80 THE DESEADO FORMATION OF PATAGONIA 
by a broad connection which is especially wide at the lower 
ends. I find no traces of a connection with the bulla as 
described by Sinclair for Pachyrukhos. Further down are 
two small knobs apparently also representing cavities in 
the squamosum, and also connected with the brain case. 
In considering the brain these should be overlooked; but 
they doubtless represent some nervous function to which 
I have as yet no clue. 
Ameghino considered that Eutrachytherus was the con- 
necting link between Archaeohyrax and Typotherium. 1 
feel that this genus is too highly specialized to be a con- 
necting form, though it doubtless belongs to the series 
which ends in Typotherium; and such a form as Argyro- 
hyrax is more likely to be the really ancestral form. 
Two species are described, E. spegazzinianus, and FE. 
conturbatus, which is about 15% smaller. Our collection 
offers a third species, EZ. grandis, which is nearly 50% larger 
than the first named species. 
Eutrachytherus spegazzinianus Ameghino 
Trachytherus spegazzinianus Amegh., 1889, Act. Acad. Nac. Cienc. Cordoba, 
t. VI, p. 919. 
Trachytherus spegazzinianus Lydekker, 1894, Anal. Mus. La Plata, pt. 3, p. 2. 
Trachytherus spegazzinianus Amegh., 1895, Bol. Inst. Geog. Argen., t. 15, p. 
622. 
Eutrachytherus spegazzinianus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, 
p. 428. 
This species was founded on the anterior part of a skull 
with the full upper dentition. My specimen differs from 
Ameghino’s in having a tiny alveolus for the upper canine, 
the difference being due to my specimen being younger. 
The upper dentition is very characteristic. Incisor 1 
is a powerful, deep-set, curved gnawing tooth, with a 
heavy layer of enamel on the anterior face, and none on 
the other sides; and is moderately beveled in the rear as a 
result of wear. The second and third incisors are much 
smaller, each having enamel on the outer face only, and 
