452 Reviews Annals of Museum of Buenos Ayres. 
the quadruped in question, have only three toes on the hind-foot. 
Again, in referring the Macrauchenia to the tridactyle family of — 
Pachyderms, we find towards the close of our analysis, and by a 
detailed comparison of individual bones, that the Macrauchenia has 
the closest affinity to the Paleothertum.* But the degree of con- 
fluence of the radius with the ulna, and of the tibia with the fibula, 
indicated a closer resemblance than in Palgotherium to the ruminant 
state of those bones ; and, guided by such indications, it seems that 
although certain fossil neck-vertebre closely repeated, on a large 
scale, characters which Owen had discovered to be peculiar to the 
small South American Camelide, he did not hesitate to associate 
those fossil vertebrae with his new three-toed pachyderm. It is to 
be remembered that at this period (1837) the reform of the Cuvierian: 
distribution of hoofed mammals had not been established; they were 
still either.‘ Pachyderms’ or ‘ Ruminants.’ In pointing out how 
the new three-toed Pachyderm showed alliance to the Ruminant, 
Owen recalls ‘in how many particulars the Camelide, without 
losing the essential characters of Ruminantia, manifested a tendency 
to the Pachydermatous type, and the evidence which the lost 
genera Macrauchenia and Anoplotherium bear to a reciprocal transi- 
tion from the Pachyderms to the Ruminants.t 
The position and essential affinity of Macrauchenia are, however, 
definitely stated, and its remoter alliances as a three-toed Pachyderm 
are indicated. In 1840, Owen abandoned the Cuvierian classification 
of Ungulata, and in his ‘ Odontography’ divides them (p. 523) into 
‘isodactyle,’ ‘anisodactyle, and ‘proboscidian’ groups. He had 
found in the British Museum a fossil lower jaw with the molar 
series, from South America; and, firm in his convictions of the 
essential affinity of Macrauchenia to Paleotherium, he does not hesi- 
tate to refer the specimen to his new genus. In Plate 135, fig. 7, 
the teeth are figured as ‘ molars of the lower jaw of the Macrauche- 
nia patachonicha. (‘ Odontography,’ 4to., Description of the Plates, 
p- 33.) Inthe description of this Spe oie § 219, Macrauchenia, 
comes between ‘ Palgotherium’ and ‘ Tapirus’ in the chapter 
‘ Anisodactyle Pachyderms’ (p. 572). 
In 1846, Owen made known a new pattern of grinding surface of 
upper molar teeth, combining the main characters of that in Rhz- 
noceros and Paleotherium with an unusual number of detached 
rings or islands of enamel. This pattern was exhibited by certain 
fossil teeth from South America, and on them was based the genus | 
Nesodon. (‘Reports of British Association,’ ‘ Sections,’ 1846, p. 66.) 
In 1847, in the ‘Classification of Ungulata’ (Quart. Journ. Geol. 
Soc., vol. iv.), Owen, substituting the more classical terms Artio- 
dactyla and Perissodactyla for ahose used in the ‘ Odontography,’ 
places Macrauchenia in the series Perissodactyla, with the following 
association: ‘ Tapirus, Macrauchenia, Nesodon’ (p. 139). In the 
Memoir on the latter genus (‘ Phil. Transactions,’ 1853), its affinity 
to Macrauchenia is more fully elucidated, and it is remarked that 
* Zoology of the Voyage of the Beagle—Fossil Mammalia. 4to., p. 54. 
Ibid., p. 55. 
