826 SINOIDIUES, JOUR SIMGTOVEIN TES 
Eutheria: the Cetacea, Sirenia, Ungulata, Tillodontia (?) Rodentia, 
Carnivora, Insectivora, Chiroptera, Edentata and Primates. 
Edentata.— These are the lowest of the Eutheria in the scale 
of development. The group is characterized by the imperfect 
development of the dentition; the teeth are few in number, and 
the enamel is lacking from the surface in the more recent forms. 
That they are degenerate forms is shown by the fact that the 
earlier order had perfectly formed teeth; many of the steps in 
process of degeneration have been traced. Three suborders are 
recognized : Nomarthra, Xenarthra, and Ganodonta. The first of 
these is of little importance from a paleontological standpoint ; 
itis composed of forms confined to the tropical parts of Asia and 
Africa. It is separated from the Xenarthra by characters of the 
vertebre. 
The Xenarthra is divided into five suborders, the Zardigrada, 
Dasypoda, Gravigrada, Glyptodontia, and Ganodonta. The first two 
are confined to the recent and the later Tertiary of South and 
Central America. 
Gravigrada.— These forms, now extinct, were of gigantic 
size 7 the body was large and clumsy witha powerful tail that, 
perhaps, aided the animal in assuming the upright position; in 
the later forms, perhaps more than in the earlier, the animals 
walked with the side of the foot presented to the ground; the 
teeth were few and confined to the posterior part of the jaws; 
they were without any enamel upon the surface. The animals 
were in fact large ground sloths; they probably obtained their 
nourishment by uprooting trees and shrubs and feeding upon 
the leaves and smaller branches. 
Megatherium was the largest of the forms, reaching a length 
of 18 to 20 feet, and a height of about 8 feet. The teeth placed 
close together at the posterior part of the jaw, exhibit cross 
ridges from the presence of slightly harder dentine. The animal 
is known from all parts of South America, and as far north as 
Georgia, South Carolina, and Texas. 
Megalonyx.—This form is the representative of a separate 
family from the preceding ; the most anterior of the molar teeth 
