38 PROCEEDINGS OF THE GEOLOGICAL SocIETy. [June 16, 
less deeply indented than in Merycopotamus, but show a trace of a 
longitudinal rismg at their middle part. The imner sides of both 
outer and inner lobes (fig. 5. 7, 7) are strongly convex, and more 
angular‘than in Merycopotamus. Attrition of the summits of these 
semiconical lobes would, however, produce the same double crescentic 
islands of enamel which characterize the upper molars of Merycopo- 
tamus and Dichobunes, and were once supposed to be a peculiar cha- 
racteristic of the Ruminantia*. 
In the young animal under consideration the lobes of all the molars 
terminate in sharp enamelled pomts; those of the first true molar 
(m 1) being slightly abraded at their summits and anterior angles. 
The upper true molars differ from those of Merycopotamus in the 
absence of the “ strong rugged ridge”’ (fig. 7. 7) “‘along the mner side 
of the base of the crownt,’’ and in the presence of the series of five 
small but sharp accessory cusps (a, 4, ¢, d, e, M 2, fig. 3, PI.IV.) along 
the outer side of the base: one of these cusps (a) terminates exter- 
nally the sharp ridge continued from the anterior angle of the base 
of the inner and interior Icbe (¢) along the anterior side of the base 
of the crown: the other four cusps are placed at the angles of the 
bases of the outer sides of the two external lobes, and answer to the 
corresponding angles of the outer lobes in Merycopotamus, which 
angles are, as it were, pinched up and pulled outwards in that genus. 
A sharp ridge is continued from the posterior angle of the base of 
the posterior and inner lobe, along the posterior part of the base of 
the crown, to the corresponding angle of the posterior and external 
lobe ; but there is no ridge beneath this, as in Merycopotamus. The 
contiguous angles of the bases of the two imner lobes (2, 7, M 2, fig. 3) 
are prolonged outwards far into the interspace between the two outer 
lobes. A small tubercle (p) is situated at the ner entry to the 
fissure between the two inner lobes: a ridge penetrates this fissure in 
Merycopotamus. 
The three upper true molars progressively increase in size from the 
first (M 1) to the last (M 3) in Dichodon; they are equal-sized in 
Merycopotamus. All the lobes and ridges are remarkably sharp, and 
the fissures are deep and neatly defined in the molars of Dichodon ; and 
the enamel is smooth, not rugous as in Merycopotamus. Each true 
molar is implanted by four fangs. The first true molar (M 1) has its 
outer side relatively longer than the others, by reason of the larger 
size of the anterior basal cusp. The characteristic modification of the 
last premolar (P 4, fig. 3) may be understood by supposing the ho- 
mologue of the anterior and external basal cusp (@) to have been 
* “ Order RUMINANTIA :— ; 
_ The molars, almost always six in number on each side of both jaws, have their 
crowns marked by two double crescents, the convexity of which is turned inwards 
in the upper jaw and outwards in the lower jaw.”’ (Régne Animal, ed. 1829, vol. i. 
p. 254.) And again, defining the supposed peculiarities of the Ruminantia, ‘“ Les 
trois arriére-molaires supérieures des ruminans semblent étre des inférieures re- 
tournées ; elles sont de méme formées de deux demi-cylindres, présentant chacun 
un double croissant, mais dont la convexité regarde en dedans.” (Cuvier, Ossemens 
Fossiles, t.iv. p. 7.) 
+ Odontography, 4to, p. 566. 
