12 BANGS —NOTES ON DEER MICE PEs 
islands presents to a small mammal any surroundings particularly 
different from what he would find on the adjacent mainland, and 
the inference naturally is that the deer mouse has been on Nan- 
tucket a much shorter time than on Martha’s Vineyard. . 
On Monomoy it is easy enough to see how change must be 
very rapid. ‘The white sand dunes covered with Ammophila and 
other sand-loving plants, but where no trees of any sort can grow, 
offer to the deer mouse a home entirely different from the oak 
woods, the bushy old fields and maple swamps of the mainland. 
In such a place food is in the greatest abundance, and the deer 
mouse fairly swarms on the sand-hills of Monomoy, but if hé wore 
his usual coat of reddish brown he would stand out like a red rag 
on the white sand and among the gray grasses. Nature has seen 
to this, however, and the Monomoy Leromyscus is clothed in a 
coat of pale gray, with the hairs of the belly white to their very 
roots. So far as color goes, he is an exact counterpart of Pero- 
myscus niveiventris, which lives under precisely similar conditions 
on the beach of the east peninsula of the Indian River in Florida. 
Martha’s Vineyard and Monomoy are, among the islands I have 
visited, the only ones upon which the deer mouse has become 
sufficiently differentiated to need a special name. Specimens 
from the other islands — Nantucket, Tuckernuck (only in recent 
years separated from Nantucket), Muskeget, Block Island, and 
even Plum Island and Montauk Point, Long Island,’— represent 
collectively a form slightly —too slightly to be recognized in 
nomenclature — different from that of the mainland, and strangely 
enough the specimens from these various islands can hardly be 
told apart. In color this series does not differ from an equal 
series from the mainland, but the island examples are rather more 
robust and have slightly heavier skulls and dentition. 
Wilfred H. Osgood has carefully gone over all my material dur- 
ing the preliminary work on his forthcoming review of the genus 
Peromyscus, and agrees with me in all the conclusions here set 
forth. 
1 Specimens from the last two places, from the U. S. Biological Survey collection, have been 
kindly lent me for comparison by W. H. Osgood. 
