_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. _Specimens examined._--Thirty-three, all from North China, as follows: JEHOL: Hsin-lung-shan, 65 mi. NE Peking, 3000 ft., 4. KANSU: 15 mi. S Lanchow, 7400 ft., 1. SHANSI: Chiao-cheng-shan, 90 mi. W Taiyuan, 7000-8000 ft., 4; 30 mi. W Kuei-hau-cheng, 7000 ft., 5; Lung-wang-shan, 20 mi. E Taiyuan, 4000 ft., 10; 18 mi. W Taiyuan, 5000 ft., 1; 50 mi. NW Taiyuan, 5500 ft., 4. SHENSI: 12 mi. S Yenan, 4000 ft., 4. _Apodemus peninsulae_, then, is known or suspected to occur over much of southeastern Siberia, Manchuria, Korea and North China. The western limits of its geographic range are unknown. Over this vast area only four subspecies, one newly named, can be ascribed with certainty to _peninsulae_ whereas only two other kinds, _giliacus_ of Thomas from Sakhalin and _rufulus_ of Dukelsky from extreme southeastern Siberia are probably conspecific with it, the latter possibly a synonym of _praetor_. These considerations underscore the preliminary nature of the present paper. The mammalian fauna of northeastern Asia is scarcely better known today than was that of North America in 1885 when Dr. C. Hart Merriam organized what was later to become the U. S. Biological Survey.