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 Pachymkhos. 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. \ 

 feel that this genus is too highly specialized to be a con- 

 necting form, though it doubtless belongs to the series 

 w T hich 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 E. 

 conturbatus, which is about 15% smaller. Our collection 

 offers a third species, E. grandis, which is nearly 50% larger 

 than the first named species. 



Eutrachytherus spegazzinianus Ameghino 



Trachythcrus spegazzinianus Amegh., 1889, Act. Acad. Nac. Cienc. Cordoba, 



t. VI, p. 919. 



Trachytherus spegazzinianus Lydckkcr, 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 i 

 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 



