388 Bulletin American Museum of Natural History. [Vol. XX, 



than the shoulder bands, which are thus internally obscurely 

 denned. 



VARIATION IN COLOR. The light and dark areas not only 

 vary in extent and form, as above described, but in color. 

 The dark areas vary in tone from light reddish brown, or 

 brownish rufous, to clear black, the average condition being 

 dark brown. The posterior border of the dark area on the 

 back is sometimes sharply denned, and sometimes shades off 

 gradually into the light color of the rump. This is due to the 

 hairs being dark basally at the edge of the white area and 

 light apically, and the transition is either abrupt or gradual, 

 according to the extent of the junctional area covered by 

 light-tipped hairs. Also there are not infrequently light- 

 tipped hairs on the back and sides of the body within the 

 dark area, giving a superficial yellowish-gray wash to the 

 surface, as is commonly the case in one-fourth- to half -grown 

 young. 



The light areas vary from nearly clear white (several speci- 

 mens) to deep rusty yellow. The nuchal region is generally 

 much deeper colored than the limbs and tail. In an average 

 Specimen the light parts are yellowish white or pale buffy, 

 shading to ochraceous buff, or even ochraceous on the 

 nuchal region. 



SKULLS. The skulls are found to be remarkably constant 

 in their characters. A series of 24 adult skulls selected at 

 random for study shows that the skull varies very little in- 

 dividually, or with age. It is smooth or wholly without 

 crests or ridges, even in old age. A young adult skull is dis- 

 tinguishable from a very old skull only by the comparative 

 obsolescence of the sutures and the denser structure of the 

 bone in the latter. The variation in size is not great, as is 

 shown by the subjoined table of measurements (p. 397), which 

 includes measurements of young adult, middle-aged, and old 

 skulls. One specimen (No. 23423) is noticeably different 

 from the others in being unusually short and broad, with an 

 unusual convexity of the interorbital region. Another. (No. 

 14675) differs in the rostral portion of the skull being un- 

 usually narrow and deep. The nasals vary in depth and 



