| Measurements | ||
|---|---|---|
| Upper molar 1, | length 29 mm., | width 21 mm. |
| Upper molar 2, | length 30½ mm., | width 18 mm. |
Argyrohyrax Ameghino
Argyrohyrax Amegh., 1897, Bol. Inst. Geog. Argen., t. 18, p. 435.
The genus is distinguished by the full dentition in closed series, and by the upper molars having a deep internal inflexion which is bifurcated, making the teeth at least incipiently three-lobed. Incisor 1 is relatively somewhat wider than in the preceding genus. It seems to me that it is from such a genus that Typotherium arose, by the reduction of the lateral incisors, the canine, and the first two premolars, and by the increase of the bifurcated internal fold. Three species have been described, A. proavus, 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. Argen., t. 18, p. 436.
This species occurs three times in the Amherst collection. The best specimen has pm. 1, 3, 4, and m. 1 and 2 of the upper jaw. The species is characterized by a narrow furrow near the anterior external margin of the premolars and molars; and by pm. 3 and 4 and the molars having a deep internal bifurcated inflexion, which tends to make these teeth three-lobed.
Fig. 50. Right upper dentition, the outline teeth
after Ameghino—natural size.
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 dentition, like Plagiarthrus, is that lower dentition.