MAMMALS OF THE MEXICAN BOUNDARY. 



443 



PEROMYSCUS MERRIAMI Mearns. 

 SONOYTA DESERT MOUSE, 



Peromyscus merriami Meakns. Proc. U. S. Nat. Mus., XIX, 1896, p. 138 (p. 2 of ad- 

 vance sheet, issued May 25, 1896; original description). — Millee and Rehn, 

 Proc. Bost. Soc. Nat. Hist., XXX, Dec, 1901, p. 79 (Syst. Results Study N. Am. 

 Land Mam. to close of 1900). 



[Peromyscus] merriami, Elliot, Field Col. Mus., Zool. Ser., IV, 1904, p. 198 (Mam. 

 Mid. Am.). 



-Village of Sonoyta, on the Sonoyta River, State of 

 (T;^'pe, skin and skull, Cat. No. 59234, U. S. National 



Type-locality. - 

 Sonora, Mexico. 

 Museum.) 



Geographical range. — The Sonoyta desert mouse is known only from 

 the Sonoyta River, Sonora, near the Boundary Line between Mexico 

 and the United States. 



Description. — This species has the appearance of the Peromyscus 

 erendcus, living in the same locality, "except that itis larger and'stouter. 



Fig. 105.— Peeomtscus meeriahi. Skull. 



a, DOBSAL view; 



VIEW. 



6, VENTEAL view: 



The two have the same coloration, except that P. merriami is some- 

 what darker, has the light cinnamon color extending down the outer 

 side of the fore limb to the hand, and a large pectoral patch of cinna- 

 mon that is usually, wanting in P. eremicus. 



Cranial characters. — The skull (fig. 105) resembles that of P. eremi- 

 cus, except that it is much larger and heavier, with the rostral portion 

 relatively longer, the zygomatic arches wider anteriorly, and the brain 

 case more elevated. Its larger size serves to identify the skull of tliis 

 species at a glance, the two anterior molar teeth about equaling 

 the lateral tooth-row of P. eremicus. In P. eremicus from Yuma the 

 skull measures 25.2 mm. in length, P. merriami measuring 27 mm. 

 In P. merriami the zygomatic arches stand out more prominently and 

 are more nearly parallel to the long cranial axis, because the zygo- 

 matic processes are more produced and angular anteriorly. The pro- 



a Ten specimens of Peromyscus merriami were taken at Sonoyta and one at Quitobaquita. 

 Large series of P. eremicus were taken at the same places. 



