88 MOSTLY MAMMALS 
macrauchenia were certain contemporaneous ungulates from 
Patagonia, of which the largest did not exceed a tapir in 
size. With cheek-teeth so like those of the odd-toed 
ungulates from the Paris basin described by Cuvier as 
Palaeotherium, these Patagonian ungulates differed from 
the macrauchenia in having the dental series reduced in 
number and interrupted by gaps. Their most remarkable 
peculiarity is, however, to be found in the structure of 
their feet, which, in some forms at least, resembled those 
of the extinct three-toed horses, or hipparions, in which 
the middle toe is very large, while the two lateral ones 
are small and functionless. In one genus, moreover, the 
toes were reduced to a single large one on each foot, as 
in the modern horse. And the fact that there existed in 
South America a group of ungulates which exactly paralleled 
the horses in the evolution and structure of their feet is 
one of the most wonderful features in mammalian de- 
velopment. 
Among all the extinct mammals of the Argentine, none 
strike the beholder with more astonishment than those 
gigantic cousins of the modern armadillos of South America, 
collectively known as glyptodons, their name being derived 
from the peculiar sculpture with which the grinding surfaces 
of their cheek-teeth are ornamented. Both armadillos and 
glyptodons differ from the other members of the group to 
which they belong in having their bodies protected by a 
bony shell, or carapace, covering all but the under-parts, 
the top of the head being covered by a similar bony shield, 
while the tail is encased by a series of bony rings, or in 
rings at the base and a long tube at the tip. Whereas, 
however, the armadillos (exclusive of the aberrant little 
pichiciago) have a larger or smaller portion of the middle 
region of the carapace formed of movable transverse bands 
