RHYNCHIPPUS 95 
gulus, and on the distal end a flattened slightly concave 
facet for the calcaneum. 
The calcaneum is longer than in Nesodontidae. It is, 
however, heavy and stout, the tuber broadening slightly 
toward the free end, on the plantar side of which there is a 
tendinous sulcus as in Nesodon. The fibular facet is wide, 
rectangular, and convex. Of the astragular facets, the 
sustentacular extends well back onto the tuber, and the 
ectal is the usual ovoid surface. Distally there is a broad 
slightly concave facet for the cuboid, and external to this 
a narrow surface for contact on the navicular. Except in 
length, this bone is very like that of Adinotherium. The 
astragulus and rest of the tarsal bones are wanting. Parts 
of the metatarsals and a phalanx indicate that the hind 
foot is of the same tridactyl type as the front, differing 
only in that the median digit seems to be relatively a little 
heavier. 
Ameghino described three species of Rhynchippus, R. 
equinus, R. pumulis, and R. medianus. 
Rhynchippus equinus Ameghino 
R. equinus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 463. 
This species is the dominant one in the Deseado from 
the Chico del Chubut, west of Puerto Pisser, no less than 
fourteen individuals being represented in our collection, 
three by skulls, and one by the major part of a skeleton 
which was found associated with the skull of Leontinia, 
but was determined as belonging to this species, by the 
duplication of the radius with a specimen having the radius 
and lower jaws associated. The description of the generic 
characters is largely based on this skeleton. The three 
species are differentiated largely by their size, R. equinus 
being the largest, but as compared with R. pumulis it is 
not only larger but much heavier built. 
The skull has been described under the generic discus- 
sion. In young individuals, the furrow in the incisors and 
