16 



NOETH AMERICAK FAUNA. 



[No. 40. 



examples are considerably reddened or darkened by stain, either on 

 the upper and lower body or uniformly throughout the pelage. 

 Specimens in complete fresh summer coat are rather uncommon as 

 the vernal molt is so slow that the forward parts, renewed first, are 

 abeady considerably worn before the tail, last to renew, is in fuU 

 fresh coat. 



Molt, — The spring molt and renewal are very conspicuous but the 

 fall molt, especially in northern localities, is often obscure. There 

 is considerable variation in the dates of renewal but the following 

 schedule is about the average for northern and central Great Plains 

 States : Late March and early April skins are worn, pale, and faded, but 

 already show some signs of molt and renewal on the underparts, where 

 the first new hair appears on the pectoral region and axillse. May 

 specimens have completely renewed below and the renewal has com- 

 menced on the head, shoulders, and in irregular patches on the back. 

 June specimens are almost completely in fresh coat, but still show, as 

 a rule, some of the old pelage on the rump and tail. July and early 

 August skins are usually completely renewed, except for a few in 

 which the tails above are still in the winter coat. The hair of the 

 body is short and harsh, and rapidly becomes broken, worn, and 

 faded. Late August adults show considerable progress in the fall 

 renewal; the winter underfur and long soft hair is appearing on the 

 lower back, and the animal looks generally lighter colored. The 

 tails are fully renewed, November specimens are in complete new 

 fur, and the hair on the tails still appears fresh and unworn after its 

 single annual renewal ; all traces of the summer coat have dis- 

 appeared. In December skins, the coat has thickened, grown longer, 

 and appears considerably lighter in color. This is in part due to 

 fading, but is also caused by the general effect of the long white 

 imderfur showing through the reddish hair tips. 



Slcull and teeth, — The skull of Cynomys ludovicianus ludovicianus 

 differs from that of C, I, arizonensis in its distinctly smaller audit al 

 bullae and narrow, deeply emarginate anterior face of maxillary root 

 of zygoma. It may readily be distinguished from skulls of 0, leucurus 

 (whose range meets that of C, ludovicianus in parts of Wyoming) by 

 its slightly larger size, smaller buUse, more notched anterior face of 

 maxiUary root of zygoma, less flattened zygoma (muscle attachment 

 reaching farther forward, nearly or quite to plane of first tooth), gen- 

 erally heavier mandible, lighter postorbital processes, and small audi- 

 tory meatus. The incisors vary in color from white to deep yeUow in 

 specimens from one locality. The variation in size and shape of skull 

 among specimens of the same sex and age from one locality is remark- 

 able (see PL VI). 



Measurements, — Averages of 13 adult males from South Dakota: 

 Total length, 388 (360-415); tail vertebrae, 86 (75-98); hind foot, 



