ao6 FIELD COLUMBIAN MUSEUM ZOOLOGY, VOL. i. 



causing the animals of the extremes of the seasons to present a 

 very different appearance. Indeed not a few so-called species 

 have been described that have possessed less differences than 

 these. The yellow on the chest is very variable, and apparently 

 not dependent on season or sex, some examples showing it very 

 conspicuously and of considerable extent, and others not even 

 having a trace of it. Numerous examples have a conspicuous 

 white tip to the tail. 



30. Peromyscus boylii. 



Hesperomy's boylii. Baird, U. S. Pac. R. R. Expd., 1857, 

 vol. vii, p. 471. 



Sitomy's gilberti. Allen, Bull. Am. Mus. Nat. Hist., vol. v, 

 1893, page 188. 



One hundred and ninety-two specimens from the following 

 localities: 41, Snow Mountains, Calusa Co. ; 27, Mt. Hamilton, 

 Santa Clara Co.; 32, Alum Rock Park, Santa Clara Co.; 44, San 

 Antonio, San Bernardino Co. ; 48, Carmel River, Monterey Co. 



The Snow Mountain examples were taken in September, those 

 from the other localities in May, June, July and August. The 

 pelage varies in color, caused more by age than any other appre- 

 ciable reason, and the fully adult specimens are typical individ- 

 uals as described by Baird. The type is said to have come from 

 Eldorado Co., and it is rather strange that in the great num- 

 ber of mice obtained in that county and present in this collec- 

 tion, no specimen of boylii was procured. It seems to be more 

 generally distributed to the westward and southward. The ears 

 vary greatly in length from 19 to 23 mm. not always caused by 

 age. In 1893, Dr. Allen (1. c.) described a 'mouse from Bear 

 Valley, San Benito Co., and Mount Hamilton, Santa Clara Co., 

 represented by a small series of fourteen adults and four 

 young, as Sitomy's gilberti. On comparing a topotype of this 

 species with my specimens I was convinced that boylii and gilberti 

 were the same, and Dr. Allen, who saw the examples compared, 

 agreed with me. But in order that there might be no error in 

 this identification, I wrote to President Jordan of the Stanford 

 University, to which institution Allen's series belonged, request- 

 ing him to forward them to me, which he most kindly did, and 

 on comparing the type with my series, it appeared to me beyond 

 question that it was the same as boylii, and gilberti will there- 

 fore have to become a synonym. Allen's type resembles exactly 

 specimens of boylii from Alum Rock Park, Snow Mountains and 



