MAMMALS OB' THE MEXICAN BOUNDARY. 



409 



molar teeth of P. tomillo have the subsidiary cusps, especially those 

 of the anterior upper molar more or less obsolete (fig. 85), whereas 

 they are distinct in P. arizonx. 



The above description is based on fifteen adults taken near El Paso, 

 Texas, in February and March. An*immature female (No. f Hlf ? U. S. 

 N. M.) taken by the writer at Fort Hancock, 

 Texas, June 16, 1893, is mouse gray where 

 the juvenile coat is retained, the sides and 

 forehead being smoke gray. Two specimens 

 from the Upper Corner Monument (No. 40) 

 are essentially like those from the vicinity of 

 El Paso. 



Habits and local distribution. — The Tomillo 

 mouse is very abundant under groves of the 

 screw bean in the Rio Grande River bottom. 

 It was taken on both sides of the river, in Chi- 

 huahua and Texas. To the westward it was 

 only found at Doyles Well (Monument No. 40), where two were taken. 

 At Fort Hancock, Texas, a female contained four young on Jime 16, 

 1893. 



Measurements of 18 specimens of Peromyscus tormJlo. 



Via, 85. — PEBOMYScra <roB- 

 NiLLO. Crowns of molak 



TEETH. a, LOWER SERIES; 

 6, UPPER SERIES. 



