A new chiton from the New England coast

VOL._XVIII, PP.

203-204

SEPTEMBER 2,

1905

PROCEEDINGS

OFTHE

BIOLOGICAL SOCIETY OF WASHINGTON

A NEW CHITON FROM THE NEW ENGLAND COAST.

BY WILLIAM HEALEY DALL.

Mr. Dwigbt Blaney

^of

Boston, summering

^at

Bar Harbor, Maine, has

^interested

himself

in the

marine

invertebrates

and engaged

energetically in

dredging. Among ^{some mollusks}

^sent

to

the

writer for

examination was a handsome chiton which,

after careful

study and _comparison with American and North European

species,

appears

^to

be undescribed.

The number

of species of chiton

on

the

New England

^coast

is very

small and, with the exception

^of

one deep-sea

species,

none has been

described

during

^thelast

quarter

century. ^{It is} therefore exceptionally interesting ^to

know

of the

presence

^of

a new

species in this district.

The

_species is

somewhat interme

diate in its characters

between

Tonicella

and Trachydermon, with a leaning toward

the

former, and seems most _nearly

related to T.

marmorea

_Fabricius,

from which, however,

^{it is}

abundantly

distinct.

Tonicella bfaneyi sp. nov.

Shellofa deeprose-color, withfinewhitelineations

and

reticular

mark

ings^;girdlebrow^r_n,apparentlynaked, butexhibitingunder high magnifi cationa microscopic granulationwitha

row

ofsmall spinules^attheextreme edge,^{as in T.}

marmorea

;the coloration of the valves outside, in thetype specimen^isfairlyuniform but probably

more

orlessvariable

among

^indi

viduals_;the valves inside are of adeeprose-pink, palertoward_{the edges};

surface minutely

more

or less quincuncially punctate, but this is visible only

when

_magnified;the sculpture^consistsof (on^the

mid

valves usually

37 PROC. BIOL.Soc.WASH.,VOL. XVIII,^1905. (203)

204 Dall A New

Chiton

from

^the

New _England

Coast.

three)radial ribletswith a tendency^{tobifurcateor}break

up

^intosegments distally; there areno_distinctly

marked

areason the midvalves,but the part of the valves

which

bears

what

in

many

chitons arecalledthelateral areas, in this species carries

two

or _three,sometimes _bifurcate,thread-like ribs

which

are flattenedabove

and

rarely reach the

mucro

ofthe_valve, beingusuallyevanescent_dorsally;there arealso

more

or less deeply im- presse'd linesofgrowth^;the

median

part of the valves ^is nearly

smooth

except ^for the microscopic punctation; anterior valve semicircular,with numerous,

more

or lessirregular, radial ribletsthatresemblethose

on

the midvalves_; the eaves are conspicuously spongy^; the insertion _platesare blunt, crenulate^atthe edge,butnotradially striate;the anterior valve in thetype has10,but

would seem

_normallytohaveeither9 or11_slits,asone seems _{missing or in excess,}

on

one _side; the midvalves haveoneslit

on

each side, their anterior lamellae are nearly continuous acrossthedorsal sinus; theposteriorvalveissmall without a mucro,^the incremental lines strong,the ribbing obsolete or nearly^so; in the type,whilethereisnota posterior sinus^likethatofChsetopleura,there^isacertain flattening

and

the insertion plates bordering ^thispart of the valve are poorly developed^; there are 7-9 slits between

which

the distal edges of theplatesare

more

or lessirregularlycrenate;ⁱⁿthe driedspecimen^themuzzle hasapromi nent^"veil"

ortegumentary margin;the ctenidia

number

about15on each side

and

extend forward

on

each side ofthe foot to the fourth valve_; lengthoverall (dry), 13

mm.;

width, 8

mm.;

dorsal angle,120.

Dredged

^{in20fathomsoffIronbound} Island,Frenchman's Bay, nearMt.

Desert Island,Maine.

From

Trachydermon ruber, Tonicella

marmorea and

similarspecies, this form canbeatoncedistinguished

by

^the ribbing. Ifthe type specimen becharacteristic in its color,the pattern

and hue would

be _equally dis tinctive. In T.ruberthe_girdleispubescent

and

particolored, in ^T.

mar

morea

and

the presentspecies^itisof auniform brown.

The

_typespecimen hasbeen_generouslydonatedtothe U. S.National

Museum.