1847. ] OWEN ON ENGLISH EOCENE MAMMALIA. Z1 
parated by a vacant tract from the series of alveoli of the two canines 
and six incisor teeth ; which series describes two-thirds of a circle at 
the slightly expanded anterior extremity of the jaw: an interspace of 
scarcely two lines extent separates the canine on each side from the 
incisors. The molar teeth progressively increase in size from the 
first to the sixth : the last four have the crown composed of two cres- 
centic or semicylindrical lobes corresponding with the type of those 
of the genera Rhinoceros, Hyrax, Macrauchenia and Paleotherium : 
the last (M 2), like the penultimate one, having only a small tubercle 
(¢) at its back part, in the place of the third lobe characteristic of the 
last molar of the true Palzeotheres. 
The first molar (Pl. III. figs. 3 & 4, D1) has a conical crown, convex 
externally, flat and slightly indented internally, with a basal ridge or 
cingulum, which, instead of completing the circle behind, bends up- 
wards to near the summit of the cone: this tooth is implanted by 
two diverging fangs. The crown of the second molar (2d. D 2) also 
consists chiefly of one conical lobe with two mdentations on its inner 
side ; the cingulum is interrupted at both the outer and inner sides 
of the base of the cone ; but its posterior part rises, or sends a strong 
ridge upwards to the mner part of the apex of the cone, and there is 
a depression both before and behind this ridge. This tooth is implanted 
by two fangs, as is each of the other grinders. The crown of 
the third tooth (4. D 3) assumes the general character of those of 
the Paleotherium, consisting of two semi-conical lobes, which from 
the attrition of their summits and the deep indentation of their inner 
sides assume the form of half-cylinders ; their contiguous angles are 
confluent and form the middle lobe (7) of the imner surface of the 
tooth; there is no ridge at the base of this surface. On the outer 
side of the crown a ridge extends from the base of the anterior lobe 
to its anterior upper angle ; anda second ridge curves from the outer 
part of the base of the hinder lobe upwards to its hinder summit ; 
a short ridge closes the base of the outer vertical cleft between the 
two lobes. The fourth molar (2d. D 4) shows, in addition to its supe- 
rior size, a minute worn tubercle (¢) behind the hinder angle or sum- 
mit of the hinder lobe o'; and the anterior and posterior oblique ridges 
are more decidedly distinct from the short middle external basal ridge. 
The fifth molar (M 1) differs from the fourth in the greater depth of 
the inner excavations or cavities of the lobes, which partly depends on 
its having been less worn : the hinder angle of the hinder lobe (0') has 
not been worn down to the level of the small tubercle (¢) which forms 
the summit of the posterior ridge ; which ridge, like the anterior one, 
is now nearly vertical. The sixth grinder (m 2) has only come into 
use at the fore part of the anterior lobe; the enamelled summit of 
the hind lobe is intact, and forms a semicircular ridge slightly mam- 
millated ; its anterior angle is below the level of the posterior one of 
the anterior lobe, from which it is separated by a tubercle (7) formed 
by the obtuse summit of the middle lobe of the inner surface of the 
crown. The hinder ridge expands at its summit into an obtuse 
tubercle (4), terminating about two lines below the summit of the 
hinder lobe. 
