1914] Grinnell: Mammals and Birds of the Colorado Valley 241 



young. Tracks were to be seen far and wide between the scattering 

 groups of burrows. 



At Mellen, February 25. .specimens of Dipodomys deserti trapped 

 had their cheek-pouches filled with the minute blossoms and stem ends 

 of Achyronychia cooperi. an inconspicuous plant growing prostrate 

 upon the surface of the broad, sandy intervals between the creosote 

 and Atriplex polycarpa bushes (pi. 11, fig. 16). 



The series of specimens from Mellen, on the Arizona side at the 

 north, is faintly darker in color dorsally on an average than the series 

 from near Pilot Knob on the California side at the south. Otherwise 

 I can see no differences between specimens from the two sides of the 

 river. 



Like Pcroiityscus eremicus and Perognathus penieillalus. Dipo- 

 domys deserti inhabits the second bottom in places along the river, 

 though much less continuously than these smaller rodents. Doubtles.s. 

 as with them, individuals occasionally forage on to the first bottom, 

 and thus run the chance of being transferred from one side of the river 

 to the other by means suggested in other parts of this paper. 



Dipodomys merriami merriami iMearns 

 Jlerriam Kangaroo Rat 



A series of 168 specimens of this small kangaroo rat were pre- 

 served, and besides these many were discarded. The Museum numbers 

 are: 10186-10351 (skins with skulls), 10710-10712 (skeletons). 10733- 

 10741 (alcoholics). The following localities are represented: Arizona 

 side : Mellen, 18 ; foot of The Needles, 6 ; above Bill Williams River. 6 : 

 Ehrenberg, 10 ; twenty-five miles below Ehrenberg. 3 ; ten miles below 

 Cibola, 8; five miles northeast of Laguna, 12; Yuma, 2. California 

 side: five miles below Needles, 3; opposite The Needles. 4; Cheme- 

 huevis Valley, 10 ; near River.side ^Mountain, 6 ; above Blythe. 3 ; oppo- 

 site Cibola, 19; twenty miles north of Picaeho, 21; eight miles below 

 Picacho, 12 ; Potholes, 5 ; Pilot Knob, 20. 



As indicated above, this was a widespread and abundant desert 

 rodent, being taken in nearly every line of traps outside of the over- 

 flow bottom. Its greatest abundance occurred on sandy ground 

 ad.jacent to desert washes, on tracts of aeolian sands on the desert 

 mesa, and on the second bottom paralleling the river on either side 

 through the broad vaUeys, but wholly above the reach of the highest 

 floods. In a number of eases specimens were trapped on the packed 



