Cephalomys prosus Ameghino
C. prosus Amegh., 1902, Bol. Acad. Nac. Cienc. Cordoba, t. 17, p. 37.
This is the tiniest species of the genus, and least frequently found, probably because on account of the small size it was more frequently destroyed before burial, and also because it is hard to find such tiny specimens; so that the sixteen which we found would hardly represent the real proportion of the species in the fauna.
The jaws are not only small, but also slender and delicately built, with the premolar about the same size or slightly larger than the molars. The drawings represent the proportions accurately so I will give but a few measurements.
| Specimen 3009 | Ameghino’s Type | |
|---|---|---|
| Upper premolar 4 to molar 3 | 8.5 mm. | |
| Lower premolar 4 to molar 3 | 9.5 mm. |
Scotamys gen. nov.
A lower jaw, with premolar 4 and molars 1 and 2, from the Deseado beds on the Chico del Chubut River, west of Puerto Visser, indicates a genus of hystricomorph rodents not previously reported. The lower molars suggest those of Perimys, but premolar 4 is similar to that of Scotaeumys from the Santa Cruz. Scotamys differs, however, from Scotaeumys, in that its molars do not have the third lobe found in the Santa Cruz genus. I have, therefore, made a new genus which appears to be ancestral to Scotaeumys.
Scotamys antiquus sp. nov.
Fig. 125. Lower premolar
4—molar 2, × 4/1.