MUEID^E— ARVIOOLIN^E— ARVICOLA RirARIUS. 



181 



The shade is slightly grizzled with dull yellowish-brown. Beneath, the plum- 

 beous hairs are all tipped with white, resulting in a hoary-ash, which is clearest 

 (whitest) on the breast and belly, darkest on the throat; there is no line of 

 demarkation between upper and under parts. There is no cinnamon, tawny, 

 nor muddy tinge underneath; but a faint brownish wash, like an extreme 

 dilution of the color of the sides, is barely perceptible. 



This typical coloration prevails in the majority of eastern specimens in 

 the present collection. Nearly all those from t he Middle States, others from 

 Nova Scotia, Massachusetts, the Carolinas, Wisconsin, &c, are not appreciably 

 different. Other specimens show a departure from this standard in three 

 courses: toward "red", "black", and "gray". The extreme of the rufescent 

 variation is reached in No. rkW, type of "rufidorsum". In this, the color is 

 an intense tawny above, a little darker on the rump, paler on the sides, and 

 washing the under parts. The feet share the general tawny hue. This 

 extreme case is not nearly matched by anything else in the collection, and 

 raises a strong suspicion of an albinotic element. We know by the "albo- 

 rufescens" of Dr. Emmons that such a state does occur; although there is 

 really a gap in the eastern series between "rufidorsum" and the rest, yet many 

 specimens grade nearly up to it. In the Massachusetts series, where some 

 (particularly winter and early spring skins) are quite as dark as any Philadel- 

 phia ones, others are very much brighter. No. tWs, for example, is very 

 rufescent, from predominence of bay in the hairs. A Labrador specimen 

 (rWg) is rather brighter still ; No. JHii from Nichols, N. Y., and a Pennsyl- 

 vania skin, No. 4724, labeled "riparius" by LeConte, are epiite as bright; so 

 are a few of the Illinois and Missouri ones, and one from Louisiana (tWo). 

 But the link between the extreme of rnfidormm is afforded by No. 10083. the 

 type of "occidentalis", which might be described in identical terms; and, 

 although the tawny is not quite so vivid, it similarly tinges the feet. 



The extreme of paleness or grayness is illustrated in what has been called 

 "breweri". In this, the upper parts are of a light dull grizzly-gray, with a 

 small proportion of yellowish-brown, and the under parts soiled white; the 

 hairs being only plumbeous at the extreme base, and consequently scarcely 

 shading the whitish. The cause and nature of this variation have been so 

 perfectly explained by Mr. Allen* that I shall quote his words: — "On Mus- 

 keget Island (a small, uninhabited, low sandy island between Nantucket and 



* Mammals of Massachusetts, in Bull. Mus. Comp, Zool. No. 8, p. 232. 



