RHITHRODONTOMYS, 
257 
groove, nearly as broad as the face of the tooth; lower incisors simple; 
anterior upper molar with four roots, three large, one very small. 
The lower half of the descending ramus is abruptly twisted inward 
nearly at a right angle to the lower border of the process; antor- 
bital foramen is situated in the zygomatic portion of the maxillary 
and is almost circular above, contracting to a slit below; palate 
terminates opposite the posterior border of last molars as a trans- 
verse shelf; bulle large, widely separated, but approximating from 
behind anteriorly. 
KEY TO 2aE SPECIES AND SUBSPECIES: 
A. Tail about one-half the total length. 
a. 
b. 
=, 
a. 
b. 
Above yellowish brown lined with black; 
o SHA ERED PISTON Ps 0 ATS ee eee R. australis 
Above sepia, shading to isabella; beneath 
MU Utne Se em MRT WINGS ere 9) sec eo 2 baker 182A R. a. vulcantus 
Above mouse gray; beneath yellowish or 
Pee NE A aU ie ienleick We fa be ee setae R. megalotis 
. Above gray, strongly varied with black; be- 
PRAM Iie Ids cok Ae oR cel 8 Sela svete The R.m. sestinensts 
. Above dull fulvous brown; beneath buffy 
eu eNIe S) acme ciata tet AOD One dca R. m. zacatece 
Above black and rufous; beneath buffy 
SIRS 8 em oe eo ae R.m. obscurus 
Above yellowish brown and black; beneath 
ich ELSI Vil he a ae re R. longicaudus 
merpowe Wuny gray; beteath white../....... R. 1. pallidus 
Above dark brown and black; beneath whitish 
Dun SVE UG AE co ee R. saturatus 
Above yellowish brown and black; beneath 
PPCM OMMMOCOME: Gin fos. ok Aleck ee ees R. s. cinereus 
Above fulvous brown lined with black; be- 
VE BATU IBY 2G' 72 ya R. s. alticola 
B. Tail more than half the total length. 
EOC VE COGCIeM LOWY Ss hs cece cata eae sb R. peninsule 
Above fulvous and black; beneath pale ful- 
mous, including chin and throat. ...........+.% R. dafficilis 
Above rufous brown; beneath white........ R. mexicanus 
. Above grayish brown and yellowish; beneath 
A CLSUL SIR eA JP Seed a rr R.m. intermedius 
. Above yellowish brown and black; beneath 
whitish. 
ae suarve-atoral leneth,-183 mm... 5..52' R. m. fulvescens 
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