natural sciences of philadelphia.

NATURAL SCIENCES OF PHILADELPHIA. 133

There can be no doubtasto the validity of thisspecies, asitwidely^diflFers

ill the

number

ofitsraysfromallexceptoneotherspecies of Priacanthus, and especiallyfrom the formerly

known

American ones. Theonlyspecieswhich rersemblesitinthe

number

of the rays ofthe finsisaJapanese species

—

the Priacanthusniphonius of Cuvier andValenciennes, and the Fauna Japonica.

Inother respects also the Japaneseand NorthAmerican species are closely related. Thef)rHiisnearlysimilarbut the heightevengreater inoursthanin the Priacanthus niphonius, and consequently exceeding that of any othei

known

species ofthegenus; the scales ofthebody and headareveryrough;the ventral finsintheyoung, at least,entirelyblackish; the spinous portionof the anal fin is alsovery dark. ^{It is}probable that the species undergoesa change ofcolorsomewhatsimilartothe Priacanthusniphonius.

Thediscoveryof three

new

species of fishes onthe coast of Rhode Island, allrepresentingformsalmost entirely confinedto

warmer

seas,insuchrapid succession, isan eventof nolittle interestand importance. The specimens obtainedwereallyoung; singleexamplesonlywere found ofthe Sarothrodus (Chceto'^lon RVLCt.) 7naculo-cinctusa.Tid the Priacanthus,and two of the Hijpor- thodus flavicauda. Theywerealldoubtlessbroughttothe

New

Englandshores

by

the Gulf Stream, which runs near the RhodeIsland coa-t, andinwhich thetraveller often ilnds small fishes, aswell asother animals, ofwhichthe Isopod Criistacean, described belowbyDr. Stimpson, is an example.

None

of the three species offishes previouslymentioned haveyetbeen seeninthe

West

Indian seas, where they will undoubtedly be hereafter found. It is

important alsoto comparethediscoveryofthesefishes on our

own

northern shores with the discoveryontheScandinavianandGreenlandcoasts of forms equallycharacteristic ofthetropics. In another article I will allude to the analogybetweenthe denizensoftheCarribeanandJapaneseseas.

On

an oceaaic

ISDPOD

found naar the south-eastern shores of 2IassachusettE.

BY WM. STIMPSON.

Inthe

summer

of 1859, whilecruising

among

the south-eastern islands of Massachusetts in

company

with

my

friends Dr. Slack and Mr. Ordway,

we

approachedthe shores of thebeautiful island ofMartha'sVineyard

—

^theIsle

ofWightof

New

England.

When

becalmedintheVineyardSoundnorthof

Gay

Head,

we

were occupiedin observing the smallmedusseaniotherpelagic animalswhich appeared nearthe surfaceof the water.

Among them we

no- ticedsome pretty blue isopods quite

new

to our shores, which reminded

me

offorms whichIhad met withinthetemperateparts ofbothgreatoceans.

They

were

swimming

at the .surface andcould be easilydistinguishedfrom thedeckofour^boat, evenatsomedistance,bythe ripplethey

made

intheir progress. Several of

them

were caught, and found to be IdothecB of that oceanictypewhichhasthe habits of the miniature sailors Ph/jsalia, Velella and Janthina, which areoccasionally cast

upon

our south-easternshores. It

provestobe

Idothea robcst.v Kr.

Body

stronglyconvex,two and two-thirds aslongasbroad, and broadest atthefifththoracic segment;lateraloutlineconvexatthe thorax, butsome- whatconcave attheabdomen. Surface pubescent. Inner antennre reaching tothepenultimatejoint of the peduncle ofthe outer ones, which areless

than one-half the length of thebody. Thoracicsegments protuberant, and laterallysomewhat rugose; their epimera large, distinct andrathersharply projecting.

Abdomen

stroncrly three-jointed, with partial separation of a

1862.]

134 TROCEEDINGS OF THE ACADEMY OF

fourthjoint,as inother species of the gronp. Extremity of the

abdomen

truncated, or slightlyexcavated. Color in lifedeep blue beneaththe silvery or pearlypubescence.

Length0*8; greatestbreadth0-29 inch.

Itsnearest allyis/.margaritaceaDana, found inthe ocean between Aus-

tralia and

New

Zealand,inwhich the

abdomen

isregularlyrounded at the extremity, whileinourspeciesthereisawell-marked angleoneitherside.

OntheWest African genus

HEMICHROMIS

and descriptions of

new

species in the

Museums

ofthe

Academy

and Smithsonian Institution.

BY THEODORE

GILL.

Mr. P. DuChaillu, the African traveller, obtained

among

other objects of naturalhistory, specimensof several species offishes,oneof whichisa

new

formofPetwrs' genus Hemichromis.

Thegenus Hemichromiswasproposed, in 1857,byDr. PetersforChromoids, havingthehabit of Chromisor Tilapia,andwitha rowof conic,browntipped teeth ineachjaw, the two median ofwhichinthe upper were considerably larger, andalsowithaninteriorrowofsmaller teeth intheupperjaw. The onlyspecieswasobtainedin Guinea byPel.

Recently,M. August Dumerilhasdescribed and figuredaspecies as a

new

generictypeunderthe

name

of Chromichthys dongatus Guichenot. Itagrees ineveryrespectwith Hemichromis, exceptinthe presenceof only onerowof teeth in theupperjaw. As, however,the innerrowofHemichromisisformed by very small ^{teeth, itis}probable thatithasbeen overlookedbyGuichenot and Dumeril, and that their species is therefore a genuine Hemichromis.

That genus will then embrace four species, which

may

be distinguishedas follows

:

Hemichromis fasciatpsPeters.

HemichromisfasciatusPeters,Monatsberichte derKoniglichen Preuss.Akade- miedieWisseuschaften zuBerlin, 1857,p.403.

"Fasciis transversis fuscis sex, macula opercular! nigra; pinna dorsaliet anali oblique fasdatis, albo marginntis;pintiacaudalisupra injraquealbomargi- nata; pinnis ventralibusexternefuscis."

D. XIV. 11—12. A.in.

9—10.

Habitat. Guinea. (Peters.)

Hemichromis apritusGill.

Fasciisquinque,lateremedioexpansis,maculaoperculari nigra,margaritacea supra infra jueminjinata_; pinnis ventralibus externa fusco-purpureis

.

D. XIV. 11. A.III. 8.

Habitat. Gaboon^River?

Hemichromis bimaculatusGill.

Unicolor,D. XIV.1.macula

Sy. 11corporis latereA.III. 6j. Squam.unicaetser.operculi25y.3 apicenigris.

HemichromiselokoatusGill.

Chromichthys elongatus (^Guich.,) Dum., Archives

du Museum,

tome x. p.

257, pi. xxii. lig.3.

Fasciisquinque{maculaopercidirinulla)^: squamisbuccis quiuqueseriatis.

D. XIII. 9. A.III. 8.

Habitat. GaboonRiver.

[March.