Diagnosis.—Size medium to small for the species; dorsum Buffy Brown to fawn color; dorsal ground color of unworn pelage of adults varying from Buffy Brown in darkest series (especially those from higher altitudes) to Avellaneous with grayish overtones in palest series; worn pelage in mid-dorsal region of adults fawn to grayish; terminal parts of individual hairs buffy, gray basally; guard hairs on dorsum black-tipped, grayish basally; belly Light Gull Gray, distal half of hairs white, proximal half Neutral Gray; hairs in region of throat and chin white to base (some specimens with faint buffy overtones); forefeet dusky below, whitish above; hind feet whitish above, ventral surface whitish to dusky; dorsal and lateral vibrissae black, other vibrissae white. Average and extreme measurements of six adults from the type locality are as follows: total length, 109 (106-117); length of tail, 44.5 (43-48); length of body, 63 (57-69); length of hind foot, 13.1 (12.7-14.0); occipitonasal length, 17.5 (17.4-18.0); zygomatic breadth, 9.3 (9.1-9.5); postpalatal length, 6.6 (6.2-6.9); least interorbital breadth, 3.5 (3.4-3.6); length of incisive foramina, 3.8 (3.6-4.1); length of rostrum, 5.9 (5.7-6.0); breadth of braincase, 8.6 (8.5-8.8); depth of cranium, 6.6 (6.2-6.9); alveolar length of maxillary tooth-row, 3.2 (3.1-3.4); for photographs of the skull, see [Plate 2e] and [Plate 4f].
Comparisons.—For comparisons with B. t. allex, B. t. canutus, B. t. ater, and B. t. taylori, see accounts of those subspecies. From B. t. analogous, B. t. paulus differs as follows: dorsal color paler having more reddish-brown than blackish-brown tones; venter whitish to buffy, instead of gray to light-gray; tail bicolored (not unicolored), usually having more hairs; hind feet white (not sooty) above. Cranially, B. t. paulus differs from B. t. analogous in: skull slightly smaller in all dimensions; maxillary part of zygoma narrowing and forming oblique angle rather than a near right angle with rostrum; anterior incisive foramina constricted posteriorly; tips of nasals truncate (less rounded).
Remarks.—J. A. Allen (1903:599) correctly pointed out that young specimens, in first pelage, were gray brown; young adults were darker and more varied with some blackish; adults and old adults were buffy to grayish. The change in color of pelage with increasing age is more pronounced in paulus than in other subspecies of B. taylori. Of two males collected on April 12, 1949, one, an adult, is buffy brown, and the other, an old adult with worn pelage, is grayish-brown. In mice in the earlier stages of adulthood, underfur of the dorsum is buffy at the tips and gray basally. With increased wear, the buffy tip is lost. Consequently, mice in the later stages of adulthood are grayish.
B. t. paulus intergrades with ater to the north in Chihuahua (see account of that subspecies), with analogous to the south in Jalisco, and with allex (see account of that subspecies) to the southwest in Nayarit and Jalisco. The zone of intergradation between paulus and analogous in Jalisco approximately borders the Río Grande de Santiago from the western part of the State to the northwest shore of Lago de Chapala. Nineteen specimens from 2 mi. WNW Lagos de Moreno in northwest Jalisco seem to be intermediate between paulus and analogous in color, averaging slightly grayer than typical paulus. The series of 19 is referable to paulus on the basis of cranial characters.
A series of 34 specimens from 3 mi. W La Venta, Jalisco (referable to paulus), is indistinguishable in color of pelage from two series of paulus from 5 mi. N Durango, and from 8 mi. NE of Durango, except that the antiplantar surfaces of the hind feet are sooty as in analogous. Seemingly, features of color mentioned above as diagnostic of the two subspecies are either present or absent and there is no tendency toward intermediacy in color in the population from 3 mi. W La Venta.
The Río Grande de Santiago may have acted in the past as a physical barrier reducing gene flow between allex and paulus and in separating completely the two populations for limited periods.
Specimens examined.—Total 176, all from the Republic of México and distributed as follows: Chihuahua: Rancho Sanignacio, 4 mi. S, 1 mi. W Santo Tomás, 1; El Rosario, 6700 ft., 1; 2 mi. W Miñaca, 6900 ft., 11; Balleza, 1[50]. Durango: Rosario, 1[51]; type locality, 14[51] (including the type); San Gabriel, 2[51]; Rancho Santuario, 2[51]; 1 mi. N Chorro, 6450 ft., 1; 8 mi. NE Durango, 6200 ft., 2; 5 mi. N Durango, 6400 ft., 2. Zacatecas: Valparaíso, 6500 ft., 10[50]. Aguascalientes: 18 mi. W, 2 mi. S Aguascalientes, 6000 ft., 1; 16 mi. S Aguascalientes, 5[52]. Jalisco: 1 mi. NE Villa Hidalgo, 6500 ft., 1; 2 mi. WNW Lagos de Moreno, 6370 ft., 19; 2 mi. ESE Tequila, 4000 ft., 11; 3 mi. W La Venta, 33, 1[53]; 12 mi. W Guadalajara, 3[54]; Atemajac, 12[50]; 4 mi. W Guadalajara, 5100 ft., 3; 2 mi. N, 1/2 mi. W Guadalajara, 11; 2 mi. NW Magdalena, 4500 ft., 7[50]; 1 mi. N Tala, 4400 ft., 3; 3 mi. W Tala, 4300 ft., 18.
Marginal records.—Chihuahua: Rancho Sanignacio, 4 mi. S, 1 mi. W Santo Tomás; El Rosario; Balleza. Durango: Rosario, 6700 ft.; 1 mi. E Zarca (Blossom and Burt, 1942:1); 1 mi. N Chorro, 6450 ft. Zacatecas: Valparaíso, 6500 ft. Aguascalientes: 1 mi. N Chicalote (Blossom and Burt, 1942:4). Jalisco: 2 mi. WNW Lagos de Moreno, 6370 ft.; 4 mi. W Guadalajara, 5100 ft.; 3 mi. W Tala, 4300 ft.; 2 mi. NW Magdalena, 4500 ft. Durango: 5 mi. N Durango, 6400 ft.; type locality. Chihuahua: 2 mi. W Miñaca, 6900 ft.
[50] United States National Museum (Biol. Surv. Collections).