1914] Grinnell: Mammals and Birds of tJu Colorado Valley 221 



The Needles, liarrisi was observed as close as within one hundred yards 

 of the water's edge. The animals did not, however, even here, show 

 the least disposition to visit the water for any purpose whatever; so 

 that the chances of being transported across to the opposite shore are 

 practical!}' nil. That in this part of the range of liarrisi the Colorado 

 River is the limiting barrier is a fact beyond question. There is a per- 

 sistent statement in literature (for example, Elliot, 1905, p. 97) to the 

 effect that liarrisi occurs in California; but I am not cognizant of any 

 basis for this assertion and I doubt its correctness. 



Two races of Ammospermopliilus liarrisi have been distinguished 

 within the state of Arizona. Mearns (1896, p. 444, and 1907, pp. 303- 

 309) has characterized a form A. h. sa.rkola from extreme south- 

 western Arizona, thus restricting liarrisi proper to central Arizona. I 

 fail to find grounds, either in tone of coloration or relative length of 

 tail, to warrant separate recognition of the Colorado River series 

 from the animal of the vicinity of Tucson. Even Mearns' own tables 

 of measurements do not bear out the size characters of his saxicola, 

 which name might be expected to be usable for our specimens. The 

 measurements of the Colorado Valley series are given herewith, as is 

 also a table showing comparison with the near-related form leucurus, 

 of the opposite side of the river (see pp. 220, 223). 



Ammospermophilus leucurus leucurus (Merriam) 

 Antelope Ground Squirrel 



Seventeen specimens obtained, all on the California side: 5 miles 

 below Needles, 1 ; opposite The Needles, 5 ; Chemehuevis Valley, 2 ; 

 Riverside Mountain. 1; opposite Cibola, 2; twenty miles above Picacho, 

 4 ; eight miles east of Picacho, 2. This rodent was not notably numer- 

 ous anywhere, and was closely restricted to rocky or gravelly ground, 

 chiefly among hills. It occupied the same ecologic niche on the Cali- 

 fornia side that liarrisi did on the Arizona side; and where the hills 

 closely abutted upon the river, as at The Needles, the two species 

 existed in places not more than three hundred yards apart, but with 

 the river between. In no case was there any evidence of crossing; 

 all individuals captured or seen were unquestionably one form or the 

 other, and always appropriately segregated as regards the river. 



No young of leucurus were taken; but a female taken five miles 

 south of Needles, February 20, contained eight embryos, and another 



