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) 12 mm. 



A. annectens (Bol. Acad. Nac. Cienc. Cordoba, 1902, t. 1 7, p. 37) 1 1 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 tipper premolar 4 Fig. 129. Left lower 



molar 3, x 4/1. molar 2, x 4/1. 



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 2.3 mm. 



Upper dentition, each molar, width 2 . mm. 



Lower dentition, molar 2, length 2 -75 nun. 



Lower dentition, molar 2, width 1 . 75 mm. 



