Litodontomys gen. nov.
One set of lower teeth found by the Amherst party shows a simplicity of pattern found in no other genus of South America; and this is, therefore, named Litodontomys. The teeth are brachydont, the premolar and the molars each being divided into two laminae by an external and an internal fold, the distinctive generic feature being in that this fold is narrowest at the margin of the tooth and expands internally. In connection with the expanded folds, the ends of the laminae are curved toward each other, so that in a worn specimen they would meet on the margins of the tooth, and leave the folds to appear as pits. No indication of a furrow is evident on either lamina.
Litodontomys chubutensis sp. nov.
The type is number 3086 of the Amherst collection, from the Deseado beds on the Chico del Chubut River, west of Puerto Visser, and consists of the lower premolar-molar series.
Fig. 127. Right lower
premolar 4
—molar 3, × 4/1.
Premolar 4 is elongated, the anterior lamina being considerably longer than it is wide, whereas the laminae of the other teeth are wider than they are long.
The following measurements with the figure give the specific details.
| Measurements Specimen 3063 | ||
|---|---|---|
| Lower dentition, | premolar 4, to molar 3 | 10.5 mm. |
| Lower dentition, | premolar 4, length | 3.5 mm. |
| Lower dentition, | molar 1, length | 2. mm. |
| Lower dentition, | molar 2, length | 2.5 mm. |
| Lower dentition, | molar 3, length | 2.5 mm. |
| Lower dentition, | width of molars | 2. mm. |
ERETHIZONTIDAE