The order of arrangement of the following accounts is that of Miller (1924) with some modifications. For example, the Chiroptera are arranged according to Tate (1942), the Sciuridae according to Bryant (1945) and the Cetacea according to Scheffer (1942). A few other minor changes are included.

Although the principal purpose of this report is to describe and interpret the distribution of the various species and races of mammals that occur in Washington, a brief description and account of the habits of the animals is included. Each species account begins with a description, based principally on external characters. This is followed by pertinent information regarding the range of the species, its relationships within the genus and a brief account of its habits. The habits are dealt with in most detail for the species that are of greatest economic importance.

The accounts of subspecies are largely technical. The account of the type specimen is rather complete. Subspecific diagnoses are brief, stating often only the principal racial characters. Standard external measurements are usually given for each subspecies. All measurements, unless otherwise stated, are in millimeters and weights are in grams. Specimens are adult, unless otherwise stated.

No formal list of specimens examined is included. Localities from which specimens have been examined are usually shown on the distribution maps by solid circles. Open circles indicate localities from which specimens, not examined by me, have been recorded by other persons. Most of these records are published but a few are based on authentic trappers' reports, photographs, or other evidence. Unusual occurrences of animals outside their natural ranges are not shown on the maps. Not every record from well within the range of a subspecies has been plotted, but care has been taken to plot all records of occurrences from peripheral areas.

When more than one race of a species occurs in Washington, specimens from localities where the geographic range of one subspecies meets or approaches that of another are listed as "marginal occurrences" in the paragraph on the distribution of the race to which they are best referred. Marginal occurrences are listed from north to south and from west to east. The authority for the record, if published, is given. When the record is based on specimens examined by the author, the collection containing the specimen is indicated as follows:

(E.S.B.) Ernest S. Booth collection. College Place, Washington.

(J.M.E.) J. M. Edson collection, Bellingham, Washington.

(K.U.) University of Kansas, Museum of Natural History, Lawrence, Kansas.

(M.V.Z.) Museum of Vertebrate ZoÖlogy, University of California, Berkeley, California.

(U.S.N.M.) United States National Museum, Washington, D. C. Specimens from the Biological Surveys Collection are included here.

(V.B.S.) Victor B. Scheffer collection. United States National Museum, Washington, D. C.

(W.S.C.) Washington State College, Charles R. Conner Museum, Pullman, Washington.

(W.S.M.) Washington State Museum, University of Washington, Seattle, Washington.

(W.W.D.) Walter W. Dalquest collection, Seattle, Washington.

In all, 230 kinds (species and subspecies) of mammals are listed for the state of Washington. Of these, 9 kinds (opossum, eastern gray squirrel, fox squirrel, 3 kinds of Old World rats, house mouse, nutria, and eastern cottontail) have been introduced into Washington from elsewhere. The dog of the Indians might be listed as a tenth introduced species. The grizzly bear, the sea otter, the wolf, the moose, one race of mountain sheep, one race of mountain goat, and, if they ever occurred in the state, the pronghorn antelope and bison, are nearly or completely extinct in Washington. Mammals other than cetaceans possibly occurring in Washington, but of which satisfactory record is lacking, are mentioned in a hypothetical list at the end of the accounts of species. Of the 220 kinds of native mammals, known to occur in the state, 23 are marine (4 pinnipeds, 19 cetaceans). The 197 living, native, land mammals include 6 orders, 20 families, 58 genera and 101 full species.