Classification and terminology of the Cambrian Brachiopoda

Walcott, Charles Doolittle

Classification and
terminology of the Cambrian
Brachiopoda

SMITHSONIAN MISCELLANEOUS COLLECTIONS
PART OF VOLUME LIII

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WITH Two PLATES. ‘ss

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SMITHSONIAN MISCELLANEOUS COLLECTIONS

PART OF VOLUME LIII

CAMBRIAN
GEOLOGY AND PALEONTOLOGY

No. 4.—CLASSIFICATION AND TERMINOLOGY OF
THE CAMBRIAN BRACHIOPODA

WITH Two PLATES

BY

CHARLES D. WALCOTT

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No. 1811

CITY OF WASHINGTON
PUBLISHED BY THE SMITHSONIAN INSTITUTION
OCTOBER 13, 1908]

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CAMBRIAN GEOLOGY AND PALEONTOLOGY

No. 4.—CLASSIFICATION AND TERMINOLOGY OF
THE CAMBRIAN BRACHIOPODA?
By CHARLES D. WALCOTT

(WitH Two PLatTEs)

CONTENTS

f PAGE
GEOG CLIO DIRE A Rane ie 4 ford set ceed sehereinyn-s sate GOES) apse eoehe ee ee rene eae 139
Schematie diaeramvOr evGliitt OM-ticcccciitos sc = aaa ao ce = aeleeictes = oases 139
DevelopmentsinuGambitan time. te ccs... 0 oac.c a deise aaclo ae male ce eter I4I
Scheme: OL ClassiicattOue:. epee sa yects casas eels. 54 ld RE eos SANE ee 141i
SERMCtare OngEMet Sel lepwe: aeeMEs ooo ote eocst costs ane se cee PRIS TR a eee epee ae aes 149
Microscopic structure of the Cambrian Brachiopoda................. 150
Werminologyanelatme to thepsiiell. + 005. Boe desk pep acne lade clone Cos Bae 153
IBYestrobh Voy Aas. 5 BRS anc. «SIRS MRE She APNG RCE Sethi Ry fel = eae nei 154

INTRODUCTION

My study of the Cambrian Brachiopoda has advanced so far that
it is decided to publish, in advance of the monograph,? a brief out-
line of the classification, accompanied by (a) a schematic diagram
of evolution and scheme of classification; (b) a note, with a diagram,
on the development in Cambrian time; (c) a note on the structural
characters of the shell, as this profoundly affects the classification ;
and (d) a section on the terminology used in the monograph. ‘The
monograph, illustrated by 104 quarto plates and numerous text fig-
ures, should be ready for distribution in the year 1909.

SCHEMATIC DIAGRAM OF EVOLUTION

In order to formulate, as far as possible, in a graphic manner a
conception of the evolution and lines of descent of the Cambrian
Brachiopoda, a schematic diagram (see plate 11) has been prepared
for reference. It is necessarily tentative and incomplete, but it will
serve to point out my present conceptions of the lines of evolution of
the various genera, and it shows clearly the very rapid development
of the primitive Atrematous genera in early Cambrian time.

1 Published by permission of the Director of the U. S. Geological Survey.
* Monograph LI, U. S. Geological Survey.
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MISCELLANEOUS COLLECTIONS VOL. 53

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EVOLUTION OF CAMBRIAN BRACHIOPODA

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CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTTY I4I

DEVELOPMENT IN CAMBRIAN TIME

We do not know of any brachiopoda in strata older than that con-
taining the Olenellus or Lower Cambrian fauna. ‘That such existed
in pre-Cambrian time seems almost certain when the advanced stage
of development of some of the earliest known forms is considered.

In the preceding diagram the known occurrence of the families of
brachiopoda in strata of Cambrian age is graphically shown. The
diagram is based on the data contained in tables prepared for the
monograph giving a summary by families. The Obolidz, with 7 gen-
era, 9 subgenera, 183 species, and 17 varieties, has the greatest devel-
opment, and the family continues into the base of the Ordovician
with 2 genera, 7 subgenera, and 36 species. The Acrotretide has
6 genera, I subgenus, 93 species, and 19 varieties, with the greatest
development in the Middle Cambrian and with a smaller representa-
tion in the Lower Ordovician. The Billingsellide, with 9 genera,
2 subgenera, 95 species, and I2 varieties, has a strong develop-
ment in the upper Middle Cambrian and passes into the Ordovician,
where it disappears. The three families mentioned include about 48
per cent of the genera, 80 per cent of the subgenera, 81 per cent of
the species, and 81 per cent of the varieties included in the Cambrian
brachiopoda. The development of genera of the remaining families
containing 3 genera or more is as follows: Paterinide, 4; Obolel-
lide, 4; Siphonotretide, 6; Syntrophiide, 3; or 17 genera of the 24
outside of the Obolidz, Acrotretide, and Billingsellide, which con-
tain 23 genera. ‘The remaining 7 families include 7 genera.

Of the 46 genera from the Cambrian, 20 occur in the Lower
Cambrian, 31 in the Middle Cambrian, and 23 in the Upper Cambrian.

SCHEME OF CLASSIFICATION

In order that we may have a graphic illustration to aid in de-
scription, the following table is inserted. The ordinal classification
of Beecher [1891], with emendations, is taken as the basis for the
orders, while the arrangement of superfamilies is practically that of
Schuchert [1897], with such emendations and additions as greater
information has rendered necessary. Dr. Charles Schuchert has
been most helpful in discussion and criticism of this scheme of classi-
fication, and I am also indebted to Mr. E. O. Ulrich for a discussion
of the classification of the Protremata. Due acknowledgment will
be made in the monograph to many persons who have aided in
various ways in making the monograph much more complete and
useful than it otherwise would have been.

valves.

ATREMATA

142

“~

Obolacea

Rustellide
|
4
|
!

| Paterinidz

Rustellacea

Curticiidze

Obolinz

Obolidze

Z

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|
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|
|
|
|
|
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|
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|
|
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Kutorginidz

f
=
4
|

Kutorginacea

l

Elkaniine

veoboline

Schuchertinide

SMITHSONIAN MISCELLANEOUS COLLECTIONS

TABLE OF CLASSIFICATION.

{ Rustella

{ Mickwitzia

| Micromitra

J (Paterina)

| (Iphidella)

| Volborthia

l ()Helmersenia

( Re
1 Curticia

{ Obolus

| (Broggeria)
(Palzobolus)

| (Fordinia)

| (Lingulobolus)
(Mickwitzella)

4 (Acritis)
(Schmidtia)
(Westonia)

Lingulella

(Leptembolon)
(Lingulepis)

| Delgadella

{ Elkania

{ Neobolus

Bicia
Dicellomus

{ Kutorgina

{ Schuchertina

NEOTREMATA

PROTREMATA

Siphonotretacea

Orthacea Craniacea Discinacea Acrotretacea

Stropho-
menacea

Pentameracea

f

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|
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Obolellidz

Si

Acrotretidz

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phonotretide

Acrotheline

Acrotretine

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Craniidze

Billingsellidee

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Nisusiine

|

1 Billingsel-
| line.
ie Eoorthine

Rafines-
quinze

Stropho-
menide

ee et eed

yutrophiide

VOL. 53

{ Obolella

| (Glyptias)
4 Botsfordia

! Schizopholis
L @)Quebecia

( Yorkia
Dearbornia
‘Yrematobolus
Schizambon

; Siphonotreta

| Keyserlingia

Acrothele
(Redlichella)
Discinolepis
( Linnarssonella
j Acrotreta
1

Acrothyra
Discinopsis

{ Orbiculoidea

{ Philhedra

{ Nisusia

J (Jamesella)
\ Protorthis

lL (Leperia)

{ Wimanella
| Billingsella
4 Orusia

| Otusia

| Wynnia

{ Eoorthis
1 Finkelnburgia

J Eostrophomena

l

{ (?)Swantonia
J Syutrophia
|} Huenella
Clarkella

Order ATREMATA Beecher, 1891 (emend)

Primitive inarticulate, corneous or calcareo-phosphatic Brachio-
poda with the pedicle emerging more or less freely between the two

lateral margins.

mentary

articulation.

Growth takes place in general around the anterior and
Specialized forms show tendency to develop rudi-
Delthyrium originally unmodified,

in later

genera modified by pseudodeltidia and pseudochilidia, or by thick-

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 143

ened, striated, and more or less furrowed or even cleft vertical car-
dinal margins, the ventral cleft in most specialized forms tending to
enclose the pedicle and finally restrict it to the ventral valve; when
completely so the genera are referred to the order Neotremata.

Superfamily RUSTELLACEA Walcott, new

Primitive, thick-shelled, corneous or calcareo-phosphatic Atremata
developing more or less of pseudodeltidia and pseudochilidia.

Family RUSTELLIDA Walcott, new

Primitive Rustellacea with the delthyrium small, open, and not
much modified by pseudodeltidia or pseudochilidia. Muscle scars
and vascular sinuses not well defined in the shell.

Rustella

Family PATERINID/ Schuchert, 1893 (emend)

Progressive Rustellacea with the delthyrium more or less closed
by pseudodeltidia or pseudochilidia.

Mickwitzia

Micromitra
(Paterina)
([phideila)

V olborthia

(?) Helmersemia

Superfamily OBOLACEA Schuchert, 1896 (emend)

Derived (in Rustellacea), progressive, thick-shelled, calcareo-
phosphatic or corneous Atremata without pseudodeltidia and pseudo-
chilidia. Rounded or linguloid in outline, more or less lens-shaped
and fixed by a short pedicle throughout life to extraneous objects.

Family CURTICIID# Walcott and Schuchert, new

Primitive Obolacea with a high, well-defined delthyrium. Interior
characters much as in Obolide.
Curticia

Family OBOLIDZE King, 1846 (emend)

Derived, progressive Obolacea with thickened, striated, vertical
cardinal areas traversed by pedicle grooves. Muscles and vascular
trunks strongly impressed in the valves.

Subfamily OBOLIN AE Dall, 1870 (emend)

Primitive Obolidz with the pedicle grooves more or less shallow
or deeply rounded, but never tending to form a sheath or to com-

144 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

pletely restrict the pedicle opening to the ventral valve. The radicle
of the Trimerellide, by way of the Neobolinz, appears to be in this
subfamily in the thick-shelled Middle Cambrian forms of Obolus
(s."54)
Obolus
(Bréggeria)
(Paleobolus)
(Fordinia)
(Lingulobolus )
(Mickwitzella)
(Acritis)
(Schmidtia)
(Westonia)
Lingulella
(Leptembolon)
(Lingule pis)
Delgadella

Subfamily ELKANIINA® Walcott and Schuchert, new

Divergent Obolidz with posterior or marginal (not central) plat-
forms, to which are attached the central and outside and middle

lateral muscles.
Elkania

Subfamily NEOBOLINA{ Walcott and Schuchert, new

Progressive Obolide with posterior platforms, to which were
probably attached the central and outside and middle lateral muscles.
Subfamily apparently progressive from the Obolinz to the Trimerel-
lide, though the platform is posterior and not subcentral as in the
Trimerelloids.

Neobolus

Subfamily BICIINAZ Walcott and Schuchert, new

Progressive Obolidz with the pedicle restricted to the ventral
valve and more or less enclosed by a pedicle tube, and with rudi-
mentary articulation. The transgressing stock from the Atremata
to the Neotremata (Obolellidz).

Bicia
Dicellomus

Superfamily KUTORGINACEA Walcott and Schuchert, new

Progressive, thick-shelled, almost calcareous Atrematous-like
shells, tending to be transverse and developing rudimentary articula-
tion, more or less rudimentary cardinal areas, pseudodeltidia, and

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 145

muscle scars prophetic of the Protremata. Derived out of Rus-
tellacea.

Family KUTORGINIDA® Schuchert, 1893

Progressive transverse Kutorginacea with rudimentary .cardinal
areas, great delthyrial opening, rudimentary articulation, and imma-
ture pseudodeltidia. Muscle scars prophetic of the Strophomenacea.

Kutorgina

Family SCHUCHERTINIDA Walcott, new

Primitive round Kutorginacea with small cardinal areas. Exter-
nally like Obolus, with an open subtriangular delthyrium which
apparently is without a pseudodeltidium. Muscle scars and vascular
markings prophetic, through the Billingsellide, of the Stropho-
menacea.

Schuchertina

Order NEOTREMATA Beecher, 1891 (emend)

Derived and specialized inarticulate Brachiopoda (through the
Obolidz of the Atremata), as a rule more phosphatic than calcareous,
more or less cone-shaped, with the pedicle emerging during life
through a perforation or sheath in the ventral valve, or a triangular,
more or less open cleft, or only so in the youngest shelled stage, after
which the ventral valve becomes attached by a pedicle to foreign ob-
jects. Pedicle cleft in derived forms modified by a listrium. Pseudo-
deltidia and pseudochilidia as a rule not well developed.

Superfamily SIPHONOTRETACEA Walcott and Schuchert, new

Primitive, thick-shelled, calcareous or corneous, oboloid Neotre-
mata, with the pedicle passing through a ventral sheath, the aperture
of which may remain apical and circular in outline, or it may become
elongate through resorption by passing anteriorly through the pro-
tegulum and umbo of the shell. A listrium is not developed. Dor-
sal protegulum marginal.

Family OBOLELLIDA® Walcott and Schuchert, new

Primitive Siphonotretacea with the pedicle emerging through a
small circular perforation in the apex of the ventral valve, posterior
to the protegulum. Derived out of the Obolide.

Obolella
(Glyptias)
Botsfordia
Schizopholis
(?) Quebecia

146 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53.

Family SIPHONOTRETIDZ Kutorga, 1848 (emend)

Progressive Siphonotretacea with the circular or elongate pedicle
opening at the apex or passing by resorption anteriorly through the
protegulum,and the umbo of the shell.

Yorkia
Dearbormnia
Trematobolus
Schizambon
Siphonotreta
Keyserlingia

Superfamily ACROTRETACEA Schuchert, 1896 (emend)

Progressive Neotremata with corneous or calcareo-corneous shells.
The pedicle opening is a simple, circular, more or less conspicuous.
perforation through the apex of the ventral valve. Dorsal protegu-

lum marginal.

Family ACROTRETIDA® Schuchert, 1893
Same characters as superfamily.

Subfamily ACROTHELINZ® Walcott and Schuchert, new

Depressed, large Acrotretide.
Acrothele
(Redlichella)
Discinolepsis

Subfamily ACROTRETINAZ Walcott and Schuchert, new

Small Acrotretidze with more or less high ventral valves.
Linnarssonella
Acrotreta
Acrothyra
Discinopsis

Superfamily DISCINACEA Waagen, 1885

Derived Neotremata with phosphatic shells, a listrium modifying
the pedicle slit, and without pseudodeltidia and false cardinal areas.

Dorsal protegulum usually subcentral.

Family DISCINIDZ Gray, 1840

Discinacea with an open pedicle notch in early life in the pos-
terior margin of the ventral valve, which is closed posteriorly during

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 147

neanic growth, leaving a more or less long, narrow slit partially
closed by the listrium.
Orbiculoidea

Superfamily CRANIACEA Waagen, 1885

Cemented calcareous specialized Neotremata without pedicle or
anal openings at maturity.

Family CRANIIDA® King, 1846

Craniacea with the pedicle functional probably only during nepi-
onic growth.
Philhedra

Order PROTREMATA Beecher, 1891 (emend)

Progressive (though atrematous Kutorginacea), articulate cal-
careous Brachiopoda with well-developed cardinal areas. The
pedicle opening is restricted to the ventral valve throughout life or
during early growth and is often modified and more or less closed
by a deltidium. Often there is a chilidum. Brachia unsupported
by a calcareous skeleton other than crura.

Superfamily ORTHACEA Walcott and Schuchert, new

Derived, progressive Protemata. Cruralia and rudimentary spon-
dylia (pseudospondylia) free or cemented (through sessility) directly
to the valves. Sometimes without deltidia and chilidia. Cardinal
process more or less well-developed except in the most primitive
genera.

Family BILLINGSELLIDZ Schuchert, 1893

Primitive Orthacea with an open or more or less closed delthyrium.
Cardinal process well developed, rudimentary, or absent. Usually
with a clearly defined pseudospondylium, to which the muscles of
the ventral valve were attached. Shell structure dense, granular,
lamellar, non-fibrous.

Subfamily NISUSIIN A Walcott and Schuchert, new

Primitive Orthacea with more or less well-developed deltidia and
with or without rudimentary chilidia. Spondylia and cruralia rudi-
mentary or small and not supported by septa. Cardinal process
rudimentary or absent.

Nisusia
(Jamesella)

Protorthis
(Loperia)

148 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

Subfamily BILLINGSELLINZ: Schuchert, 1893

Primitive Orthacea very much like Nisusiinze but without true
spondylia and cruralia. There is a more or less well-developed car-
dinal process except in Lower Cambrian forms.

Wimanella
Billingsella
Orusia
Otusia
Wynnia

Subfamily EOORTHINA Walcott, new

Derived Orthacea nearly always with large open delthyria; del-
tidia and chilidia occasionally retained throughout life, but more
often only in the younger growth stages. Cardinal process well de-
veloped. Shell structure dense, granular, and with punctate lamelle.

Eoorthis
Finkelnburgia

Superfamily STROPHOMENACEA Schuchert, 1896

Derived, progressive, terminal Protremata, out of Orthacea (Bil-
lingsellidz). Deltidia and chilidia nearly always well developed.
Cardinal process always well developed.

Family STROPHOMENIDA King, 1846
Subfamily RAFINESQUINZ: Schuchert, 1893

Strophomenoids having generally a convex ventral and a concave
or nearly flat dorsal valve.
Eostrophomena

Superfamily PENTAMERACEA Schuchert, 1896 (emend)

Specialized Protremata with well-developed free or supported
spondylia and cruralia. Deltidia and chilidia usually absent.

Family SYNTROPHIID/ Schuchert, 1896

Primitive Pentameracea with long, straight cardinal areas.
(?) Swantonia
Syntrophia
Huenella
Clarkella

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 149

STRUCTURE OF THE SHELL

The classification of the Protrematous genera is so profoundly
influenced by the structure of the shell that it was decided to include
the following notes:

The general structural characters of the shell of the Ordoviciaa
and later brachiopoda have been so fully described by authors that
it does not appear to be necessary or desirable to repeat them. The
student will find a full description given by Messrs. Hall and Clarke
in their “Introduction to the Study of the Brachiopoda” [1892, pp.
150-225].

Some of the more important works that contain data on the struc-
ture of the shell are Hancock, “On the Organization of the Brachio-
poda” [1859, pp. 791-869] ; King, “On Some Characters of Lingula
anatina”’ [1873, pp. I-17] ; Carpenter, “On the Intimate Structure of
the Shells of Brachiopods” [1853, pp. 23-45]; Davidson, “On the
Classification of the Brachiopoda” [1853, pp. 41-136] ; and Mickwitz,
“Ueber die Brachiopodengattung Obolus” [1896].

The greater proportion of the Cambrian brachiopoda is largely
corneous or chitinous. These brachiopoda are restricted to the in-
articulates, but the inarticulates of the Cambrian do not all possess
corneous shells. Dr. Mickwitz has shown [1896, pp. 102-142] that
the shells of Obolus and its subgenera are essentially the same as
those of Lingula in composition and structure. In both the shells
are composed of successive calcareous and corneous lamelle that
vary in thickness and structure. The calcareous lamelle are pris-
matic and penetrated by minute tubules; the corneous lamelle are
compact and imperforate.

Messrs. Hall and Clarke, in speaking of the shells of the articu-
late brachiopoda, say: “Among the articulate genera, under favor-
able preservation, there may be distinguished three distinct calcareous
shell layers: an inner prismatic or fibrous layer, which constitutes
the greater portion of the shell; above this is a thin lamellar layer,
and the outer surface of the shell is covered by a tenuous epidermal
film or periostracum. When the shell is punctate the tubules open
on the inner surface in narrow apertures, whence they widen up-
wards, abruptly expanding in the lamellar layer, at whose upper
margin they terminate. They do not pierce the periostracum.”
[1892, p. 175.]

Among the calcareous, inarticulate brachiopoda the shell of the
Cambrian genus Obolella shows a dense, compact, slightly lamellated
structure made up of a granular ground-mass pierced by extremely
small tubules or pores. The substance of the shell of Rustella and

150 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

Yorkia is unknown, but from the character of the casts and the fact
that the shells of Micromitra in the same matrix are preserved, it is
probable that it was calcareous. The shells of Quebecia, Trematobo-
Jus, and Dearbornia are also calcareous.

In Kutorgina and Schuchertina, forms that may be referred to
either the Atremata or the Protremata, the shells appear to be cal-
careous, compact, and without fibrous structure. Messrs. Hall and ~
Clarke, when speaking [1892, p. 174] of the composition of the
shell of fossil linguloids, said: “In the group of fossil linguloids,
beginning with Lingula, passing through Lingulops and Lingulasmua
to Trimerella and its allies, there is a regular increase in the relative
amount of calcareous matter in the shell, so that the 7rimerellas,
which are large and ponderous shells, seem to have wholly lost their
corneous matter.”

The predominance of corneous or calcareous shell matter does not
appear to be of more than generic importance in the classification
of the brachiopoda. It is true that the known articulate genera are
all calcareous, but it is equally true that among the inarticulate group
calcareous shells occur. Alteration, replacement, and removement
of original shell substance have changed the shell of so many species
that other characters must be depended upon for classification.

Microscopic STRUCTURE OF THE CAMBRIAN BracHIopopa.-—In
previous work on the Cambrian Brachiopoda, except in the cases
above cited, practically no attention has been paid to their micro-
scopic shell structure. ‘The importance of this feature in the classi-
fication of later species suggested the possible value of a microscopic
study of the earlier forms, and at my request Mr. R. S. Bassler, of
the United States National Museum, prepared thin-sections and also
assisted in the preparation of the accompanying illustrations and in
the preliminary study of the sections.

The preparation of thin-sections of these early brachiopoda is
accompanied with difficulties which, together with the lack of suffi-
ciently extensive collections, have undoubtedly prevented previous
study along the same line. Specimens suitable for sectioning, espe-
cially of the calcareous forms, are not at all common, and when they
do occur they are almost invariably buried in the rock, and are so
thin that the parting of the enclosing matrix does not leave sufficient
shell substance fdr the preparation of sections. In the present work
the specific identity of a shell was first determined by uncovering
about one-half the valve, and the other half, still embedded in the
matrix, was then used in making the section. ‘The structural fea-
tures are often restricted to individual lamellz, and the right zone

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT I51

for microscopic examination was determined simply by close observa-
tion as grinding proceeded. Both vertical and tangential sections
were prepared, the former cutting the shell at right angles and the
latter cutting the shell in planes more or less parallel to the layers
or lamellae of which it is composed. The most interesting results
were obtained from the tangential sections, as the thin shells showed
little decided structure in vertical sections.

2

io»)

Fic. 2. Billingsella plicatella Walcott [1905, p. 240]. Upper Cambrian, Gal-
latin Valley, Montana. ‘
Diagrammatic sketch of a small portion of a tangential section,
200. The granular ground-mass, with small pores and tubules 4 or
5 times their own diameter distant from each other, is also typical
of other members of the Billingsellide.
Fic. 3. Dalmanella subequata (Conrad) [1843, p. 333]. Ordovician (Stones
River), St. Paul, Minnesota.
Photograph of a tangential section, X 35, showing the fibrous struc-
ture and comparatively large pores.
Fic. 4. Kutorgina cingulata (Billings) [1861, p. 8]. Lower Cambrian, Swan-
ton, Vermont.
A small portion of the tangential section figured on Plate 12, fig. 4,
X 200. The minute structure of this and the following species is
essentially the same as that shown in fig. 1, the only difference be-
ing the closer arrangement of the pores.
Fic. 5. Obolus apollinis Eichwald [1829, p. 274]. Upper Cambrian Obolus
sandstone, Esthonia, Russia.
Small portion of tangential section X 200. ‘The minutely porous
granular structure is beautifully shown in this species, in which the
pores are arranged more closely than in any other observed.

The general resemblance of the Cambrian eoorthoids to certain
Ordovician Protremata is so striking and the lines of descent so
suggestive that particular attention was devoted to this group, and
the examination brought out the fact that this apparent relationship
disappears when the shell structure of the two groups is compared.

Sections of the shells of members of the Billingsellidee, of which

152 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

figure 2 is typical, all show a lamellar structure with indications of
more or less numerous and scattered, very minute pores or tubules
passing without interruption through one lamella. In some sections
the spots indicating the tubules are arranged in rows radiating from
the beak of the shell to the margins, but no other regular arrange-
ment can be seen. “Ihe great mass of the shell is made up of a com-
pact, finely granular base with dark spots and occasional minute
crystals of calcite—a ground-mass which, under the microscope,
appears very much like that of a fine argillaceous shale.

The Ordovician Protremata have a clearer, more crystalline aspect
or color than the Cambrian Billingsellidee—a difference which prob-
ably indicates either a purer lime composition for the former or
more probably a higher percentage of calcium phosphate for the
latter. In chemical aspect the shells of the Billingsellidee appear to
resemble those of the Atremata and Neotremata more closely than
do the Orthide. Analyses of the respective shells would be neces-
sary to prove these relations, but to note them is interesting in view
of the possible derivation of the Billingsellidze from the Atremata.

In the Cambrian articulate genera, with the possible exception of
Syntrophia and Huenella, there is an entire absence of the minute,
fibrous structure so characteristic of most, if not all, orthoids. But
these two representatives of the Pentameracea greatly resemble each
other. ‘Thus sections of the shell of Huenella abnormis (Walcott)
of the Upper Cambrian (see pl. 12, fig. 9) and Syntrophia lateralis
(Whitfield) of the Lower Ordovician (see pl. 12, fig. 7) show the
same radial arrangement of the pores seen in the Billingsellide,
but the shell structure is fibrous and the rows are coincident in direc-
tion with the fibers. Upon closer study this apparent fibrous struc-
ture can be resolved into more or less parallel bands or walls of shell
substance separating rows of closely arranged, rectangular, pore-like
spaces. ‘hese spaces may be seen distinctly in thick sections, but
when the section is made sufficiently thin to give a clear image under
very high power, the pore structure disappears.

Sections of the linguloid genera were also prepared and studied,
but the thinness of the shells and their phosphatic character prevented
very satisfactory results. The irregular large tubules mentioned by
Dr. Mickwitz [1896] are beautifully shown in the sections of Obolus
apollinis before me. Some of the tubules penetrate several lamellze
of the shell and suggest the tubules of some of the orthoids. (See
figures II and 12, pl. 12.) The same general structure, with the
exception of the larger tubules, appears to be characteristic of all of

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 153

the corneous shells of the Atremata and Neotremata, and, as far as
known to me, all of the Cambrian corneous shells are of this type.

The figures on the accompanying plate, with the exception of
figures 11 and 12, are from photographs which have not been re-
touched. Unfortunately higher magnifications could not be used
without a loss of clearness; but, even at the present magnification,
these views show a decided difference in structure.

In conclusion, it appears that the Cambrian Billingsellide are
further removed from the Ordovician and later Protremata than
hitherto suspected, the microscopic shell structure in the former
being of granular material pierced by small pores and in the latter of
fibrous material. On the other hand, the microscopic structure of
the Cambrian and later Pentameracea is so similar that an unbroken
line of descent is indicated.

TERMINOLOGY RELATING TO THE SHELL

The definitions given in the following pages are largely those of
Schuchert [1897, pp. 73-75], with the exception of the muscle scars
of the inarticulate brachiopods. For the Atremata and Neotremata
the terminology proposed by Professor William King [1873, pp. 5, 6]
is adopted, and for the Protremata that used by Messrs. Hall and
Clarke [1892, pp. 183-188] and given under the terminology of
Schuchert [1897, pp. 73-77]. I agree with Messrs. Hall and Clarke
that Professor King’s terminology has claims for its adoption, owing
to its simplicity. Dr. F. Blochmann has proposed [1900, p. 108] a
set of terms for the muscles of the inarticulate brachiopods that has
much to commend it. The terminology of Mr. Albany Hancock
[1859, p. 800] has been extensively used by authors. The numbers
below correspond to the numbers given the terminology of King,
Schuchert, and Blochmann.

Hancock, 1859
Inarticulates Articulates

. Anterior occlusors.
. Posterior occlusors.
Accessory divaricators.

. Anterior occlusors.
. Posterior occlusors.
. Divaricator.
Central adjustors.

. External adjustors.
. Posterior adjustors.
. Peduncular.

WwW nN 4

t Ventral adjustors.

. Dorsal adjustors.
. Peduncular.

NAN BR wWDH

WANS

2——W.

154 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

Kinc, 1873 ScHUCHERT, 1897
1. Anterior laterals. 1. Retractors.
2. Centrals. 2. Adductors.
3. Umbonal. 3. Pedicle.
4. Transmedians. 4. Rotators.
5. Outside laterals. 5. Protractors (externals).
6. Middle laterals. 6. Protractors (middles).
7. Diductors.

BLOCHMANN, 1900

. Lateralis.

. Occlusor anterior.
. Occlusor posterior.
. Obliquus internus.
. Obliquus externus.
. Obliquus medius.

Am BW N

DEFINITIONS

Appuctor Musci“es.—(See Central muscles.) The term adductor
is used for the central muscles of the Protremata.

ANTERIOR LATERAL (ReETRActor) Muscies—In the Atremata
these extend from the outer lateral margins of the visceral area
in the ventral valve to its anterior extremity in the dorsal valve and
serve to readjust the dorsal shell.

ANTERIOR REGION.—That portion of the shell in front of the
transverse axis and opposite the pedicle opening.

ApEX.—The place of initial shell growth. It may be the most
posterior portion of the valve or it may be situated near the trans-
verse axis.

Apicat CaLosity.—The thickened boss at the inner side of the
apex of the ventral valve of Acrotreta and other Neotrematous
genera through which the pedicle tube or foramen passes.

AREA.—See Cardinal area.

ARTICULATE BrACHIOpopA.—In the orders Protremata and Telo-
tremata the valves articulate by means of teeth and sockets. In
some Atremata rudimentary articulation is also developed.

ATREMATA.—Primitive inarticulate, calcareo-phosphatic or cor-
neous brachiopods with the pedicle emerging more or less freely
between the two valves. (For a more detailed description see page
142.)

BracutiA.—The fleshy, coiled or spiral, ciliated appendages of
brachiopods serving in water circulation and respiration.

BracHioc@éLe.—All of the anterior half of the valves outside of
the anterior portion of the parietal band. (After King.)

CLASSIFICATION CAMBRIAN BRACHIOPODA—-WALCOTT 155

CarpINAL AREA.—A more or less well-developed triangular area
on each side of the delthyrium, distinctly set off from the general
surface of the shell. It is best developed on the ventral valve of
articulate brachiopods, but is also present on the dorsal valve, and
generally in a rudimentary condition in many inarticulate species.
When the area is rudimentary it is often called a false or pseudo-
area. The area of some of the inarticulate genera is frequently
divided by a line between the delthyrium and the outer margin. In
such areas the line is called the flexure line, owing to the slight inter-
ruption in the striz of growth, and the spaces separated by the flex-
ure line are called the inner and outer lateral spaces of the area.
(See Deltidium and Foramen.)

CARDINAL EXTREMITIES.—The terminations of the hinge line.

CarpInAL Muscie Scar.—A large scar within which the pos-
terior and anterior lateral and transmedian muscle scars were ,at-
tached.

CaRDINAL Process.—A variously modified apophysis, situated pos-
teriorly at the center of the hinge of the dorsal valve in articulate
brachiopoda. To it are attached the diductor muscles, which by
their contraction serve to open the valves anteriorly.

CARDINAL SLOPES.—The inclined surfaces extending from the
umbonal slopes to the hinge margins.

Central (Appuctor) Muscrrs.—In the Protremata and Telo-
tremata these muscles have their ventral insertion one on either side
of the central axis, between the diductors. In passing to the dorsal
valve they divide into four and produce in that shell the two pairs of
principal scars known as the anterior and posterior centrals. By
contraction these muscles close the shell. In the Neotremata they
are the essential muscles, the anterior centrals closing the valves,
while the posterior pair serves to open the valves. In the Atremata
there is a simple pair of centrals placed near the anterior extremity
of the visceral area.

Cui_ip1um.—A dorsal plate, in appearance similar to the del-
tidium, covering the exterior portion of the cardinal process in many
Protremata. Its development does not begin uniil early neanic or
later growth and it is probably secreted by the dorsal mantle lobe.
In the Atremata and Neotremata there is a similar plate continuous
with the dorsal cardinal region of the shell, and it is named the
pseudochilidium.

Crura.—Processes on the dorsal hinge plate of the Telotremata
and some Protremata, to which are attached the fleshy brachia and
brachidia. ‘These usually form the inner walls of the dental sockets
and may be supported by septal plates.

150 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

CruRALIuM.—The dorsal equivalent of the ventral spondylium.

DeL_tHyriuM.—The triangular aperture transecting medially the
ventral cardinal area, or the posterior surface from the apex to the
posterior margin of the ventral valve, through some portion of
which the pedicle passes. It has also been termed the fissure or
foramen. ‘The delthyrium may or may not be closed either by a
calcareous deltidium or a phosphatic pseudodeltidium.

DeL_ripiuM.—A plate more or less continuous with the cardinal
margin on the ventral valve covering the delthyrium in Atremata,
Neotremata, and Protremata. When present in inarticulate brach-
iopods it is called the pseudodeltidium, and in the Protremata, where
it is always more calcareous, thicker, and more sharply defined, the
deltidium and pseudochilidium.

DentaL PLatEs.—Vertical plates supporting the teeth of the ven-
tral valve in articulate brachiopods.

DENTAL SOCKETS.—Excavations in the dorsal cardinal margin of
articulate brachiopods in which the teeth of the ventral valve articu-
late. ‘The inner wall of the socket is elevated and forms the base of
the crural plate.

Dipuctor Muscri#s.—In the Protremata and Telotremata the
principal pair of diductor muscles has the larger end attached to the
ventral valve near the anterior edge of the visceral area, while the
other end has its insertion on the anterior portion of the cardinal
process. By contraction these muscles open the valves.

Dorsat, VALVE.—Usually the smaller and imperforate valve and
the one to which the brachia are always attached. Brachial, hemal,
socket, and entering valves are other terms more rarely employed.

EpHEBic.—Designating the mature shell.

Fais— ARrEA.—See Cardinal area.

FLEXURE Linre.—See Cardinal area.

ForAMEN.—A small circular passage through the deltidium, either
below or at the apex of the ventral valve. Sometimes the foramen
encroaches by pedicle abrasion upon the umbo of the ventral valve.

FoRAMINAL ‘TusE.—The pedicle opening through the ventral
valve of Neotrematous genera.

GreniTa, Marxincs.—Radial markings or pits within the pos-
terior portion of the visceral space, indicating the position and ex-
tent of the genitals.

Grronvtic.—Designating old age. It is indicated in the ontogeny
of many species of brachiopods by extreme thickness of the valves,
obesity, or by numerous, crowded growth lines near the anterior
margin—a condition which sometimes produces truncation and ab-
sence of strize at the margin.

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 157

H®eaART-SHAPED CaAvity.—Central depressed portion of visceral
area (Mickwitz).

Hince Linge.—The line along which articulation takes place ; also
sometimes developed among inarticulate brachiopoda.

INARTICULATE BRACHIOPODA.—In the orders Atremata and Neo-
tremata the valves do not, as a rule, articulate by means of teeth
and sockets, as is the case in the articulate orders Protremata and
Telotremata.

LATERAL AREAS.—That portion of the shell on each side of the
longitudinal axis.

ListriuM.—In some Neotremata a plate closing the progressive
track of the pedicle opening or pedicle cleft, posterior to the apex of
the ventral valve.

LONGITUDINAL Axis.—A median line through the shell from the
beak to the anterior margin.

MEDIAN SEPTUM.—An internal vertical plate commonly developed
along the longitudinal axis and between the muscles of the ventral
valve. Sometimes there is also a dorsal median septum. Lateral
septa are rarely developed.

Mippie LATERAL MuscLe Scar.—See Outside lateral.

NrANiIc.—Designating youthfulness, or the stage in which specific
characters begin to develop.

NEotTREMATA.—Circular or oval, more or less cone-shaped, inar-
ticulate calcareo-phosphatic brachiopods with the pedicle opening
restricted throughout life to the ventral valve. (For a more de-
tailed description see page 145.)

NEprionic.—Designating the smooth shell stage succeeding the
protegulum.

OutTsIDE AND MippLé LATERAL (Prorractor) Muscres.—In the
Obolidz one pair has the ventral ends fastened at the anterior ex-
tremity of the visceral area, extending backward and inserted near
the lateral margin of the dorsal valve, outside the transmedians. A
second pair originates just behind the centrals of the ventral valve
and is inserted posterior to the first pair. These muscles draw the
dorsal valve forward.

PaRIETAL BAND.—The point of attachment of the muscular wall
surrounding the visceral area.

PrpicLk.—The flexible muscular organ of the ventral valve by
means of which brachiopods may be attached to extraneous objects.

PEDICLE Furrow.—The external furrow adjoining the foramen
or pedicle opening in certain Neotrematous genera.

158 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

PEpICLE GroovE.—The median groove on the cardinal areas of the
valves formed by the pedicle extending through the posterior mar-
gin of the valves when they were closed.

PrepicLe Muscies.—In the Protremata and Telotremata one pair
originates on the ventral valve at points just outside and behind the
diductors, and another on the dorsal valve behind the posterior
centrals, while the opposite ends of both are attached to the pedicle.
Besides these, there is an unpaired muscle lying at the base of the
pedicle, attaching it closely to the ventral valve.

PEDICLE OPENING.—See Delthyrium.

PrpicLé TuBE.—See Foraminal tube.

PLATFORM.—An internal median thickening of the shell elevating
the muscles. Seen in certain families of the Atremata and more
rarely in the Neotremata. (See Spondylium.)

PLEUROCG@LES.—Areas between the parietal band and the outer
postero-lateral margins. (After King.)

PostERIoR Recion.—That portion of the shell back of the trans-
verse axis and toward the beak, or apex.

PRoTEGULUM.—The initial shell of brachiopoda. It is smooth and
of microscopic size, in outline being semicircular or arcuate and
without cardinal areas. Rarely seen in adult shells.

PROTRACTOR MuscLes.—See Outside and middle lateral muscles.

PROTREMATA.—Articulate, calcareous brachiopods, with the ped-
icle opening restricted to the ventral valve throughout life or during
early growth. Pedicle aperture modified by the deltidium. Brachia
unsupported by a calcareous skeleton, but nearly always by a more
or less long crura. (For a more detailed description, see page 147.)

PSEUDO-AREA.—See Cardinal area.

PsEUDOCHILIDIUM.—See Chilidium.

PSEUDOCRURALIUM.—Dorsal equivalent of pseudospondylium.

PSEUDODELTIDIUM.—The convex medial portion continuous with
the ventral cardinal areas in Atremata and Neotremata. (See Del-
tidium. )

PSEUDO-PEDICLE Groove.—See Pedicle groove.

PSEUDOSPONDYLIUM.—See Spondylium.

Retractor Musci&es.—See Anterior lateral muscles.

SEPTAL PLATES.—Plates supporting the crural processes; also
known as crural plates.

SESSILE SPONDYLIUM == Pseudospondylium.

SPLANCHNOC@LE.—The area within the parietal band. (After
King.)

CLASSIFICATION CAMBRIAN BRACHIOPODA—-WALCOTT 159

SponpyLiuM.—A plate in some articulate brachiopoda, mainly the
Pentameracea, formed by the union of converging dental plates, to
the upper surface of which are attached the adductor, diductor, and
pedicle muscles. The spondylium may rest upon the ventral valve
or may be supported by a median septum. The spondylium appears
to be first indicated in the articulates by a thickening of the shell of
the ventral valve beneath the umbonal region so as to form an area
upon which all the muscles of the valve have their points of attach-
ment. In Billingsella this is beautifully illustrated by B. exporecta
and B. plicatella. In its development the spondylium is foreshad-
owed in the Atremata by the so-called platform of Fordinia and the
still more primitive form in Obolus. For the purpose of reference,
the rudimentary spondylia attached directly to the inner surface of
the valve, as in Billingsella, may be called pseudospondylia (sessile
spondylia, Ulrich), and those free or supported by a septum or
septa, spondylia. In the Cambrian Atremata the homologous equiv-
alent has been known as the platform. In Obolus, etc., there is
sometimes developed in the dorsal valve a plate similar in appear-
ance to the spondylium, but different in origin and known as the
cruralium.

TEETH.—Two processes of the ventral valve of articulate brachio-
poda, serving for articulation.

TRANSMEDIAN (Rotator) Muscries.—In Obolacea these are sit-
uated posteriorly just in advance of the umbonal muscle, two on one
side and one on the other. By their contraction the dorsal valve
turns alternately first in one direction and then in the other.

TRANSVERSE Axis.—A line through the shell from right to left,
midway between the beak and anterior region. (See Longitudinal
axis. )

TRAPEZOIDAL AREA.—The area on each side of the heart-shaped
cavity in Obolus in which the outside and middle lateral scars and
central muscle scars are attached.

Umszo.—The elevated or prominent portion of the valve anterior
to the apex.

Umponat Cavity.—The hollow space in the interior of the shell
beneath the umbo.

Umpona, Muscie.—A single muscle situated in the umbonal
region of most Atremata. By its contraction the valves are opened
anteriorly. In Obolus this muscle divides toward the ventral valve.

UmponaL Sropes.—The inclined surfaces about the umbo and
opposite the cardinal slopes.

VENTRAL VALVE.—Usually the larger valve situated on the ventral
side of the animal. Among articulate brachiopoda the valve is usu-

160 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

ally easily distinguished by the presence of a delthyrium or pedicle
opening through which the pedicle is protruded. In many Atrema-
tous genera the ventral valve is not readily distinguished. When the
shell is cemented to foreign bodies it is always by the ventral valve.
It is usually the larger and deeper of the two valves. Pedicle,
larger, dental, neural, and receiving valves are synonymous terms.

VASCULAR (PALLIAL) SINUSES.—Two convergent or divergent
primary sinuses of the circulatory system, traversing the mantle and
originating in the posterior medial region. They usually have
numerous secondary (lateral and peripheral) branches and both
often leave impressions in the shell.

VISCERAL AREA.—The posterior region of the interior of the
valves between the pallial sinuses; in general, the immediate area of
the median muscle tracks.

VISCERAL Cavity = Visceral area.

161

CLASSIFICATION CAMBRIAN BRACH IOPODA—WALCOTT

BIBLIOGRAPHY

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1845. Géologie de la Russie d’Europe, et des Montagnes de 1’Oural, by
R. I. Murchison, E. P. de Verneuil, and A. de Keyserling, II, Pt.
3, 1845, Paleontologie; 4to, Paris.

WAAGEN, W. H.
1885. Memoirs of the Geological Survey of India, Paleontologia Indica,
13th series, Salt Range Fossils, I, Productus Limestone Fossils,
Pt. 4, fas. 5, 1885 (July 2), pp. 720-770, plates LXxxXII-L.XXXVI.

Watcortt, C. D.
1905. Proceedings United States National Museum, XXVIII, 1905 (Feb-
ruary 17), pp. 227-337: Cambrian Brachiopoda, with descriptions
of new genera and species.

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 163

WuitFlELp, R. P.

1886. Bulletin of the American Museum of Natural History, I, No. 8, 1886
(December 28), pp. 293-345: Notice of Geological Investigations
along the eastern shore of Lake Champlain, with descriptions of
new fossils.

WINCHELL, N. H.
1886. Fourteenth Annual Report of the Geological and Natural History
Survey of Minnesota for 1885, 1886, pp. 313-318: New Species of
Fossils.

164 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53

DESCRIPTION OF PLATE 12

Billingsella coloradoensis (Shumard) [1860, p. 627]:

Fic. 1. Photograph of horizontal thin-section enlarged fifty diameters.
This shows the characteristic granular ground-mass of the Cam-
brian Billingsellide. Upper Cambrian, Morgan Creek, Burnet
County, Texas.

Nisusia festinata (Billings) [1861, p. 10]:

Fic. 2. Photograph of horizontal thin-section enlarged fifty diameters.
This section shows a granular ground-mass in which there are
faint indications of small pores or tubule which may be seen
with a high power. Lower Cambrian, 2 miles east of Swanton,
Vermont.

Eoorthis remnicha (N. H. Winchell) [1886, p. 317]:

Fic. 3. Photograph of horizontal thin-section enlarged fifty diameters.
This section shows the same type of ground-mass as that illus-
trated by fig. 2. Upper Cambrian, Cold Creek Canyon, Burnet
County, Texas.

Kutorgina cingulata (Billings) [1861, p. 8]:
Fic. 4. Photograph of horizontal thin-section showing granular sheil sub-
stance. There are few slight indications of pores. Lower

Cambrian, Swanton, Vermont.

Dalmanella multisecta (Meek) [1873, p. 112]:
Fic. 5. Horizontal thin-section enlarged fifty diameters. This shows the
fibrous structure of the shell penetrated by numerous fine
tubules. Ordovician Eden formation, Cincinnati, Ohio.

Dalmanella parva (de Verneuil) [1845, p. 188]:
Fic. 6. Horizontal thin-section showing fibrous structure; also section of
the tubules that penetrate through the shell. Middle Ordovi-
cian of Russia.

Syntrophia lateralis (Whitfield) [1886, p. 303] :

Fic. 7. Horizontal thin-section enlarged fifty diameters, showing the ar-
rangement of the pores in lines that radiate from the apex
toward the margin. Lower Ordovician Cassin limestone, Fort
Cassin, Vermont.

Plectorthis plicatella (Hall) [1847, p. 122]:

Fic. 8. Horizontal thin-section enlarged fifty diameters. This section
shows the fibrous structure so characteristic of the Ordovician
orthoids. Ordovician Lorraine shaly limestones, Cincinnati,

Ohio.

SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53, PL. 12

MICROPHOTOGRAPHS OF ROCK SECTIONS

CLASSIFICATION CAMBRIAN BRACHIOPODA—WALCOTT 165

Huenella abnormis (Walcott) [1905, p. 289] :

Fic. 9. Horizontal thin-section enlarged fifty diameters. The pores in
this genus are smaller than in Syntrophia, but their arrange-
ment is essentially the same and shows the line effect char-
acteristic of the Pentameracea. Upper Cambrian, Gallatin Val-
ley, Montana.

Obolella crassa (Hall) [1847, p. 290]:

Fic. 10. Horizontal thin-section enlarged fifty diameters. This shows the
fine granular ground-mass, with an indication in the upper left
side of the section that a surface ornamentation has been cut
across. Lower Cambrian, Bic, Canada.

Obolus apollinis Eichwald [1820, p. 274]:
Fics. 11 and 12. Transverse, vertical thin-section enlarged so to to show
the lamellz and the presence of a large tubule that appears to

have more or less imperfectly penetrated through the shell.
Upper Cambrian Obolus sandstone, Russia,

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Classification and
terminology of the Cambria
Brachiopoda

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