (PI. VII. figs. 6, 7, 8), show- 
ing the same subgeneric modifications of the true molars, together 
with a well-marked generic deviation from Anthracotherium proper, 
in the greater complexity and different form of the posterior upper 
remolars. 
Of these the fourth (p 4, figs. 6 & 7) resembles the true molars, 
except in its rather smaller size ; the anterior basal ridge developes 
a small cusp at the antero-external angle of the tooth. The entering 
angle between the two exterior lobes is more acute. The posterior 
basal ridge is continuous with the internal one, rounding the base of 
the postero-internal lobe. The tooth is implanted by two external 
fangs and two internal ones partially connate. The third premolar 
(p 3) has a subtriangular crown, elongated in the axis of the jaw, 
with four lobes ; two, o! and %, in the same transverse line forming 
the base, and the fourth (a), at the fore-part of the crown, forming 
the rounded apex. The third intermediate lobe (0) consists of two 
confluent lobes, indicated by a notch on its outer side. Viewed ex- 
ternally, therefore, this tooth appears trilobate, as at p 3, fig. 7. 
Here, therefore, a well-marked and important generic distinction 
of Hyopotamus is afforded, and we are taught to appreciate the sig- 
