1 86 Bulletin American Museum of Natural History. [Vol, XIX, 



ally there is a very narrow median dusky line, extending from the tip 

 anteriorly for a part or the whole of the length of the tail; in a few 

 specimens it is strongly developed, broadens and increases in black- 

 ness towards the tip, and in rare cases the whole tip is black, with a 

 short black stripe on the lower surface on the apical fourth or third of 

 the tail. 



Young examples,, differ from the adults in the general tint being 

 duller and the pelage less lustrous. 



Measurements. Type: Total length, 290; tail vertebrae, 73; hind 

 foot, 40. Nine adult males measure as follows: Total length, 303.5 

 (290322, only one above 310, and only two above 298); tail verte- 

 bras, 81.5 (73-88); hind foot, 40.5 (4042). Five adult females: 

 Total length, 275 (256-300; only one above 280); tail vertebras, 75 

 (70-80); hind foot, 37 (35-40). 



Skull, type: Total length, 52.5; basal length, 47; zygomatic 

 breadth, 30; interorbital breadth, 10; mastoid breadth, 29.5; length 

 of nasals, 20; palatal length, 25; diastema, 16; upper molar series, 

 9.6; lower jaw, inner base of incisors to posterior border of condyle, 

 33; inner base of incisors to tip of angular process, 41; height at 

 condyle, 16; lower molar series, 10.3; distance between condyles, 18; 

 distance between tips of angular processes, 37. Ten adult male skulls: 

 Total length, 53.6 (51-55); zygomatic breadth, 30.5 (29-33). Five 

 adult female skulls: Total length, 48 (46-50); zygomatic breadth, 

 27.5 (26.2-28.6). The mastoid breadth is practically the same as the 

 zygomatic breadth, varying in different specimens from slightly more 

 to slightly less. The greater part of the skulls in the present series 

 are middle-aged, with all the sutures distinct; only two or three give 

 evidence of being very old. 



Represented by 23 specimens, all from the upper Rio Chico, 

 Cordilleras, and all collected by Mr. Peterson, February 7 to 

 28 (except one taken March 9). All but three are in adult 

 pelage, and these have nearly acquired it, only the lower part 

 of the back and rump retaining the pelage characteristic of 

 immaturity. The general color above of the adults varies 

 from strong yellowish brown to slightly rufescent brown, and 

 below from deep ochraceous buff to brownish ochraceous. 

 The color of the tail is very variable, as already noted; except 

 in the case of a few which have the tail practically uniform 

 yellowish gray, no two have the tail colored alike, in respect 

 to the median dorsal line, which varies from a slight trace 9f 

 dusky to a well-defined blackish median stripe, the black 

 -widening and increasing in intensity apically ; in three speci- 



