248 



MONOGRAPIiS OF NORTH AMERICAN RODENTIA. 



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uniform ".izzle of gray, black, and luteous or fulvous, and below muddy-gray, 

 rustier on the breast. It may be, indeed, tiiat tliese differences are somewhat 

 regular and seasonal, as well as the change to white ; but as few of our speci- 

 mens are marked for season, we cannot make this out. As, however, several 

 of our richest-colored skins arc spring and early summer ones, we judge that, 

 with the disappearance in spring of the white winter-coat, the brightest, 

 sharpest pelage is put on, the vividness of the rufous or mahogany attaining 

 a maximum in the breeding- season, or rather a little at\erward, in midsummer; 

 and that subsequently tlie hues grow cooler and more intimately mixed, until 

 at length in the fall the whitening becomes manifest. 



Winter. — In perfect dress, the animal is pure white all over. In the fall, 

 the whitening seems to begin underneath and on the sides, to progress then 

 over the lower back; the heavy color of the upper back and breast being the 

 last to yield. Several specimens are white, with a narrow dorsrl rea of color, 

 that spreads forward over the upper back and shoulder, and underneath still 

 tinges the breast; others are curiously white, with lateral rufous stripes that 

 nearly meet on the rump and then curve round the sides to the chest; others 

 are pure white, except a sharp spinal stripe of grayish-black ; some are white, 

 uniformly tinged willi pale rufous all )ver. But it would be idle to attempt 

 an enumeration of all the intermediate stages ; although, in the midst of appa- 

 rently interminable changes, doubtless rules of very general applicability may 

 be deduced from observation of a few hundred specimens accurately marked 

 for season. 



The two middle fore claws attain their maximum of development in 

 winter. In spring and early summer, these claws do not appear very differ- 

 ent from those of Myodes, though averaging larger, more bulbous at base 

 underneath, with the terminal portion slenderer, straighter, and sharper. This 

 bulbous portion underneath grows out simultaneously with increase in length 

 and amount of curvature of tlie main portion of the claw, until it equals or 

 even exceeds the length of the latter, and is quite as stout, or even stouter, 

 being somewhat broad and pad-like. At this period, it runs the whole length 

 of the claw, from which it is separated by a groove along the sides, and by a 

 notch at the end, botii of. varying depth. The claw then looks nearly like 

 two claws, one underneath the other. The pad would then seem to gradually 

 sc'^r its connection with the main claw by progressive increase of the con- 

 striction marked by tlie lateral groo\u and terminal notch, as well as by loos- 



