390 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



the base of the tail; toward the end and on the sides of the tail, the}' pass 

 again into long, thick bristles and stiff hairs. The lower surface of the body 

 is clothed merely with brownish-black hair, scantily mixed with fur. The 

 long, white-tipped hairs are generally most abundant on the head and the 

 sides of the neck and shoulders and hips, disappearing entirely over the mid- 

 dle of the hell}'. 



Different individuals vary greatly in respect to the abundance of the long 

 light-tipped hairs, they being most abundant in the younger animals, in which 

 t lay often give a decidedly whitish cast to the general color. In one specimen 

 (No. 1309, M. C. Z. Coll.), the long bristly hairs are black, tipped occasionally 

 with whitish. The pelage is very longand full, through which very few of the 

 quills are visible. In another specimen (No. 5038, M. C. Z. Coll.), the exposed 

 portion of the long bristly hairs is generally yellowish-white. In other speci- 

 mens, there is a mixture of the wholly black, bristly hairs with those that are 

 whitish-tipped. In young and full-pelaged specimens, the epulis are generally 

 entirely concealed ; in the majority of the examples before me, they are visible 

 on the head, sides of the neck, hinder part of the back, and the basal portion 

 of the tail. In old specimens, in worn pelage, the spines are visible over 

 most of the dorsal surface. The under-fur varies in different specimens from 

 brownish-black to grayish. The young are born without quills, and of a 

 uniform black color. 



Full-grown specimens average about 35 to 40 inches in total length; the 

 head about 6 ; tail (to end of vertebrse) about the same. Seventeen skulls, 

 all of which have attained mature dentition, average 3.82 in length and 2.69 

 in breadth; nasals, 1.21 ; muzzle (from anterior border of intermaxillaries to 

 the first molar), 1.29. As usual, there is a considerable range of variation 

 in size, in color, and in the proportion of parts in specimens of corresponding 

 ages. The few specimens in which the sex is known seem to indicate little, 

 if any, strictly sexual variation in either size or color. Seven very old skulls 

 vary in size as follows : length, 3.90 to 4.25 ; breadth, 2.60 to 3.00 ; nasals, 

 1.20 to 1.50; muzzle, 1.25 to 1.60. Three middle-aged skulls vary in length 

 from 3.55 to 3.90; in breadth from 2.50 to 2.80; nasals from 1.12 to 1.33; 

 muzzle from 1.12 to 1.30. Five younger skulls range in length from 3.40 to 

 3.65; in breadth from 2.35 to 2.60; nasals from 1.06 to 1.15; muzzle from 

 1.00 to 1.22. The largest skull measures 4.25 by 3.00 ; the smallest, 3.40 by 

 2.35. The nasals vary from 1.06 to 1.50 (in the very old skulls from 1.20 to 

 1.50) ; the muzzle from 1.00 to 1.62 (jn the very old skulls from 1.25 to 1.62). 



