MAMMALS OF THE MEXICAN BOTTNDARY. 



457 



from topotypes of Baird's Eeithrodontomys longicauda, his R. paUidus 

 thus becoming a complete synonym of B. longicauda, it is equally plain 

 that Allen's pollidus is thoroughly composite, his table of 157 speci- 

 mens embracing series of true longicauda and typical deserti, which I 

 myself examined and measured in the field, from several localities on 

 the Colorado Desert and the Pacific slope, west of the Coast Range, 

 as well as specimens from the San Bernardino Valley and other locali- 

 ties, which perhaps represented intergrades between the form of the 

 interior desert region (R. ni.. deserti) and that of the Pacific Coast strip 

 (R. longicauda). I regard it as probable that the four forms of the 

 R. megalotis group, named above, will eventually be proved to be 

 conspecific, in which case the latter three {arizonensis, deserti, and 

 longicauda) will have to stand as subspecies of Reithrodontomys mega- 

 lotis (Baird), which was the first one named. 



The several forms of this genus known from the region of the Bound- 

 ary may, perhaps, be identified by reference to the following 



KEY TO EEITHEODONTOMYS FOUND ON THE MEXICAN BOUNDARY. 



o. Total length more than 150 mm. 



h. Total length less than 170 mm. Above yellowish brown mixed with black, but with- 

 out a darker vertebral area; sides faintly iuWous. -Eeithrodontomys laceyi (p. 458). 

 ib. Total length more than 170 mm. 



c. Length, 178 mm. ; tail vertebrae, 99 ; ear, 12. Above grayish brown with a yellow- 

 ish wash; sides strong yellowish fulvous; below dull whitish. 



Eeithrodontomys mexicanus intermedius (p. 457). 

 cc. Length, 172 mm; tail vertebrae, 99; ear, 14. Above pale yellowish brown, lined 

 with black, with a blackish median area; sides light yellowish; below white. 



Eeithrodontomys fulvescens Sj>. 459). 

 aa. Total length less than 150 mm. 



d. Coloration pale, above yellowish gray, lined with darker, and more fulvous on 



e. Tail one-half the total length; color above yellowish gray, considerably mixed 



with blackish; pelage full and soft Eeithrodontomys megalotis (p. 460). 



ee. Tail more than half the total length; color above yellowish, but little mixed 

 with darker; pelage short and somewhat harsh. 



Eeithrodontomys megalotis deserti (p. 462). 

 dd. Coloration dark; above yellowish brown, lined with blackish, with a darker 

 median dorsal area. 

 /. Length, 148 mm.; tail vertebrse, 77; hind foot, 17. Top of head grayish 



brown Eeithrodontomys longicauda (p. 464). 



ff. Length, 149; tail vertebrae, 78; hind foot, 17. Top of head reddish brown. 



Beithrodontomys arizonensis {p. 459). 



REITHRODONTOMYS MEXICANUS INTERMEDIUS Allen. 



TAMATJLIPAS HARVEST -MOUSE. 



Beithrodontomys mexicanus intermedium Allen, Bull. Am. Mus. Nat. Hist., VII, p. 136, 

 May 21, 1895 (original description); VIII, 1896, p. 236 (in text).— Miller and 

 Rehn, Proc. Bost. Soc. Nat. Hist., XXX, No. 1, Dec. 27, 1901, p. 99 (Syst. 

 Results Study N. Am. Mam. to close of 1900). 



