488 The American Naturalist. [June, 
Like Protypotherium, but all the inferior incisors with ex- 
panded crown, which is bilobate on the internal side; 
Patriarchus Amegh. 
All the genera and most of the species of this family have 
been derived from the Eocene beds of Patagonia. One species 
of Protypotherium has been found in the Oligocene of the 
same region, and another species of the same genus in the 
Miocene of Buenos Ayres. 
There are two species of Interatherium which were about 
the dimensions of hares and rabbits. The four species of Ico- 
chilus and the five of Protypotherium ranged from the size of 
our Lepus silvaticus up to that of a fisher weasel or a little 
larger. The single Patriarchus, P. paluridens Amegh., rather 
exceeded the latter animal. Its incisor teeth are peculiar in 
their expanded crowns, with a deep longitudinal groove on 
the internal side. 
The genera and species of the PROTOXODONTIDÆ are all from 
the Eocene beds of Patagonia, with one uncertain exception. 
The former differ as follows, according to Ameghino :— 
I. Molars with base more or less rooted, and with crown with 
unequal lobes. 
œ Superior incisors regularly diminishing outwards. 
Molars with imperfect roots and open base ; 
Adelpbothevitim Amegh. 
aa Second incisor largest and with open base; I. 3 rudi- 
mental or small. 
ß I. 1 present. 
Eight superior molars ; Acrotherium Amegh. 
Superior molars 7 ; first inferior premolar one-rooted ; . 
Adinotherium Amegh. 
Superior molars 7; Pm. } and 2 one-rooted ; 
Protoxodon Amegh. 
* 
221.1 wanting. 
I. 2 triangular in section; Phoberotherium Amegh. 
II. Inferior molors rooted and with opposite lateral grooves. 
Anterior column of molars smaller than posterior ; 
Calpodon Burm. 
