No. 3.— The Beach Mouse of Muskeget Island. 
By Gerrit S. Miller, Jr. 
The Muskeget Island beach mouse, Microtus brevceri (Baird), 
although described nearly forty years ago 1 is still imperfectly 
known. 
The few published references to it are brief and have added little 
to the information contained in the original description. 
The first notice of the species appeared in Baird’s work on North 
American mammals, published as volume 8 of the Pacific Railroad 
Survey Reports. Here the animal — named after its discoverer, 
Dr. T. M. Brewer— was briefly described, but no account was given 
of its habits or of the peculiar conditions under which it lives. The 
next mention of Microtus breiceri was by Mr. J. A. Allen, who wrote 
in 18G9 2 : — “On Muskeget (a small, uninhabited, low sandy island 
between Nantucket and Martha’s Vineyard) I recently found the 
so-called A. [ J£] Breiceri excessively abundant.” Mr. Allen consid¬ 
ered the mouse the same as the Microtus pennsglcanicus of the 
mainland, since 44 Specimens occasionally occur [on Muskeget] of 
nearly the ordinary color, or which are undistinguishable from the 
lighter-colored specimens from the interior.” He adds, that “The 
mice living on the extensive sand-dunes at Ipswich, [Mass.,] under 
circumstances similar to those of the Muskeget mice, often present 
as I have recently ascertained, the half white appearance of A. \_M.~] 
4 Breiceri .’ ” Dr. Cones in his monograph of the American species of 
4 Arcicola ’ {Microtus) accepts Mr. Allen’s conclusions with regard to 
the Muskeget mouse and gives additional reasons for considering 
Microtus breiceri a synonym of M. pennsglcanicus . 3 In summing 
up he says (p. 182): “We were at first inclined to regard 
[ Microtus'] 4 breiceri ’ as an isolated case of [il£] riparius [_ pennsgl -- 
canicus ] ; but the facts of the Ipswich mice, as given by Mr. Allen, 
and some intermediate specimens before us, show such a gradation 
that we cannot draw any line.” With the exception of a passing 
allusion to the species made by Dr. Merriam in 1888 4 Microtus 
breiceri has received no attention during the past eighteen years. 
1 Mam. N. Amer., p. 525, 1857. 
2 Bull. Mus. Comp. Zool., 1, p. 232. 
3 Monogr. N. Amer. Rodgntia, p. 180, 182, 1877. 
4 Amer. Nat., 22, p. 703, Aug., 1888. 
