448 The American Naturalist. [May, 
distinguishes the North American species. However, the 
South American species (Periptychus argentinus Amegh.) is — 
easily distinguished by its size—almost a third smaller—an 
by the insertion of the molar teeth which are closer together 
forming a continuous series. This specimen was found in th 
Lower Oligocene or the Upper Eocene in the neighborhood of 
Parana. 
While I am speaking of the fossils of that region, I must — 
add that the doubts which I had concerning the real nature — 
of Ribodon are now set at rest. The new material at han 
one of the family of Halitheriide. 
TG 
Argentine Republic, and particularly to the assertion of Pro- 
fessor Steinmann, who maintains that the beds I have desig- — 
nated Miocene and Pliocene are only Plistocene (or Quater- | 
nary). * 
I have not the complete work of Professor Steinmann, and 
therefore will refer only to the extracts that he has published. 
I am more and more convinced that the Pampean forma 
tion is tertiary, and not quaternary. The Araucanian, of whic! 
Professor Steinmann speaks, is entirely distinct from the Pam 
pean formation. The vast difference which exists between the 
Parana fauna and that of Monte-Hermoso is easily explai 
by taking into account the fact that the first is Lower Oli 
cene or Upper Eocene of the old geologists, while Monte-Her- 
moso is Upper Miocene. Some day, when the Lower Miocem 
of Catamarca (an Araucanian bed) is explored, and the mam: 
malian fauna of that formation is satisfactorily known, the 
great break that is now held to exist between the fauna of tf 
Parana and that of Monte-Hermoso will largely disappear. 
I am astonished that any one can still speak of a glac 
epoch and of traces of glacial action in connection with | 
Pampean, and still more so in regard to the pre-Pam 
formations. The Araucanian bed is formed by the accum 
‘American Naturalist, 1891, p. 855. : 
