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 THE SPECIES AND SUBSPECIES. 
A. Tail about one-half the total length. 
a. Above yellowish brown lined with black; 
NEI NE, 5 Sha a nn a ia a R. australts 
b. Above sepia, shading to isabella; beneath 
IE RS AF 250 aairnpe tr ag¥nGtal ya ws Sewvere Se ont R. a. vulcanius 
c. Above mouse gray; beneath yellowish or 
SNELL ks tie nahi ON ene sed ths ea ee A R. megalotis 
d. Above gray, strongly varied with black; be- 
RIE ican clas gow wares Cadre! eons 9242 R.m., sestinensts 
e. Above dull fulvous brown; beneath buffy 
MRE et ag ese PF ade haa tetone AS R. m. zacatece 
f. Above black and rufous; beneath buffy 
RIM IA i Pe Rs a cy Pte Ci anno wie wo R.m. obscurus 
g. Above yellowish brown and black; beneath 
1 SES LS ee i R. longicaudus 
h. Above buffy gray; beneath white.......... R. 1. pallidus 
i. Above dark brown and black; beneath whitish 
RUNNERS Msn. Gah c is doo tne my bis «vies 3 hk R. saturatus 
j. Above yellowish brown and black; beneath 
BEEN SLERESOCOUSS S200 kale 6G ON sk wot R. s. cinereus 
k. Above fulvous brown lined with black; be- 
BREA ORAS fF -c ls < es stats F's ew vs R. s. alticola 
B. Tail more than half the total length. 
meeineyve Teddish Drowm. «25.56.16 cee ee es R. peninsule 
b. Above fulvous and black; beneath pale ful- 
Tous, wicludime chin and throat............. R. difficilis 
c. Above rufous brown; beneath white........ R. mexicanus 
d. Above grayish brown and yellowish; beneath 
MMM eee ht, ae SRS os Oe Soe Adee nee nd oe R. m. intermedius 
Above yellowish brown and black; beneath 
whitish. 
ae *eatee; total leneth, 183 mi... 42. 0s R. m. fulvescens 
PAGE 
264 
