AQ - PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 16, 
in an entire right ramus and in a nearly entire left ramus of the same 
lower jaw (Pl. IV. figs. 2 & 3). 
The first and second true molars (fig. 4, M 1 & 2) consist each of 
four semiconical high and sharp-poited lobes, in two transverse pairs, 
with the convex sides turned outwards. The imner sides of the outer 
lobes 0, o', are smooth and nearly flat ; the basal angles extend wards, 
embracing the base of the imner lobes 2, 7; and the ridge from the hind 
angle of the base of the hinder and outer lobe terminates by expanding 
into a small cusp behind the base of the hinder and inner lobe; from 
this cusp a sharp ridge extends not quite across the hind part of the base 
of the crown. The inner surface of the inner lobes is smuous, convex 
in the middle, concave before and behind this part: each angle of the 
base is produced into a small ear-like lobule or cusp: thus there are 
five basal cusps along the inner side of the base of the crown, besides 
the two lofty pointed conical lobes (M 1, 7 and 2). 
As the number of the restored annectent links increases in the Un- 
gulate series of Mammalia, the marks of distinction become less salient, 
and the necessity for more minute attention to them is entailed upon 
the describer. The anterior margin of the outer and anterior lobe 
is slightly raised and swollen at its termination upon the fore-part of 
the base of the mner lobe: below this margin the fore-part of the base 
of the crown is traversed by a thin but sharp ridge (PI. IV. fig.6). There 
is a mere rudiment of a tubercle at the outer entry of the great median 
transverse cleft dividing the two pairs of lobes. ‘The outer convexities 
(0, o') of the principal lobes are subangular. Each lower true molar 
is implanted by two long fangs. The distinction between the four-lobed 
lower molars of Dichodon and those of Dichobunes is shown by the 
fifth inner basal cusp (fig. 5, M 1) posterior to the one at the back 
part of the base of the second inner lobe, and in the anterior and pos- 
terior basal ridges. 
The premolars of Dichodon deviate still further from those of Dieho- 
bunes. I at first thought that the tooth (P 4) must be the last of 
the deciduous series, and that it indicated, as m the Anoplotherium 
and Ruminants, a third posterior division of the last molar tooth ; 
but on excavating the jaw beneath it (as shown at P 4, fig. 2), not the 
slightest trace of either the germ of a successor or of the cavity for 
its matrix appeared, and it was evident from the length of the fangs 
and the small depth of the jaw,—only half that of the same part in 
the young Paloplothere,—that the tooth im place was destmed to 
have no successor. This tooth agrees moreover in the antero-posterior 
extent of the crown and its three chief divisions with the last premolar 
above; the slightly-worn summits of which concurred, with the absence 
of any trace of a successor, in showing that it likewise could not have 
been in use during the period of the milk-dentition. 
The last premolar (fig. 4. P 4) in the lower jaw has six semiconical 
lobes in three transverse pairs, slightly decreasing im size as they ad- 
vance forwards, but repeatmg the characters of those of the true 
molars; the imner side of the base of each of the three inner lobes 
having the ear-like cusp on each side, and the posterior basal ridge 
terminating on the inner side in a smaller seventh cusp. There is a 
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