Diagnosis.—Over-all size small for species (see measurements), but tail, maxillary tooth-row and incisive foramina relatively long; upper parts dark (individual hairs banded subterminally with cinnamon and tipped with grayish, yielding an over-all color of grayish brown); lips gray, especially anteriorly and medially; alveoli of incisors narrow (4.8-5.2); posterior branch of premaxilla extending only slightly behind nasals; rostrum short; braincase broad; mastoid breadth averaging 51.1 (47.8-52.7) per cent of basilar length.
Comparisons.—Neotoma albigula subsolana, differs from topotypes of N. a. leucodon, the subspecies geographically adjacent to the southwest, as follows: size smaller, especially length of palatal bridge (6.9-8.1 instead of 8.2-9.6), alveolar length of maxillary tooth-row (8.3-8.9 instead of 8.8-9.7), and greatest length of auditory bulla (7.3-7.9 instead of 8.2-8.9); mastoid breadth relatively greater, 51.1 (47.8-52.7) instead of 47.0 (45.5-49.1) per cent of basilar length; posterior process of premaxilla extending only slightly beyond posterior border of nasals; auditory bulla conspicuously smaller; upper parts darker, especially middorsally; over-all color grayish instead of ochraceous or yellowish; lips gray instead of nearly white.
Neotoma albigula subsolana differs from N. a. albigula, geographically adjacent to the northwest (specimens from Pima County, Arizona) as follows: size averaging slightly larger, except length of nasals; mastoid breadth averaging 18.8 (17.9-20.2) instead of 17.9 (17.7-18.2), its ratio to basilar length therefore greater, 51.1 (47.8-52.7) instead of 49.4 (47.9-50.0); zygomatic arches expanded posteriorly instead of nearly parallel as in albigula; interparietal longer and narrower; mesopterygoid fossa broader; auditory bulla slightly smaller; upper parts distinctly darker.
Remarks.—N. a. subsolana is characterized by the combination of small size, dark color, small auditory bulla and relatively broad braincase. Typical specimens have been collected only at higher elevations in the Sierra Madre Oriental where no other species of Neotoma is known to occur.
Intergradation between N. a. subsolana and N. a. leucodon occurs at lower elevations on the west side of the Sierra Madre Oriental as shown by specimens from nine miles southwest of Tula, Tamaulipas, and Sierra Guadalupe, Coahuila, from which places some specimens are paler than others, approaching leucodon in color, and are slightly larger than typical subsolana. Specimens assigned to leucodon from vicinity of Presa Guadalupe and from 1 to 6 kilometers south of Matehuala, San Luis Potosí, are typical of that subspecies in measurements but are darker than topotypes.
N. a. subsolana intergrades with N. a. albigula in southeastern Coahuila (specimens from 6 to 9 miles east of Hermanas and from Panuco) where some individuals average paler and smaller than topotypes of subsolana and some have skulls that combine characters of subsolana and albigula. These specimens, which were referred to N. a. leucodon by Baker (Univ. Kansas Publ., Mus. Nat. Hist., 9:281-282, June 15, 1956), are assigned to subsolana on the basis of relatively dark upperparts and broad mesopterygoid fossa (narrow in only one specimen).
On geographic grounds, specimens not studied by me from Municipio de Galeana, Nuevo León (Koestner, Great Basin Nat., 2:13, 1941), and those from Jaumave, Tamaulipas (Goldman, N. Amer. Fauna, 31:37, October 19, 1910), probably are referable to N. a. subsolana.
The subspecific name subsolana (Latin adjective for eastern) is proposed for this woodrat because of its eastern geographic occurrence.
Measurements.—Average and extreme measurements of nine topotypes (6 males and 3 females) are as follows: total length, 338 (315-370); length of tail-vertebrae, 157 (130-182); length of hind foot, 35 (33-37); length of ear from notch, 31 (29-34); basilar length, 36.5 (34.7-39.2); zygomatic breadth, 23.9 (22.5-25.0); interorbital constriction, 5.5 (5.7-6.2); length of nasals, 15.5 (15.2-16.5); length of incisive foramina, 9.4 (8.8-10.1); length of palatal bridge, 7.7 (6.9-8.1); alveolar length of maxillary tooth-row, 8.7 (8.3-8.9); length of auditory bulla, 7.6 (7.3-7.9); mastoid breadth, 18.7 (17.9-20.2).