MILLER: BEACH MOUSE OF MUSKEGET ISLAND. 
83 
damp and fresh. I found several of these store houses on December 
28, 1892. The grass — nearly a peck in each — was perfectly green, 
while all that growing on the island had long been dead. In prepar¬ 
ing their winter supply of grass, the animals do not cut off the succu¬ 
lent bases, but gather the stalks entire and afterward select the parts 
that they use as food. On South Point Island there is no fresh 
water, so it is probable that the mice get what moisture they need 
from the juicy grass stems. 
Among the mice caught on June 21, 1893, the larger were very 
fierce, while the smaller ones were timid. A few medium-sized 
individuals, however, were from the first perfectly tame, and took 
food from the hand without fear. They would seize a stalk of 
beach grass with their front feet, and biting off a piece of convenient 
length, sit on their haunches and eat it, passing it quickly back and 
forth between the rapidly moving incisors until only the toughest 
fiber remained. 
As the supply of Ammophila on Muskeget is practically unlimited 
the beach mice never suffer from hunger, but the struggle for exis¬ 
tence must be fierce, notwithstanding, for few small mammals live in 
as exposed situations. The effect of these two factors has been the 
production of a species differing from the Microtus pennsylvanicus 
of the mainland and neighboring islands in its large size, coarse fur, 
pallid color, and certain cranial peculiarities. The latter bear no 
conceivable relation to the peculiar needs of the animal, but the 
characters of size and fur are distinctly adaptive and fit the mice 
better to meet the requirements of their peculiar environment. 
Microtus breweri (Baird). 
1857. Armcola breweri Baird, Mam. N. Amer., p. 525. 
1869. Armcola riparius Allen, Bull. Mus. Comp. Zobl., 1, p. 
231-234 (part). 
1877. Arvicola riparius Coues, Monogr. 1ST. Amer. Rodentia, p. 
180, 182 (part). 
1888. Armcola breweri Merriam, Amer. Nat., 22, p. 703. 
Specific characters. — Larger than Microtus pennsylvanicus 
(Ord), and with proportionally shorter tail. Color throughout paler 
than usual in the submenus Microtus and much as in the American 
o 
