_Reproduction._--There is normally a single litter of from four to eight young per year according to Bailey (_loc. cit._). Newly born young have been described by Svihla and Svihla (1933:132) as follows: slightly smaller than newly born harvest mice (_Reithrodontomys m. megalotis_), average weight .8 grams, hairless (without even vibrissae visible), pink, eyes closed, ears folded, heads short and stubby, tails long (longer than those of newly born _Peromyscus_), and bodies surprisingly small (when compared with newly born _Peromyscus maniculatus_). =Zapus trinotatus eureka= A. B. Howell _Zapus trinotatus eureka_ A. B. Howell, Univ. California Publ., Zool. 21:229, May 20, 1920. _Zapus trinotatus trinotatus_, Preble, N. Amer. Fauna, 15:26, August 8, 1899 (part--the part from Crescent City and Carsons Camp, Mad River, California). _Zapus orarius_ Preble, N. Amer. Fauna, 15:29, August 8, 1899 (part--the part from Eureka and Carsons Camp, Mad River, California). _Type._--Female, adult, skin and skull, No. 11703, Mus. Vert. Zool.; Fair Oaks, Humboldt County, California; obtained on August 27, 1910, by Joseph S. Dixon, original No. 1743. _Range._--Northwestern coastal region of California, from Russian Gulch State Park, Mendocino County north to Trinidad, Humboldt County. Zonal range: humid Transition. _Description._--Size medium; color dull; back near Ochraceous-Buff with heavy admixture of black hairs, forming broad dorsal band; sides from near Ochraceous-Buff to near Ochraceous-Salmon, sometimes with heavy admixture of black hairs; lateral line usually distinct, sometimes blending with color of belly and side; ventral surface usually suffused with color of sides; tail bicolored, dark brown above, white to yellowish-white below; feet grayish-white above; ears dark, edged with color of sides; auditory bullae large; pterygoid fossae broad; incisive foramina relatively short; palatal bridge short; maxillary tooth-rows relatively short; narrow across zygomata; braincase narrow; interorbital region narrow; zygomatic arch relatively short. _Comparisons._--From _Zapus trinotatus trinotatus_, _Z. t. eureka_ differs in: Size smaller; ventral surface with much greater suffusion of ochraceous; auditory bullae larger; pterygoid fossae relatively broader; frontal region less inflated; palatal bridge shorter; braincase narrower; narrow across zygomata; upper tooth-rows shorter. For comparison with _Zapus trinotatus orarius_ see account of that subspecies.