SCOTT: ENTELONYCHIA OF THE SANTA CRUZ BEDS. 
279 
Toxodontia and the Litopterna as well, is very characteristic. Aside 
from the neck, the bone has an almost square outline, with proximo- 
distal and transverse diameters nearly equal. The trochlea is but feebly 
grooved, almost flat, and is divided into a much broader internal and a 
narrower, but elevated and prominent external condyle, somewhat as in 
Nesodon , but a very exceptional feature is the proximal prolongation of 
the condyles as narrow tongues, which are separated from each other by 
a broad V-shaped surface. On the plantar side are two narrow, elongate 
and parallel surfaces for the calcaneum, separated by a straight, deep 
sulcus, which is much narrower than in Nesodon. Of these, the external 
facet is oblique and concave, more directly plantar and of more uniform 
width than in the last named genus ; the sustentacular facet is slightly 
convex proximo-distally and is longer, broader and of more uniform 
width than in Nesodon and, as in that genus, extends to a junction with 
the navicular facet, but is not produced so far proximally. The neck of 
the astragalus is decidedly longer and more constricted than in theToxo- 
donta and ends in a narrower, more convex head, which, as in that sub- 
order, articulates with the navicular only. 
The calcaneum (PI. XXX, figs. 5-5$, 7) is likewise highly characteristic 
and differs in many respects from that of the Santa Cruz Toxodonta. 
The tuber is much longer proportionately than in that group and is more 
compressed, with thinner and more prominent dorsal border and the 
ventral border concave proximo-distally, instead of convexly arched. 
The tuber broadens to the free or proximal end, which is immensely 
expanded, thickened, rugose and club-shaped ; the internal portion of the 
free end is still further elongated as an additional process, the length of 
which varies in the different individuals and species and is most developed 
in the very large II. crassum. The fibular facet is peculiar in several 
respects: (1) it is very large and projects prominently on the external 
side as an overhanging shelf, which is not to be found in the Toxodonta; 
(2) it is but moderately convex proximo-distally and very slightly concave 
transversely ; (3) it presents distally rather than dorsally, a very excep- 
tional arrangement, which is in correlation with the unusual obliquity of 
the corresponding surface on the fibula. The external astragalar facet is 
large and has a more dorsal, less lateral presentation than in Nesodon; 
another difference from the latter is that the proximal border of this facet 
is sharply defined and raised above the level of the tuber, not continued 
