244 NORTH AMERICAN FAUNA [No. 55 



give it a more delicate support for the trigger and also to extend and 

 lower the trigger or pan so that the trap can be set across the artificial 

 runway in the sand in such a way that the lightest step on an in- 

 visible trigger will spring it. 



Breeding habits. Practically nothing is known of the breeding 

 habits of these rare little animals, except that the females have 3 

 pairs of mammae 2 inguinal and 1 pectoral as do the kangaroo 

 rats. 



Food habits. Little is known of the food of these mice beyond 

 the few seeds that have been found in the fur-lined cheek pouches, 

 and the rolled oats and other grains available as trap bait or fed to 

 them when in captivity. Seeds of Eriogonum, lupine, little burs 

 (Krintzkia), and the little desert plantain (Plantago purshii), and 

 the seeds and green capsules of desertstar (Mentzelia albicaulis] 

 are eaten. In captivity they eat rolled oats or any small seeds, 

 and stuff their pockets so full that their cheeks stick out in a 

 grotesque manner, then carry it to a corner of the cage, dig a hole in 

 the sand, and quickly empty the pockets and go back for more. Evi- 

 dently they are regular storers, laying up food in times of abundance 

 to last through times of scarcity. Their stomachs are small and usu- 

 ally contain a clean, white mass of starchy material from the carefully 

 shelled seeds. 



There is no trace of fat even in cold weather and no indications 

 of hibernation. In Nevada the typical form, Microdipodops mega- 

 cephalus, was found active well into November in freezing weather 

 at altitudes above 5,000 feet. 



Economic status. It would be difficult to accord any commercial or 

 economic value to these dainty little denizens of the desert nor can 

 any serious sins of omission or commission be laid to them. Still 

 they have a value sufficient to warrant many in making a long journey 

 into the desert to gain a few specimens of a unique type and to learn 

 a little of the causes that have glided its development along lines 

 different from all other forms of life. As the writer looks back more 

 than 45 years to the capture of the type of this genus and the first 

 thrill of realizing its remarkable characters, so different from even 

 its nearest relatives and opening up a whole new field of possibilities 

 for the multiform kinds of desert life, it is no wonder that the hard- 

 ships of bitter winter and scorching summer camps should have 

 vanished before the fascination of this first-hand study of desert life. 

 With all our intelligence and versatility of adaptation we are still 

 far behind such animals in the perfection of physical mechanism for 

 our needs, and we can surely learn humility if not wisdom from 

 many of our inferior mammalian brothers. 



PEROGNATHUS PARVUS PARVUS (PEALE) 

 OREGON POCKET MOUSE 



Oricetodipus parvus Peale, U. S. Expl. Expd., 8, pp. 52-54, 1848. 

 Peroffnathus monticola Baird, Mammals North Amer., Pacific R. R. Rept. 8: 

 422, 1857. Type probably from the region of The Dalles. 



Type locality. Given as Oregon, assumed to be The Dalles, Oreg. 

 General characters. Rather large for a pocket mouse (pi. 39, B) ; tail long 

 and slightly crested toward the tip; ears small with distinct inner lobe at 



