PEROMYSCUS. 177 
texanus ! medius Mearns, Proc. U. S. Nat. Mus., 1895, p. 446. 
texensis medius Elliot, Syn. N. Am. Mamm., 1901, p. 130. 
THURBER’S FIELD MOUSE. 
Type locality. San Pedro Martir Mountains, Lower California, 
Mexico. Altitude, 7,000 feet. 
Geogr. Distr. Region of San Pedro Martir Mountains, Lower 
California, Mexico, north into southern California to Colorado desert 
at least. 
Genl. Char. General color pale grayish fulvous lined with black. 
Color. Upper parts grayish fulvous, darkest on dorsal line where 
it is blackish; sides fulvous; lower sides and under parts and feet 
white; ears dusky, at base a tuft colored like head; tail blackish 
above, white below. 
Measurements. Total length, 177; tail vertebre, 78; hind foot, 
z1; ear, 18. Skull: occipito-nasal length, 25.1; Hensel, 99.2; zygo- 
matic width, 13; interorbital constriction, 4; length of nasals, 9.2; 
width of braincase above roots of zygomata, 11.5; palatal length, 10; 
length of upper molar series, 4; length of lower molar series, 4. 
a.—mesomelas (Peromyscus), Osgood, Proc. Biol. Soc. Wash., xv, 
1904, Pp. $7- 
Type locality. Orizaba, State of Vera Cruz, Mexico. 
Genl. Char. Similar to P. thurbert, darker; tail shorter; hind 
foot larger; pectoral spot present. 
Color. Upper parts Prout’s brown; under parts creamy white; 
pectoral spot fawn; hands and feet white; ankles dusky brownish; 
tail bicolor; ears dusky, edges whitish. 
Measurements. Total length, 169; tail vertebre, 76; hind foot, 
23. Skull: greatest length, 26.5; Hensel, 20.2; zygomatic width, 
13.6; interorbital constriction, 4; interparietal, 8.6 x 2.3; length of 
nasals, 10.4; palatal length, 3.8; palatal foramina, 5.2 x 2; postpalatal 
length, 9.1; length of upper molar series, 3.7. 
b.—castaneus (Peromyscus), Osgood, Proc. Biol. Soc. Wash., xvu, 
1904, p. 58. 
YOHALTUN MOUSE. 
Type locality. Yohaltun, State of Campeche, Mexico. 
Genl. Char. Similar to P. mesomelas, but smaller; no pectoral 
spot. 
Color. Upper parts between Prout’s brown and burnt umber; 
under parts white; no lateral line; hands and feet white; ankles dusky. 
Measurements. ‘‘Total length, average of ten adults, 163 (156- 
169); tail vertebre, 73 (68-79); hind foot, 21.5 (20-22). Skull of 
type: greatest length, 25.3; Hensel, 19; zygomatic breadth, 13; inter- 
