MAMMALS OF THE MEXICAN BOUNDARY. 



437 



slate-gray above and grayish white l^elow, where the whitish points on 

 the hairs are very narrow. When two-tliirds grown, the adult pelage 

 is assumed coincidently with the occurrence of the molt, which 

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

 median extension is produced upward mitil it meets the opposite side 

 and completes the girdle, appearing above as anarrow band 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 limbs and 

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

 and another on the upper part 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 tlie eastern slope of the Coast Range, where 

 intergradation with typical P. erendcus begins. 

 At Mountain Spring, halfway up the eastern 

 slope of the Coast Range Mountains, we ob- 

 tained specimens almost as pale as typical 

 P. erendcus, with nearly white underparts, 

 though most specimens from there were nearer 

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

 described the intergrade between subspecies 

 erendcus and fratercidus, from the San Bernar- 

 dino Valley, California, under the name Sitomys 



herronii, and true Peromyscus erendcus fraterculus was afterwards 

 redescribed by him as Sitomys herronii nigellus, from West Cajon 

 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 de>sert mice in 

 the U. S. National Museum. 



Local distribution. — This mouse was conmion 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.— Peromyscus 

 eremicus fraterculus. 

 Crowns of molar teeth. 

 Type of Sitomys her- 

 ronii Rhoads (= Sitomys 

 fraterculus miller). 



O, LOWER series; 6, UPPER 

 SERIES. 



