ALLEN : MAMMALIA : MURIDi^;. 67 



approximated' in Etineomys ; (4) 'condyloid process of lower jaw con- 

 cave internally' in Reithrodon, and 'condyloid process of the lower jaw 

 flat internally ■ \n Einieoniys ; (5) ' coronoid process slender, very oblique ' 

 in Reif/irodoii, and 'coronoid process very broad, nearly vertical' in Eii- 

 neouiys. To these may be added (6) the very different enamel pattern 

 of the molar teeth in the two groups, in Reithrodon the folds being trans- 

 verse with the outer and inner loops alternating, and in Euneomys oblique, 

 with one less fold in each of the last two upper teeth, and in the first two 

 lower teeth — a very radical difference in tooth structure, which alone 

 warrants the generic separation of the two groups. As Waterhouse fig- 

 ured the crown surface of the teeth in only R. cunicnloides, this most im- 

 portant difference of all necessarily escaped Coues's attention. 



"In both these genera — Reithrodon and Euneomys — the tooth struc- 

 ture is remarkably distinctive for genera of Muridae, and, as compared 

 with each other, presents almost the extremes of unlikeness. But a further 

 noteworthy difference (7) is seen in a pair of depressions on the posterior 

 third of the palatal surface in Eimeojnys, which are absent in Reithrodon 

 and in all the allied genera." 



The only species I can confidently refer to Euneomys are the two de- 

 scribed below, namely E. chinchilloides (Waterh.), fromTierra del Fuego, 

 and E. pefersoni, from the upper Rio Chico, in the foothills of the Cor- 

 dilleras, Patagonia. 



Phyllotis boliviensis and P. picfus, which have been referred to Eune- 

 omys, appear to be merely somewhat aberrant forms of Phyllotis. 



Euneomys chinchilloides (Waterhouse). 



Reithrodon chinchilloides'^ 2X^x\\o\xit, Zool. Voyage Beagle, II, Mammalia, 

 1839, 72, pi. xxvii, animal, pi. xxxiv, fig. 20, skull and teeth. "South 

 shore of the Strait of Magellan, near the eastern entrance." — Bur- 

 meister, Descrip. phys. Rep. Argent., Ill, 1879, 217 (ex Waterhouse). 

 — Milne-Edwards, Mission Scient. du Cap Horn, VI, Zool., Mamm., 

 1890, 29, pi. iii, animal. Orange Bay, southern Tierra del Fuego. 

 Reithrodon [Euneomys) chinchilloides Coues, Proc. Acad. Nat. Sci. Phila., 

 1874, 185, footnote; Nat. Hist. No. i, Muridae, 1874, 17; N. Am. 

 Roden., 1877, 1 19. 

 As this species is unrepresented in the present collection, the descrip- 

 tion here given is transcribed from Waterhouse. 



