142 Mr. 0. Thomas on the Grouping of 



Skull in general form like that of Phyllotis^ but the supra- 

 orbital edges ridged and divergent as in the larger species of 

 Hesperomys. Anterior edge of zygomatic plate undercut, 

 concave. Bullae generally large. 



Type. Graomys griseo-Jlavus (Mus griseo-jiavus, Waterh.). 



Other members of the genus : — 



Graomys chacoensis, All. (described as Phyllotis cJiacoensis) , 



„ cackiniis, All. (^Phyllotis cachinus). 



„ domorum, Thos. (^Eligmodontia domonim). 



„ griseojlavus centralis, Thos. (£'. g. centralis). 



Phyllotis, Waterh., 1837. 



Size various. Form slender, graceful. Ears long. Tail 

 about as long as or (generally) longer than head and body, 

 thinly haired, not pencilled. Feet normal, slender, with the 

 usual pads small and well defined. Mammae 2 — 2=^^. 



Skull, compared with that of the Euneomys group, long 

 and narrow, the zygomata not widely expanded. Interorbital 

 region more or less parallel-sided, its edges, at least in the 

 larger forms, not broadly divergent posteriorly and not 

 ridged. Anterior edge of zygomatic plate straight or occa- 

 sionally slightly concave, but never distinctly undercut. 

 Bullas generally small, though larger than in Hesperomys. 



Teeth brachyodont. 



Type. Phyllotis darwini {Mus darwini, Waterh.). 



About a score of other species appear rightly referable to 

 Phyllotis. 



Euneomys, Coues, 1874. 



Size various. Form comparatively stout, more or less 

 Microtine. Tail medium or short, well-haired, especially at 

 tip. Feet stout, dumpy, generally heavily fringed ; pads 

 large, low, more or less filling up the surface of the palms 

 and soles. Mammse 2 — 2 = 8. 



Skull comparatively short, stout, rounded, the zygomata 

 widely expanded. 



Incisors grooved or smooth. Molars more liypsodont than 

 in Phyllotis and the other allied genera. 



Type. Euneomys chinchilloides (JReithrodon chinchilloides, 

 Waterh.). 



Three subgenera, as follows : — 



Euneomys, s. s. 



Tail of medium length. Palms and soles completely 

 naked. 



