1847.] OWEN ON ENGLISH EOCENE MAMMALIA. 39 
developed at the expense of the anterior and internal lobe (7, M 1) 
which has disappeared: the crown of the tooth is thereby extended 
from behind forwards and diminished in breadth: it presents also a 
trilobed character externally, but has a fourth lobe, %, at the inner side 
of the posterior and external one, answering to the hinder and inner 
lobe 7 of the true molars. The base of the outer side of the hinder 
and outer lobe (0') has its two tubercles-like those of the true molars, 
and its inner convex base is similarly girt by the outwardly prolonged 
angles of the base of the mner-lobe 7% From the mner side of the 
base of this lobe a ridge is continued forwards along the inner sides 
of the middle (0) and anterior (a) lobes. This tooth is implanted by 
one anterior and two posterior long fangs: there was no cavity of re- 
serve, or germ of a successor, in the substance of the jaw above it. 
The upper penultimate premolar (P 3) has also a long and narrow 
crown, three-lobed externally, but with the fourth posterior and inner 
lobe (2) reduced to a simple cusp: a ridge is continued from the hind 
part of its base to the hinder angle of that of the lobe (0') external to 
it, and a second ridge extends from the fore-part of its base forwards to 
the anterior lobe (a). The middle of the three outer lobes (0) is the 
largest ; they are all conical and pomted: there is a rudiment of the 
cusp answering to e in the true molars; the others are suppressed. 
This tooth is implanted by two long and divergent fangs. 
The premolars corresponding to the first and second below have 
not been obtained ; but a single-fanged tooth (fig. 2, C) with a simple 
trenchant crown appears to be the canine of this species, and it will be 
shown to belong to the upper jaw. The antero-posterior diameter of the 
crown of this tooth, C, is more than double its vertical extent ; its chief 
summit is followed by a lower rising of a trenchant edge: the fang is 
grooved longitudinally on the outer side, indicating it to consist of 
two connate fangs, one for each division or rising of the crown. 
The left premaxillary bone supports three incisors; their crowns, 
like the canine, are low but long, with a slight obtuse point near their 
fore-part, trenchant behind ; convex outwardly, concave and with a 
basal ridge on the inside; the three teeth are set close together, the 
second slightly overlapping the third. 
Thus of the dentition of the upper jaw of Dichodon we have the 
three true molars and last premolar zm situ with a portion of the 
upper jaw, the penultimate premolar and the canine detached, and 
the three incisors with the premaxillary bone. The true molars mani- 
fest the type of crown most allied to that of the Merycopotamus, 
Anthracotherium, and other genera closely approximating to the Ru- 
minant type ; while the premolars have peculiarities of form and struc- 
ture quite different from those in any known recent or extinct Her- 
bivorous Mammal. In Merycopotamus the canines and incisors closely 
accord with the hippopotamic type of those teeth: in Dichodon they 
offer a nearer resemblance to the anoplotherian type. 
The dentition of the lower jaw corresponds as closely with that of 
the upper jaw as it does in Merycopotamus or Dichobunes, and. the 
true molar teeth present a strong resemblance to those of the latter 
Anoplotherioid subgenus. The inferior teeth are beautifully displayed 
