

Sn aig QE. $<“ eo eee aad 

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1891.] The Litopterna. 687 
opsis of the Families of the Vertebrata ” (1889). Here the 
results of my study of the preliminary papers of Ameghino and 
Burmeister were embodied in the following systematic form. The 
Macraucheniide were placed in the suborder Toxodontia (p. 28). 
Ameghino having shown that.the supposed Palzotherium and 
Anoplotherium of Bravard were allied to this family, and should 
be referred to the genera Proterotherium and Oxyodontotherium, 
a family, Proterotheriidz, was proposed for the former, and it was 
also placed in the Toxodontia. The Toxodontia were placed in 
the Taxeopoda. Ameghino’s researches having shown that the 
fore-foot structure of the Toxodontide and Mesotheriidz is that 
of the Amblypoda, while the posterior foot only has the taxeo- 
pod structure, it became evident that the Toxodontia must be 
regarded as a distinct order between the Taxeopoda and the 
Amblypoda. The Proterotheriide and Macraucheniidz having 
the taxeopod structure of both extremities, must remain where I 
' placed them. M. Ameghino, disregarding the question of taxe- 
opody and diplarthry, places these families under the Perisso- 
dactyla, and proposes to regard them as a suborder, with the 
name of the Litopterna. This name will be retained, and will 
apply in my system to a suborder of the Taxeopoda. 
The structure of the feet of the Astrapotheriidz remains 
unknown. Their location will depend entirely on the solution of 
this question. M. Ameghino places them in the Amblypoda. 
This position is rendered extremely improbable by the structure 
of the true molar teeth. Those of Astrapotherium resemble 
those of the Toxodontia, but still more those of Macrauchenia. 
Homalodontotherium resembles Rhinoceros. Until the question 
is positively settled by the discovery of the feet, I place them 
in the Litopterna as their most probable position, following 
Ameghino, so far as regards Homalodontotherium, which he 
places here. ; 
The suborder Litopterna is nearly related to the Condylarthra, 
and it is probable that future discovery will obliterate the differ- 
ences which we find to characterize the known types. The prime 
characters in which the Litopterna differ from the Condylarthra 
are the absence of epitrochlear foramen of the humerus, and the 
