1889.] The Edentata of North America. 659 
mammals, as M. Ameghino has discovered some extinct genera 
from the Parana, in which the teeth possess a narrow band of 
enamel. The connection is to the Bunotheria, which were 
probably the ancestors of the Edentata. 
The Megatheriidse are probably the ancestors of both the 
Bradypodidae and the Myrmecophagida;. The modification of the 
tarsus characteristic of the former is probably due to the assump- 
tion of the habit of suspension from limbs of trees by the ances- 
tors of the sloths. This is not only probable from the mechan- 
ics of the case, where support on the ground has been followed 
by suspension below a branch, but also by the analogy of the 
bats. In these animals, as Dr. H. Allen has pointed out, the 
similar habit of suspension has produced in the hind limb a sim- 
iliar modification of the forms of the astragalus and calcaneum. 
The Megatheriidae embrace a large variety of genera, all ex- 
tinct, and nearly all restricted to the Neotropical Realm, They 
embrace mostly species of large size, though there is much varia- 
tion in dimensions. They differ in the number of digits, and the 
extent to which progression was accomplished on the external 
edge or sole of the foot. They are also distinguished into 
Mylomorpha and Rodimorpha (Ameghino), the former having 
a homogeneous molar dentition, the latter having the anterior 
tooth in each jaw developed into a canine-like form and function. 
These types graduate into each other through the genera 
Mylodon and Lestodon, but not so completely as to destroy the 
diagnostic value of the character. The genera may be then dis- 
tinguished as follows : 
I. Mylomorpha. 
a Molar teeth \. 
Molars with two cross-crests ; Cce/odon Lund. 
aa Molar teeth |. 
Molars with cross-crests ; Ocnobates Cope.* 
Molars not ridged ; nasal bones connected 
with premaxillary spine ; Grypotherium Reinh. 
