•136 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



PEROMYSCUS EREMICUS FRATERCULUS (Miller). 

 SAN DIEGO DESERT MOUSE. 



Sitomys frati /villus Miller, American .Naturalist , XXVI, Mar., 1S92, 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 In iron! nigdlus Rhoads, Proc. Acad. Nat. Sci. Phila., 1894, pp. 257, 258 . 

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



[Peromyscus] fratercidus Trouessart, Catal. Marn.,Pt. 3, 1897, p. 515. — Elliot, Field 

 Col. Mus., Zool. Ser.,LT, 1901, p. 136 (Synop. Mam. X. Am.): IV, 1904, p. 184 

 (Mam. Mid. Am.). 



Peromyscus fraterculus, Miller and Rehn, Proc. Bost. Soc. Nat. Hist., XXX, No. 1, 

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



Type-locality. — Dul/Aira, San Diego County, California. (Type in 

 the collection of Gerrit S. Miller, jr.) 



Geographical raTWjre.— 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. caUfornicus, except in 

 size, suggested the name fraterculus. 

 As stated by Mr. Rhoads, in the 

 American Naturalist for September, 

 1893, "Mr. Miller, who described 

 fraterculus as a full species, now con- 

 siders it a 'dark coast form of 



Fig. 102.— Peromyscus eremicus frater- 

 culus. Skulls, a, type of Sitomys 

 herronii Rhoads (= Sitomys fratercc- 

 lus Miller): &, type of Sitomys her- 

 roni nigellus klioads (= sitomys fra- 

 TERCULUS Miller). 



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 

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

 an minus 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 indiscrinmately throughout the year. The first pelage is 



