1911 _luteus_ (_Zapus_) Miller [= _Zapus princeps luteus_], Proc.

Biol. Soc. Washington, 24:253, December 23, 1911, applies to the jumping mouse in north-central and southern New Mexico and eastern Arizona.

1913 _australis_ (_Zapus luteus_) Bailey [= _Zapus princeps luteus_], Proc. Biol. Soc. Washington, 26:129, May 21, 1913, was applied to the jumping mouse of southern New Mexico, but is here regarded as a synonym of _luteus_.

1920 _eureka_ (_Zapus trinotatus_) Howell, Univ. California Publ.

Zool., 21:229, May 20, 1920, applies to the jumping mouse of the humid coastal district of northern California.

1931 _cinereus_ (_Zapus princeps_) Hall, Univ. California Publ.

Zool., 37:7, April 10, 1931, applies to the jumping mouse of extreme northwest Utah and south-central Idaho.

1931 _curtatus_ (_Zapus princeps_) Hall, Univ. California Publ.

Zool., 37:7, April 10, 1931, applies to the jumping mouse of the Pine Forest Mountains, Humboldt County, Nevada.

1931 _palatinus_ (_Zapus princeps_) Hall [= _Zapus princeps oregonus_], Univ. California Publ. Zool., 37:8, April 10, 1931, was applied to the jumping mouse of Lander and Nye counties, Nevada, but is here regarded as a synonym of _oregonus_.

1932 _kootenayensis_ (_Zapus princeps_) Anderson, Ann. Rept. Nat.

Mus. Canada for 1931:108, November 24, 1932, applies to the jumping mouse of southeastern and central British Columbia, northern Idaho, and eastern Washington.

1934 _idahoensis_ (_Zapus princeps_) Davis, Jour. Mamm., 15:221, August 10, 1931, applies to populations in parts of British Columbia, Alberta, Idaho, Montana, and Wyoming.

1939 _utahensis_ (_Zapus princeps_) Hall, Occas. papers Mus. Zool.

Univ. Michigan, 296:3, November 2, 1934, applies to the jumping mouse of southeastern Idaho, western Wyoming, and eastern Utah.

1941 _burti_ (_Zapus_) Hibbard, Univ. Kansas Publ., Bull. State Geol. Surv. Kansas, 38:214, July 14, 1941, refers to two fragmentary right rami of Pleistocene age (Borchers fauna) from Loc. No. 9, Meade County, Kansas.

1942 _brevipes_ (_Zapus hudsonius_) Bole and Moulthrop [= Zapus hudsonius america.n.u.s], Sci. Publ. Cleveland Mus. Nat. Hist., 5:168, September 11, 1942, based on specimens from Bettsville, Seneca County, Ohio, which are inseparable from _america.n.u.s_ that has priority.

1942 _rafinesquei_ (_Zapus hudsonius_) Bole and Moulthrop [= _Zapus hudsonius america.n.u.s_], Sci. Publ. Cleveland Mus. Nat. Hist., 5:169, September 11, 1942, was applied to jumping mouse of southeastern Ohio but is here regarded as a synonym of _america.n.u.s_.

1943 _ontarioensis_ (_Zapus hudsonius_) Anderson [= _Zapus hudsonius canadensis_], Ann. Rept. Provancher Soc. Nat. Hist., Quebec, 1942:52, September 7, 1943, was applied to animals from eastern Ontario but is here regarded as a synonym of _canadensis_.

1950 _pallidus_ (_Zapus hudsonius_) c.o.c.krum and Baker, Proc. Biol.

Soc. Washington, 63:1, April 26, 1950, refers to the jumping mouse from Kansas, Missouri, Oklahoma, Nebraska, and south-central South Dakota.

1951 _rinkeri_ (_Zapus_) Hibbard, Jour. Mamm., 32:351, August, 1951, refers to single incomplete right ramus of upper Pliocene age, Rexroad formation and fauna, from Loc. UM-UK-47, Fox Canyon, sec. 25, T. 34S, R. 30W, XI Ranch, Meade County, Kansas.

1953 _intermedius_ (_Zapus hudsonius_) described as new on page 447 of this paper.

1953 _preblei_ (_Zapus hudsonius_) described as new on page 452 of this paper.

CHARACTERS OF TAXONOMIC WORTH

EXTERNAL PARTS.--The total length, the length of the tail, and the length of the hind foot are useful to some extent in distinguishing species and subspecies. Geographic variation in these measurements is clinal in some species. For example, _Zapus trinotatus_, which inhabits the western coast of North America, decreases in size from the northern to the southern part of its range. There is considerable overlap in external measurements, in specimens of the same age, between the species _Z. trinotatus_ and _Z. princeps_, but only slight overlap between _Z.

princeps_ and _Z. hudsonius_ and between _Z. trinotatus_ and _Z.

hudsonius_. If all collectors measured external parts in the same way the measurements would be more useful for differentiating one species from another.

PELAGE.--The pelage, both in its entirety and as individual hairs, provides taxonomic characters as has been pointed out by Moojen (1948:324) for the genus _Proechimys_, by Williams (1938:239) for the Insectivora, and by Hausman (1920:496) for several groups of mammals.

In addition to the sensory hairs, facial vibrissae, nasal hairs, and carpal vibrissae, there are three kinds of hairs in the normal coat of _Zapus_: guard hairs, overhairs, and underfur. The guard hairs and underfur differ in different species (see figs. 35-37).

The guard hairs taper at both ends, are elliptical in cross section, and are wider and longer than the other two kinds of hair. The bases of the guard hairs are grayish, and the amount of pigment gradually increases distally to a dark brownish or blackish shade. The guard hairs vary in greatest diameter from 96 microns to 168 microns, depending upon the species, and variation in diameter provides characters of taxonomic worth. No clinal variation in diameter of the guard hairs was detected.

In _Z. hudsonius_ the guard hairs average 115 microns (96-140) and are significantly narrower than those of _Z. princeps_ and _Z. trinotatus_, which average 142 microns (130-168) and 141 microns (133-154), respectively. Pigmentation of the guard hairs contributes little information useful in separating the species of _Zapus_. All of the species have a prominent compounded medulla in which the pigment cells anastomose to form a labyrinthine column.

The individual hair of the underfur is cylindrical and tapers abruptly at each end; it is short, thin, flexible, and usually is bicolored on the back and sides of the mouse. The apical zone is yellow-brown (for example, Ochraceous-Buff) and the proximal part is whitish or grayish, which gradually darkens to near black subapically.

The width of a hair in the underfur is of no taxonomic significance, in that individual variation exceeds that between species.

The pattern of the pigment in the medulla of the hair, however, does vary specifically. Comparable samples from _Z. trinotatus_, _Z.

princeps_, and _Z. hudsonius_ of the same age, s.e.x, and season reveal a pattern characteristic for each species (see figs. 35-37).

All species of _Zapus_ agree closely in color pattern. A broad longitudinal dorsal band of some shade of yellow-brown flecked with black hairs is bordered by a lateral band of a lighter color usually containing fewer black hairs than on the dorsum. The underparts are usually white but are sometimes suffused with color resembling that on the sides. Between the white underparts and the darker color of the sides there is often a narrow, clear ochraceous stripe. Dorsal and lateral hairs are uniformly grayish-white at their bases; only the distal parts of the hairs are responsible for the external color of the animal.

The pelage of juveniles is usually finer and softer than the pelage of adults. The lateral and dorsal bands are not so conspicuously marked in young animals, and individual hairs are not so long or so wide as in adult animals.

[Ill.u.s.tration:

FIGS. 35-37. Photomicrographs of underhairs (middle third) from each of the species of the genus _Zapus_. 500.

FIG. 35. _Zapus t. orarius_, adult, female, No. 20293 MVZ, 3 mi. W Inverness, 300 ft., Marin County, California.

FIG. 36. _Zapus p. oregonus_, adult, male, No. 47856 KU, Harrison Pa.s.s R. S., Ruby Mt's, Elko County, Nevada.

FIG. 37. _Zapus h. pallidus_, adult, male, No. 22954 KU, 4 mi. N, 1-3/4 mi. E Lawrence, Douglas County, Kansas.]

Preble (1899:7) and Howell (1920:226) remark as to the noticeable difference between pelages of spring and early fall. The pelage in spring is described as bright and fresh whereas that in fall is dull and worn. Actually both bright and worn pelages can occur in any one population at any one time. Some newly molted individuals are in fresh unworn pelage; some individuals, which are molting, are in ragged, worn pelage; and other individuals perhaps could be found to represent intermediate stages.

Variations from the normal color of the pelage are rare. Among more than 3,000 specimens of _Zapus_ examined there were only 12 individuals (five _Z. princeps_, 6 _Z. hudsonius_, and 1 _Z. trinotatus_) that were abnormally colored. A single white spot was noted on each of 10 (5 _Z.

princeps_, 4 _Z. hudsonius_, and 1 _Z. trinotatus_) of these individuals; the spots were on the dorsal, anterior half of the body.

The skin beneath the patch of white hair was in each animal like that beneath the neighboring normally-pigmented hair. One specimen of _Z.

hudsonius_ (NMC No. 6669) is everywhere black, excepting the dorsal surface of the toes of the forefeet. Most of the individual hairs from various areas of the body are black for their entire length; some, however, have non-pigmented silvery tips. One specimen of _Z. hudsonius_ (KU No. 645) lacks any black; dorsally the pelage is nearest to Ochraceous-Buff and it is white on the venter. Individual hairs of the dorsal area are white for the basal two-thirds of their length (as compared to gray and brown in the animals with normal pigmentation) and near Ochraceous-Buff on the distal third (as compared to hairs which are dark brown tipped with Ochraceous-Buff). The feet and tail are white.

MOLT.--The sequence of molt for _Zapus_ has been ascertained from examination of the study skins. In all species of this genus there seems to be only one annual molt in adults. In the young of the year this molt occurs after August first and before hibernation. All individuals of a single population do not molt at any one time; females continue to molt later in the autumn than do the males; some individuals begin the molt as early as mid-June and others show molt as late as the end of October; approximately three weeks are required for an individual to complete its molt (Quimby, 1951:74); readiness for molt and early stages in molt can be detected (in museum specimens) by the greater thickness of the skin.

Hairs lost accidentally are quickly replaced, regardless of the condition of the molt.

In _Zapus hudsonius_, new hair appears simultaneously on the anterior dorsal surface of the nose and on the mid-dorsal surface between the scapulae. The molt proceeds anteriorly from the shoulders and posteriorly from the nose. At the same time that the head is covered, new hair appears on the sides of the body from the forelegs to the cheeks. New pelage then appears posteriorly, and molt continues as a wave from these points over the sides and back with the rump receiving new hair last (see figs. 42 and 43).

In _Zapus princeps_ new hair appears first on the mid-dorsal surface between the scapulae. From this starting point molt progresses anteriorly, laterally, and posteriorly. Progress over the head is rapid; the head receives its new hair sooner than the caudal region. Molt moves progressively nearer to the base of the tail and progressively nearer to the mid-ventral surface. The rump is the last area to complete its molt (see figs. 40 and 41).

The progress of molt in _Z. princeps_ might be likened to the flow of a drop of paint on the curved surface of a ball where the paint flows in all directions but is speeded at one point and slowed at the opposite by a slight tilting of the ball from the horizontal.

In the species _Zapus trinotatus_ new hair appears simultaneously on the anterior, dorsal surface of the nose and on the mid-dorsal surface between the scapulae. In this respect the progress of molt of _Z.

trinotatus_ resembles that of _Z. hudsonius_. From these starting points molt progresses rapidly over the head, the molt moving anteriorly from the shoulders and posteriorly from the nose with the result that it covers the dorsal surface of the head; hair then appears on the cheeks and sides of the neck. The progress of molt on the remaining areas of the body is comparable to that of _Z. princeps_; molt progresses toward the tail and toward the mid-ventral line. The rump, as in _Z. princeps_, is the last area to complete its molt (see figs. 38 and 39).

[Ill.u.s.tration: FIGS. 38-43. Diagrams showing differences in progress of molt in the three species of the genus _Zapus_. All approximately 1/2 natural size. Figs. 38, 40 and 42 lateral view. Figs. 39, 41 and 43 dorsal view.