246 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 
smooth, continuous outer wall, in which the distinction of cusps is nearly 
obliterated. So far as the development of tooth-patterns is understood, 
it would be quite impossible to derive either type from the other. 
(2) That the phalanges have a resemblance in the two families, though 
not an especially close one, is undoubtedly true, but this of itself forms 
a very insecure foundation for any theory of relationship. The distal 
trochleae of the metapodials are very peculiar in the Santa Cruz genus, and 
quite different from the convex, hemispherical knobs of the chalicotheres, 
which are more like those of the clawed oreodont Agriochocrus. 
(3) The discovery of nearly complete skeletons of the chalicotherian 
genus Moropus in the lower Miocene of North America, and the descrip- 
tions given by Mr. Peterson (’07) and Professor Barbour (’08) clearly 
indicate that in the Chalicotheriidse the greater development of the external 
digit was acquired within the limits of the family, not inherited from any 
Santa Cruz or earlier South American ancestry. Moropus is much less 
extremely specialized than the genera found in the middle and upper 
Miocene of Europe and its feet are nearly mesaxonic, the third metapodial 
being the longest. In the manus the second digit is much the heaviest of 
the series and has by far the largest claw, while in the pes the third and 
fourth digits are of nearly equal size. (See Peterson, ’07, 746, fig. 26.) 
That the so-called Ancylopoda are aberrant perissodactyls, is the con- 
clusion reached by all who have examined Moropus and in my judgment, 
it is equally clear that the Entelonychia represent an analogous variant of 
the toxodonts. The likeness between these two aberrant groups is really 
a remote one and is confined to the phalanges of the fore-foot, while the 
resemblance between the chalicotheres and the perissodactyls, on the one 
hand, and between the homalodontotheres and the toxodonts, on the 
other, is fundamental, involving all parts of the dentition and skeleton. 
Whichever conclusion be adopted, it will be impossible to avoid the 
admission of a convergent development, either of the Ancylopoda toward 
the Perissodactyla, or. of the Entelonychia toward the Ancylopoda. 
HOMALODONTOTHERIUM Flower. 
(Plates XXVIII-XXX.) 
Homalodotherium Huxley; Quart. Journ. Geolog. Soc. London, Vol. 
XXVI, 1870, p. lvii ( nomen nudum). 
