A certain means for distinguishing the skulls of the black-tailed jack rabbit from those of all of the white-sided jack rabbits has not yet been found. The same is true of the skulls of the white-tailed jack rabbit and the black-tailed jack rabbit in the Great Basin region of Nevada. The skulls, at least of adults, of these two species, in the region east of the Rocky Mountains can be readily distinguished by the pattern of infolding of the enamel on the front of the first upper incisor teeth; _L. townsendii_ has a simple groove on the anterior face of the tooth and _L. californicus_, east of the Rocky Mountains, has a bifurcation, or even trifurcation, of the infold that can readily be seen by examining the occlusal surface of the incisor. In Arizona, Vorhies and Taylor (1933:478) found the weight of 23 adult males to average 5.1 (4.4-6.1) lbs. In that state, 70 pregnant females averaged 2.24 (1-6) young per litter and the authors (_op. cit._) thought that a female had three or four litters each year. LEPUS CALIFORNICUS ALTAMIRAE Nelson. 1904. _Lepus merriami altamirae_ Nelson, Proc. Biol. Soc. Washington, 17:109, May 18, type from Alta Mira, Tamaulipas. Known from type locality only. 1951. _Lepus californicus altamirae_, Hall, Univ. Kansas Publ., Mus. Nat. Hist., 5:45, October 1, 1951. LEPUS CALIFORNICUS ASELLUS Miller. 1899. _Lepus asellus_ Miller, Proc. Acad. Nat. Sci., Philadelphia, p. 380, September 29, type from San Luis Potosí, San Luis Potosí. 1909. _Lepus californicus asellus_, Nelson, N. Amer. Fauna, 29:150, August 31. _Marginal records_ (Nelson, 1909:151).--Coahuila: Jaral. Nuevo Leon: Miquihuana. San Luis Potosí: Río Verde. Aguascalientes: Chicalote. Zacatecas: Valparaiso. LEPUS CALIFORNICUS BENNETTII Gray. 1844. _Lepus bennettii_ Gray, Zoology Voy. _Sulphur_, p. 35, pl. 14, type from San Diego, San Diego County, California. 1909. _Lepus californicus bennetti_, Nelson, N. Amer. Fauna, 29:136, August 31. _Marginal records._--California: Mt. Piños (Orr, 1940:73); Arroyo Seco, Pasadena (Orr, 1940:74); San Felipe Valley (_ibid._); Jacumba (Nelson, 1909:137), Baja California: San Quintín (Nelson, 1909:137). Northward along coast at least to California: Montalvo (Orr, 1940:73). LEPUS CALIFORNICUS CALIFORNICUS Gray. 1837. _Lepus californica_ Gray, Charlesworth's Mag. Nat. Hist., 1:586, type from "St. Antoine," California (probably on coastal slope of mts. near the Mission of San Antonio, Jolon, Monterey County). 1926. _Lepus californicus vigilax_ Dice, Occas. Papers Mus. Zool., Univ. Michigan, 166:11, February 11, type from Balls Ferry, Shasta County, California.