1903.] Allen, New Rodents from Patagonia. 1Q5 



tion of the two groups. As Waterhouse figured the crown 

 surface of the teeth in only R. cuniculoides , this most impor- 

 tant difference of all necessarily escaped Coues's attention. 



In both these genera Reithrodon and Euneomys the 

 tooth structure is remarkably distinctive for genera of Muri- 

 dae, 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 Euneomys, which are absent in Reith- 

 rodon and in all of the allied genera. 



A comparison of Euneomys with" Reithrodon' 1 pictus shows 

 that there is only the superficial and purely incidental resem- 

 blance of the grooved upper incisors, which, however, are only 

 slightly sulcate in R. pictus, Phyllotis bolivianus, and their 

 allies, and deeply sulcate in Euneomys, In all essential re- 

 spects Reithrodon pictus is a Phyllotis, but sufficiently aberrant, 

 perhaps, to warrant its subgeneric separation; but its rela- 

 tionship appears not to be with Euneomys, as has been as- 

 sumed (cf. Thomas, Ann. and Mag. Nat. Hist. (7), VIII, 1901, 

 p. 254). 



ADDENDUM TO ARTICLE IV, ON SIBERIAN 

 MAMMALS. 



At the time of preparing my report on the mammals collected in 

 northeastern Siberia by the Jesup North Pacific Expedition, a series 

 of 9 Arctic Foxes (Vulpes lagopus) in summer coat, purchased by Mr. 

 W. Bogoras at Mariinski Post (mouth of Anadyr River), had been 

 mislaid and were overlooked. They have since been found and seem 

 worthy of record. 



These specimens show that the summer coat presents two phases, a 

 light and a dark phase. Four of the specimens represent the dark 

 phase, three the light phase, two are intermediate (one approaching 

 the light phase and one nearer the dark phase), and one, the most 

 interesting of all, in moult, showing the process of change from winter 

 to summer dress. Dark phase: Whole dorsal area dark, almost black- 

 ish brown, passing into light yellowish brown on the flanks, and still 

 lighter yellowish brown on the ventral surface. This is the color of 

 the longer overhair; the woolly underfur is dark grayish brown over 



