436 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



PEROMYSCUS EREMICUS FRATERCULUS (Miller). 

 SAIf DIEGO DESERT MOTTSE. 



Sitorhysfrateradus Millee, American Naturalist, XXVI, Mar., 1892, pp. 261, 264 (origi- 

 nal description). 



Sitomys herronii Rhoads, American Naturalist, XXVII, pp. 832, 833, Sept. 1, 1893 

 (type-locality, San Bernardino Valley, southern California). 



Sitomys herroni nigellus Riioads, Proc. Acad. Nat. Sci. Phila., 1894, pp. 257, 258 

 (type-locality, West Cajon Pass, San Bernardino Mountains. California). 



[Peromj/scMs] /ratercitZus, Trouessart, Catal. Mam., Ft. 3, 1897, p. 515. — Elliot, Field 

 Col. Mus., Zool. Ser.,II, 1901, p. 136 (Synop. Mam. N. Am.); IV, 1904, p. 1§4 

 (Mam. Mid. Am.). 



Peromyscus fratercvZus, Millee and Rehn, Proc. Bost. Soc. Nat. Hist., XXX, No. 1, 

 Dec. 27, 1901, p. 73 (Syst. Results Study N. Am. Mam. to close of 1900). 



Type-locality. — Dulzura, San Diego County, California. (Type in 

 the collection of Gerrit S. Miller, jr.) 



GeograpJdcal range. — Sonoran Zone of the Pacific Coast Tract of 

 southern and Lower California. 



Description. — Larger and darker than typical Peromyscus eremicus; 



underparts with a muddy staining, 

 whereas the more eastern forms of 

 P. eremicus have the under surface 

 pure white unless there is a pectoral 

 spot of cinnamon. Its general resem- 

 blance to P. californicus, except in 

 size, suggested the name fraterculus. 

 As stated hj Mr. Rhoads, in the 

 American Naturalist for Septeihber, 

 1893, "Mr. Miller, who described 

 fraterculus as a full species, now con- 

 siders it a 'dark coast form of 

 eremicus.'" 



The coloration, as a whole, is darker 

 than in the other subspecies of P. 

 eremicus; ■ the upper surface being 

 liberally mixed with black-tipped hairs; under surface grayish 

 white, stained with clay color, often with a spot of cinnamon on 

 the chest; sides tawny cinnamon instead of ochraceous buff; tail 

 nearly naked except near the end, dusky below, not at all bicolored. 

 In typical eremicus the under side of the tail is decidedly paler than 

 the upper, but without any line of demarcation; while the subspecies 

 arenarius has the tail practically bicolored, its under surface being 

 pure white. 



In the Coast Range Mountains, where the winters are cold, the 

 young of the first litter are born about March and mature about 

 August. Near the coast, where there is uniformity of temperature, 

 they breed iudiscrimnately throughout the year. The first pelage is 



u b 



Fig. 102. — Pebomyscus eremicus fkateb- 



cui.ua. Skulls, a, type of Sitomys 



HEKKONii Rhoads (= Sitomys fratekcu- 



lus Miller) ; b, type of Sitomys her- 



RONI NIGELLUS RHOADS (= SiTOMYS FRA- 

 TERCULUS Miller). 



