FROM CENTRAL AND SOUTH AMERICA. 
571 
I have given, in Plate LXII. fig. 13, a view of the grinding-surface of the second true 
molar of the Macrauchenia in the British Museum, of the natural size ; the reduced 
figure in the ‘ Odontography ’ may have suggested to Dr. Lund the idea of its being the 
same animal as his Equus principalis (see above, p. 561). The degree of resemblance 
is, however, not greater than both figs. 13 & 14, Plate LXII. offer to the corresponding 
teeth of Palceotherium * and Paloplotherium f , at a similar degree of abrasion. 
In the upper molars of Macrauchenia we find an interesting transitional modification 
between the generic pattern of the grinding-surface of the American extinct Equines 
[E. neogceus, E. principalis, E. arcidens) and that in Nesodon. The outer surface of the 
crown is impressed by two wide and moderately deep longitudinal channels, more 
angular as in Palceotherium than rounded as in Equus ; a pair of depressions, answering 
to those marked h and i in Equus, appear to be shallower, are sooner blended together 
and obliterated. Three enamel-folds penetrate the inner side of the tooth, answering 
to those marked r, e, g in Equus, the middle one, e, also extending the furthest ; but 
all these are shallower, save at their blind terminations, which consequently remain in 
the partially abraded crown as distinct islands of enamel including cement, and thus 
produce a characteristic resemblance to the dental pattern in Nesodon. The upper 
molars of Nesodon$ differ from those of Macrauchenia in the crown being longer and 
transversely narrower ; the outer longitudinal ridge is near the anterior border, not at 
the middle of that border ; the inner border is penetrated by two enamel-folds, of which 
the anterior is bifurcate or three-branched ; and the extremities of the folds, when 
insulated by wear, are nearer the outer border of the tooth. 
The lower molars of Nesodon § differ from those of Macrauchenia in the crowns being 
longer and transversely narrower ; the outer longitudinal groove is nearer the anterior 
border ; the anterior inner fold penetrates a plane behind the outer groove, advancing 
obliquely forward to meet it. Besides the posterior fold there is an island, which, if 
originally a part of that fold, is, in the worn tooth figured, separated from it. The 
canines are small and subequal to the other teeth in both genera, but are implanted 
by a divided fang in Macrauchenia. The lower incisors have an imbricate or slightly 
overlapping arrangement in Nesodon. 
The upper molars of Macrauchenia, in the proportion of their fore-and-aft to their 
transverse diameters, are intermediate between Equus and Nesodon, but nearer the 
former. The high or backward position of the external nostrils in Macrauchenia is 
significant evidence of its affinity to Toxodon ; and it may be that Nesodon shows more 
of this character than the fragment of skull on which the genus was founded led me to 
discern [|. 
Howsoever this may prove to be, the additional evidence which has been obtained 
* Ossemens Eossiles, 4to, t. iii. pi. i. fig. 3. 
t Quarterly Journal of Geological Society, vol. iv. pi. iv. fig. 3. 
X Philosophical Transactions (1853), PI. XVII. fig. 10. 
|| Philosophical Transactions (1853), PL XV. figs. 1 & 2. 
§ Ibid. fig. 14. 
