MAMMALS OK TI1K MEXICAN HOUNDARY. 



409 



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

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

 they are distinct in /'. arizonse. 



The above description is based on fifteen adults taken near El Pa^., 

 Texas, in February and March. An immature female (No. -;.'.',';;;,. IT. S. 

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

 Texas, ,]\u\o 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 Tornillo 

 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 June 16, 

 1893. 



Measurements of 18 specimens of Peromyscus tornillo. 



Fig. 85. — Peromyscus tor- 

 nillo. CROWN'S OF MOLAR 

 TEETH. a. LOWER SERIES; 

 b, UPPEK SERIES. 



