408 Bulletin American Museum of Natural History. [Vol. XIV, 

 Phyllotis chacoensis, sp. nov. 



Type, No. 98-5-14-2, British Museum, ? adult, Waikthlatingwayalwa, 

 Chaco boreal, Paraguay ; Graham Kerr, Sept. 5, 1897. 



Pelage thick and soft. Above strongly yellowish brown, varied with black- 

 tipped hairs, chiefly on the back ; sides with fewer black-tipped hairs, and 

 more strongly yellowish, or ochraceous buff ; nose and top of head more gray- 

 ish ; cheeks like the sides ; below pure white to the base of the hairs ; fore 

 arm, thighs, and hind legs like adjoining parts of the body ; upper surface of 

 fore and hind feet white, well clothed ; palms and soles naked, the former 

 flesh color, the latter darker, or brownish flesh color ; ears large, dull brown, 

 thinly haired on both surfaces ; a small yellowish white tuft at posterior base of 

 ear ; tail much longer than head and body, bicolor, dark brown or blackish 

 above, white below, well haired, the hairs increasing in length toward the end 

 of the tail, forming a brushy pencil at the tip. 



Measurements. Total length (of type), 327 mm.; head and body, 142 ; tail, 

 185 ; hind foot, 31 (without claws, 33 with claws); ear, 24. Another specimen 

 gives the following measurements, taken from a well-made skin : Total length, 

 267; head and body, 120; tail, 147; hind loot, 29; ear, 18. 



Skull long and narrow, with a narrow brain case, interparietal very broad, 

 the anterosuperior border of the maxillary plate of the zygoma produced to form 

 a slight angle, in this feature diverging from the Phyllotis darwini type toward 

 Euneomys ; bullae large ; molars (including m-) nearly as in Phyllotis darzvini, 

 but bullse much larger, molar series much broader, and brain case relatively 

 much narrower. The type skull measures as follows : Total length, 38; basilar 

 length, 29 ; length of nasals, 16 ; zygomatic breadth, 18 ; mastoid breadth, 14; 

 interorbital breadth, 6 ; palatal length, 7.2 ; palatal foramina, 8 X 2.5 ; upper 

 toothrow, 5 ; lower jaw (from inner base of incisors to condyle), 19 ; height at 

 condyle, 10 ; lower toothrow, 5.3. 



This species resembles most nearly Phyllotis griseoflavus 

 (Waterh.), with the type of which it has been compared, but 

 from which it differs in its brighter, more buffy coloration, and 

 in the fur on the ventral surface being wholly white to the base, 

 instead of basally pale plumbeous. It is also apparently larger. 

 The type locality of P. griseoflavus is the mouth of the Rio 

 Negro, Patagonia, to which species three other specimens from 

 Chupat, Patagonia, are evidently referable. The type locality of 

 P. chacoensis is the northern Chaco country of Paraguay, north- 

 west of Asuncion. 



P. chacoensis is based on three specimens from Waikthlating- 

 wayalwa. They all agree very closely in external features, in- 

 cluding the wholly white fur of the ventral surface. 



