444 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



file of the skull is flatter than in the other desert mice. Compared 

 with ty])ical P. eremicus, the teeth are larger (fig. 106), with the 

 cusps and corresponding enamel folds of the 

 worn grinding surfaces more complex. The 

 skull is of the eremicus type, having the nasals 

 truncate posteriorly and ending well in advance 

 of the nasal branches of the premaxillaries. 



Local Distribution. — The Sonoyta desert 

 mouse was fairly common at Sonoyta, Sonora, 

 and was found on the north side of the 

 boundary, in Pima County, Arizona, as well as 

 in ^lexico. Fields and brush fences were its 

 habitat. In the flesh it was very evidently 

 distinct from Peroinyscus eremicus, which is 

 abundant in the same region. 



Fig. 106.— Peromyscus mer- 

 RiAMi. Crowns of molar 



TEETH, a, lower SERIES; 

 b, UPPER SERIES. 



Measurements of 9 specimens of Peromyscus merriami. 



Museum 

 number. 



59249 



59254 

 59241 

 59237 

 59242 

 59234 

 59235 

 59244 

 59781 



59249* 



59254' 

 59241" 

 59237" 2807 

 59242' 2808 



2776 

 2802 



59234 

 59235 

 59244 

 59781 



2815 

 2816 

 2824 

 2868 



Locality. 



Sonoyta, Sonora, Mexico, near 



Monument No. 1G8. 



....do 



....do 



....do 



....do 



....do 



do '■ Jan. 22 



do Jan. 23 



Quitobaquita, Pima County, Ari- Jan. 31 



zona. " I 



Date. 



1894. 

 Jan. 12 



...do... 

 Jan. 20 

 Jan. 21 

 ....do... 

 ....do.., 



Sex and 



ocfad. 



''9 ad. 



cfad. 



9 ad. 



9juv. 



9 ad. 



(fan. 



JJuv. 

 c?ad. 



"Head and body, 97. 



b Contained two large fetuses. 



<■ Head and body, 95. Contained three fetuses. 



mm. 

 16.5 



16.5 



19 



17.3 



16 



20 



17 



19 



17 



PEROMYSCUS TIBURONENSIS Mearns, 

 TIBTIRON ISLAND DESERT MOUSE. 



Peromyscus tihuronensis Mearns, Proc. U. S. Nat. Mus., XIX, 1897, pp. 720, 721 

 (original description). — Miller and Rehn, Proc. Best. See. Nat. Hist., No. 1,XXX, 

 Dec. 27, 1901, p. 87 (Syst. Results Study N. Am. Mam. to close of 1900). 



[Peromyscus] tiburonensis, Elliot, Field Col. Mus., Zool. Ser., IV, 1904, p. 175 (Mam. 

 Mid. Am.). 



Type-locality. — Tiburon Island, Gulf of California, Mexico. (Type, 

 skin and skull, No. 63186, U. S. National Museum.) 



Geogra'phical range. — An insular form, known only from the type 

 locality (Tiburon Island), 



