444 



BULLETIN 56, UNITED STATES NATIONAL MUSEUM. 



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

 with typical 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 

 iu Mexico. Fields and brush fences were its 

 habitat. In the flesh it was very evidently 

 distinct from Peromyscus eremicus, which is 

 abundant in the same region. 



Fig. 106.— Peromyscus mi.h- 

 riami. Crowns of molar 

 teeth, a, lower series; 

 6, upper series. 



Measurements of 9 specimens of Peromyscus merriami. 



Locality. 



Sonoyta, Sonora, Mexico, near 



Monument No. 168. 

 do 



do 



do 



do 



do 



do 



do 



Date. 



1894. 

 Jan. 12 



...do.. 

 Jan. 20 

 Jan. 21 

 ...do.. 

 ...do.. 

 Jan. 22 

 Jan. 23 



Sex and S 



Quitobaquita, Pima County, Ari- Jan. 31 

 zona. 



<»c?ad. 



h ?ad. 

 oT ad. 

 9 ad. 



OjUV. 



9 ad. 



cfim. 



cfjuv. 



c$ad. 



mm. mm. 



211 

 218 

 197 

 193 

 217 

 194 

 208 



111 

 118 

 in.' 

 102 

 113 

 104 

 111 



mm. 

 22.0 



22 



22.7 



22.4 



22 



23 



22.8 



23 



22 



mm. 

 16.5 



16.5 



19 



17.3 



16 



20 



17 



19 



17 



« Head and body, 97. 



b Contained two large fetuses. 



e Head and body, 95. Contained three fetuses. 



PEROMYSCUS TIBURONENSIS Mearns. 

 TIBURON ISLAND DESERT MOUSE. 



Peromyscus tiburonensis Mearns, Proc. U. S. Nat. Mus., XIX, 1S97, pp. 720, 721 

 (original description). — Miller and Rehn, Proc. Bost. Soc. 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.) 



Geographical range. An insular form, known only from the type 

 locality (Tiburon Island). 



