PART III. ENTELONYCHIA. 
The members of this suborder are relatively rare in the Santa Cruz beds 
and the Princeton and New York collections contain but few and unsatis- 
factory specimens. For this reason, the following account is largely 
drawn from the collections of Dr. Ameghino and the La Plata Museum. 
I am under great obligations to Dr. Ameghino and to Sr. Moreno for 
the very liberal manner in which the material in their charge was placed 
at my disposal. It is much to be regretted that I was not permitted to see 
the skeletal material in the Paris Museum on the occasion of my last visit, 
August, 19 1 1, the absence of M. Boule rendering the Patagonian collec- 
tions of M. Tournouer inaccessible to me. 
In Santa Cruz times the Entelonychia were evidently verging toward 
extinction, for the group is not known to be represented in any later 
formation and their rarity is in striking contrast to the abundance and 
variety of them in the more ancient Deseado stage ( Pyrotherium Beds). 
From this latter formation, Ameghino has described no less than twelve 
genera, which are distributed in three families, while but one family and, 
at most, two genera are known from the Santa Cruz. Individual abun- 
dance corresponds to this variety of form and members of the Entelo- 
nychia are among the commoner fossils of the Pyrotherium fauna, which 
thus records the culmination of the group, followed by swift decline and 
extinction. The interval of time between the Deseado and the Santa 
Cruz Beds, which is occupied by the marine Patagonian formation and 
its presumable equivalents, the Colpodon , Astrapothericulus and Noto hip- 
pus faunas of Ameghino, cannot have been very great, as measured by the 
degree of structural change in the mammalian groups common to both, 
but the difference in regard to the Entelonychia in the two formations is 
a very marked one. Obviously, the Entelonychia of the Santa Cruz are 
the reduced and vanishing remnants of a previously dominant group. 
Any description of them which leaves their predecessors out of account 
must necessarily be partial and even misleading. It will therefore be 
advisable to depart from the method followed in the other sections of 
2 39 
