124 PEROMYSCUS. 



Feet small, digits slender, palms naked. Hind feet long, soles with 

 six tubercles. Tail terete, tapering, slender, hairy, sometimes longer 

 than head and bodj' and occasionally tufted. Pelage soft, frequently 

 glossy. Skull thin, papery; brain case broad, rather flat; superior 

 outline curving both ways from highest point just behind orbits. 

 Zygomata slender, thread-like and dip midway to level of the palate 

 Arch composed mainly of processes of the maxillary and squamosal; 

 orbital foramena just above the level of the alveolus. Interorbital 

 constriction considerable, but wider than nostrum. Nasals and imer- 

 maxillaries project beyond the incisors. Auditory bullae small, thin, 

 and obliquely situated. Lower jaw straight, coronoid very short. 

 Molar series short, narrow, the teeth decreasing in size from front to 

 rear. Upper molars with three roots each, lower with two; the 

 unworn teeth have a double series of conical tubercles, which grad- 

 ually are reduced by abrasion and the pattern varies constantly. 



Fig. 30. Peromysi-us 



No. 3644 Field Columbian Musci 



Lower tooth row 

 Enlarged 6 times. 



iMERICANUS. 



m Coll. Nat. size. 



Upper tooth 

 Enlar^-ed 6 tin 



158. americanus. {AJiis agraiius), Kerr., Anim. King., i, 1792, p. 231. 



leucopus. Rafin. Am. Month. Mag., 1818, vol. iii, p. 446. 



Type locality. Tennessee, or Kentucky? 



Geogr. Distr. New Jersey to South Carolina, east to Missis- 

 sippi, north to Minnesota. 



Genl. Char. Larger than domestic mouse. Tail nearly as long 

 as body; soles hairy. 



Color. Above and sides pale yellowish brown: dorsal area darker, 

 sometimes nearly black, outer surface of hind legs like back; rest of 



