300 



VERTEBRATE ANIMALS OF THE UNITED STATES 



di Belly pure white; fur fine 3. Peromyscus. 



6-2 Belly not pure white; fur coarse 4. Oryzoniys. 



a.2 Tubercles of molars form flattened S-shaped loops 5. Signiodon. 



I. Onychomys Baird. Grasshopper mice; scorpion mice. Body 

 stout; fur dense and velvety; tail short; fore feet strong; ears hairy: 

 2 species, in western America; nocturnal burrowing animals which 



WSP^ 



♦W5^ 



<Rtt» 



Fig. 160. — Skull and tuberculate molars of Onychomys leucogaster (frotn Elliot). 



feed largely on insects, scorpions and other small animals; several litters 

 of from 2 to 6 young each raised each year; the animals do not hibernate. 



Key to the Species of Onychomys 



ai Tail usually less than half the length of the head and trunk 0. leucogaster. 



a2 Tail usually more than half the length of tl^e head and trunk. . . .0. torridus. 



O. leucogaster (Weid) (Fig. 160). Body Hght mouse-brown above, 

 being darker middorsally, and snow-white beneath; length 150 

 mm.; tail 40 mm.; hind foot 20 mm.: western America, from eastern 

 Dakota and Kansas to eastern California; Mexico. 



Subspecies of 0. leucogaster. 



O. I. leucogaster (Wied). Size large; length 164 mm.; color dark: 

 eastern and central North Dakota. 



0. /. missouriensis (Audubon & Bachman). Size large; color pale: 

 western North Dakota and Montana. 



