66 PATAGONIAN EXPEDITIONS: ZOOLOGY. 



(the type, taken March ii) between February 4 and 21, 1897. ^^^^ of 

 the specimens, including the type, are in the dress of the breeding season, 

 while others have partly or wholly acquired the postbreeding dress. 

 These have a stronger suffusion of yellowish buff on the sides and ventral 

 surface, but are otherwise similar to the type. A quarter-grown young 

 example is similar in general coloration to the adults except that the ears 

 have the external surface blackish and the internal surface deep buff, with 

 the hairs at the anterior base of the ears and the postauricular patch also 

 deep buff, in prominent contrast with the surrounding pelage, as is not 

 the case in the adults. 



Reithrodon hatcJieri is readily distinguishable from R. citniculoides by 

 its much darker and less fulvous coloration, the contrast in color between 

 the two series being conspicuously noticeable. There are apparently no 

 cranial differences of importance. 



Genus EUNEOMYS Coues. 



Etmeomys Coues, Proc. Acad. Nat. Sci. Phila., 1874, 185 (as a subgenus 

 oi Reithrodon). Type, Reithrodon chinchi/loidesWdLitxh. — Thomas, 

 Ann. & Mag. Nat. Hist. (7), VIII, Sept., 1901, 254 (as a full genus). 

 — Allen, Bull. Amer. Mus. Nat. Hist., XIX, May, 1903, 194. 

 The early history of Etmeomys has already been given under that of 

 Reithrodon. The two genera differ so radically in certain cranial charac- 

 ters, especially in the structure of the last two molars, both above and 

 below, that they have no close relationship, and the two are placed together 

 for treatment in the present connection only as a matter of convenience. 

 Their differences were, in part, clearly indicated by the late Dr. Coues, on 

 the basis of Waterhouse's plates of the skulls and teeth of the two spe- 

 cies Coues designated respectively as the types of the two groups. These 

 I have already summarized in another connection as follows : 



"The most important of these [the differential characters pointed out 

 by Coues] are : (i) 'Anterior root of zygoma deeply emarginate in front' 

 in Reithrodon and ' about straight in front' in Eitneouiys ; (2) 'palate end- 

 ing much behind the molar series and showing a median ridge intervening 

 between lateral paired deep excavations' in Reithrodon, and 'palate ending 

 nearly opposite the last molars, slightly ridged or excavated ' in Euneomys ; 

 (3) 'pterygoid fossae deeply excavated, and the bones very closely approx- 

 imated' in Reithrodon, and 'pterygoid fossae shallow and these bones less 



