MAMMALS OF THE MEXICAN BOUNDARY. 



437 



slate-gray above and grayish white below, where the whitish points od 

 the hairs are very narrow. When two-thirds grown, theadull pelage 

 is assumed coincident ]y with the occurrence of the molt, which 

 begins on the under surface, extends thence to the sides, whence a 

 median extension is prod need upward until it meets the opposite side 

 and completes the girdle, appearing above as a narrow hand across the 

 middle of the back, but covering all of the under surface from the neck 

 to the inguinal region. The coating then extends to the limb- and 

 head, the dorsal band broadening until only a small spot on the nape 

 and another on the upper pari of the rump remain — the last to be cov- 

 ered by the new hairs. In immature specimens 

 the coloring is duller than in adults. 



This subspecies grows paler in the notches and 

 on the eastern slope of the Coast Range, where 

 intergradation with typical P. eremicus begins. 

 At Mountain Spring, halfway up the eastern 

 slope of the Coast Range Mountains, we ob- 

 tained specimens almost as pale as typical 

 P. ere?7iicus, with nearly white underparts, 

 though most specimens from there were nearer 

 to P. e. fraterculus. Mr. S. N. Rhoads has 

 described the intergrade between subspecies 

 eremicus and fraterculus, from the San Bernar- 

 dino Valley, California, under the name Sitomys 



herronii, and true Peromyscus eremicus fraterculus was afterwards 

 redescribed by him as Sitomys herronii nigellus, from West Cajoii 

 Pass, San Bernardino Mountains, southern California. I am indebted 

 to Mr. Rhoads for an opportunity of examining these types (figs. 102 

 and 103) and of comparing them with the series of desert mice in 

 the U. S. National Museum. 



Local distribution. — This mouse was common in the Pacific Coast 

 Tract, living in dry places among bushes and rock. Four females, 

 taken May 13 to June 8, would have given birth to 2, 3, 4, and 4 

 young, respectively. 



Fig. 103.-Peromy.mvs 

 eremicus fraterci'lis. 

 Crowns of molar teeth. 

 Type of Sitomys her- 

 r.<>Mi Rhoads (= Sitomys 



FRATERCULUS M I I. L E I! ) . 



a, lower series; b, upper 



SERIES. 



