282 
PATAGONIAN EXPEDITIONS ! PALAEONTOLOGY. 
able that the pes was plantigrade, and the peculiar position of the fibulo- 
calcaneal articulation suggests that only the massive and club-like free 
end of the calcaneum rested on the ground and that the pes was arched 
upward somewhat in the manner of the human foot. The improbability 
of Ameghino’s view, that the pes rested its weight chiefly on the external 
border, has been pointed out in a previous page (p. 276). 
Species . — As the material is so scanty and incomplete, it would be 
premature to attempt any revision of the species, of which Ameghino 
recognizes four. These are distinguished almost entirely by differences 
of size, a notoriously untrustworthy criterion, yet so great is the range in 
this respect that more than one species must certainly be admitted. 
Much importance has been attached to the development of the cingulum 
of the upper molars, but this is subject to such fluctuation that it cannot 
be regarded as even a sexual character, though it is quite possible that it 
may be constant in some of the species. 
Homalodontotherium cunninghami Flower. 
(Plates XXIX, Figs. I, la, 3; XXX, Figs. 3, 3 a, 6, 6 a.) 
Homalodontotherium cunninghami Flower; Phil. Trans., Vol. CLXIV, 
1884, p. 173. 
This, the type-species, is the commonest, or more accurately, the least 
uncommon of the Santa Cruz forms. It can at present be characterized 
merely by its large size, less than that of H. crassum , greater than in H. 
segovice and H. excursum. 
Measurements. 
Type. 
No. X. 
No. ip, 4 
Upper dentition, length C to m-, inch 
.238 
Canine, length (i. e. ant. -post, diam.) 
. .017 
.026 
Upper cheek-teeth series, length 
.223 
Upper premolar series, length . 
. .087 
.090 
PT length ...... 
. .020 
.020 
“ width ...... 
. .023 
.0225 
P-, length ...... 
. .022 
.0225 
“ width ...... 
. .0295 
•0375 
P-, length ...... 
. .025 
.025 
.026 
“ width ...... 
. .029 
•0375 
.029 
P-C length ...... 
. .027 
.030 
.027 
“ width ...... 
• -035 
•043 
•035 
Upper molar series, length 
•133 
.121 
