674 THE MONTHLY BULLETIJN. 



coat is so short and thin that any scars there may be in the skin show through as 

 dark spots. These appear irregularly on certain specimens, usually those which 

 examination of the teeth shows to be the older individuals. 



Measurements. — Average and extreme measurements, in millimeters, of twenty 

 adult specimens from Whitewater, Palm Springs and Mecca, in Riverside County, are 

 as follows: Ten males: total length, 241 (220-251); tail vertebrae, 90 (79-97); 

 hind foot, 36 (35-iO) ; greatest length of skull, 36.6 (35.2-.38.9) ; zygomatic breadth, 

 23.0 (21.6-24.6) ; interorbital width, 8.9 (8.0-9.7). Ten females: total length, 240 

 (229-264) ; tail vertebrse, 89 (80-102) ; hind foot, 35.7 (34-39) ; greatest length of 

 skull, 36.1 (35.6-37.5) ; zygomatic breadth, 22.8 (22.0-23.4) ; interorbital width, 8.8 

 (S.6>-9.4). 



Type locality.— Palm Springs, Riverside Coimty, California (Elliot, 1903, p. 242). 



Distribution area. — The northwestern arm of the Colorado Desert between Salton 

 Sea and San Gorgonio Pass (see fig. 18). Life-zone, Lower Sonoran. More specifi- 

 cally, the Coachella Valley, entirely within Riverside County, from Mecca northwest 

 to Whitewater Station ; altitude from — 200 to 1,130 feet. 



Specimens examined. — A total of 41 from the following localities, all in Riverside 

 County : Palm Springs, 6 ; Whitewater Station, 18 ; Mecca, 17. 



This race of Round-tailed Ground Squirrel was first made known from 

 specimens collected in the vicinity of Palm Springs, out on the Colorado 

 Desert near the northeast base of San Jacinto Peak. Subsequent 

 exploration has shown it to be limited to the relatively small area of flat 

 desert lying between Salton Sea and the upper part of San Gorgonio 

 Pass, and shut in narrowly by the mountain walls on either side. 



The slight features by which this subspecies is distinguishable from 

 the Yuma Round-tailed Ground Squirrel of the Imperial Valley south- 

 east of Salton Sea may be inferred to have arisen as a result of the 

 action of the body of water which formerly filled the Salton Sink to 

 sea level in cutting off or isolating the animals in the northwestern arm 

 of the Colorado Desert and thus giving them a chance to develop 

 peculiarities all their own. The ancient predecessor of the present 

 Salton Sea is known to geologists as Blake Sea, and this inland sea 

 extended from the base of the Chocolate Range of mountains on the 

 northeast to the very foot of the Santa Rosa Mountains on the south- 

 west, thus constituting an impassable barrier to any animal closely 

 restricted, as is the Round-tailed Ground Squirrel, to dry, level, sandy 

 ground. However this may have been, the Palm Springs subspecies 

 now ranges down the Coachella Valley from the northwest nearly to the 

 upper end of the present Salton Sea, in the vicinity of Mecca. One 

 can imagine the animal life of the desert floor now retreating, now 

 advancing, with the fluctuations of the old Blake Sea since the time it 

 was first cut off from the Gulf of California by the slowly growing delta 

 of the Colorado. 



The general habits of the Palm Springs Round-tailed Ground Squirrel 

 are probably closely similar to those of the Yuma and Death Valley 

 animals. The first-named is fairly common locally, though it rarely 

 forces itself on the attention; it has to be specially looked for. At 

 Mecca in March and April (1908) one or two were caught nearly every 

 day in oat-baited rat-traps set on sandy mounds beneath mesquites. 

 Yet the animals themselves were rarely seen. On April 26 one was 

 surprised up in a mesquite ; upon being shot it was found to have parts 

 of a mesquite flower in its mouth. The senior author was told that at 

 the experimental date farm near Mecca these squirrels had been seen 

 eating the dates. 



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