148 CALIFORNIA MAMMALiS. 



Family Heteromyidse. Pocket-Rats and Pocket-Mice. 



Cheek pockets large and opening externally, similar to 

 those of Geojuyidse; fore legs of moderate length; hind legs more 

 or less lengthened; tail usually as long as or longer than head 

 and body ; skull thin and smooth ; rostrum long and tapering ; 

 nasals long, projecting beyond the incisors and semi-tubular an- 

 teriorly; frontals wide; no inteorbital foramen but a perforation 

 on the sides of the maxillary instead; occipital region formed 

 mostly of the mastoids; temporal region inflated, sometimes enor- 

 mously; zygomatic arches very slender, depressed; lower jaw 

 small and weak ; coronoid process very small ; angular process 

 twisted obliquely. 



Dental formula, I, i — i ; C, o — o; P, i — i ; M, 9 — 3X2^20. 



This is a small family of seven genera, divided in two sub- 

 families. The family is American, Mexico being apparently the 

 center of distribution, none of the family being found east of 

 the Mississippi River. It has been very imperfectly known until 

 recently and has many interesting peculiarities. A singular 

 characteristic of Pocket-Rats and Pocket-Mice is their ability 

 to go without water and if necessary without eating moist food. 

 Most species inhabit arid regions or deserts, though a few species 

 are found in regions of moderate rainfall, provided the climate 

 is comparatively warm. They do not endure cold well, very few 

 being able to live in localities where the ground freezes too hard 

 to plow. 



The food is principally seeds, but leaves and stems of 

 plants are occasionally eaten. Seeds are commonly stored in 

 chambers of burrows or sometimes in surface caches. In some 

 of the Californian valleys harm is done by members of this 

 family through carrying off and hiding grain, though it is seldom 

 done to a noticeable extent. Yet the total loss to grain growers 

 must annually amount to a considerable sum, because of the 

 abundance and industry of these little animals. I am not aware 

 of any other harm being done by them and there is some compen- 



