436 BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



PEROMYSCUS EREMICUS FRATERCULUS (Miller). 

 SAN DIEGO DESERT MOUSE. 



Sitomys fratercidus'Mjhi.ER, Ameiic&n Naturalist, XXVI, Mar., 1892, pp. 261, 264 (origi- 

 nal description). 



Sitomys herronii Ehoads, American Naturalist, XXVII, pp. S32, 838, Sept. 1, 1893 

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



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

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



[PeroTO)/sf«s]//a^e/TuZMs, TROUESSART,Catal. Mam.,Pt. 3, 1897, p. 515. — Elliot, Field 

 Col. Mus., Zool. Ser.,II, 1901, p. 136 (S\Tiop. Mam. N. Am.); IV, 1904, p. 184 

 (Mam. Mid. Am.). 



Peromyscus fmterculus, Miller 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). 



Ti/pe-Iocality. — Dulzura, San Diego County, California. (Type in 

 the collection of Gerrit S. Miller, jr.) 



Geograpliical mii^e.- Sonoran Zone of the Pacific Coast Tract of 

 southern and Lower California. 



Description. — Larger and darker than typical Peromyscus eremicus; 



imderparts 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 by IVIr. 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 

 eremicus y^ 



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 ocliraceous buff; tail 

 nearly naked except near the end, dusk}^ below, not at all bicolored. 

 In tj'pical 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 w^hite. 



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

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

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

 they breed indiscrimnately throughout the year. The first pelage is 



Fig. 102.— Peromyscus eremicus frater- 

 culus. Skulls, a, type of Sitomys 

 nERRoxii Rhoads (= Sitomys fratercu- 

 lus Miller); b, type of Sitomys her- 

 roni nigellus Rhoads (= Sitomys fr.\- 

 terculus Miller). 



