6o PATAGONIAN EXPEDITIONS: ZOOLOGY. 



the phase of pelage corresponding to the present March and April speci- 

 mens taken on the plains at the eastern base of the Andes. 



Mr. Darwin says of this species (Voy. Beagle, /. c.) : "Extremely abun- 

 dant in the coarse grass and thickets in the ravines at Point Desire and 

 Santa Cruz ; was caught in a trap baited with cheese." 



Mr. Peterson says that the Rio Coy specimens were collected " around 

 a large spring, in heavy grass and brush"; and that the upper Rio Chico 

 specimens were taken " in the Rio Chico valley, close to the river." 



Phyllotis xanthopygjis, in the full brown pelage of winter, bears a strong 

 resemblance in coloration to P. micropns, but it is considerably larger in 

 external measurements, with a relatively longer and a much more hairy 

 tail. The skulls of the two species, however, are practically of the same 

 size. It can be quite closely matched in pelage and color by specimens 

 of P. darwini, but the latter has a longer tail and much weaker dentition. 

 Mr. Waterhouse compared it with his Phyllotis griseoflavus, probably its 

 nearest ally, from northern Patagonia (Rio Negro), from which he says it 

 differs in much smaller size, relatively much shorter tail, and in the struc- 

 ture of the molar teeth, as illustrated in plate xxxiv of the "Voyage of 

 the Beagle" (Mammalia). 



Phyllotis micropus (Waterhouse). 



(Plates XII, Fig. 13, Skull ; XIV, Fig. i, Teeth.) 



Mus micropus Waterhouse, P. Z. S., 1837, i? (Santa Cruz River, Pata- 

 gonia) ; Z06I. Voyage Beagle, Mamm., II, 1839, 61, pi. xx, animal, 

 pi. xxxiv, fig. 13, teeth. Interior plains of Patagonia, in lat. 50°, 

 near the banks of the Santa Cruz. 

 Hesperomys {Habrothrix) micropus Burmeister, Descrip. phys. Rep. 



Argent, III, 1879, 217 (ex Waterhouse). 

 [Akodon] micropus Trouessart, Cat. Mamm., ii, 1897, 53^ (ex Water- 

 house and Burmeister). — Lahille, Congr. Cien. Lat. Amer., Ill, 

 1899, 188. 

 ^rt'//// (February). — Above yellowish brown, with a slightly rufescent 

 cast, strongly varied with black-tipped hairs ; sides lighter, more yellowish ; 

 nose less yellow, dusky gray ; below gray, washed more or less with buff 

 or tawny, chiefly on the pectoral and post-pectoral areas ; ears large, well 

 haired, similar in color to the median dorsal area ; tail rather more than 

 one third of the total length, bicolor, dark brown above, gray or yellowish 



