ASTEROMYS 195 
Asteromys; but as we know only the teeth from the Deseado 
beds, it is probable that, when the skull is found, larger 
differences will be recognized. Asteromys appears to be 
the direct ancestor to Acaremys. 
The species are all tiny, the following three being dis- 
tinguished by Ameghino. 
LENGTH OF LOWER 
MOLAR SERIES 
A. punctus (Bol. Inst. Geog. Argen., 1897, t. 18, p. 495) I2 mm. 
A. annectens (Bol. Acad. Nac. Cienc. Cordoba, 1902, t. 17, p. 37) It mm, 
A. prospicuus (Bol. Inst. Geog. Argen., 1897, t. 18, p. 495) each molar 1.6 to 
1.8 mm. 
Of these three we found only the last. 
Asteromys prospicuus Ameghino 
A. prospicuus Amegh. loc. cit. above. 
The species is rare, only three specimens turning up in 
our collections. The upper molars are as described in 
Fig. 128. Right upper premolar 4— Fig. 129. Left lower 
molar 3, x 4/I. molar 2, x 4/I. 
the generic discussion, but premolar 4 is simpler than the 
molars, the posterior lamina being small and without any 
sort of furrow. In the upper molars the anterior lamina 
is larger than the posterior, and the anterior furrow wider 
than the posterior. The following measurements, with 
the figures, indicate the character of the species. 
Upper dentition, premolar 4 to molar 3 8.75 mm. 
Upper dentition, premolar 4, length 2. mm. 
Upper dentition, each molar, length 222 ins 
Upper dentition, each molar, width 2: mm. 
Lower dentition, molar 2, length 2-75, mins 
Lower dentition, molar 2, width 1.75 mm. 
