account along similar lines for all of the kinds of mammals native to North America is in prospect. Corrections of, and additions to, the material presented here will be welcomed and I shall be especially grateful for suggestions as to a more useful arrangement of the data.

In arranging the families, genera and species the aim has been, in each category, to list the most primitive members first and to list last the one which presents the highest total of specialization. The term total of specialization is used here, as Miller (1924:2) used it, to denote the sum of the physical modifications which any mammal, or taxonomic category of mammals, is supposed by the author to have undergone during the course of its development away from its original or generalized mammalian stock.

Subspecies of any one species are arranged alphabetically. On the maps, of course, the subspecies are shown in their correct geographic positions.

For each subspecies, or species if it has not been divided into subspecies, there is given (1) the accepted scientific name (selected in accordance with the rules of the International Commission of Zoological Nomenclature); (2) a citation to the account in which the terminal part of the name was first proposed (the original description of zoological parlance) followed by a statement of the type locality; (3) a citation to the account in which the combination of names (generic, specific and subspecific) used in the present account first was employed unless the name combination used here is the same as that in the original description; (4) synonyms arranged in chronological order, and (5) marginal record stations of occurrence.

These marginal records are arranged in clockwise order beginning with the northernmost locality. If more than one of the marginal localities lies on the line of latitude that is northernmost for a given kind of mammal, the westernmost of these is recorded first. The marginal localities that are represented by symbols on the corresponding distribution map are in Roman type. Italic type is used for those marginal localities that could not be represented by symbols on the map because undue crowding, or overlapping, of the symbols would have occurred. An understanding of how these localities are arranged and knowledge as to which of these localities are shown on the map will permit a person to associate any symbol on a map with its corresponding place name.

Measurements are in millimeters unless otherwise indicated. Capitalized color terms are after Ridgway (Color Standards and Color Nomenclature, Washington, D. C., 1912), and uncapitalized terms refer to no particular color standard. Several of the drawings of skulls were reproduced originally in the "Mammals of Nevada" (Hall, 1946) and I am grateful to the University of California Press for permission to use them here. Those drawings were made by Miss Viola Memmler. The other drawings are the work of Mrs. Frieda Abernathy, Mrs. Diane (Danley) Sandidge, and Mrs. Virginia (Cassel) Unruh. Initials on the drawings identify the individual's work. The study here reported upon was aided by a contract between the Office of Naval Research, Department of the Navy, and the University of Kansas (NR 161-791). Also, assistance with some of the field work was given by the Kansas University Endowment Association and by Dr. Curt von Wedel. For the corrected dates on several publications I am indebted to Dr. A. Remington Kellogg. For assistance with the organization of the data for the present account I am grateful to several persons, especially to my wife, Mary F. Hall, and to Dr. Keith R. Kelson.

Order LAGOMORPHA—Hares, Rabbits and Pikas