Description of a new vole from Eastern Siberia

VOL. _XIII, PP. 11-12 JANUARY _31,

1899

PROCEEDINGS

OFTHE

BIOLOGICAL SOCIETY OF WASHINGTON

DESCRIPTION OF A NEW VOLE FROM EASTERN SIBERIA*

BY GERRIT

S.

MILLER,

^JR.

A small Microtm 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 (inalcohol), No. arViV United^{StatesNational}

Museum,

collected atPlover Bay, EastSiberia,

by

^Lt.

Dawson

(receivedin 1866).

General diameters.

Most

like Microtus kamtschaticus(Polyakoff), from Petropaulski,

Kamchatka,

^but smaller; ^skull with shorter _nasals, less perforatedpalate,

and much

smallerangularprocess of themandible _(in thischaracterresembling M. kadiacensis).

Ears.

Except

^fortheir very small^size they^are

much

_overtopped

_by

the surrounding^{fur the ears}

show

nocharacters of importance.

Feet.

The

feetare similar to those ofM. arvalis.

Palms

with fivetu bercles,^all well developed. Soleswith five large tubercles

and

a rudi

mentary

^sixth.

Far and

color.

The

furisremarkably^soft

and

_long,

some

ofthehairs

on

theback reaching alength of nearly 20

mm.

After its long

immer

sioninalcoholthefurhas probably^{lostalltraceofits}original color. It is

now

dullchestnut

on

_{the back,}soiledyellowish white

on

the_belly.

Skull.

The

skull of Microtus tsuktshorum is small

and

_rounded, little ridged^formuscular attachment. In _generalformit agreescloselywith thatofM.kamtschaticus, butthe nasal bones areverynoticeably shorter (5.8

mm.

inM. tshuktshorum, ^as opposed ^toa range of from6.8 to 7.8in

*Published

by

permissionof Secretary of theSmithsonian Institution, tTshuktskorum, Tschuktski,atribeof nativesineastern Siberia.

3 BIOL. Soc. WASH., ^Vol. XIII, ¹⁸⁹⁹ (11)

12 Miller A New Vole from ^Eastern

^Siberia.

sevenskullsofM. kamtochaticus),

and

_{the palate}differs notably from^that of

any

^{of the}specimens^ofAf.kamtochaticusLathesmallsize

and

_insignifi cant

number

offoramina immediately^{in frontofthelateral}bridges.

As

aresultthe bridges arenot distinguishable.

The mandible

is conspicu ously

more

slender than that of M. kamtscliaticus,

and

the articular

and

angularprocesses areverynoticeably weaker. Inthis respect ^Af.tshuk- Ishorum

shows

an approach ^toM. arvalijt ofEurope,

and an

even closer resemblancetoM. kadiacensis.

Teethas in ALkamtschatlcus.

Measurements. Total length, 113; ^tail vertebrae; 29; pencil, 8; hind foot (with claws), 19; ear from meatus, 10; ear

from

_crown,8. Skull^: greatest length,23.8; basal length, 23; ^basilarlength, 21.6; zygomatic breadth, 13; interorbital constriction, 4_; mastoid _{breadth, 12; palatal} length,^12.4; diastema,^7.8; nasals, 5.8; incisiveforamen,⁴; mandible, 14.8; maxillary^tooth

row

(alveoli), 0.4 ; mandibulartoothrow, ^6.