SINCLAIR i TYPOTHERIA OF THE SANTA CRUZ BEDS. 
95 
fore limb. If the pes were placed in a digitigrade position the spinal 
column would incline obliquely upward. The approximate correctness 
of the position of the hind feet in the restoration receives additional con- 
firmation from specimen No. 9481 of the American Museum collection, 
which shows the death pose of an animal smothered by a fall of the vol- 
canic ash of which the Santa Cruz formation is largely composed. The 
back is strongly arched, more so than is shown in the restoration, and the 
long hind feet project forward between the fore feet, and are strongly 
flexed, more so than seems probable in a digitigrade form. The evidence 
furnished by the astragalar trochlea in favor of a plantigrade position for 
the hind foot has already been mentioned (p. 94). The great length and 
strength of the hind limb, the shortness of the fore limb and the planti- 
grade pes are regarded as indicative of a saltatorial gait. The fore foot 
may have been as digitigrade as in the rabbit. The shape of the scapula 
is largely hypothetical. It has been given the same shape as in Proty- 
potherium. The tail may have been longer, but the small size of the 
proximal caudals does not seem to justify such an inference. 
Pachyrukhos moyani Ameghino. 
(Plates X, XI, Text Fig. 1, C.) 
Pachyrukhos moyani Amegh.; Nuevos restos de mamif. fos. oligocenos, 
recogidos por el Prof. Pedro Scalibrini, etc., p. 160, 1885. 
Pachyvucos moyani Amegh.; Contrib. al Conoc., etc., pp. 430-431, PI. 13, 
figs. 28, 29, 34, 35, 1889. 
Pachyvucos ncevius Amegh.; Contrib. al Conoc., etc., p. 430, PI. 13, fig. 
30, 1889. 
Pachyvucos absis Amegh.; Contrib. al Conoc., etc., pp. 429-430, PI. 13, 
figs. 32-33, 1889. 
But one species of Pachyrukhos is represented in the collections studied. 
It may be distinguished from Pachyrukhos typicus of the Monte Hermoso 
horizon by the different shape of the postorbital process which is exceed- 
ingly slender in the Santa Cruz form and large, triangular and perforated 
by a foramen in the later species, by the shallower lower jaw, less heavy 
rostrum and the possession of pointed, uncleft, terminal phalanges. 
Doubtless other characters of specific importance would appear if it were 
possible to make comparison directly with the type. A specimen in the 
