MAMMALS OF THE MEXICAN BOUNDARY. 429 



wagon road crosses the Coast Range Mountains by way of Moun- 

 tain Spring, in San Diego County, California, at the easl base of the 

 mountains. Others were taken, farther north, by Mr. Frank Ste- 

 phens. This species was not met with later, although we trapped 

 assiduously at Mountain Spring and to the westward. 



Subgenus HAPLOMYLOMYS Osgood. 



Hapiomylomys Osgood, Proc. Biol. Soc Wash., XVII, pp. 53, 54, fig. 1, March 21, 



1904. 



Tgju. -Peromyscus eremicus (Baird), from Fori Yuma, California. 



Characters. Size medium or small; pelage usually very soft and silky; tail longer than 

 head and body, subterete, rather thinly haired: soles of hind feet naked i at least in median 

 line) to calcaneum, 6-tubcrculate and paved with minute imbricate scales; skull with cra- 

 nium rather large and rostral region relatively weak; first and second upper molars with 

 three salient and two reentrant outer angles at all stages of wear; small secondary tubercles 

 never present between outer primary tubercles; lower molars correspondingly simple. 

 (Proc. Biol. Soc. Wash., XVII, p. 53. 



PEROMYSCUS CALIFORNICUS INSIGNIS (Rhoads). 

 SOUTHERN PARASITIC DESERT MOUSE. 



Peromyscus insignis Rhoads, Proc. Acad. Nat. Sci. Phila., 1895, pp. 33, 34 (original 

 description). — Miller and Rehn, Proc. Bost. Soc. Nat. Hist., XXX, No. I, Dec. 

 27, 1901, p. 76 (Syst. Results Study N. Am. Mam. to close of 1900). 



[Peromyscus] insignis, Elliot, Field Col. Mus., Zool. Ser., II, 1901, p. 138 (Synop. 

 Mam. N. Am.); IV, 1904, p. 203 (Mam. Mid. Am.). 



Type-locality. — Dulzura, San Diego County, California. (Type in 

 the collection of S. N. Rhoads.) 



Geographical range. — Sonoran Zone of the Pacific Coast Trad of 

 southern and Lower California. 



Description. — PeroTti/yscus californicus belongs strictly to the group 

 of Desert Mice, typified by Peromyscus eremicus (Baird', which are 

 characterized by bare soles, long, tapering, scant-haired tails, large 

 membranous ears, flattened skulls, with shortened rostrum and pos- 

 teriorly truncate, advanced nasal bones, and teeth (fig. 98, p. 430) 

 having the subsidiary marginal cusps reduced to the merest trace 

 only a step removed from the Onyckomys form, in which the notches 

 are smooth, without a trace of these minor cusps. The southern sub- 

 species 'insignis) differs from the typical form (californicus) in being 

 larger, paler, and grayer, without the brown vent and fulvous suffusion 

 of throal and breast characteristic of northern specimens. 



This is the largest species of Peromyscus found in the United States 

 (for measurements, see page 431). Its appearance suggests a -mall 

 Neotoma, which resemblance is strengthened by its large, nearly 

 naked, highly sensitive membranous ears, which in life are in as con- 

 stant motion as its nose. Its proportions are similar to those of the 

 other members of the desert mice group. The tail is more hairy than 



