704 New Species of Field Mouse. 
prominent, but this peculiarity probably is subgeneric. An exami- 
nation of the skulls and teeth at once shows the animal to belong 
to tke subgenus Chilotus of Baird, to which but one species 
(Arvicola oregonus, from the Pacific coast region) has been hereto- 
fore definitely assigned. The range of the subgenus is thus ex- 
tended more than a thousand miles to the eastward. The present 
species is nearly as large as Arvicola riparius, and consequently 
considerable larger than A. oregonus. Of the four specimens at 
hand, two are males and two females, all fully adult. The females 
bear evidence of recent nursing. The species may be easily dis- 
tinquished by the following diagnosis : 
ARVICOLA (CHILOTUS) PALLIDUS sp. nov. 
Type no. 3852, ọ adult, Merriam Collection. Fort Buford, 
Dakota, September 10,1887. Vernon Bailey. 
General characters.—Size medium, nearly equalling that of 
Arvicola riparius (average total letigth of four specimens 126.25 
mm.). Tail very short (average length in four specimens 23.75 
kota (Type). 
ford, or molar series 
ieee. Merriam, From Ft. Bu 
1 and 2, 2 skull,double natural size ; 3, upper r molar series, X53 4 
male Arvicola (Chilotus 
mm. from actual base; apparent length only about 18 a 
with a long terminal petoli. Ears medium ; thick; well haired, 
superior border inflexed, giving them a prominence not seen in m 
ears of the same size; antitragus medium (smaller than 
