444 



BtJLLETIN 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 

 in Mexico. Fields and brush fences were its 

 habitat. In the flesh it was very evidently 

 distinct from Peromyscus eremicus, which is 

 abundapt in the same region. 



Measurements of 9 specimens of Peromyscus merriami. 



Fig. 106. — Peromyscus mek- 



KIAMI. CEOWNS of molar 

 TEETS. a, LOWER SERIES; 

 fe, UPPER SERIES. 



Muaetini 

 number. 



Locality. 



Date. 



Sex and 

 age. 



69249 



59264 

 59241 

 69237 

 59242 

 69234 

 69235 

 69244 

 59781 



69254 

 69241 

 59237 

 69242 

 59234 

 69235 

 69244 

 69781 



2775 



2776 

 2802 

 2807 

 2808 

 2815 

 2816 

 2824 

 2868 



Sonoyta, Sonora, Mexico, near 

 Monument No. 168. 



do 



do 



....do 



....do 



do 



....do 



do 



Quitobaquita, Pima County, Ari- 

 zona. 



Jan. 12 



...do... 

 Jan. 20 

 Jan. 21 

 ...do... 

 ...do.. 

 Jan. 22 

 Jan. 23 

 Jan. 31 



ttcfad. 



''Sad. 

 (fad. 

 5 ad. 

 5juv. 

 ?ad. 

 (fim. 



(fjUV. 



cjad. 



211 

 218 

 197 

 193 

 217 

 194 

 208 



114 

 118 

 102 

 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 



a Head and body, 97. 



& Contained two large fetuses. 



= Head and body, 96. Contained three fetuses. 



PEROMYSCUS TIBURONENSIS Mearns. 

 IIBURON ISLAND DESERT MOUSE. 



Peromyscus tihuronensis Meakns, Proc. U. S. Nat. Mus., XIX, 1897, 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] tihuronensis, 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). 



