272 University of California Publications in Zoology. [VoL 
7 
Color—The pelage on the dorsal surface of the new mouse 
consists of two different sorts of hair. The most numerous are 
soft hairs, blackish slate at the base and broadly tipped with 
tawny ochraceous; sometimes there is a narrow terminal band of 
black. The long, coarse black hairs sprinkled over the dorsal 
surface are the other kind, and give a general dark hue to that 
part of the body. The hairs on the underparts are slate-colored 
at the base and tipped with white. The chin is white. There 
is a decided black spot on each side of the nose at the base of the 
whiskers, and a black ring encircles the eye. The ears are very 
dark as are also the hind feet. The fulvous spot at the anterior 
base of the ear is very noticeable, and the tail is long, rather 
bi-colored, and well covered with hair. 
In an immature specimen (no. 7148, Univ. Calif. Mus. Vert. 
Zool.), the ochraceous band on the hair is much restricted, giving 
a more slaty tone to the entire dorsal and lateral surfaces. 
Measurements.—A series of twenty-four, thirteen males and 
eleven females, collected in the salt marsh at Petaluma, March 
28-29 and December 22-30, 1908, average: length, 151.3 (130- 
168) ; tail, 77.5 (60-88) ; hind foot, 17.5 (17-19); average ratio 
of tail to total length, 51.2 per cent. Skull measurements of 
type: basal length, 17.3; nasals, 7.8; zygomatic breadth, 11.4; 
alveolar length of upper molar series, 8. A female (no. 7147, 
Univ. Calif. Mus. Vert. Zool.) measures: basal length, 17.5; 
nasals, 7.6; zygomatic breadth, 11.3; upper molar series, 3. 
Food —On March 28 several stomachs of these mice contained 
tender tips of a species of rush that was just coming up over the 
marsh at that time. 
Remarks.—The material from the vicinity of Petaluma seems 
to show that there are two forms of Reithrodontomys to be found 
there: a light-colored, small, fine-haired, upland form (R. longi- 
cauda) and a larger, darker, thick-furred form which is restricted 
to the salt marsh. Their ranges seem to be distinet and as far as 
T was able to learn, do not overlap. 
Mr. W. H. Osgood, formerly of the Biological Survey, states 
in a letter: ‘‘Typieal longicauda is undoubtedly an upland 
species much paler in color than the salt marsh forms. Of the 
specimens originally listed by Baird only one skull is now to be 
