1936] MAMMALS OF OREGON 239 



is attempted they feast on the sown seed and later on the growing 

 and ripening grain. In irrigated sections they may do some mis- 

 chief around the edges of the fields. On the stock range, which in 

 eastern Oregon has been almost ruined by overgrazing, they have 

 doubtless done their share to exterminate many of the grasses and 

 forage plants by consuming the few remaining seeds. In fact there 

 are now not enough seeds to support them over wide valleys where 

 there is nothing for stock to eat. Wild mustard and shadscale were 

 the only seeds they were getting in some localities. Their numbers 

 are not sufficient to do serious harm in a more fertile region, but in 

 places they can now take all the seed that is left. 



As pets they are gentle, cleanly, inoffensive, interesting, and amus- 

 ing. They are contented in captivity and are fond of running on 

 revolving wheels or inclined disks, thus getting good exercise. 



PERODIPUS MICROPS PREBLEI GOLDMAN 

 PEBBLE'S KANGAROO RAT 



Perodipus microps preblei Goldman, Jour. Mammal. 2 : 233, 1921. 



Type. Collected at the Narrows, Harney County, Oreg., by Edward A. 

 Preble, July 23. 1896. 



General characters. In external characters scarcely distinguishable from 

 columbianus but slightly larger, with relatively longer, darker tails, and dusky 

 lining of cheek pouches ; skull slender, with narrower antorbital arches ; upper 

 incisors unequally grooved, not recurved, set approximately at right angle to 

 plane of palate. 



Measurements. Of type, female : Total length, 263 mm ; tail, 154 ; foot, 41 ; 

 ear (dry), 11. Of female topotype: 168; 156; 42; 11. Weight of adult female 

 topotype 65.5 g. 



Distribution and habitat. There are specimens from Narrows, 

 Tumtum Lake, White Horse Creek, and Summer Lake in southern 

 Oregon, and from Granite Creek in northwestern Nevada, all from 

 the sandy bottoms of low, hot desert valleys in Upper Sonpran Zone. 



General habits. The only striking peculiarity of habits of this 

 species observed to differ from those of columbianus is that of 

 building mounds over the den or group of burrows. In the light 

 sandy soil and mellow sand dunes around Harney Lake and extend- 

 ing along the side of the valley to Narrows their mounds are com- 

 mon, often a foot high by 5 or 6 feet across, with several openings 

 into the sides. In the White Horse Creek Valley some of the mounds 

 are 10 or 12 feet across with a dozen openings. Part or sometimes 

 all of the doorways are closed if the occupants are inside. The earth 

 from the burrows is thrown out and then kicked back onto the 

 mounds, and thus with age and use the mounds increase in size. 

 Some become almost as well developed as those of Dipodomys spec- 

 tabilis in Arizona, but never so large. 



Trails and runways lead from mound to mound or off to the feed- 

 ing grounds, and the paired tracks of the hind feet show in the 

 sandy or dusty trails in short or long hops according to the speed 

 of the animals. Feeding and breeding habits seem to be the same 

 as in colwribianus, while the economic importance in these sandy 

 desert areas is negligible. 



