Distribution.—Known presently from eastern Kansu eastward through Shensi, Shansi and Hopeh to southern Jehol, probably also in northeastern Szechuan, exact limits of range unknown.
Diagnosis.—Size small for species (see measurements). Color: Upper parts (fresh summer pelage) averaging near (15'a) Ochraceous-Buff, suffused with blackish (especially mid-dorsally); winter pelage much paler; underparts grayish-white, individual hairs plumbeous at base, tipped with white; ears pale brownish; feet whitish above, darker below; tail bicolor, pale brownish above, whitish below. Skull: Small (see measurements); rostrum somewhat shortened and conspicuously down-curved; zygomatic notches relatively shallow; zygomatic plates narrow; braincase proportionally more inflated than in other subspecies of the species; auditory bullae moderately inflated; upper incisors slender, their faces averaging bright yellowish-orange.
Measurements.—External measurements of the holotype, followed by those of an adult male and female from the type locality, are, respectively: Length of head and body, 101, 102, 100; length of tail, 93, ——, 102; length of hind foot (su), 21, 21.5, 23; length of ear from notch, 14, 16, 15.5. Corresponding measurements for an adult female from 20 mi. E Taiyuan, Shansi, are: 91, 99, 23, 16. For cranial measurements see Table 1.
Table Key:
A: Occipitonasal length B: Zygomatic breadth
C: Mastoid breadth
D: Interorbital length
E: Frontonasal length
F: Nasal length
G: Depth of skull
H: Alveolar length of maxiary tooth-row
TABLE 1.—Cranial Measurements of Adults of Several Subspecies of Apodemus peninsulae
| Sex and catalogue number or number of individuals averaged | A | B | C | D | E | F | G | H |
| Apodemus peninsulae peninsulae, various localities in central Korea | ||||||||
| Average 10 (4♂, 6♀) | 29.2 | 14.2 | 11.8 | 4.7 | 20.1 | 11.4 | 10.2 | 4.3 |
| Minimum | 28.3 | 13.8 | 11.5 | 4.6 | 19.2 | 10.8 | 9.9 | 4.1 |
| Maximum | 29.8 | 14.6 | 12.2 | 5.1 | 20.7 | 12.0 | 10.5 | 4.4 |
| Apodemus peninsulae nigritalus, Tapucha, Altai Mts., Siberia | ||||||||
| USNM 175164, ♂ (type) | 28.8 | 14.8 | 12.4 | 4.5 | 20.8 | 11.7 | 11.0 | 4.4 |
| USNM 175171, ♀ | 28.2 | 13.7 | 11.8 | 4.5 | 19.8 | 11.2 | 10.3 | 4.5 |
| Apodemus peninsulae praetor, Sungari River, 60 mi. SW Kirin, Manchuria | ||||||||
| USNM 197792, ♂ (type) | 30.5 | .... | 12.5 | 4.7 | 21.5 | 12.5 | 10.3 | 4.6 |
| USNM 197798, ♀ | 30.2 | 14.4 | 11.8 | 4.6 | 21.6 | 12.7 | 10.6 | 4.6 |
| Mukden, Manchuria | ||||||||
| USNM 197782, ♂ | 29.5 | 14.8 | 12.4 | 4.8 | 20.6 | 12.2 | 10.5 | 4.2 |
| Apodemus peninsulae sowerbyi, Kuei-hau-cheng, Shansi | ||||||||
| USNM 175523, ♀ (type) | 27.9 | 13.3 | 11.7 | 4.5 | 19.6 | 11.4 | 9.9 | 4.0 |
| USNM 175521, ♂ | 27.6 | .... | 11.5 | 4.6 | 18.9 | 11.4 | 9.7 | 4.1 |
| USNM 175522, ♀ | 27.9 | .... | 11.8 | 4.6 | 19.4 | 11.3 | 9.8 | 4.2 |
| 20 mi. E Taiyuan, Shansi | ||||||||
| USNM 172558, ♀ | 27.4 | 13.8 | 11.5 | 4.6 | 19.4 | 11.6 | 10.1 | 4.4 |
| 12 mi. S Yenan, Shensi | ||||||||
| USNM 155072, ♂ | 27.8 | 14.1 | .... | 4.4 | 19.5 | 11.0 | .... | 4.3 |
| USNM 155073, ♀ | 27.7 | 13.3 | 11.5 | 4.5 | 19.4 | 11.0 | 10.0 | 4.2 |
| USNM 155075, ♂ | 27.9 | 13.5 | 11.4 | 4.5 | 19.2 | 11.0 | 10.0 | 4.3 |
| Hsin-lung-shan, 65 mi. NE Peking, Jehol | ||||||||
| USNM 219229, ♂ | 27.7 | 13.8 | 11.4 | 4.5 | 19.0 | 10.9 | 10.4 | 4.4 |
| 15 mi. S Lanchow, Kansu | ||||||||
| USNM 155171, ♂ | 27.7 | 13.6 | 11.7 | 4.6 | 19.0 | 11.3 | 9.9 | 4.5 |
Comparisons.—From Apodemus peninsulae peninsulae (specimens from various localities in central Korea), A. p. sowerbyi differs in: External size smaller throughout, especially hind foot; upper parts, especially in summer pelage, and dorsal aspect of tail paler; skull smaller and less massive; braincase proportionally more inflated; rostrum shorter and noticeably down-curved. From Apodemus peninsulae praetor of Manchuria (holotype and paratypes), A. p. sowerbyi differs in most of the same ways in which it does from peninsulae as well as in having more shallow zygomatic notches, narrower zygomatic plates and smaller, more slender, upper incisors. From Apodemus peninsulae nigritalus of the Altai Mountains of Siberia (holotype and paratypes), A. p. sowerbyi differs in: Smaller size, both external and cranial; paler dorsal coloration; less convex cranial outline in lateral view; smaller auditory bullae.
Remarks.—Apodemus peninsulae sowerbyi is named in honor of the late Arthur de Carle Sowerby whose collections of mammals from North China and Manchuria have added so much to our meager knowledge of that part of the world.
Four specimens from Hsin-lung-shan, 65 mi. NE Peking, here assigned to sowerbyi, are darker dorsally than mice from farther to the west and in this respect may show approach to A. p. praetor. In all other features, however, they closely resemble the new subspecies.
All of the specimens of sowerbyi available to me are from altitudes of 3000 feet or higher. At lower elevations in North China, destruction of wooded habitats owing to intense land-use practices has probably restricted the distribution of sowerbyi primarily to hilly and mountainous areas where brushy, scrub and forest habitats still prevail.