522 Correspondence. 
the upper tusk or canine was actually divided, or bifid. 'The mam- 
malia are not wanting in examples of canines so implanted. Ac- 
cording to this view, the hinder division of the empty socket, 
behind the outermost incisor, did not contain a distinct tooth from 
the canine, but only the hinder division of the base is a canine. 
In this case the first premolar in place is p 1; the fourth, which 
has assumed the complex character, shape, and almost size of the 
true molars, is p 4. The number of true molars then enters into 
the rule, viz., three on each side, as in the lower jaw. I feel very 
confident that when the permanent upper canine of Macrauchenia 
be found, it will confirm the interpretation above given of the dental 
formula of the upper jaw. In the lower jaw of the Macrauchenia 
(pl. 1, figs. 8, 4, 5, 6), all the incisors are wanting, the fang of a 
simple-fanged small canine is near the outer incisor; a very short 
diastema divides the canine from the first two-rooted premolar, 
which, with the second, is wanting: p 8, p 4, and m 1, 2, and 3 
are in place. The lower jaw differed from the upper jaw, in its 
dentition, not in the number of teeth, but by the smaller size and 
simpler implantation of the canine, as well as by the difference of 
size and modified character of the grinding surface of the molar 
teeth, exemplified in my ‘Odontography,’ and in Burmeister’s edition 
of poor Bravard’s excellent drawings of the skull of Macrauchenia. 
Reasoning on the basis of the foregoing interpretation of the 
dental system, I conclude that Macrauchenia manifested the es- 
sential Perissodactyle position to which it was originally referred, 
by the extension of the character of the true molars into the pre- 
molar series; but, as in the Tapiroid genus, in which Cuvier first 
pointed out this deviation from the dental character of the type- 
Perissodactyles, ‘the premolars offer some differences from the true 
molars.’* 
In Lophiodon, however, as in Pliolophus, the last premolar p 4, 
differs from the first true molar m1 in the reduction of the two 
inner lobes of the crown to one large conical lobe: the penultimate 
premolar p 3 resembles the foregoing, but is of smaller size; the 
antecedent premolar p 2 is suddenly reduced in size, and the inner 
lobe is almost obsolete. Lophiodon has no pl. The three molar 
teeth of Lophiodon JIsselensis (Cuv.) figured in tom. cit. pl. vi., fig. 2, 
are m 3 (‘n’), p 4 (‘0’) and p 3 (‘p’): they well exhibit that cha- 
racter. - In like manner Paloplotherium differs from Paleotherium, 
in the almost suppression of the hinder of the inner pair of lobes 
in p 4. In Macrauchenia the difference between m 1 and p 4 is 
rather one of size than of structure, but the simplification of the 
crown is well marked in p 3, and is carried out in p. 2 and p. 1. 
Paleotherium resembles Equus and Rhinoceros in the conservation 
of the type of structure of the true molars in all the premolars save 
the first, which in Lguus is represented only in the deciduous series; 
* <D’un genre d’animaux voisins des tapirs,—mais dont les molaires antérieures 
et postérieures effroient quelques differences: genre auquel je donne le nom de 
Lophiodon. Op. Foss., 4to., 1822, tom. 11., p. 176. 
