Note on the genus Gilbertsocrinus, Phillips

166 PROCEEDINGS OF THE ACADEMY OF

Localityand_position.

The

_onlyspecimen of^thisfossil

we

have seenis in a granular

mass

of

decomposing

chert,containing

some

fragments^ofsmallcri- noid columns. It

was

obtained fromtheSubcarboniferous rocksof Missouri, buttheexactlocality

and

position

we

have been unableto ascertain.

Note onthe

genus GILBERTSOCRINUS,

Phillips.

BY

F. B.

MEEK.

Genus GILBERTSOCRINUS,

Phillips, 1836.

Gilbertsocrinus, Phillips,Geol. Yorkshire, partii.,p.207, 1836.

Goniasteroidocrinus,

Lyon and

Casseday,

Am.

Jour. Sci. xxviii._p.233, 1859.

Trematocrinus, Hall,Sup.

Iowa

_Report,p.10,1860.

Phillips'diagnosis^ofthisgenus reads^asfollows:

"

Basaljointsfive,forming^apentagon; suprabasal [subradials]five,hexa- gonal,forming^adecagon with ^fivere-entering angles, from

which

_proceed

fiveheptagonal ^firstcostals [firstradials]

and

fivehexagonal secondcostals, [secondradials],bearing^apentagonal scapula[third radial]supportingjoints [secondaryradials]

which combine

intorounded

arms

_perforatedinthe centre.

First in.tercostals _[firstinterradials] pentagonal.

The

_followingspecieshave been usuallyreferred toRhodocrinus,Miller,from which,^itappears^tome, they differentirely."(Phillips.)

He

mentions but thefollowingthree species,viz.,G.calcaratus,G. mammil- laris

and

G.bursa,^allfromthesubcarboniferous. Hisspecific descriptionsare very^brief

and

unsatisfactory,but his figures are tolerablygood,

and

give a

,sufficiently intelligibleidea of the generic characters^ofthegroup.

From

these .figures,andhis description,^{it is}thereforeevident thattheformula,ⁱⁿaccord-

ance withthe laterimproved nomenclature,

may

^bestated as follows:

Genericformulaof Gilbertsocrinus.

Basal_pieces5.

Subradials5.

Radials

3x5.

Secondary^orsupraradials^{3 or}

4x10.

Anal and

interradial pieces 12 to

15x5.

Pseudo-brachial appendages (arms^of

some

_authors)5,locatedoverthe rays.

Arm-openings

(ambulacral,)10,located directlyunder the pseudo-brachial appendages.

On comparing

thisformula withthe following,given

by

^Messrs.

Lyon and

Casseday, ofGoniasteroidocrinus, citedabove,the close relationsofthese crinoids will_be,apparent.

Genericformula ofGoniasteroidocrinus.

Basalpieces

1x5,

pentagonal,perforationnotvisible.

Subradial_pieces5,hexagonal,nearlyequal^insize.

Primary

radial pieces

3x5,

^firstspiniferous.

Secondary^radials

3X

10,hexagonal.

Interradialfields[including^theanalarea]

5x13

^to14,[pieceseach].

Interbrachialfields

5x1

^to9,[pieceseach].

It

may

^be proper^to explain ^thatthe term pseudo-brachial appendages isusedintheformula ofGilbertsocrinus, for the partsregarded byPhillips

and

by^Messrs.

Lyon and

Casseday^as arms,

and

thatarm-openings, not alluded to

by

Phillipsinhis description,

though

clearly

shown

inhisfigur.s,are

men-

tioned. These openings were not observed by

Lyon and

Casseday, because they

were

hiddenin theirspecimensby^theattachmentof thesmall pendulous true arms,or,in the absence ofthe latter,by portions ofthematrix,^asis

known

tothewriterfromtheexaminationofspecimensof their typical species loaned

by

Mr. Lyon.

/

[Aug.

NATURAL SCIENCES OF PHILADELPHIA. 167

Itwillthereforebe seenthat,excepting,inmerespecificdetails,theseformu- las,asfar astheygo,agree exactly. There _is,however, a character which, although not apparent^inMessrs.

Lyon

and Casseday's formula,

was

neverthe- lessmentionedintheir description,ⁱⁿwhichthetypes of thesegroupsdiffer, that _is,intheposition ofthepseudo-brachial appendages (armsof Phillips

and

of L.and C.)with relation tothe other parts. In Gilbertsocrinus these appendages^are placed directlyover the arm-openings

and

above the inter- brachial spaces,whileinGoniasteroidocrinusthey stand^overtheinterradial spaces.

There

may

be various opinionsⁱⁿregard^tothevalueofsucha difference,but to the writeritseemsofnot

more

than subgeneric importance. ^Iftheseappen- dages were^truearms,^{or likethe}

arms

inothercrinoids,designed ^tosupport thereproductive organs,("conceptacula,")^little doubt could be entertained inregard^tothefullgeneric value of such adifference intheir position.

The

fact,however,^thatalthough provided witha central cavitythroughtheir entire length,they^rhave

nowhere

_anyexternalopenings, being^asitwere hermetically sealed,^isconclusiveevidencethatthey could haveperformed no such^function.

Hence

itisprobable they should beviewedrather as being ⁱⁿ

some

respects analogous ^{tothe lateral} branches, or verticils,so often given^offfrom the

columns

of Platycrinus

and

othercrinoids. This opinion seems^toderivesup- portfromthe fact_{that, in}

some

of the typicalformsof Gilbertsocrinus, as well asin

American

species of Goniasteroidocriniis, theseappendages,^attheir origin, consistof adoubleseriesof pieces, piercedeach throughthe centreby^theonly cavitytheyposses, exactly like thejoints ofa column,or those ofits lateral branches,^for

which

latterthey mightreadilybe mistaken,^iffound detached.

From

all the factsitseemsprobable, therefore, that theonly^{relationsthese} false

arms

bore tothereproductive system,

was

that ofstrong rigid guards thrownofffromthemargins^{of the}dome,^forthe protection of the slender, true ova-bearing

arms

_hanging beneath them. Hence, although^{theirexistenceor} absence

may

^bea

good

genericdistinction,^ihe'irpositionoverthe interradial, or interbrachial spaces,canscarcelybe regarded^assuch.

Itwillprobably be

remembered

that,ⁱⁿapaper read^{before the}

Academy by

Prof.

Worthen and

the writer, inSeptember,1860,

and

_published inthePro- ceedings^forthatmonth,(p.383),

we

_suggestedthata genus proposed by^Prof.

Hall at aboutthe

same

time,underthe

name

Trematocrinus,

was

_apparently veryclosely relatedto Goniasteroidocrinus,

Lyon and

Casseday, 1859,

and

that

we

should not be_surprisedifit

would

prove^tobethesame.

Having

recently

had

an opportunity, throughthe politeness of Mr.Lyon,^to

examine good

spe- cimensofthe typical species of thelatter,the writeriscompletely^satisfiedthat there isnot the slightest generic oreven subgeneric^difference betweenthe types^forwhichthese

two names

were proposed,*

and

as

Lyon and

Casseday's

name

has_priority,itwillhavetoberetained for thegroup, whether

we

_regard

itasagenus^{or a}subgenus. ^{Itistrue the later}

name

is shorter and

more

euphonious, but

we

have no_{right for}thatreason to

make

itan exception^to the generallyaccepted lawof priority. ^{It is}surelynotgreatly

more

objec- tionablethanMacrostyloerin.ua, Hall,^stillretained by^itsauthor instead of the later

name

Cytocrinus,Roemer.

The

following are the

American

speciesofthis group,^viz.: Gilbertsocrinus (Goniasteroidocrinus) tuberosus,

Lyon

^and Casseday; Gilbertsocrinus (Goniast.) fiscellus,

=

Trematocrinus_fiscellus,

Meek

and

Worthen

; Gilbertsocrinus {Goniast.) typus,G.(Goniast.) tuberculatus,G.(Goniast.) papillatus,G.(Goniast.) robustus,

and

G.(Goiiiast.) spinigerus,

=

Trematocrinustypus, ^T.tuberculatus,T. papilla- tus,T.robustus

and

T.spinigerus, Hall.

*Asalready stated,^itwasascertainedfromtheexaminationofMr. Lyon'stypical species, thatit possessesthesame ambulacral openings^asthe speciesupon^-whichTrematocrinuswas founded;

andthat the slenderpendulous"plumose cilia'ofLyon and Casseday(here regarded as true arms)^areconnected with these openings, as thearmsofother palaeozoic crinoidsconnectwiththe armopenings, excepting thattheyhang down,iustead of ascending.

1865.]