82 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Aramophila, or beneath the stalks of a beach golden rod. Occa¬ 
sionally a mouse tyies to escape by entering a burrow among the roots 
of the beach grass, but these tunnels always afford a very insecure 
protection as they are close to the surface and seldom extend more 
than a few' inches, or at most a few feet. The mice apparently 
make these short tunnels with the sole object of reaching the softer 
parts of the beach grass stems. They are in no w r ay connected with 
the nesting burrows. Another means of shelter is, so far as I know, 
peculiar to the Muskeget mice. They construct frail nests or forms 
which may be seen scattered about everywhere. The forms are 
usually open at the top and made of the finer shreds torn off from 
the beach grass. Each is large enough to contain one animal only. 
The walls are much thinner than those of the breeding nests, being 
a mere film of grass fiber, through which the occupant can be dis¬ 
tinctly seen. The forms may be built on the bare sand or under 
some shelter indifferently. Often one partly arches a beaten path. 
The breeding nests, which resemble those of Microtus pennsylva- 
nicus , are sometimes made under the protecting stalks of the luxuri¬ 
ant iSolidac/o sempervirens or under cover of a fragment of wreckage. 
When no such convenient shelter can be found the mice construct 
short nesting burrows. These are from one to two feet in length, 
and penetrate the sand at an angle of about 45°. In this way the 
tunnel descends quickly through the dry crumbling sand at the sur¬ 
face to the more compact layers beneath, where the walls are less 
likely to cave in and smother the helpless young. At the end of the 
tunnel is a hollow, completely filled by the bulky nest. As in other 
species of Microtus the breeding season of M. breweri probably lasts 
throughout the warmer months. During the last week in June and 
first week in July, all the adult females are either pregnant or nurs¬ 
ing while the young are of every size up to those nearly half 
grown. Four or five young is the usual number in a litter. One 
nest under a beach golden rod, contained two living naked young 
and a dead one which had been partly eaten. 
The food of Microtus breweri consists chiefly of the tender bases 
of the beach grass stalks. These the mice obtain either by scratch- 
ing away the sand until the softer part of the grass is exposed, or 
by making short tunnels just under the surface. The course of such 
a tunnel is marked by tufts of withering beach grass, still standing, 
but cut beneath the sand. In the autumn the mice lay up large 
supplies of grass for winter food, burying it in the sand, where it keeps 
