desckiption of a new species of cotton rat (sig

DESCKIPTION OF A NEW SPECIES OF COTTON RAT (SIG

MODON MINIMA) FROM NEW MEXICO.

By Edgak

a.

Mearns,

M. D., Surgeon, United States Army.

Among

the.smalluiaminaLscollected

by

Mr. F, X.Holzner

and

myself onthe

Mexican

border, in coimection with the operations of theInter- national

Boundary

Commission, are

two

specimens of a species ofcot- tonrat, which,in

my

^opinion,is distinctfrom

any

heretofore described.

In thegrassy hollows

and

fiats

between

the

most

southernspurs of the

Apache

Mountains, in an arid, treelessregion,having analtitude of1,500metres (exactly l,49(j at the monument), it

was

a surprise to findany species of SU/niodoH.

Many

of their old

runways

were seen, however, inthe dry

and

dustygrass; but nearly allof the holeswere abandoned. Industrious trai)piug, persisted in for several weeks, resulted in the capture of but

two

adult male specimens.

Mexican

minersin thevicinity told us that only afew

months

beforethespecies

had

been abundant, but seemedto

have

died off; indeed,

we

frequently

saw

their remains in tbe grass

and

i)icked

up

parts of skeletons

and

oneor

two

additional skulls.

This

new

species has

many

points in

common

with Sigmodon fal- viventer, recently described

by

Dr.J. A. Allen,from Zacatecas,

Mex-

ico.* Itis still smaller than that species,being about the size of

De

Saussure's ^{^^}Hesperomys toltecus^^ {

=

Sigmodon hispidustoliecvs).\

On

capturing these specimens I

was

atoncestruck

by

^theirresemblanceto S.fulviventer,thetypeofwhichI

had

closely

examined

inthe

American Museum

of Natural History in

New

York, thelesemblanceconsisting not onlyin the fulvous tone of coloring, especiallyof theunderparts, butin the distinctly bristly character of thehairy coat

and

thedense hairiness of the ears

and

tail, in all of which particulars it differs

*Bull.Amer. Mus.Nat.Hist.,ii.No. 3,p. 180,October21,1889.

tAlleu. /..c, III, 1891, p. 207.

*Proceedings NationalMuseum,Vol.XVII

—

No.994.

129 Proc. N.

M.

04 9

130 ^A NEW ^{SPECIES OF COTTON} BAT—ME

SENS. vol.xvii.

radicallyfrom its geographically nearest neighbors

—

Sigmodon hispidus texianus, (And.

and

Bach.)

and

^;S'. hispidus arizonw, (Mearns).

SIGMODON

MINIMA,iimw species.

Type.—^o. 2L1S7,U.^S. N. M.(Coll. International

Boundary Commis-

sion). Adult male,from

Upper

Corner

Monument, New

^Mexico,onthe

Mexican boundary

^line, 100 mileswestof theinitial

monument

onthe west

bank

of the Rio Grande. Collected

by Edgar A. Mearns and Frank

X. Holzner, April 26, 1892.

Description of^type.

—

^Coat

^{bushy and}

^{hispid; under-furdarkerplum-}

beous than in S. hispidus texianus or 8. liispidusarizonce; coarse outer coat

more

bristly, especially on sidesof

head and

neck; ears, feet,

and

taildensely hairy; tailnotdistinctly bicolor. Color abovegrayish, the individual hairsbeing ringed with gray

and

brown, the

brown

annuli beingblackishintheirmiddle^portion,fadingto light-yellowish

brown

on their edges^;

under

surface of

body

^{clayeybuff; feet yellowish gray}

;

ears densely clothed with grayish hairs on inner surface, with their convex surface black anteriorly

and

buffposteriorly; tail brownish black,

somewhat

lighterbelow, the hairs almost concealing the annuli.

Another

specimen (No.1760,

male

adult,from the

same

locality, col-

lected

by Mearns and

^Holzner,

May

13, 1892) differs only in being ochraceousbuff below, with alittle

more

of the fulvous tingeon

rump and

flanks,thusapproaching

more

^{closely to}thecoloration ofSigmodon fulviventer.

Dimensions.

— Measurements

(in millimeters) ofNo.21187,adultmale:

Length,

measured

from noseto

end

of vertebrte oftail,223;tail,measured fromrootto

end

ofvertebric, 94; to

end

ofhairs,104; height of earabove crown, 14; distance

between

eyes, 12; diameter of eye, _5; length of longest whisker,30;fromtip ofnoseto eye, 16; to center ofpupil, 18.5;

to ear,30; ^{to tip} of ear, 46; to occiput, 37; toend of outstretchedhind limb,183; fore limb,

measured

fromolecranontoend of longest claw,33;

lengthof fore-foot, 15; longestclaw offore-foot (chord),3.9; hind limb,

measured

fromknee-jointto

end

of longest claw,53; length ofhind-foot, 28; longestclaw ofhind-foot,3

mm. Measurements

ofNo. 1700, adult male: Length,223^; tailto

end

ofvetebra;,91^;to

end

ofhairs,97^; height of ear above crown, 12; above notch,16; distance

between

eyes, 12;

diameter ofeye, 5; longest whisker, 26; fromtop ofnoseto eye, 16; to centerof pupil, 19; to ear,30;to tip ofear,46; to occiput, 34; to

end

of hinder extremity, 180; forelimbfromolecranon, 33; length offore-foot, 14; longestclaw offore-foot,3^;hind limb from knee-joint, 53;length of hind-foot, 27; longest clawof hind-foot, 4.2

mm.

Cranialanddental characters.

— As

comi)aredwithS.hispidus texianus, the only speciesbefore

me

for comparison, the brain-caseis higher

and

narrower, theskull

more

constrictedbetween the orbits, with shorter nasals, theirbases being nearlyeven withthe posterior border of the incisiveforamen insteadofwellbehind it.

The

dentitionisvery

much

heavier.