1847. | OWEN ON ENGLISH EOCENE MAMMALIA. 27 
chitherium, V. Meyer). The true molars of the lower jaw of the 
Paloplotherium also differ in the absence of the cingulum or basal 
ridge, and in the presence of the cusp terminating the posterior ob- 
lique ridge ; at least neither Cuvier nor M. V. Meyer allude to this 
character in the molars of the Orleans or Madrid Palzeotherioid ; 
although something like it is indicated in the lower molars of fig. 17. 
pl. 67. ‘Ossemens Fossiles,’ tom. m.* But the most decisive 
distinction in the dentition of the lower jaw of the Hordle Paloplo- 
therium is the unilobate structure of the second premolar (p 3), and 
its smaller size as compared with the first (p 2); a difference which 
will be at once appreciated by comparing the figure im Pl. IIT. fig. 4, 
P 2, with that given by Cuvier in figs. 3 and 13 6. of the plate 67, 
above-cited. This difference would have decided the distinction of 
the species, if even subsequent discoveries had not proved the generic 
difference of Paloplotherium, by showing that the Paleotherium 
Aurelianense resembled the typical Palzeotheres in the number of its 
inferior grinding teeth. 
Another known Paleotherioid pachyderm with which the Hordle 
Species might be confounded, is that to which the left ramus of the 
fossil lower jaw from the tertiary deposits at Buenos Ayres, now in 
the British Museum, belongs, and which I have provisionally referred 
to the genus Macrauchenia. ‘This portion of jaw contains six molar 
teeth, three true and three false; and the last molar differs, like that 
in the Paloplotherium, from the typical Paleeotheres by the absence 
of the third lobe: but it likewise differs from the species under con- 
sideration in the absence of the posterior tubercle, which is equally 
wanting in the other true molars of the Macrauchenia: the pre- 
molar answering to P 2, in figs. 2 and 4. Pl. III., is more compressed 
and more extended from before backwards, as is also P 3+, which 
shows a fold of enamel along its inner side which would not be present 
in the corresponding tooth of the Paloplotherium. Nevertheless this 
genus resembles the Macrauchenia in the more simple form of P 2 
and P 3; in which we may discern an approximation to the Ano- 
plotherian type, as in the number of the premolars we discern a cha- 
racter of the Equine and Ruminant dental formule. In the figure 
of the lower jaw of the Macrauchenia in my ‘ Odontography’ (pl. 135. 
fig. 7), the outline of. p 1 ‘is hypothetically added to the series” 
(7b. p. 603): but this tooth may have been normally absent, as it is 
in the Paloplotherium, the Horse, and in existing Ruminantst. The 
only known species of Macrauchenia much surpasses the Paloplo- 
therium annectens in size. 
* M. de Blainville is equally silent in respect to this character in his recent 
work on the Paleotheria: but I observed it in the specimens of the Pal. Aure- 
lianense from Sansans. 
+ See Odontography, pl. 135. fig. 7. 
{ In an extinct antelope (Dorcatherium, Kaup) the first milk-molar was suc- 
ceeded by p 1, and the number of premolars was four. 
