178 
JOURNAL OF MAMMALOGY 
A NEW KANGAROO RAT FROM THE SAN JOAQUIN VALLEY, 
CALIFORNIA! 
By Joseph Grinnell 
The kangaroo rats of the Dipodomys merriami group inhabiting the 
great San Joaquin basin of south-central California are restricted to 
the Lower Sonoran life zone there and are believed to be cut off com- 
pletely by continuous Upper Sonoran areas from the other representa- 
tions of the group inhabiting the other southwestern tracts of Lower 
Sonoran. Since there is thus little chance for intermingling, it is in- 
teresting, and corroborative, to find that there is a seemingly constant 
character by which any individual from the San Joaquin Valley can be 
distinguished from any individual, of whatever race, of merriami from 
outside this area. The character in question involves the extreme 
base of the rostrum; the premaxillary tongues, extending backwards 
dorsally on either side of the nasals, are extremely narrow, and the 
entire rostrum at its base, in dorsal aspect, is notably narrow as compared 
with the condition in merriami from outside the San Joaquin Valley. 
Then, too, the sides of the rostrum are more nearly parallel to one 
another, and the angle made by each side with the anterior margin of 
the adjacent maxillary arch is better defined — less obtuse. The nasals, 
and the rostrum itself, are shorter. 
Furthermore, within the San Joaquin basin there is geographic 
variation, involving other cranial features than those possessed in 
common, as well as features of color and general size. Three sub- 
species are recognizable: Dipodomys merriami nitratoides Merriam, of 
the eastern side of the valley southeast of Tulare Lake, from Tipton 
south to the vicinity of Bakersfield; Dipodomys merriami exilis Merriam, 
of the eastern side of the valley north of Tulare Lake, in the immediate 
vicinity of Fresno (perhaps now extinct as a result of the close culti- 
vation of the country) ; and the race, now described, from the western 
side of the valley, from western Fresno County (across the river bottom 
lands from the Fresno district) south to near the mouth of San Emigdio 
Creek. 
1 Contribution from the Museum of Vertebrate Zoology of the University of 
California. 
