The systematic position of the crinoid family Plicatocrinidae

the changes ^{in its excess} energy ^{content. In calcite the} change in crystal angleswith temperature^ispractically ^linear

up

^{to 600° .} This indicates that in quartz the ^{excess in} energy content repre- sents an internal reaction or equilibrium ^condition which even- tually causes the inversion. It will be of interest to study ^other minerals, showing inversion points, with _{respect to} their energy content

and

crystallographical

and

_optical properties at ^different temperatures; also to ascertain the form of the curves near the melting points.

PALAEONTOLOGY. —

The _{systematic position of} the Crinoid family Plicatocrinidae.

Austin

_{H. Clark,} National

Museum.

In the preparation ^of the section dealingwith the Crinoidea in the

new

edition (1913)^ofEastman's translationof Zittel'sPalaeon-

tologie, Springer

and

Clark^ were unableto

come

^to asatisfactory conclusion regarding the proper systematic position of the family Plicatocrinidae _(as defined

by

^us including the genera ^Plicato- crinus, Hyocrinus, Gephyrocrinus, Thalassocrinus, Ptilocriiius

and

Calamocrinus)^, which

we

tentativelyplaced

among

^{the Crinoidea}

Articulata, just

beyond

the comatulids, the

young

^{of which the}

species ^{in this} family greatlyresemble.

The

Articulata include all of the other recent crinoids so far discovered

and

this fact, together with the close resemblance of the _species of Plicatocrinidae to the

young

^{of the} comatuHds,

was

largely responsible ^for our placing ^this family ^here.

But

the species ^of the Plicatocrinidae differ from ^all of the other formsin- cluded in the Articulata in a

number

of

most

_important

and

fun- damentalfeatures.

1.

The _tegmen

is entirely covered with a

pavement

^{of solid}

plates.

2.

The

oralsare always present;they^are not planeor spherical triangles, as they ^{are in all of} the (comparatively few) species of Articulatawhich_possessthem, but^theiredges^areturned

upwards

so that instead of presenting ^five sharp angles to the

mouth

_they

^Whenthispaperwas_preparedandsent to pressMr._Springerwasabsentfrom Washington, but he returned^tothe_{city just}beforeits publication. After adis- cussionof the subjectmatter he requestedme toaddanotestating thatheis in complete accord with

my

conclusionsasherein expressed.

meet above ^{it in five} _sharp parallel edges, as do the orals of the stalked

young

^ofthe macrophreate comatulids.

3.

The

_calyx is

more

^or less asymmetrical; the two posterior radials

may

^be enlarged, as in Calamocrinus, ^{or there}

may

^{be a}

very^small basal just tothe_rightofthe anal_area, as inHyocrinus.

In the

young

^{of the} comatulids the

two

posterior radials

may

^be

larger than the _others,

and

there is always a radianal, situated

more

^{or less to the} right

hand

side of the posterior interradius.

4.

The

^dorsal _cup ^is _very large, entirely enclosing the visceral

mass

dorsally

and

laterally; this condition is identical with that foundinthe

young

^ofthecomatulids, but only occursⁱⁿtheadults ofthe Articulata in thehighly aberrant Marsupites.

5.

The

plates ^of the dorsal cup ^are very thin, entirely lacking the extensive inward calcareous development so characteristic ofalltheother_species ofthe Articulata;^{in this} the Plicatocrinidae agree with the

young

^{of the} comatulids,

and

with _{the highly} aberrant _pelagic comatulids Marsupites

and

Uintacrinus.

6. Instead of occupying ^{the entire distal} edge ^of the radials as intheArticulata (exceptingonly^thehighly aberrant Marsupites), the

arm

bases occupy ^only a small _part, as in the stalked

young

of the comatulids.

7. There areno infrabasals.

8. There are no _pinnules on the

arm

_bases; proximal pinnules are, except ⁱⁿ a few _very exceptional instances

among

^{the coma-}

tulids, alwayspresent ⁱⁿthe Articulata;but_theyareabsentinthe

young

^{of the comatulids untila} considerable size is attained.

9.

Tho

the pinnuleshaveessentiallythe

same

basalstructure as those oftheArticulata, they^{arein all}

ways more

generalized,

and

suggestⁱⁿ

many ways

^{ramules ordegenerate}

arm

branchesrather than_{perfectpinnules} oftheArticulatatype^{; inthis} they^resemble the pinnules ^of the very

young

comatulids, or ^of the growing tip of the

arm

_{in larger specimens.}

10.

The

_apex ofthedorsalcup shows ^atendency^to form a con- cavity^for the reception^ofthe column.

11.

The column

lacks alltrace ofthe modifiedcolumnal

known

as the proximale, but adds

new

_segments at its

summit

thruout

life; in this respect thecolumn resembles that ofthe

young

^coma-

tulids before the appearance ^{of the final} stem _segment, which eventually ^will

come

^to form the centrodorsal.

12. There are no cirri; the

column

is attached

by

^a

heavy

^ter- minal

stem

plate as inthe

young

^ofthe comatulids.

A

^{few words of}explanation regarding the

column

oftheArticu- lata

may

^{not beout of}place ^here.

The column

ofthe Articulata (entirely absent in the Comatulida Innatantes, the one suborder of comatulids not representedⁱⁿ therecent _seas) ^is entirely^differ- entfrom ^thatof

any

^{othercrinoids}for,insteadofgrowing^continu- ously thruout^life thru the formationofcolumnals _just under the crown,^itpossessesadefinitegrowth^limitatwhichfurther increase inthe

number

ofcolumnals abruptlyceases,

and

the last columnal to be formed becomes attached to the calyx

by

^{closesuture (usu-}

ally fusing with the infrabasals), enlarges,

and

becomes the so- called proximale which is, to all intents

and

_purposes, an _apical

cal.yx plate. Immediately below ^{this enlarged} columnal or prox- imale is another

more

^{or less} modified columnal to which ^{it is} at-

tached

by

^{a modified close suture, the so-called} stem syzygy which, except^forasuperficialresemblance, has nothingⁱⁿ

common

with the brachial syzygies.

The

_typical form of the

column

^{in the Articulata is seen in the}

young

^of the comatulids ^at the time of the formation ofthe cen- trodorsal; but this typical form _persists in the adults only ⁱⁿ the genus Thioliericrinus,

and

in the family Phrynocrinidae. In

.such types ^as the Apiocrinidae the proximale ^{is so} enormously enlarged that ^{it involves} with itself in thisprocess a considerable

number

^of the columnals beneath it, so that a coneshaped^series

of enlarged columnals^is formed, each ofwhich is areduplication, progressivelyJess perfect, of the proximale just beneath_{the calyx.}

Essentially the

same

^{state of affairs is seen in the} Bourgueticri- nidae, especiallyⁱⁿ the recent genusIlycrinus. In the comatulids (exceptingⁱⁿ the Innatantes, whichneverpossess one) the

column

is discarded at the stem syzygy between the proximale

and

the columnal _just beneath it.

In the

young

pentacrinitethe proximale ^is formed_exactly as in the

young

comatuUd; but ^the great excess ^of

column

_growth ^in- duces the formationof

new

columnalsbetween theproximale

and

the csdyx ^before the proximale has time ^to

become

attached; the proximale ^therefore becomes pushed

away

^from the calyx, but exactly as in the case ^of the comatulids, ^cirri are protruded from

it,

and

it becomes united to thecolumnal _just below it

by

^{a stem} syzygy,^these

two

columnals

now

_forming

what

^is

known

asa nodal

and

an infranodal, the nodal _{(with the} cirri) being in origin a true proximale,

and

the infranodal the columnal _just beneath the true proximale. Following the formation ^{of this first} nodal the pen- tacrinite proceeds ^to

grow

^an entirely

new

_column, of which the

firstnodal_represents theterminal stem_plate; this second

column

grows ^{to a definite} length,andthen the

same

nodalformingproc- ess is repeated.

Each

pentacrinite nodal with the series of internodals beneath it, therefore, ^is morphologically the equiva- lentofthe entirecolumninsuch types^astheApiocrinidae,Phryno-

crinidae, orthe comatulids.

In the adult pentacrinites only nodals ^are formed _just beneath the_calyx, so that here

we

haveaseries ofreduplicatedproximales, just as in the Apiocrinidae; but none of these nodals

become

at- tached to the _calyx, for they ^are constantly being pushed

away

from the calyx

by

^{the formation of}

new

nodals.

At

a Uttle dis- tance from _{the calyx} intercalated columnals begin ^to appear ^be- tween _them, with the nearest of which they always ^unite them- selves

by

syzygy, ^so that at a

somewhat

greater distancefrom the crown the nodals (proximales), united

by

syzygy ^{to the infra-} nodals, with which they form syzygial pairs,

become

_regularly

spaced, forming ^the typicalpentacrinite

column

as

we commonly

find it.

In the bourgueticrinoid type ^of

column any

^{two of the colum-}

nals

may

^{be united}

by

^stem syzygy; ^these double columnals are rare inthe distalportion ^of the column, but increase in frequency toward the crown.

Each

^of these syzygially united _pairs of col-

umnals _represents an effort to form a proximale which, thru excessive stem growth, has been thrust

away

^{from the} calyx exactly ^{as in} the case of the pentacrinites. In addition to these there is just under the crown a definite series of proximales, ^cor- responding^to the continuouslygrowing

and

indefinite seriesfound in the pentacrinites.

To

_emphasize^theessentialsimilarity ^of the

columns of the pentacrinites

and

of the Bourgueticrinidae ^it

may

be mentioned that the earhest nodals in the

young

pentacrinite

column

resemble far

more

the _syzygially united columns in the bourgueticrinoid

column

than they do ^{the nodals of the} adult, for they ^are

much

_elongated,

and

the cirri are usually defective, three, two, ^or sometimes _{only one, in} number.

Itisevident that the structure ofthePlicatocrinidae inall ofits details corresponds very closely to that of the

young

^comatulids

beforetheappearance ^ofthecolumnal whichiseventually^toform the centrodorsal; it is also evident that this family can scarcely find a_{logicalposition}

among

^theArticulata, from all of the other forms in which ^it differs so_radically.

The

order Inadunata of

Wachsmuth and

_Springerincludes Cri- noidea in which the

arms

are free above the _radials; the dorsal cup ^{is limited to} radials, basals, infrabasals (when present)

and

anal _plates; no interradials nor interbrachials occur except^at the posterior (anal) side,

and

the brachials are never incorporated in the cup; ^all the_plates ofthecup ^areunited

by

^closesuture; the

mouth

^is subtegminal^; the

column

is circular insection (with very rare exceptions), without a proximale.

Itisatonce evident that thePlicatocrinidaeagreewiththe

mem-

bers of thisorderfar betterthan they do with ^{those of}the Articu-

lata, differing only ⁱⁿ a lack of a distinct differentiation of the posterior area,

and

in the _possession of open food grooves

and

an open mouth.

But

in theEncrinidae, which are referred to ^this order, the _posterior area is in no

way

^{different from the others,}

while in at least three of the recent genera ^ofthe Plicatocrinidae

it is not _quitethe same, ^so that this difference is very slight. In

many

^{of the fossil Inadunata}

^we

^{do not}

^know

^{the disk; while}

among

^recent types the genera ^of the Plicatocrinidae have the deepest food grooves

and

the nearest approach ^to a subtegminal

mouth;

^it

may

^{be that} in reality ^this apparent ^{difference is non-}

existent.

A

rapid survey ^of the various families of the Inadunata

—

in thesuborderLarviformia the Stephanocrinidae,Pisocrinidae,

Hap-

locrinidae, Allegecrinidae, Synbathocrinidae

and

Cupressocrinidae,

and

in the suborder Fistulata the Hybocrinidae, Heterocrinidae,

Anomalocrinidae, Cremacrinidae,Catillocrimdae,Belemnocrinidae, Dendrocrinidae, Crotalocrinidae, Cyathocrinidae, Botryocrinidae and Poteriocrinidae

—

cannot ^fail _{to give} the impression that ^there

is certainly

more

thana superficial similaritybetween thesetypes

and

thePlicatocrinidae. As aninterestingpoint^it

may

^benoticed

that the systematic interrelationships within the family order Inadunata are decidedly heterogeneous,

and

the

same

character

is clearly reflectedwithin the family Plicatocrinidae.

While the Phcatocrinidae, broadly speaking,

may

^{be said to}

agree perfectlywith these families collectively

—

thatis to say the characterspresented

by

^the

component

species

may

^allbe

^matched

in the order Inadunata

and

in no other order

—

the family cannot

definitely be assigned ^to

any

^{certain position.} Therefore the most _{logical position} for the Plicatocrinidaeappears ^to

me

^to be within the order Inadunata, ^at the end of the series of families,

beyond

the Poteriocrinidae.

Long

ago(1899)Dr.F.A.Batherreachedtheconclusionthat the Plicatocrinidae fwhich he divided into Plicatocrinidae

and

the Hyocrinidae) were really inadiuiate forms,

and

he accordingly included

them

in the Inadunata, which he considered as compris- ing the Hybocrinidae, the Stephanocrinidae, the Heterocrinidae, the Calceocrinidae, the Pisocrinidae, the Catillocrinidae, the Zophocrinidae, theHaplocrinidae,the Allegecrinidae,theSynbatho-

crinidae,the Belemnocrinidae,the Plicatocrinidae,theHyocrinidae

and

theSaccocomidae.

Of thefour great orders of crinoids, two, the

Camerata and

the Flexibilia, range from the Ordovician thru the Carboniferous.

The

Inadunata

began

ⁱⁿ the Ordovician, one _{(possibly two)} families persisting to the Permian,

and

one to the _Trias, in which horizon the stalked pentacrinites were already developed.

The

Articulata began, ^{so far as}

we

can _ascertain, in the _Trias,

and

all

of the fossil types (excepting only the Thiolliericrinidae

and

the Eugeniacrinidae) persistin the recent seas. It is thus not at all

surprisingthat

we

shouldfindin the recent_{seas, in}additiontothe dominant Articulata, a

remnant

of the Inadunata.