Vol. XIII, pp. 11-12 January 31 , 1899 



PROCEEDINGS 



OF THE 



BIOLOGICAL SOCIETY OF WASHINGTON 



DESCRIPTION OF A NEW VOLE FROM EASTERN 



SIBERIA* 



BY GERRIT S. MILLER, Jr. 



A small Microim taken at Plover Bay, East Siberia, has re- 

 mained unidentified in the United States National Museum for 

 more than thirty years. It differs from any of the Asiatic species 

 of which I can find descriptions, and may be known as : 



Microtus tshuktshorum sp. nov. 



Type, 9 adult (in alcohol), No. -irij^, United States National Museum, 

 collected at Plover Bay, East Siberia, by Lt. Dawson (received in 1866). 



General cJtaraders. — IMost like Microtus Irimtscliatims (PolyakofF), from 

 Petropaulski, Kamchatka, but smaller ; skull with shorter nasals, less 

 perforated palate, and much smaller angular process of the mandible (in 

 this character resembling 3f. kadiacensis). 



Ears. — Except for their very small size — they are much overtopped by 

 the surrounding fur — the ears show no characters of inii^ortance. 



Feet. — The feet are similar to those of M. arvalis. Palms with five tu- 

 bercles, all well developed. Soles with five large tubercles and a rudi- 

 mentary sixth. 



Fur and color. — The fur is remarkably soft and long, some of the hairs 

 on the back reaching a length of nearly 20 mm. After its long immer- 

 sion in alcohol the fur has probably lost all trace of its original color. It 

 is now dull chestnut on the back, soiled yellowish white on the belly. 



Skidl. — The skull of Microtus tsuktshorum is small and rounded, little 

 ridged for muscular attachment. In general form it agrees closely with 

 that of M. kamfschaticus, but the nasal bones are very noticeably shorter 

 (5.8 mm. in M. tshuktsJiornm, as opposed to a range of from 6.8 to 7.8 in 



* Published by permission of Secretary of the Smithsonian Institution, 

 t Tshuktskorum, Tschuktski, a tribe of natives in eastern Siberia. 



3— Biol. Soc. Wash., Vol. XIII, 189'J (11) 



