ARGVROHVRAX 83 



two premolars, and by the increase of the bifurcated in- 

 ternal fold. Three species have been described, A . pro- 

 avus, the type species, A. acuticostatus, of a little smaller 

 size, and A. proavunculus of still smaller size. 



Argyrohyrax proavus Ameghino 



A. proavus Amegh., 1897, Bol. Inst. Geog. Argcn., t. 18, p. 436. 



This species occurs three times in the Amherst collec- 

 tion. The best specimen has pm. 1, 3, 4, and m. 1 and 2 

 of the upper jaw. The species is characterized by a nar- 

 row furrow near the anterior external margin of the pre- 

 molars and molars; and by pm. 3 and 4 and the molars 



Fig. 50. Right upper dentition, the outline teeth after Ameghino — 

 natural size. 



having a deep internal bifurcated inflexion, which tends to 

 make these teeth three-lobed. 



The genus is known only by the upper dentition, and 

 while I did not find any associated lower teeth, I believe 

 that some one of the genera known only by the lower den- 

 tition, like Plagiarthrus, is that lower dentition. 



Measurements 



Upper dentition, length inc. 1 to m. 3 (® Ameghino) 



premolar I, length 7 mm., width 

 premolar 3, length 7 mm., width 

 premolar 4, length 8 mm., width 

 molar 1, length 8 mm., width 6 \ mm. 



Argyrohyrax proavunculus Ameghino 



A. proavunculus Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 436. 



The species is simply said to be much smaller than the 

 preceding, which, by the measurements, would figure out 

 about 27%. The measurements given are pm. 1 to m. 3, 

 33 mm. 



