PROCEEDINGS

Vol.XIX,'^pp. 3-6 January 29, 1906

PROCEEDINGS

OF THE

BIOLOGICAL SOCIETY OF WASHINGTON

IDENTITY OF THOMOMYS UMBRINUS (RICHARDSON), BY VERNON BAILEY.

In _1829,

Richardson

described

and named Geomys umbrinus from

a

specimen

^thenin possession^of

Mr. Lead

_beater,a

London

dealer in natural history specimens.

The name

has since

been

the cause of

much

confusion

and

has been applied ^{to or}placed in

synonomy ^under

various species^of Thomomi/s ^orelse rejected as undeterminable. This state of confusion has resulted

from

lack of a definite type locality. Richardson's statement that the

specimen "came from

Cadadaguois, ^a

town

in the south- western part ^of Louisiana," ^is evidently

an

_error, as the only use ofsuch

name

in that region

was

forthe

Cadadaguois

^Indian settlements

on

the

Red

River in northeastern Texas. This place, however, ^{is several}

hundred

miles

from

the range^of

any

species^of

Thomomys. Hence,

^{if the}

name

umbrinusis ever fixed

it nuist be

by

identification of a

known

specieswiththe original Leadbeater specimen,

now

in the British

Museum.

^In

March,

1905, Dr.

Merriam

sent to

Mr.

Gerrit S. Miller, Jr., then in

London,

specimens ^of

Thomomys

fulvus, fossor,

and

lachnguilla, the three species nearest in range ^tothe region thatⁱⁿ 1829

was comprised

ⁱⁿ southwestern Louisiana, ^for

comparison

^{with the} type

specimen

^ofumbrinus.

Mr.

^Miller

found

that

none

of these agreed ⁱⁿ either cranial or external characters with the _type,

which he

described in detail as follows:

The

_type^ofThomomys^umbrinusisaformerlymounted_specimen in the British Museum,^{No. 55.12. 24.}205,a male in good condition,and with skull in good condition except ^for one zygoma, onebulla,andthe_right half of the _{occipital region.} ^Itisa Thomomys ^{butnot the} same as any of those sentforcomparison. Externally^{it is}mostlike fulvus,butsmaller andwithmoreslenderclaws, especially in front. Colorabove aboutasin fulvus,but_slightlydarker,underpartsentirely different,

much

as infossar [pale buffy]buteven_paler,with almostasharp^lineofdemarkation along

2—Proc. Biol. Soc. Wash., Vol. XIX, ^1906. (3)

4 Bailey

—

Identity of

Thomomys

umbrinus (Richardson).

sides;a white_patchonchinandthroat;tailas in fossor,butalittledarker, apparentlydirty,notbicolor asin fulvus; feet dullwhitish.

Skull nearer that of fulvusthan of_fossororlachuguilla,but _smaller,the rostrumshorter and _relativelybroader, nasalsand premaxilla;ending ⁱⁿ linewdth eachother; anterior base ofzygoma, viewed fromabove, emargi- nate instead of rounded, lachrymalappliedalmostentirely tozygoma ^in- stead of frontal. [Description accompanied by rough drawing showing peculiarity ofzygoma.]

Measurements.

—

_Skin,measured dry^: Total length 220;^tail 45;hind foot 2fi. Skull: Greatest length37.6; diastema14; front of occiput to tip of nasals 34; nasals 13; interorbital constriction 6.4; zygomatic breadth (approximately) 26^; upper^toothrow _(alveola)7.8.

From

^this description ^it

was

evident that the type did not agree with

any

species^of

Thomomys from

^the

United

States,but that ^it did _agree closely with

an

unrecognized species in the Biological

Survey

Collection,

from Boca

del

Monte, Vera

Cruz, Mexico. After

Mr.

Miller's return, oneof the

Boca

del

Monte

specimens

was

sent to ,]Vtr. Oldfield

Thomas,

^{Curator of}

Mam-

mals

in the British

Museum,

^for

comparison

^{with the} type.

Mr. Thomas

kindly

made

the

comparison and was

not convinced thatthey were ^the

same

; butthe discrepancies

which

_{he pointed} out,

namely,

^broad

and

strongly orange-coloredincisors,longer nasals, broader _{posterior tip} of premaxilla?, larger size,

and much

stronger color of the type specimen, ^are practically covered

hy

^{individual variation in the series}

from Boca

del

Monte. The

full size

photograph

^{of the skull of the type, fur-} nished

by Mr. Thomas and

here reproduced,

shows

unmistakable characters,restrictingumbrinustoa

group

^offorms occurring only in southern Mexico.

The

_strongly emarginate, ^{instead of} rounded,anterior baseofthe

zygoma

^{doesnotocc-ur in}

any

species of TJiomomys

from

the United States.

The combination

of this character with a short

wide

_{skull, projecting incisors,}

wide

_pos-

terior part ^of premaxilla?,

and

the peculiar position ^of the

lachrymal which

^{lies almost}entirely against the jugal instead of

mainly

against the frontal, occurs onlyⁱⁿ orizabse, peregrinus

and

the

Boca

del

Monte

form. Externalcharacters

which

still

further ^restrict the

name

umbrinusto the

Boca

del

Monte form

are thewhitethroat

and

light lowerparts, in strong contrast^tothe

dark

upperparts.

Boca

del

Monte

also has the advantage ^of beingthe farthest east

and

probably, previous ^to 1829,

one

of

Bailey

—

Identity of

Thomomys

umbrinus (Richardson). 5

SkulI/Sof Thomomysfulvusandumbrinus. All natukalsize.

No._32,058ThomomysfulvusfromSpringerville,Arizona.

No.1,122 Thomomysumbrinus. Photograph^oftypespecimen^{in British}Museum.

Nos.64,091and64,092Thomomysumbrinus fromBocadelMonte,VeraCruz,Mexico.

6 Bailf)/

—

Identity of

Thomomys

umbrinus (Richardson).

the

most

accessible localities in

Southern Mexico from which any

species ^of

Thomomys

^is

known.

The

following description ^isbased

on

8 specimens

from Boca

del

Monte, Vera

Cruz,

Mexico:

Thomomys ^umbrinus

(Richardson).

Geomys umbrinus Richardson. Fauna BoreaU-Americana,I, pp.190 and

202, 1829.

Generalcharacters.

—

Size medium,^{hindfoot27 to}28; ^colorsdichromatic, dullumber brownorplumbeous^{black; skullshort}andwidewith strongly projecting^incisors.

Color.

—

Upperparts,ⁱⁿbrown_phase,dullburntumberorProutsbrown, varj'ing to nearly black ⁱⁿ some _{specimens; lowerparts lightly} washed with pale buff or whitish,ⁱⁿsome_specimenssharply contrasted with dark upperparts; feet,tipof _tail,chin,andsometimes _throat,white. Inblack phaseslaty Ijlack^allover exceptwhite_chin,feet,andtipoftail.

Skull.

—

_Shortandwide withincisorsprojecting^wellbeyond^nasals;angle of frontal projecting ^into notched anterior base of zygoma^; lachrymal applied^fornearly^itswhole_lengthtozygoma^;premaxillse ofapproximately the same _length as nasals andwidestnear blunt posterior tips; incisors slender, incomi)arison withthoseoffalms; ^{colorofincisors}varying from lightyellow ^todark_orange.

Measurements.

—

_Average of seven adults from Boca del Monte: Total length,19.3; tail vertebrae,58; hind _{foot, 27. Skull,} No. _{64,091, c?,}from BocadelMonte^: Greatest length, 36^;diastema,^{13.5; front}of occiputto tip of_nasals,33;nasals, 12.5^;interorbital constriction,^6.4;zygomaticbreadth, 24; alveolar length ofupper molarseries, 7.5.