Type.—Female, adult, skull and skin; no. 2490/1886, Amer. Mus. Nat. Hist.; San Francisco Forest [then (1886?), Yavapai County], Arizona; June 20, 1886; obtained by Edgar A. Mearns.
The skull (plates [31]-[33]) is complete and unbroken save for a small puncture in the right squamosal. The incisors above and below and M2 and P2 on each side are missing. Four canines are preserved separately. Otherwise the teeth are in place. The skin has been taken down from a mount. Some hair has been lost from in front of the ears. Seven mammae are evident and show the animal to have been nursing young. The slightly faded color was mentioned by Mearns in the original description. He says (1891:234): "The memorandum of the colors was made before skinning, the specimen having been subsequently preserved in a solution of alum and salt, which extracted much of the coloring matter."
Range.—Transition to Hudsonian life-zones of Arizona and extreme western New Mexico, along the Colorado River, and south of the Little Colorado River, from San Francisco Mountain region along Mogollon Plateau to extreme western New Mexico. See figure 29 on page [221].
Characters for ready recognition.—Differs from M. f. neomexicana by near (14 n) Brussels Brown rather than Buckthorn Brown color of upper parts, in absence rather than presence of white frontal spot continuous with color of underparts, in basilar length of less than 44 in males and 39.3 in females; from M. f. nevadensis in that total length averages less than 375 in males and 330 in females, basilar length averaging less than 41 in males and less than 36.7 in females.
Description.—Size.—Male: No. 24679/32071, from Springerville, and no. 248993 from the Kaibab Plateau, measure respectively, as follows: Total length, 363, 367; length of tail, 140, 143; length of hind foot, 41.5, 41.0. Tail is 63, and 64 per cent as long as head and body. These males, the only specimens of that sex of which external measurements are available, probably are grading toward nevadensis and therefore are nontypical.
Female: Three specimens, one young from Little Spring, a subadult from Deadmans Flat and the type specimen, measure respectively as follows: Total length, 323, 296, 302; length of tail, 110, 101, 109; length of hind foot, 38, 33, 36. These average, 307, 107, 36. Tail averages 53 per cent as long as head and body.
Differences in external measurements of the two sexes are: Total length, 56; length of tail, 39; hind foot, 5.5.
Externals.—Longest facial vibrissae black, brown or white (often all three colors in same specimen) and extending beyond ear; carpal vibrissae same color as underparts and extending to apical pad of fifth digit; hairiness of foot soles (in summer pelage) about as shown in figure [19].
Color.—Winter pelage unknown. Summer pelage with upper parts near (14 n) Brussels Brown or tone 2 of Raw Umber of Oberthür and Dauthenay, Pl. 301, darker on top of head from nose to line connecting posterior margins of ears. Tip of tail always black. Chin and upper lips white. Remainder of underparts Buff Yellow to Straw Yellow and rarely Ochraceous Buff. Color of underparts extends distally on posterior sides of forelegs over toes onto antipalmar faces of feet and wrists, on medial sides of hind legs to ankles and over antiplantar faces of toes, medial third of tarsus, and over proximal fifth to fourth of ventral side of tail. Least width of color of underparts averaging, in 8 specimens, 44 (29-54) per cent of greatest width of color of upper parts. Black tip of tail, in four females averaging 35 (33-38) mm. long. Thus, averaging shorter than hind foot and 32 per cent of length of tail-vertebrae. Three of the eight specimens before me (no. 242671 from 25 mi. SE Flagstaff, not available at time of this accounting) have the dark spot near the angle of the mouth faintly indicated, whereas the other five lack the spots. The color is as in M. f. nevadensis.
Skull and teeth.—Male (based on 55211, 65231, and 248993; see page [422]): See measurements and plates [19]-[21]; weight 2.7 and 3.1 grams; basilar length, 40.4; zygomatic breadth more than distance between condylar foramen and M1 or than between anterior palatine foramen and anterior margin of tympanic bulla; mastoid breadth more than postpalatal length; postorbital breadth less than length of upper premolars and more than width of basioccipital measured from medial margin of one foramen lacerum posterior to its opposite; interorbital breadth more or less than distance between foramen opticum and anterior margin of tympanic bulla; breadth of rostrum less than length of tympanic bulla; least width of palate more or less than medial length of P4; anterior margin of tympanic bulla as far posterior to foramen ovale as width of 3-1/2 (including I3) upper incisors; height of tympanic bulla more than distance from its anterior margin to foramen ovale; length of tympanic bulla more than length of lower molar-premolar tooth-row and longer or shorter than rostrum; anterior margin of masseteric fossa below talonid of m1.
Female (based on the type specimen): See measurements and plates [31]-[33]; weight, 1.6 grams; basilar length, 35.5; zygomatic breadth less than distance between condylar foramen and M1 and more than distance between anterior palatine foramen and anterior margin of tympanic bulla (nearly equal in each instance); postorbital breadth less than length of upper premolars and greater (7.1-8.4) than width of basioccipital measured from medial margin of one foramen lacerum posterior to its opposite; least width of palate equal to inside length of P4; tympanic bulla as far posterior to foramen ovale as width of 3 (including I3) upper incisors; height of tympanic bulla more than distance from its anterior margin to foramen ovale; length of tympanic bulla more than length of lower molar-premolar tooth-row and greater than length of rostrum.
The skull of the female averages 41 per cent lighter than that of the male.
Compared with the skull of M. f. nevadensis, that of arizonensis is smaller, less heavily ridged and has more inflated tympanic bullae and a relatively greater mastoid breadth. Comparison with the skull of M. f. neomexicana is made in the account of that subspecies.
Remarks.—In 1891 Mearns (234-235) named this weasel as a full species on the basis of two individuals taken by him in 1886 and 1887. Since that time only a few additional specimens have been preserved. Only four are adults. Although this material does not permit of a definition of the subspecies as precise as could be wished, still, it clearly shows that the animals from the plateau region of Arizona are recognizably different from those farther north in the Sierra Nevada of California and those of the Rocky Mountains and Great Basin region northward to the Canadian border. These more northern animals have gone by Mearns' name, arizonensis, since the date of its proposal until 1939 when the name nevadensis was proposed.
The smaller size, especially of the skull, and the greater inflation of the tympanic bullae are the outstanding characters which distinguish arizonensis from the similarly marked nevadensis. The bullae are relatively much inflated throughout but especially so on the posteromedial parts.
Although the three adult males and two subadult females available of this subspecies are smaller in most parts measured than any of the scores of nevadensis of similar age that have been measured, overlap in size probably will be found as additional specimens of arizonensis become available. A young female, no. 18513, coll. D. R. Dickey, from Little Spring, does have certain cranial measurements as large as are found in the minimum-sized nevadensis from farther north.
Intergradation with the two subspecies whose geographic ranges adjoin that of arizonensis is indicated by specimens at hand. One of these is the adult male from 25 miles southeast of Flagstaff, which shows decided approach to neomexicana, in color and in possessing white facial markings less well developed than in neomexicana. Even better developed white facial markings, with intervening blackish coloration, are displayed by no. 148271, U. S. Nat. Mus., from 8500 feet altitude on Willow Creek, New Mexico. This subadult female shows approach to neomexicana also in larger size of the skull and entire animal. The great inflation of the posterior part of each of its bullae and the dark color of the upper parts are characters of arizonensis. The color of the underparts stops at the ankles leaving the hind feet dark colored, in which respect the specimen is unlike either neomexicana or arizonensis. If additional specimens showing the same characters as this one be found at other nearby localities they probably should be given recognition as a separate subspecies. For the present it seems best to regard the specimen merely as an intergrade. Although it might, with almost equal propriety, be referred to either neomexicana or arizonensis, the specimen is here placed with the latter. The subadult male from Springerville, Arizona, is of larger size than the topotypical male of arizonensis and in this respect shows slight approach to nevadensis. The narrower mastoidal breadth and slightly less inflated tympanic bullae of the male from the Kaibab Plateau may reflect merely individual variation or may represent intergradation in these features with nevadensis.
The statement made by Merriam (1896:22) that, "The type specimen . . . is an immature female and is of unusually small size. A male obtained by him [Mearns] near the same place is of the normal size, as is another male in the Department collection from Springerville, Ariz., collected by E. W. Nelson," needs correction. The female is not immature. The specimen obtained by Mearns near the same place probably refers to Amer. Mus. No. 2489, from Quaking Asp Settlement, which lacks both the skull and external measurements. As stuffed it is of small size for a male. The male from Springerville, as shown by the external and cranial measurements, is not of normal (i. e. average) size, but is smaller than the average for the other populations of similarly colored weasels referred to by Merriam (op. cit.) as arizonensis but here described under the name nevadensis.
None of the skulls shows signs of infestation of the frontal sinuses by parasites.