414 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



mens, tin* vertebral area is decidedly blackish, in which respect the 

 typical forms differ from P. boylii pinalis, in which that pari is paler 

 and browner, and P. boylii penicillatus, in which the dark vertebral 

 area has practically disappeared, the whole upper surface being pale 

 grayish drab. The cinnamon-colored area of the sides is more 

 restricted than in pinalis and the coloration in general darker, while 

 P. h. penicillatus and P. b. attwateri are still paler forms. Mammae, 

 ;> pairs. 



The young, which on the higher portions of the Coast Range are 

 born in May, are one-half to three-fourths grown by the middle of 

 June. They are at first mouse-gray above, darker about the orbit, 

 and white below, where the gray basal portion of the coat can be dis- 

 cerned through the narrowly white-tipped hair. -As they grow older 

 they acquire a paler, more drab coloration. The adult coat is 

 assumed in the usual way, the nape being the last place to receive the 

 long coat, which, as usual, is darker and grayer at first, lacking the 

 warm cinnamon color along the "water line." The young, like 

 adults, can be identified by the penciled termination of the tail. The 

 pelage of this form is dense and silky, like that of the members of the 

 P. sonoriensis group. 



A fine adult male from the eastern base of the Coast Range Moun- 

 tains is paler and lias much more of the cinnamon color than those 

 from the summit and western slopes of these mountains. In this 

 respect it agrees more closely than the rest of our series with the type 

 of Baird's boylii and topotypes of Rhoads's major, these representing 

 the form of the interior region of California, which is not so dark as 

 that of the coast, in middle and northern California, which latter 

 may be recognized as Peromyscus boylii robustus (Allen) ". Our speci- 

 mens from west of the Coast Range are somewhat intermediate 

 between true boylii and robustus, but they seem to me to be nearest 

 to the former. 



Measurements. — Average of eight adult males: Length, 201 mm.; 

 tajl vertebra', 104; ear from crown, 14.9; length of hind foot, 22.1. 

 Average of seven adult females: Length, 205 mm. ; tail vertebra'. 1 10; 

 ear from crown, 15.4; length of hind foot, 22.6. As usual, the females 

 are a trifle larger than the males. 



Cranial and dental characters. — The skull of the type (No. We," 

 U.S.N.M., skull and caudal vertebrae in fair condition) of Hesperomys 

 boylii Baird measures 27.5 by 13.7 mm. It is indistinguishable from 

 a series of skulls of this species from the coast region of southern Cali- 

 fornia, when individuals of corresponding age (i. e., youngish adults) 



a bitomys rdbustus Allkx,Bu11. Am. Mus. Nat, Hist., V, Art. XIX, Doc. Hi. 1S<)3, pp. 33"), 

 336. (Original description; typo, skin and skull, from Lakeport, Lake County, California, 

 in the American Museum cf Natural History, New York.) 



