76 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
Muskeget Island, the only locality in which Microtus breweri is 
known to occur, lies at the extreme western end of Nantucket 
(see figure 1). It is fifteen miles west of the town of Nantucket, 
eight miles southeast of the extreme eastern point of Martha’s 
Vineyard, and thirty miles south of Cape Cod. From the western 
end of Nantucket, Muskeget is separated by six miles of very 
shallow water interrupted about midway by Tuckernuck Island 
and on the south side partly cut off from the ocean by long narrow 
beaches. Although these beaches are constantly changing in form 
and position, they are always broken through by tidal openings 
so that a land communication is never established between the 
three islands. That part of the beach which extends westward 
from the west end of Tuckernuck is known as Smith’s Beach. 
Muskeget itself (figure 2) is about two miles long and at the 
a 
Eig. 2. Muskeget Island. 
