1847.] OWEN ON EXTINCT ANTHRACOTHERIOID QUADRUPEDS. 117 
inner side, with the margins blunt and subcrenate: along the middle 
of the subconcave side runs an irregular ridged longitudinal promi- 
nence, with a channel or groove on each side, bounded outwardly by 
the margins of the crown: these margins incline to each other at 
their origin, but do not meet at the base of the mner surface of the 
tooth. The convex side of the crown (fig. 20) is indented by a lon- 
gitudinal groove near one of the margins; where this groove begins 
the enamel does not pass so far upon the fang, as m the rest of the 
basal circumference of the crown. This tooth, therefore, with the 
same general character as the Anthracotherian incisors above-cited, 
differs from them in the much less breadth of the longitudinal rising 
along the middle of the subconcave surface of the crown, and in the 
absence of the ridge continued across the base of that surface. 
A second (upper incisive’) tooth (figs. 18, 19) presents little more 
than the crown, which is triangular or heart-shaped, and more pointed 
than the former; convex in front, concave behind; with the longi- 
tudinal rising between two lateral channels on the concave side, and 
the submarginal longitudinal groove on the convex side, where the 
enamelled crown is shortest. 
A third specimen (figs. 16, 17) consists of the crown only of a 
tooth similar to, but rather smaller than, the second, with the margins 
more unequal: the median ridge on the inner side stronger and nar- 
rower ; the sublateral groove on the outer side shallower. 
The position of this groove proves that all the three teeth are from 
the same side of the jaw; their general correspondence in form and 
character indicates that they are from the same animal ; their single 
root shows that they are not premolars, their number that they are 
not canines: I conclude, therefore, that they are upper incisors, and 
that they are probably from the same premaxillary bone. The ena- 
mel has the same partly wrinkled, partly polished surface in these 
teeth, as in all the others: both the teeth and the bones are densely 
impregnated with iron, and present a deep black colour, which re- 
sembles polished jet on the enamelled parts of the teeth. 
The tooth (figs. 13, 14, 15), in the general shape of the crown and 
the single, long, curved fang, so far resembles the preceding teeth, 
that it might pass for an incisor: but the obliquity of the basal line 
of the enamel being in the opposite direction shows it to be from the 
opposite side of the jaw: it is not, however, the precise counterpart of 
any of the three incisors which I have supposed to belong to the same 
animal: there is only one deep excavation at the concave side near 
the margin of the crown, the rest of that surface being moderately 
concave and somewhat worn: the convex side of the tooth shows a 
longitudinal ridge near the margin where the enamel is shallowest. 
That margin is a good deal worn by working against an opposite 
tooth. The fang is 0°035 in length, rounded, curved, and tapering 
to an obtuse closed point. On showing these teeth to Dr. Mantell, 
he immediately recognized their close general resemblance with those 
of his Iguanodon. ‘There is no known existmg mammal whose in- 
cisors approach more closely to those remarkable ones of the Hyopo- 
tamus than the Hog. In the upper jaw of the latter quadruped the 
