414 UNGULATA 
trochanter of the femur was.aborted. These huge animals— 
inferior in size only to the Elephant—appear to have been abundant 
in the United States during the Miocene period. 
Family MACRAUCHENIIDA. 
This extinct South American family is best known by the genus 
Afacrauchenia, as represented by Jf. patachonica and AL. boliviensis, 
which are apparently from Pleistocene formations. 'They are very 
singular and specialised forms, quite out of the line of descent of 
any of the existing Perissodactyles, and the steps by which they 
are connected with the rest of the group have not yet been 
discovered. Of the larger species, Jf patachonica, the skeleton is 
completely known. It had the full number of forty-four teeth, 
forming an almost uninterrupted series. The cervical vertebrae 
resemble those of the Camels in the position of the vertebrarterial 
canal, but the ends of the centra are flat, and not opisthoccelous as 
in the allied forms. In some of the limb characters it resembles 
the Hquide, but in the articulation of the fibula with the calcaneum 
it agrees with the Artiodactyles. The structure of the feet is, 
however, distinctly Perissodactylate, there being three toes on each. 
The teeth approximate to a Rhinocerotine structure ; and the incisors 
have an infolding of the enamel of their crowns, as in those of the 
Horses. The nares open on the top of the skull, and it is probable 
that the muzzle was produced into a short proboscis. Several 
other South American forms have been referred to this family, 
some of which have received distinct generic names, but further 
evidence is required before many of them can be accepted. Pos- 
sibly Homalodontotherium should be placed here. 
Family PROTEROTHERIID. 
Proterotherium.—Here may be noticed certain very remarkable 
Perissodactyles from the South American Tertiaries, for which the 
name Proterotherium has been proposed. The cheek-teeth are so 
like those of Anchitherium that they have been described under 
that name. The upper jaw has one pair of canine-like incisors and 
no canines, while the lower jaw carries two pairs of incisors. In 
the skull the orbits were completely closed, as in the Horses. The 
feet were tridactyle, like those of Hipparion, but the tarsus was 
constructed on an Artiodactyle type. 
SUBUNGULATA. 
By far the greater number of the Subungulata are extinct, and 
of many of those whose former existence has been revealed, chiefly 
by the labours of the American paleontologists, our knowledge is 
at present necessarily imperfect, though daily extending. It will 
