MEMOIRS OF THE PFABODY MITSEUM OF NATURAL HT'^TORY
VOLUME IV, PART J
Brachiopod Genera
of the
Suborders Orthoidea and Pentameroidea
BY
CHARLES SCHUCHERT
PROFESSOR OF PALEONTOLOGY, FMFRtTUS, YALE UNIVERSITY
AND
G. ARTHUR COOPER
ASSISTANT CURATOR OF STRATIGRAPHIC PALEONTOLOGY
U. S. NATIONAL MUSEUM
LVX ET
VERITAS
NEW HAVEN, CONN.
1932
MEMOIRS OF THE PEABODY MUSEUM OF NATURAL HISTORY
YALE UNIVERSITY
Volume I. Odontornithes: A Monograph on the Extinct Toothed Birds of North
America. By Othniel Charles Marsh. Pp. i-ix, 1-201, pis. 1-34,
text figs. 1-40. 1880. To be obtained from the Peabody
Museum. Price $3.
Volume II. Parti. Brachiospongidse : A Memoir on a Group of Silurian Sponges.
By Charles Emerson Beecher. Pp. 1-28, pis. 1-6, text figs. 1-4.
1889. To be obtained from the Peabody Museum. Price $1.
No more published.
Volume III. Part 1. American Mesozoic Mammalia. By George Gaylord Simp-
son. Pp. i-xvi, 1-171, pis. 1-32, text figs. 1-62. 1929. To be
obtained from the Yale University Press, New Haven, Conn.
Price $5.
Part 2. A Remarkable Ground Sloth. By Richard Swann Lull.
Pp. i-x, 1-20, pis. 1-9, text figs. 1-3. 1929. To be obtained
from the Yale University Press, New Haven, Conn. Price $1.
Part 3. A Revision of the Ceratopsia or Horned Dinosaurs. By
Richard Swann Lull. In preparation.
Part 4. The Merycoidodontids, an Extinct Group of Ruminant
Mammals. By Malcolm Rutherford Thorpe. In preparation.
Volume IV. Part 1. Brachiopod Genera of the Suborders Orthoidea and Pentam-
eroidea. By Charles Schuchert and G. Arthur Cooper. Pp.
i-xii, 1-270, pis. A and 1-29, text figs. 1-36. 1932. To be
obtained from the Peabody Museum. Price $7 (bound in cloth),
$6 (bound in paper).
Addenda et Corrigenda
Date of publication: August 23, 1932.
All photographs of specimens figured on the plates were made hy the
author, with the assistance of Mr. Percy A. Morris. With the
exception of Plate A, and Figure 24 of Plate 1, these photo-
graphs are entirely without retouching.
Page 57, column 1, line 14 from bottom, for impunctate read
■punctate.
Page 80, column 1, delete first two lines.
Page 81, column 2, line 7, for Oxarkian read Canadian.
Page 84, legend for Fig. 17, next to last line, for lejt read right.
Page 88, column 2, lines 14 and 15, delete which is rather strongly
convex.
Page 109, column 2, lines 4 and 5, delete We refer it doubtfully to
our new genus Paurorthis.
Page 141, table 14, Aulacophoria should be derived from Schizo-
phorta, instead of from Orthotichia.
MEMOIRS OF
Volume I. Oc
Volume II. Pa
Nc
Volume III. Pa
Pa
Pa
Pa
Volume IV. Pa
BRACHIOPOD GENERA
OF THE
SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
"The esthetic satisfaction to be derived from contemplating the mere
variety of animal forms and from tracing the order that runs through all
its diversity appeals to a very deep instinct in human nature."
David Sharp
"There is only one way of seeing things rightly, and that is seeing the
whole of them."
John Kuskin
MEMOIRS OF THE PEABODY MUSEUM OF NATURAL HISTORY
VOLUME IV, PART 1
Brachiopod Genera
of the
Suborders Orthoidea and Pentameroidea
BY
CHARLES SCHUCHERT
PROFESSOR OF PALEONTOLOGY, EMERITUS, YALE UNIVERSITY
AND
G. ARTHUR COOPER
ASSISTANT CURATOR OF STRATIGRAPHIC PALEONTOLOGY
U. S. NATIONAL MUSEUM
LVXET
■
1 a-ip.m
■
■
^
VERITAS
^
NEV^ HAVEN, CONN.
1932
PRINTED IN THE UNITED STATES OF AMERICA
THE TUTTLE, MOREHOUSE & TAYLOR COMPANY
NEW HAVEN, CONNECTICUT
CONTENTS
Page
Introduction *
Division of work •^
Location of specimens ^
Technique "^
Species lists
Genetic lines
Acknowledgments
Part I. Brief definitions of brachiopod terms "
Part II. Principles of morphogenesis or evolution of form 12
12
Need of taxonomy
12
Rise of brachiopod genera
13
The genus concept
Paleoecology
Homoeomorphy
Part III. Morphology of the orthoid shell 18
Morphology of the exterior 18
Orientation of the shell 18
Commissures '"
Convexity '
Interareas ^^
Deltidium •■■ 21
Modifications of the delthyrium (deltidium) 21
Function of the deltidium 22
Lateral plates
Modifications of the notothyrium (chilidium and chilidial plates) 23
Morphology of the ventral interior
Articulation
Teeth Ys
Sockets -P
Dental plates
Spondylium ^,
History of the term
Present views and definitions
«j , 29
Septa
.; , 30
Musculature
32
Paliial and genital markings --
Pallial markings ^^
» Genital or ovarian markings
viii CONTENTS
Part III. Morphology of the orthoid shell — Cont. Page
Morphology of the dorsal interior 34
Notothyrial platform 34
Denticles and sockets 34
Denticles 34
Sockets 34
Cardinalia 34
Cardinal process 34
Brachiophores or brachial apparatus 37
Cruralium and pseudocruralium 39
Septa 39
Musculature 39
Pallial markings 40
Microstructure of the shell 41
Exopuncts 42
EndopunctEC 42
Value of punctation in taxonomy 42
Old-age characters 42
Part IV. The genera of the suborder Orthoidea 43
Superfamily Orthacea 43
Family Nisusiidae 43
Nisusia 44
Jamesella 46
Family Protorthidje 46
Protorthis 46
Loferia 47
Family Billingsellidas 48
BUlingsella 48
Family Eoorthidje 50
Witnanella 50
Eoorthis 51
Otusia 52
Bohemiella 52
Oligomys 53
Family Finkelnburgiidse, nov 54
Orusia ^ 54
Finkelnburgia 55
Family Plectorthidas 56
Subfamily Plectorthinx 57
Plectorthis 57
Hebertella 59
Mimella 61
Schizofhorella 62
Doleroldes 63
Subfamily Cyclocoeliinas 64
Cyclocaelia 64
Subfamily Platystrophiins 64
Platystrofhia 64;
Mcewanella 69
CONTENTS >X
Supcrfamily Orthacca — Cont.
Page
Family Plcctorthidx — Cont.
• 70
Subfamily Orthostrophiinae _„
Orthostrophia -.
O. dart(F, nov
71
Family Skenidiidas yi
Skentdio'tdes ^2
S. hillingsi -o
Sken'ui'tum
73
Family Orthida: _-
Subfamily Orthinse ^5
Orthis n-j
Cyrtonotella n-j
Nicolella yg
Glossorthis ^9
Paurorthis gQ
Archtrorthis g.
Subfamily Productorthinae gj
Panderina g2
Productorthis r..
Subfamily Angusticardiniinae g^
Angusticardinia „,
Subfamily Taffiinae g5
Taffia Z'ZZZZ'Z'. 85
Eostrofbomena „-
Subfamily Hesperorthinae g5
Hesperorthis g^
Schizoramma gg
S. gotlandica, nov gg
Dolerorthis og
Subfamily Glyptorthinae gg
Glyptorthis ni
Eridorthis g2
Ptychofleurella o,
P. matapedia, nov
93
Family Dinorthidae o,
Dinorthis nc
Dinorthis s. s qc
Plasiomys ge
Retrorsirostra g,
Pionorthis g,
Marionella ' g_
Valcourea gg
V. magna, nov _„
Multicostella gg
Auitinella jqq
Palceoitrophomena .qq
Planidorsa iqi
P. hella jQj
P. crassicostella, nov
Family Porambonitidae jq2
Porambonites Iqc
Noetlingia
, ^, .._, 105
Family Lycophonidae jq5
Lycophoria
X CONTENTS
Part IV. The genera of the suborder Orthoidea — Cont. Page
Superfamily Clitambonacea 107
Family Deltatretida: 107
Deltatreta 108
Pomatotrema Ulrich and Cooper, nov 109
P. muralis Ulrich and Cooper, nov 109
Polytoechia 110
Family Clitambonitidx 110
Subfamily Plectellinae 112
Plectella 112
Ingrla 112
Subfamily Clitambonitins 113
Clitambonites 113
Vellamo 114
Clinambon, nov 115
Estlandia 115
Hemifronites 115
Pahlenella 117
Afomatella 117
Subfamily Gonambonitinas 118
Gonambonites 11°
Superfamily Dalmanellacea H'
Family Dalmanellidas 11°
Dalmanella 120
Carinijerella 1^2
Aulacella 122
Proschixofhoria *2j
Levenea ^^^
Heterorthina 124
Family Wattsellidae 124
Wattsella 125
Resserella 126
Horderleyella 1^7
Mendacella ^^'
Idiorthis 128
Parmorthis ^2o
P. crassicostata, nov 129
Fascicostella ^29
Family Bilobitidae 1^0
Bilobites 130
Family Mystrophoridae 1-^1
Mystrophora '-^^
Kayserella l-'^
Family Rhipidomellidae ^•'•^
Rhifidomella '•'■'
Perdkocardtma '•'-'
Platyorthis 1^^
Thiemella 1^^
Family Heterorthidas '•^"
Subfamily Heterorthinae j;;'
Heterorthh 1-^'
Subfamily Harknessellinae J;;^
Harknessella |^°
Reuschella |^^
Smeathenella
CONTENTS xi
Superfamily Dalmancllacea — Cont. Page
Family Schlzophoriid.-c 139
Subfamily Schizophoriinae 140
P'tonodema 141
Schizophoria 143
Orthot'tch'ta 144
Aulacofhoria 145
Subfamily Enteletinx 145
Enteletei 146
Parenteletes 147
Enieletina 148
Enteletella 148
Enteletoides 148
Subfamily Isorthinae 149
Isorthis 149
Family Linoporellidx 150
Ltnoporella 150
Orthotrofta 152
Family Tropidoleptidae, nov 152
Tropidoleftus 152
Part V. The genera of the suborder Pentameroidea 154
Superfamily Syntrophiacea 154
Family Clarkellids 155
Syntrofh'to'uies 155
Syntrofhina 155
Clarkella 156
Yangtzeella 157
Family Syntrophiids 158
Syntrofhta 158
Swantonia 159
Family Huenellidae 159
Huenella 159
Huenellina 160
Superfamily Pentameracea 161
Technique 162
Morphology of the Pentameracea 162
Exterior 162
Ventricosity 162
Ornamentation 162
Interareas 163
Ventral interior 163
Delthyrium 163
Deltidial cover 163
Deltidial plates 163
Spondylium 164
Dorsal interior 164
Septa 164
Musculature 164
Cardinalia 164
xii CONTENTS
Part V. The genera of the suborder Pentameroidea — Cont.
Superfamily Pentameracea — Cont. Page
Generic and evolutionary trends 165
Loss of interareas and development of a planarea 165
Rostration 165
Reversion of normal convexity 165
Trilobation 165
Ornamentation 165
Loss of the ventral septum 166
Development of a cruralium 166
Parallel trends 166
Summary 166
Family Camerellidx 166
Camerella 167
Branconia 168
Parastrofhtnella 169
Anastrofhia 169
Metacamerella 170
Family Pentameridas 170
Subfamily Gypidulinse 171
Clorinda 171
Barrandella 173
Gyfidula 173
S'teberella : 175
Pentamerella 176
Zdimir 177
Subfamily Pentamerinae 177
Lasves 177
Pentamerus 177
Pentameroides 179
Lissocoelina 179
C afelliniella 179
Holorhynchus 180
HarpidiuTn 180
Costatffi 180
Rhifidium 180
Conchidium 181
Brooksina 183
Cymbidium 183
Platymerella 184
V'trgiana 185
Family Stricklandidas 186
Stricklandta 187
Appendix 189
? Superfamily Rhynchonellacea 189
Rhynchocamara 189
Liocoelia 189
Index 257
INTRODUCTION
Brachiopods have interested the senior author since the days of his early youth, and by 1886,
while assistant to E. O. Ulrich in Cincinnati, he had a private collection of them so large and well
arranged that it led James Hall to transport collection and collector to Albany to assist him in the
work then in preparation, "An Introduction to the Study of the Genera of Palasozoic Brachiopoda"
(1892-1894). This recognition stimulated Schuchert all the more to add to his collection, which
he has continued to do ever since, with the exception of the twelve years spent as curator at the
United States National Museum, where each official is expected to devote his entire attention to the
care and increase of the Government collections. The first great addition was made in 1884, when
the brachiopods gathered by E. O. Ulrich were obtained, and later through purchase came the Ernst
H. V'aupel and other smaller collections from the Ohio Valley. At Albany was purchased the John
M. Clarke collection of Middle Devonian fossils. All the non-brachiopod material in these pur-
chases was exchanged with the dealers Braun of New York and Krantz of Bonn, Germany, for
European brachiopods, with the permission of the authorities of the National Museum.
Upon taking up the chair of paleontology at Yale University in 1904, the stimulus to acquire
more brachiopods was renewed. The Marshall collection of English Jurassic Telotremata was pur-
chased in 1909 through S. S. Buckman, who relabeled the material carefully, especially with regard
to stratigraphic horizons; and later the private collection of Fred Braun of New York, also rich in
European species, which that dealer had long been accumulating. Largest of all the acquisitions,
however, enriching the Schuchert Collection by many thousands of fine Paleozoic specimens, was the
private collection of D. K. Greger, most of which that devoted gatherer of brachiopods had assem-
bled, during a long life, from the Mississippi Valley and the Southwest. With this material came
an extensive library of brachiopod literature, which, together with that already in the Peabody
Museum, forms the still growing Schuchert-Greger Brachiopod Library of that institution.
From these statements it is apparent that the authors of the present work had access to one of
the largest brachiopod collections known. For Cambrian material, without which no genetic study
of brachiopod genera can have a secure foundation, we had the privilege of access to the most exten-
sive collections known from rocks of this period, made by Charles D. Walcott and forming one of
the great treasures of the United States National Museum.
At Washington the curatorial duties of the senior author made it impossible to take up any
protracted paleontological studies, due to the rapid growth and constant need for rearrangement of
the National Museum collections; but he did bring to final form a card catalogue of brachiopod
genera and species which he had begun at Cincinnati, and which appeared in print in 1897 as Bulle-
tin 87 of the United States Geological Survey. With his transfer to Yale, the hope of working up
his collections was reborn, but here again, due to university and administrative duties, it soon became
evident that if anything worth while was to be done, it must come through a colleague who could
devote his entire time to a restudy of the genera. For many years, however, neither adequate
scholarships nor museum appointments could be found, but, with the hope still in mind, the senior
author laid aside savings out of his salary and out of royalties accruing from the sale of his text-
books. Finally, in 1925, there came to Yale a post-graduate student, the junior author, who soon
showed that he possessed the necessary qualifications and inclination to undertake the work.
In the beginning privat-dozent and professor emeritus built "castles in Spain," contemplating a
revision of all the brachiopod genera, but caution led them to start with the most primitive of the
articulate forms, the orthoids. What an undertaking the original intention would have been is seen
in Schuchert and LeVene's "Generum et Genotyporum Index et Bibliographia" of 1929, which lists
about 700 valid genera, of which 456 are Paleozoic, 177 Mesozoic, and 74 Cenozoic-Recent.
The senior author had also become suspicious that all was not correct in regard to the origin of
the Telotremata as held by Beecher (1891) and Schuchert (1897), and in regard to the supposed
primordial significance of the deltidium in the Protremata, and of what had been called the pro-
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
deltidium. Yatsu (1902, 1905) had shown that there was no "third plate" in embryonic shells
and that therefore the formation of a deltidium could not have started in this way. This agam
raised the question: Of what significance in classification is the deltidium? In the meantime Walcott's
classic "Cambrian Brachiopoda" (1912) had shown that among these early forms there were no
Telotremata {Swantonia is not of this order, as was then believed), and that the few forms regarded
as Strophomenacea were probably orthoids. After we had started our studies came a penetratmg
little book entitled "Brachiopod Morphology and Genera (Recent and Tertiary)" by that clear-
thinking author, the late J. Allan Thomson, which made still more apparent the necessity for a
revision of the Paleozoic articulate brachiopods.
As is well known, studies along fundamental lines take much more time than generic revision,
and as time wore on our Spanish castles showed signs of shrinkage, and we had to limit ourselves to
Paleozoic genera. Along this line we were proceeding nicely when the call came for the junior
author to take up a position as assistant curator in the United States National Museum, and we had
to write "finis" to our work with only one-half of the Protremata done and the Telotremata not
more than started. However, we have an abundance of results, showing that the Orthacea, or
rather the greater division that we are calling Orthoidea, contains the primary stock from which all
the articulate brachiopods have arisen! This means not only that the Pentameracea and the Stroph-
omenacea have evolved out of the Orthacea, but that the order Telotremata had its origin here as
well. We have indicated these beginnings and regret that conditions prevent our proving the
genetic lines. However, a need once pointed out will soon be taken up by others, though we hope
that it may be our privilege to follow these leads further, either through independent work by the
junior author, or through studies at Yale by another budding paleontologist.
Table of the groupings discussed in the following pages
Total New
Orders
Suborders (Orthoidea and Pentameroidea)
Superfamilies
Families
Subfamilies
Genera and subgenera
Superfamilies
Orthacea
Clitambonacea
Dalmanellacea
Syntrophiacea
Pentameracea
Families
11 (6 new)
2(1 " )
9 (6 " )
3 (2 " )
3
2
2
5
28
20
135
Subfamilies
10 (7 new)
3 (2 " )
5 (2 « )
0
2
2
2
15
11
35
103
32
Genera-
Subgenera
(53 (15 new)
13 ( 4 " )
(37 (10 " )
2 " )
4
(
24 (
)
Old
2
3
13
9
100
Genera
known
in 1929
!»
I 26
28 (15 new)
20 (11 new)
135 (35 new) 78
Division of Work. — The senior author, as intimated above, made it financially possible for his
co-laborer to devote himself wholly for two years to this study of the Brachiopoda, and also turned
over to him for use his collection and library. He then sketched out the plan of work and passed
on the brachiopod lore accumulated during a lifetime, and stimulated by association with E. O.
Ulrich, James Hall, John M. Clarke, and Charles E. Beecher. The bulk of the detailed results
were thus attained by the junior author, under the guidance of the senior author and of our colleague.
Professor Carl O. Dunbar, who was at the time himself engaged in a revision of the Pennsylvanian
brachiopods of the Nebraska region.
The study so carried on has led to departures from the older lore as radical as were those of
Hall and Clarke between the years 1 890 and 1 895. These results, we are fully aware, will in turn
have to face the test of new facts brought to light by later workers. Nevertheless we are content to
INTRODUCTION 3
send them forth as a contribution to the evolutionary history of the brachiopods — a study the
importance of which was well seen by Charles Darwin when he unavailingly appealed to the lead-
ing specialist of his time, Thomas Davidson, to take up the brachiopods from the standpoint of
descent through evolution.
Location of Specimens. — As indicated above, this memoir is based mainly on material in the
Schuchert Brachiopod Collection in the Peabody Museum of Yale University. Specimens from
this collection have the letter S preceding the catalogue number (e. g., S 12). Specimens from other
collections in the Peabody Museum have the letters Y.P.M. following the catalogue number
(e. g., 120 Y.P.M.).
Technique. — In any critical revision of brachiopod genera it is paramount to know every detail
of the shells with which one is dealing. It is not difficult to find brachiopods in the field showing
the exterior, as free specimens or as molds in the rock; it is far more difficult to find free valves
with the interiors cleaned by nature, or as sharp molds. In the Schuchert Collection by far the
majority of the specimens are free individuals showing the exterior in good detail. This is a con-
sequence of the collection's being a composite one, built up of choice material brought together by
many skilled collectors. To be sure, there are great numbers of interiors in the collection, but not
of every genus. Accordingly, it became necessary to prepare interiors for a large number of the
genera that we studied. We were able, by various methods, to obtain the essential details of the
internal anatomy of every genus with which we worked. There is really no reason why, given
plenty of material, the interior of every genus of brachiopods should not be known.
The following methods were used in securing the internal anatomy of the brachiopod shell:
(1) etching, (2) cleaning with needles, (3) burning, and (4) serial sectioning (Zugmayer process).
( 1 ) When specimens of dissociated valves are filled with shale or clay, the internal surface
may be obtained by placing on the specimen lumps of potash and allowing the chemical to deliquesce.
The potash then attacks the shale and loosens it. This method is not always satisfactory, however,
because the potash usually attacks the substance of the shell, producing a white efflorescence which can
be got rid of only by the use of dilute acid. This means the loss of some details of the surface, and
is undesirable when other methods can be pursued.
When shells are silicified they can as a rule be freed from the limestone by dissolving the
matrix in dilute hydrochloric acid. Care must be taken, however, to use exceedingly dilute acid,
otherwise the shell itself may be attacked or be disrupted by violent ebullition of gas. It is not usual
to find shells properly silicified, but when one does, they show the internal characters exceedingly
well
(2) More laborious, but more satisfactory by far, than the use of potash is the careful manipu-
lation of a needle accompanied by a dentists' drill. With this combination the interior of most
brachiopods can be obtained. We found it most satisfactory to cement the specimen in plaster of
paris and then excavate the interior with a needle, carrying on all the manipulations under a binoc-
ular microscope. This method requires time and patience, but when one has prepared successfully
the interior of a rare shell, he is amply repaid for the expenditure of one-half to a day's tirne. In
some instances we took specimens in which both valves were in contact and secured the interior
of one or the other valve, depending on which we wanted. If the ventral interior was desired, the
dorsal valve was ground off, the remaining one cemented in plaster and excavated by the use of
a needle. The majority of the interiors figured in this memoir were prepared by the use of a needle.
(3) John M. Clarke and S. S. Buckman were the pioneers in the use of the method of burn-
ing or calcining the shells of brachiopods. This method was used by the latter to good advantage
in his splendid treatise on the Burma brachiopods. Buckman heated the shells to redness and
dropped them into water, the shell spalling off in the process. We found, however, that the drop-
ping of the shells into water was disastrous to the specimen in certain types of matrices. It is more
satisfactory to heat the shells in air to redness, and, after cooling, to scrape the shell off with a sharp
needle The process of heating softens the shell and allows it to be removed rather easily. Natural
casts of interiors made by this method, and internal molds in general, have their limitations; they
are excellent for details of the muscle-scars, but it is usually difficult to get sharp impressions of the
cardinalia, which are best seen in free valves. ^-«.,-
'^•LICR/
\^
4 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
(4) We used serial sectioning as a last resort, since this method usually means the total loss of
the specimen. We developed a method, however, in the study of the pentameroids, by which we
were able to save a thin section of the shell as a result of serial sectioning. This method is described
in the chapter on the Pentameroidea, as we were not obliged to use it to any great extent in the study
of the Orthoidea; it is of great aid among the rhynchonellids, spiriferids, and terebratulids, where
the interiors are of hard cemented rock.
Species Lists.— Throughout our paper we have listed under each genus the known species
which we believe have the structure of the genus as exhibited by the genotype. In some instances
our lists are complete, in others they are quite incomplete. Among the Cambrian brachiopods, for
example, there are a goodly number of species left unplaced because there was no hint of the internal
structure in the specimens available to us, and we would not place any of the species unless we could
feel reasonably sure that our reference was correct. Our lists are incomplete also because we made
no systematic attempt to track down in the literature all of the species of the Orthoidea and Pentam-
eroidea. Although this might have been desirable, we would doubtless have had to leave a large
number of these unplaced, too, because of lack of material or inadequate descriptions and figures,
particularly in the older literature. Therefore we placed only the species that came under our direct
observation. Some familiar species we left out because we could not establish any substantial generic
reference for them. An example is "Orthis" eminens, which has been placed by various writers in
Rhipdomella or Dalmanella, but belongs to neither. It appears to be closest to Idtorthis in internal
structure but varies too notably to be placed there. It appeared to us better to admit honestly that
we did not know what to do in certain instances. After us there will be many readjustments and many
new genera will ultimately gather home the flocks we have left to wander.
Genetic Lines. — A note regarding the diagrams of generic evolution which appear in the dis-
cussion of the families is necessary. These diagrams are designed to be suggestive and not final.
There is probably only one family described by us whose evolution has been fairly well established,
and that is the Schizophoriidas. But there are difficulties even here: we do not know the Middle
Ordovician (Chazy) progenitor of the group, nor do we know definitely the origin of Enteletes,
whether directly from Schizophoria or indirectly from that genus through Orthotichia. Our family
Plectorthids can be traced to Finkelnburgia and possibly to Orusia, but the antecedents beyond
those genera we can not find. It must be borne in mind that the late Cambrian and early Ordovician
brachiopods are virtually unknown and that here occur the genera that bridge the genetic gaps
between the Middle Ordovician (Chazy) and the Upper Cambrian. It might be suggested, too,
that the Chazy brachiopods are none too well known. Accordingly we find ourselves without sure
footings among the primitive brachiopods upon which to build our evolutional structure. It is there-
fore unwise at this time to link the known Cambrian forms with those of later time.
We might again cite an example. It has been maintained by some writers that the genus Billings-
ella gave rise to the Strophomenacea, and Eostro-phomena, a Lower Ordovician shell, has been
indicated as the forerunner of that great division. We now see that Eostrofhomena is an orthid.
Furthermore, genuine Strophomenacea are not known till Middle Ordovician (Chazy) time.
At most, what we are trying to do is to show that the indicated evolution is structurally possible,
but we can not say that our scheme represents the actual course of evolution. Our genera are, there-
fore, rather iceloplasmic types^ having the structure capable of producing the evolution indicated, but
this does not necessarily define the actual course of brachiopod genesis.
Acknowledgments. — During the progress of our work it has often been necessary to call on
specialists and others in order to see more material and to obtain advice along various lines. _ Every-
where we turned for assistance we have been aided very cheerfully. Miss Helen M. Muir-Wood
of the British Museum kindly loaned us an excellent series of specimens of the genus Schizophorella;
Doctor A. H. Westergaard of the Geological Survey of Sweden, at Stockholm, sent us for study
specimens of "Dalmanella" testudinaria which enabled us to make the astonishing discovery that the
chosen type of Dalmanella was different generically from all other American species referred to this
genus except one. Doctor Westergaard also loaned us an exquisite series of Orthis punctata showing
^ Kirk, Amer. Jour. Sci. (5), vol. 18, 1929, p. 345.
INTRODUCTION 5
the interior from youthful to old-age stages, which made it possible for us to understand the devel-
opment of the pseudospondylium. Doctor Chester A. Reeds of the American Museum of Natural
History sent us the Conrad types of Pionodevia, and through Doctor H. W. McGerrigle of Dart-
mouth College we were able to study a good series of Clarkella, Syntro-phina, and Finkelnburgia
from the Phillipsburg region of Quebec. Doctor E. M. Kindle of the Geological Survey of Canada
permitted the study of Billings' types of Orthis electra, now the types of our genus Archceorthis.
Professor Paul H. Dunn of Miami University helped us with material of Eridorthis. Through Pro-
fessor Percy E. Raymond, the Museum of Comparative Zoology of Harvard College loaned us a
collection of European brachiopods particularly rich in representatives from the vicinity of Lenin-
grad. Doctor B. B. Bancroft of the Sedgwick Museum, Cambridge, England, and Doctor A. Opilc
of the University of Tartu, Estonia, sent us very perfect and interesting specimens of their new
genera which are not well known in this country, and many of these specimens have been figured
by us.
Through the courtesy of Doctors R. S. Bassler and C. E. Resser of the United States National
Museum the junior author was allowed to study the incomparable collection of Cambrian brachiopods
there preserved. Doctor E. O. Ulrich of the United States Geological Survey and the National
Museum loaned us some of his choice specimens of the very rare genera Mcewanella, Deltatreta,
and Finkelnburgia. Through Miss Winifred Goldring of the New York State Museum we had
access to specimens of the strange genus Australina, which we were able to determine definitely as a
representative of some division of brachiopods other than the Dalmanellidas where the senior author
had previously placed it.
To Miss Clara Mae LeVene we are deeply grateful for her patient and exhaustive labors on
our manuscript, to Mr. Percy A. Morris for assistance in the preparation of the photographs and
figures, and to Doctor J. B. Knight, research associate in the Peabody Museum, for the generous loan
of instruments used in preparing fossils.
Finally, special thanks are due our colleague. Professor Carl O. Dunbar, who has been our
patient advisor all through this work, and on whom the junior author has tried out most of our diffi-
culties relating to the interpretation of the structural details that we have observed.
PART I. BRIEF DEFINITIONS OF BRACHIOPOD TERMS'
Adductor muscles (pi. A, figs. 4, 13). — ^The muscles that close the shell. In the Protremata
and Telotremata these muscles are inserted in the ventral valve, one on either side of the central
axis, between the diductors {q. v.). In passing to the dorsal valve they divide into four, and pro-
duce in that shell the two pairs of principal scars known as the anterior and posterior Adductor
SCARS.
Adjustor muscles. — Included in the pedicle muscles, q. v.
Adventitious deposit (pi. A, figs. 7, 10).— Extra fibrous shell substance deposited by the
mantle on the inside of the shell, filling up cavities and irregularities of the surface. By deposition
of such adventitious shell in the umbonal cavities, the dental plates may be obliterated.
Anacline. — See Pt. Ill, Interareas, and t. fig. 1.
Anterior. — ^That portion of the shell in front of the hinge region, away from the beaks.
Apical plate (pi. 23, fig. 9). — A small flat structure situated in the apex of the delthyrium
and flush with the interareas. To the under side of it probably was attached the pedicle. This plate
is not a relict of the deltidium.
Apsacline. — See Pt. Ill, Interareas, and t. fig. 1.
Area. — See Interarea.
Articulation. — ^The locking together of the two valves, effected in the main by the teeth of
the ventral valve moving in sockets in the dorsal valve, but further assisted by the brachial parts
(brachiophores) articulating with the ventral valve, at least in orthoid genera.
Brachial valve. — See Dorsal valve.
Brack idia. — Calcareous brachial supports in the spire- and loop-bearing brachiopods.
Brachiophores (pi. A, fig. 7; pi. 4, fig. 29).— Plates that bound the notothyrial cavity (q. v.)
in the orthids. More commonly known as socket-plates or brachial apparatus. In a few genera,
Brachiophore processes are seen to extend from the distal extremity of the brachiophores, and to
them were undoubtedly attached the brachia. The brachiophores may be the homologues of the
crural bases of the rhynchonellids, but in any event are more primitive than the latter.
Brachiophore supports (pi. A, fig. 14j pi. 1 1, fig. 26).— Plates attached to the dorsal face
of the brachiophore, and used to strengthen the latter. Known in Hebertella and Schizofhoria.
Camera. — See Cella.
Cardinal angles. — ^Angles formed at each of the extremities of the hinge between it and the
forward extension of the shell.
Cardinal area. — See Interarea and Palintrope.
Cardinal process (pi. A, figs. 4, 6, 10).— A median unpaired process, lying immediately
on the inner side of the dorsal umbo, and serving for the attachment of the diductor muscles.
Cardinalia. — Processes near the posterior or cardinal margin in the interior of the dorsal
valve, connected with articulation, muscle attachment, and attachment of brachial supports. (After
Thomson 1927.)
Catacline. — See Pt. Ill, Interareas, and t. fig. 1.
Cella (pi. 24, figs. 21, 26). — A small, inverted, V-shaped chamber beneath or ventrad to the
ventral median septum of Parenteletes. A similar structure occurs in Dayia, Cyclosfira, and
Camarium (Merista).
Chilidial plates (pi. 16, fig. 22). — Discrete plates, one on either side of the notothyrium, and
partially closing it.
1 For further discussion of many of these terms, see Part III, Morphology.
DEFINITIONS OF BRACHIOPOD TERMS 7
Chilidium (pi. A, figs. 4, 6, 7). — ^The covering of the notothyrium, the dorsal equivalent of
the ventral deltidium.
Commissure. — The boundary line between the anterior and lateral margins of the valves. It
may lie in a single plane or be flexed to a greater or less degree. See Plane of commissure and
Rectimarginate.
Convexity. — In describing the convexity of a brachiopod, the dorsal valve is named first; this
is for the sake of making comparisons always in the same direction, namely, from dorsal above to
ventral below. For example, Valcourea defecta would be spoken of as convexo-concave and Orthis
callactis would be termed concavo-convex. See Resupinate.
CosTA (cost/-e). — A coarse radial rib on the external surface. When a species has costx that
are simple and distant it may be called Paucicostate; when the costas are numerous and increase by
bifurcation or implantation it is Multicostate; and when they are bundled into fascicles the term
Fascicostate may be employed. Costas may be angular, subangular, or rounded.
Costella (costell^). — Fine external ribs such as those of Dalmanella. The same prefixes
may be used in connection with this term as with costje. Extremely fine radial lines, such as those
on the costs of Orthis s. s., may be termed Parvicostell^.
Crura (sing. Crus). — Processes in the dorsal valve of the Telotremata to which are attached
the fleshy brachia or the brachidia. See Brachiophore.
Crural fossette (pi. A, fig. 15). — An excavation on the inner face of the tooth of the ventral
valve which receives the postero-ventral edge of the dorsal brachiophore in the articulation of the
shell.
Crural plate. — A general term commonly applied to the brachial processes of the orthids,
strophomenids, and rhynchonellids, without regard to detailed structure, function, or homologies.
Cruralium (pi. 18, fig. 17; pi. 25, fig. 24). — The dorsal equivalent of the ventral spondylium
{q. v.). When the brachial lamellse unite with a median septum, the whole structure is called a
Cruralium simplex; when the brachial plates remain discrete, do not have the muscle attachments,
and do not unite with a median septum (as in Porambonites), the structure is known as a Discrete
CRURALIUM; and when there is no median septum, it is called a Sessile cruralium.
Deltarium. — See Deltidial plates.
Delthyrial cavity (pi. A, fig. 15). — The ventral umbonal cavity bounded by the dental
plates.
Delthyrium. — The triangular aperture which transects the ventral interarea medially, and
through some portion of which the pedicle passes. It has also been termed the Fissure. The del-
thyrium may or may not be closed by a deltidium or deltidial plates. Its equivalent in the dorsal
valve is the notothyrium {q. v.).
Deltidial plates. — In Telotremata, two plates growing medially from the walls of the del-
thyrium after neanic growth. These often unite medially, closing the delthyrium more or less com-
pletely. When united, they make a Deltarium = symphytium of Buckman, pseudodeltidium of
Schuchert (not Bronn or Walcott). In Protremata, similar plates are at times developed and these
are called Lateral plates (q.v.).
Deltidium (pi. A, fig. 2). — An independent, more or less strongly arched plate in the ventral
palintrope or cardinal area in many Protremata, growing from the apex toward the hinge-line and
partly or completely covering the delthyrium. It is always delimited from the mterarea by grooves.
It is characteristic of primitive shells, and is formed by a flap of the ventral mantle.
Dental plates or Dental lamell.^ (pi. A, fig. 5).— Vertical or nearly vertical plates associ-
ated with the teeth of the ventral valve, usually uniting the palintrope to the floor of the valve, and
bounding the delthyrial cavity. They are separated from the walls of the shell by the umbonal cavi-
ties When the latter have been filled by adventitious shell, the dental plates become Obsolete. A
spedal type of dental plates seen in Hesferorthis, etc., is called Receding dental plates. These
are ridges along the ventral surface of the palintrope, which finally reach the mner surface of the
valve at the posterior of the shell only.
g GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Dental sockets. — Excavations in the dorsal cardinal margin in which the teeth of the ventral
valve articulate. The inner wall of the socket is bounded by the brachiophore in orthids. Acces-
sory DENTAL SOCKETS, SCe SoCKETS.
Denticles (pi. 10, fig. 21). — Small processes on the posterior surface of the dorsal socket
which are inserted into the accessory sockets in the ventral teeth.
DiDucTOR MUSCLES (pi. A, fig. 13). — The muscles that open the valves. In the Protremata
and Telotremata the principal pair 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 posterior portion of the cardinal
process. There is another pair of small accessory diductor muscles, but scars of these are seldom
shown in fossil shells. When present they are situated just behind the adductor impressions.
Dorsal direction. — Toward the dorsal valve, at right angles to the plane of the commissure.
Dorsal median ridge (pi. A, figs. 7, 8). — A low axial thickening on the dorsal interior of
most orthids and rhynchonellids. See Median septum.
Dorsal valve. — Usually the smaller valve, and the one to which the brachia are always
attached. Brachial and Socket valve are other terms less often used.
In this work we shall stand by the biological usage of naming the two valves ventral and dorsal,
a position that is fortified by the work of Conklin,* which showed, from the orientation of the embryo,
that the valves are truly ventral and dorsal, although in nature the adult shells usually have the
ventral valve uppermost.
Duplex spondylium. — See Spondylium simplex.
Endopunct/E. — See Punct;e.
Euseptum (pi. A, fig. 5). — ^A ventral median ridge formed by the inner shell layers rising
into a septum that usually makes the seat of attachment for the adductor muscles.
ExopuNCT^E. — See Punct^.
Fascicostate. — See Cost^.
Fascicostellate. — See Costell^.
Fil;e. — Fine elevated concentric lines.
Fold (pi. 24, figs. 5, 19). — A broad median external undulation or plica that may be situated
on either the dorsal or ventral valve, hence dorsal or ventral fold. It is more commonly on the
dorsal valve. Its counterpart is Sulcus, q. v.
Foramen. — See Pedicle foramen.
FossETTE. — See Crural fossette.
FuLCRAL PLATES (pi. A, fig. 14). — Small concave plates attached to the outside wall of the
brachiophore support or brachiophore and the inner wall of the shell. These serve to define the
sockets and strengthen the brachiophore supports.
Genital markings (pi. 12, figs. 20, 24). — Radial markings, ridges, or pits within the
posterior portion of the visceral space, indicating the position and extent of the genitalia, and used
for the attachment of muscles which fix the ovarian bodies. Best seen on the ventral shell.
Gerontic. — Signifying old age.
Hinge-line. — ^The line along which articulation takes place.
Hypercline. — See Pt. Ill, Interareas, and t. fig. 1.
Interarea. — The posterior plane or curved surface lying between the apex and the line of
valve junction. Formerly called cardinal area.
Lateral areas. — The parts of the valves on either side of the median axis or on either side of
the fold and sulcus.
^ Conldin, E. G., The embryology of a brachiopod, Terebratulma seftentrionalis Couthouy. Proc. Amer. Philos. Soc.,
vol. 41, 1902, pp. 41-76.
DEFINITIONS OF BRACHIOPOD TERMS 9
Lateral plates (pi. A, fig. 11). — External marginal plates restricting the delthyrium and
seen only in certain orthids and pentamerids. These discrete plates appear to be formed in exactly
the same manner as deltidial plates, q. v.
Lateral septa. — See Median septum.
Median ridge. — See Dorsal median ridge, and Median septum.
Median septum (pi. A, figs. 5, 9). — ^A longitudinal vertical plate between the ventral muscles.
Lateral septa are rarely developed between the muscles of the same valve, but are more often
present when spondylia are developed.
Multicostate. — See Cost;e.
Muscle impressions. — Marks of muscle attachment on the shell, further subdivided as
follows: Muscle-scar, a more or less well defined area representing the final or last muscle attach-
ment. Muscle-track., the path due to the forward migration of the muscles during growth.
Myophore (pi. 9, figs. 3, 20; pi. 17, figs. 31, 32). — The rugose surface of muscle attachment
on the cardinal process. See Shaft.
Neanic. — Signifying youth, or the stage in which specific characters begin to develop.
Nepionic. — Designating the smooth-shell stage succeeding the protegulum.
NoTOTHYRiAL PLATFORM (pi. 1, fig. 23). — The thickened shell matter in the umbonal interior
of the dorsal valve between the brachiophore plates. It is the seat of diductor muscle attachment
in primitive brachiopods not yet possessing a cardinal process; in other shells it is the place where
the vertical cardinal process arises. This platform has also been called the Pseudocruralium.
Notothyrium and Notothyrial cavity. — The dorsal counterpart of the ventral delthyrium
and delthyrial cavity, q. v.
Orthocline. — See Pt. Ill, Interareas, and t. fig. 1.
Palintrope. — The antero-ventrally or antero-dorsally directed shelf developed at the posterior
end of the dorsal and ventral valves due to the progressive migration of the hinge margin in its
growth. Formerly called cardinal area.
Pallial sinuses (pi. A, fig. 13). — Extensions of the coelomic cavity into the mantle. Impres-
sions of these sinuses are not uncommonly seen on the inside of the shell as low ridges or shallow
furrows. There are usually two main trunks in the ventral valve and three in the dorsal.
PARVICOSTELLiE. See COSTELL^^
Paucicostate. — See Cost;e.
Pedicle callist (pi. A, fig. 13). — A callus of shell substance at the internal apex of the ventral
valve between the dental lamellas, to which the postero- ventral surface of the pedicle was attached.
Pedicle foramen (pi. A, fig. 3). — A small or large round perforation at the apex or elsewhere
through the deltidium for the protrusion of a small pedicle; with age, it may become large by abra-
sion. When this foramen is absent, the pedicle emerges between the deltidium and chilidium, or
these coverings may completely close the delthyrium and notothyrium, in which case there is no
known functional pedicle.
Pedicle muscles. — ^The muscles that retract the pedicle. In the Protremata and Telotremata,
one pair originates on the ventral valve at points just outside of and behind the diductors, and
another pair on the dorsal valve behind the posterior adductors (not known in orthids), while
the opposite ends of both pairs are attached to the pedicle. These muscles are also called the Adjus-
tors. (For adjustor scars, see pi. A, figs. 12, 13, 15.) Besides these, there is an unpaired muscle,
not known in early brachiopods, lying at the base of the pedicle, attaching it closely to the ventral
valve.
Plane of commissure. — The plane passing through the anterior commissure and the hinge-
line.
Platform. — This term should be retained as first proposed, for the elevated and thickened
muscle trace in the trimerellids. See Notothyrial platform.
10 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Plica. — See Fold.
Plicate (pi. 24, fig. 5). — Used of a shell that has undulations affecting both the interior and
outer surfaces. The primary ornamentation is superposed over the plications. Example: Enteletes.
Posterior region. — That portion of the shell back of the transverse axis and toward the beak,
or apex.
Procline. — See Pt. Ill, Interareas, and t. fig. 1.
Protegulum. — The initial shell of all brachiopods.
Pseudocruralium. — See Notothyrial platform.
Pseudoresupinate. — See Resupinate.
PsEUDOspoNDYLiuM (pi. A, fig. 11} pi. 18, figs. 13, 14, 18, 24). — ^A callus resembling a
spondylium, developed in some shells beneath the muscles of the ventral valve and confluent with
the inner lower surfaces of the dental lamellse. Examples: Glossorthis, Finkelnburgia, Linoporella.
Punct;e. — Any minute perforations of the test. Punctse are here divided into two kinds:
Endopunct;e, perforations of the internal shell layer, never reaching the exterior unless the thin
outer shell layer is abraded; these are the typical punctse of the terebratulids and the Dalmanellacea.
ExopuNCT^, perforations that indent the external surface of the shell but do not pass through to the
interior; well developed in Paurorthis, Hebertellay and Valcourea.
Recti marginate. — Having a straight anterior commissure.
Resupinate. — ^A condition wherein the relative convexity of the two valves is reversed, the
convex ventral valve of the early growth stages becoming concave and the concave dorsal valve
becoming strongly convex, producing thereby a convexo-concave shell. Strictly speaking, this con-
dition has never been attained by the orthids, but a few genera simulate it closely, e. g., Valcourea,
Dinorthis, Plcesiomys, Hebertella, etc. This latter condition might be called Pseudoresupinate.
Rostrate. — Having a long beak, produced by narrowing of the hinge-line, as in Conchidium,
Cycloccelia, etc.
Septum. — See Dorsal median ridge, and Median septum.
Sessile cruralium. — See Cruralium.
Sessile spondylium. — ^A spondylium which rests directly on the floor of the valve without the
support of a median ridge. Nearly attained in Pahlenella. See Spondyloid.
Shaft. — The stalk or shaft of the cardinal process, which bears the myophore or seat of
diductor muscle attachment.
Sinus. — See Sulcus.
Sockets. — ^There are sockets for articulation in both valves. In the ventral, there are two
kinds associated closely with the teeth: Accessory dental sockets, on the outside of the teeth; and
Crural fossettes or sockets {q. v.) on their inner sides. See t. fig. 2.
Spondylium (pi. A, fig. 9). — A spoon-shaped plate, terminating more or less freely, located
in the apex of the ventral valve of various stocks of articulate brachiopods. This plate serves as the
seat of attachment of the muscles. It is supported by a more or less elevated, long or short, median
septum. Kozlowski has recently shown (1929) that the spondylium may be divided into three
different types, as follows:
Spondylium discretum (pi. 14, fig. 20). — Here the dental plates do not converge and unite
medially, but extend directly to the floor of the valve. Strictly speaking, this is not a spondylium,
but such a condition of the dental plates is primitive and deserves a designation. This structure occurs
mostly in orthids. Also see pi. 18, figs. 13, 14, 1 8.
Spondylium duplex. — See below.
Spondylium simplex (pi. 7, fig. 31). — ^A term applied by Kozlowski to the type of spondy-
lium in CUtambonites, in which the dental plates and the vertical septum are united into a single
piece. This type is in contrast to the Spondylium duplex of Pentamerus (pi. 25, fig. 43), which is
composed of two pieces each of which is borne on a basal septum. See Pseudospondylium.
DEFINITIONS OF BRACHIOPOD TERMS 1 1
Spondyloid (pi. 14, fig. 8). — In this condition the dental plates are so thickened on their inner
basal sides that the added testaceous deposit grows together and simulates a spondylium. This con-
trasts with the pseudospondylium, which is formed by a callous thickening on the floor of the valve.
Example : Porambonttes.
Stride. — Interspaces between costx and costellae. This term has been much abused and its
current use for a radial rib is incorrect.
Sulcus (sulcate). — A median depression in the convexity of the shell, the opposite of a fold
or plica. Replaces the term sinus.
Teeth (pi. A, fig. 2). — The two articulating processes of the ventral valve. There are also
accessory small teeth in the dorsal valve in many brachiopods, which are here called Denticles
{q.v.).
Transverse axis. — A line through the widest part of the shell from left to right.
Umbonal cavities. — Chambers separating the dental lamellas from the walls of the valve.
Uniplicate. — A term applied to the anterior commissure when there is a fold in the dorsal
valve opposed by a sulcus in the ventral valve. Unisulcate is the reverse condition.
Unisulcate. — See Uniplicate.
Ventral dental sockets (pi. A, fig. 2). — Small sockets in the teeth of the ventral valve next
to the hinge margin. Into these articulate small denticles on the outer wall of the dental socket.
They are also called Accessory dental sockets. See Denticles.
Ventral valve. — The shell situated on the ventral side of the animal, and in articulate forms
having the teeth on each side of the delthyrium. Usually the larger and deeper of the two valves.
Pedicle and Dental are other names applied to it.
PART 11. PRINCIPLES OF MORPHOGENESIS OR EVOLUTION
OF FORM
NEED OF TAXONOMY
W. T. Caiman, keeper of zoology in the British Museum of Natural History, says in his recent
address, "The Taxonomic Outlook in Zoology,"^ that in the days of Linnasus (1758) an experi-
enced zoologist might have known the 4370 living species then named, but that to-day, when over
700,000 kinds have been described, the great need for the specialist is apparent. "Nothing can alto-
gether replace that instinctive perception of affinity that comes from lifelong study" (p. 280). He
goes on to say, however, that there can no longer be a "complete description" of a species, as was
thought necessary by the older systematists, but that what should be done is to enumerate the essen-
tial characters in which it differs from similar forms of the genus. This address stimulated the
editor of Nature to remark:" "There is a strong tendency to deprecate the value of taxonomy and
to ignore its claims to a fair share of the attentions of scientific workers."
All animal life is subject to change as soon as the normal conditions of the environment change,
and, according to Baker,^ "there is evidence that this change may not always be a matter of long years
but may take place in the space of five or ten years. This statement is abundantly supported by
experimental evidence. The necessity for giving names to these incipient species [ecological variants]
is, therefore, obvious."
The same writer has shown elsewhere that molluscs in streams and lakes change into different
forms in the course of one or two human generations, due to alterations in the environment brought
about by man. If subspecies change thus quickly, paleontologists with their superabundance of time
as recorded in the geological formations must expect generic change from zone to zone, and yet no
genus should be made on the basis of age alone, since a genus is to be founded on the ensemble of
characters as seen in one or more species.
It is said that Linnsus described in the tenth edition of his "Systema Naturae" (1758) one
genus and forty-two species of Homoptera. Now Professor Z. P. Metcalf, a student of this "small
order of insects," estimates that there are known no fewer than 30,000 species distributed in 500
genera, and it is thought that there will eventually be three times as many. In this group, therefore,
and in many others, it is only too plain that there can be no stability in nomenclature for a long time
to come. It does not further our subject, however, to complain of the multiplicity of Nature and the
consequent difficulties in attempting to give the proper name to each species under the Rules of
Zoological Nomenclature. It is the duty of every systematist to do the best he can and let the future
take care of itself. In other words, the grumblings of the anatomists, physiologists, experimental
biologists, etc., are all beside the mark, since the systematist is only trying to classify what he sees in
an ever changing world, namely, to determine the lines of organic descent to the uttermost ramifica-
tions possible in a stated classification that is, after all, more or less artificial. Morphology will
grow and taxonomy will change as long as there are great numbers of unknown species and genera.
RISE OF BRACHIOPOD GENERA
Fabius Columna in 1616, and Martin Lister in 1678, were the first to describe brachiopods,
calling them Conchie anomice. Grundler in 1774 was the first to give a good illustration of a living
brachiopod, TerebratuUna cafut-serfentis. Cuvier in 1792 and 1802 distinguished brachiopods from
Acephala, and in 1805 gave the class its name Brachiopoda. In 1818 Lamarck knew 5 genera,
^Science, n. ser., vol. 72, 1930, pp. 280-284; Nature, vol. 126, 1930, pp. 440-444.
-Nature, vol. 126, 1930, pp. 461-462.
^ F. C. Baker, On Genus and Species Making. Science, n. ser,, vol. 72, 1930, pp. 37-39.
PRINCIPLES OF MORPHOGENESIS 13
including among them the operculate coral Calceola. In 1849 King recognized 49 genera in 16
families, and Bronn in 1862 listed 51 genera. Hall and Clarke (1892-1894) added 58 new genera
and in their "Handbook of Brachiopoda" recognized 325 genera or subgenera. By 1913 (Zittel-
Eastman) this number had grown to about 450, Buckman alone added 5 1 new genera of rhynchonel-
lids in 1914 and now there are at least 750 genera or subgenera in good standing, in addition to some
200 rejected names, many of which will doubtless be revived. Of these 750 genera, one only belongs
with certainty to the order Palxotremata, 50 (7 7o) are Atremata, 47 (6%) Neotremata, 234 (31 %)
Protremata, and 41 7 (55%) Telotremata. The Paleozoic has about 500 genera, the Mesozoic about
180, and the Cenozoic-Recent about 75.
THE GENUS CONCEPT
"To no human question is there an immutable and final answer." — Bather 1927
All paleontologists working to discern the genetic relations of fossils should study the Presidential
Address of F. A. Bather entitled "Fossils and Life," which was delivered before Section C of the
British Association for the Advancement of Science in 1920.'' This masterly address deals chiefly
with the philosophy of ancient life in relation to that now living under the influence of the environ-
ment— the leading influence making for genetic evolution as interpreted by both paleontologist and
neontologist. Bather says:
Like Botany and Zoology, Paleontology describes the external and internal form and structure of animals and
plants; and on this description it bases, first, a systematic classification of its material; secondly, those broader
inductions of comparative anatomy which constitute morphology, or the science of form. Arising out of these
studies are the questions of relation — real or apparent kinship, lines of descent, the how and why of evolution —
the answers to which reflect their light back on our morphological and classificatory systems (p. 61).
Paleontologists, unlike neontologists, are concerned with the "concept of time ... an orderly
and related succession, coextensive, in theory at least, with the whole history of life on this planet"
Since the days of Linnasus, biologists have sought for "natural classifications," but back of 1 859
these were more arbitrary than natural j with the publication of Darwin's "Origin of Species," how-
ever, it has become more and more possible to determine the genetic relationships, or the "blood-red
clue of natural afiinity."
Descent, then, is not a corollary of succession. Or, to broaden the statement, history is not the same as evolu-
tion. History is a succession of events. Evolution means that each event has sprung from the preceding one. Not
that the preceding event was the active cause of its successor, but that it was a necessary condition of it. For the
evolutionary biologist, a species contains in itself and its environment the possibility of producing its successor
(pp. 66-67). [Not until we pursue the "line upon line" method of paleontology shall we] have linked species into
lineages, can we group them into genera; not until we have unravelled the strands by which genus is connected
with genus can we draw the limits of families. Not till that has been accomplished can we see how the lines of
descent diverge or converge, so as to warrant the establishment of Orders (p. 70).
It is undoubtedly true, as Gertrude Elles points out in her paper, "Evolutional Paleontology,"'
that species and genera have too often been made by paleontologists in the laboratory without the
knowledge of the field, since the strata entombing fossils are the only preserved environments.
Furthermore, only too often are species and genera made on the basis of chronogenesis and not on a
proved genesis, and most of our genera with large assemblages of species are polyphyletic in origin.
The modern taxonomic trend based on evolution, as used by vertebrate paleontologists, is well
illustrated in the paper by H. F. Osborn bearing the title "Final Conclusions on the Evolution,
Phylogeny, and Classification of the Proboscidea. "" His viewpoint as to the value of the divisions
appears, however, to be an extreme one. Here we learn that Lydekker in 1886 knew of but two
* Rept. British Assoc. Adv. Sci., Cardiff meeting, 1920, pp. 61-86.
° Rept. British Assoc. Adv. Sci., Liverpool meeting, 1923, pp. 83-107.
•Proc. Amer. Philos. See., vol. 64, 1925, pp. 17-35.
14 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
genera, Elefhas and Mastodon, and that not so long ago all vertebrate paleontologists regarded the
Proboscldea as a monophyletic line. Osborn, according to his "phylogenetic classification," now
divides the "phylum" Proboscidea into at least 1 6 races or lines of descent. These he arranges into
4 orders, 5 families, 13 subfamilies, 28 genera, and 290 species.
A. Morley Davies in his preface to Sahni's very careful study of the terebratulids of the British
Chalk,^ a work wrought out along the best modern lines, has the following to say regarding the most
reliable generic characters in brachiopods:
Internal structure has proved the surest clue to relationship. Beecher and others based the classification of
the "long-looped" Terebratellids primarily on the form and development of the brachial loop; Buckman relied on
the muscle-scars in the case of the Jurassic Terebratulids and RhynchoneUids . . . Once the definite clue has been
found by which distinct stocks can be separated, it becomes possible to discriminate among the multitude of seem-
ingly random external variations. Some of them, either individually or, more frequently, in particular associations,
are definitely correlated with internal features and become diagnostic for particular stocks: they belong to what
Douville has termed . . . "static characters," persisting or slowly changing as evolution proceeds. Others are
among Douville's . . . "progressive characters," which go through a series of stages often parallel in different stocks.
It is these parallel developments, sometimes predominating over the static characters so as to eflrect a "convergence"
or homoeomorphy between different stocks that are most apt to mislead in hasty determination. Yet these progres-
sive characters may sometimes remain relatively static for a period, so as to serve provisionally or partially as
diagnostic characters (pp. v-vi).
When Sahni began his work there were 14 Upper Cretaceous species usually referred to Tere-
bratula. It now appears that not one of them belongs to this genus, his memoir defining 57 forms
in 12 new genera! This shows what must be done nowadays if one's work is to stand. One must
lift the covers and delve into the insides for the most reliable characters, and then carefully
examine the covers to discover the homoeomorphs and the significance of the slight changes in external
form.
Among students of brachiopods, none has more clearly set forth the best present methods of
determining the genus from the genetic standpoint than J. Allan Thomson.* He says:
Biological classification is now an attemft to exfress the degrees of affinity through descent [italics ours].
Instead of as few characters as possible being used to decide upon the generic position of a species, as many characters
as are necessary are employed to determine the relationship to other species. It has frequently been found that the
species grouped together under the older wide genera form homoeomorphous series of polyphyletic origin — u e.,
their similarity of form has been attained through different lines of dissimilar ancestors (p. 120).
According to Buckman (1918),®
Generic division will not be complete for scientific purposes until all polyphyletic series are rightly separated.
If the criteria now obtained are insufficient for this work of separation, it is the task for future observers to note
and to utilize other characters (pp. 133-134).
Thomson says, further:
Another change in the conception of the genus has resulted from a fixation of procedure in regard to the
law of priority ... It has become necessary to define each group not only by an assemblage of characters
originally proposed for it by its author, but by a type within the group with which the aflBnity of other members
may be compared — a species by a type specimen or holotype, a genus by a type species or genotype, a family by a
type genus (p. 121).
The genetic work of paleontologists must be guided, however, by the results of the neontolo-
gists, who have the living organisms to study in their entirety, but even among them the demonstra-
tion of lines of descent lies with the experimentalist. The work of these biologists shows how
deceptive "blood-relationship" may actually be. In this connection we may summarize here the con-
' M. R. Sahni, The Terebratulids of the British Chalk, Men. Paleontog. See., 1927, 1929.
* Brachiopod Morphology and Genera (Recent and Tertiary). N. Zealand Bd. Sci. and Art, Manual No. 7, 1927.
° The Brachiopoda of the Namyau Beds, Northern Shan States, Burma. Geol. Surv. India, Pal. Indica, new ser.,
vol. 3, mem. 2, 1917 (1918).
PRINCIPLES OF MORPHOGENESIS
15
elusions of the experimental ecologists H. M. Hall and F. E. Clements, as related in their monu-
mental monograph of 1923.'"
The basis of this monograph lies in "experimental and quantitative methods," and the experi-
ments to be conclusive "must extend over a long period of time." The authors have taken many
species of sagebrush and transplanted them from one environment into another, for example, inter-
changing one growing in a dry environment with another at home under wet conditions, and this
divergence in habitats gives opportunity for convergence in characteristics that "may sometimes
become practical identity." From these experiments they got results that led them to revise the
species of three genera as follows:
"Species"
up to
1923
Present divisions
Genus
"Sections"
"Major species"
"Sub-species"
"Minor
variations"
Artemisia
Chrysothamnus
Atriplex
125
88
103
4
4
?
2
12
47
29
40
37
120
44
70
Let us look a little more deeply into what these experimentalists have to teach us: Taxonomy
in biology, as the word indicates, is
the science of arrangement or system, and hence classification [of the organic entities. Naming of species is but the
first step in taxonomy, and even their description is not the whole of this science, since taxonomy should mean the
placing of the species in nature's lines of descent; or, stated in another way, the placing of them so as to give]
the best possible record of evolution and relationship. . . Absolute adherence to phylogeny should be the basis of
classification. . . Evolution is the process and phylogeny the record of descent.
Taxonomy leans most heavily upon morphology, and should bring to its aid not only histology
and physiology, but ecology and genetics as well.
Indeed, if it [taxonomy] is to reflect evolution as accurately as it should, it must regard physiological adjust-
ment as the basic process, and morphological and histological adaptations as the measurable results. This
means that the taxonomist of the future will think in terms of evolutionary processes, and will learn to treat his
morphological criteria as dynamic rather than static. [Quantitative ecology] traces the evolution of new forms in
minute detail, in so far as they arise through adaptation or variation, and consequently furnishes the only direct
evidence of relationship by descent. It affords the sole method of testing the manifold assumptions of existing
taxonomy, and provides the foundation upon which an objective and permanent taxonomy may be reared.
At present, however, taxonomy is more often the artificial expression of organic evolution; arti-
ficial because the science is as yet mainly one of personal opinions, and naturally this is more true in
paleontology than it is in neontology.
A natural classification must maintain as well as reveal the different degrees of relationship as expres-
sions of different stages of evolution, and it can do this most accurately with genera, sections, species, and variads,
where the lines of evolution are still in a condition conducive to experimental study . . . Since the limits of orders
and families are determined by genera, and the limits of genera by species, the whole problem resolves itself into
a statistical and experimental study of species and their evolution (pp. 3-6).
It is now common practice to regard the genus merely as a concept, and often as an artificial
one. Regarding this. Hall and Clements say:
This is doubtless true for those who regard the genus merely as a pigeon-hole, chiefly convenient for the
filing of new species. Such a view has its justification in the usual practice of making genera. . . It is not sup-
"The Phylogcnetic Method in Taxonomy. The North American Species of Artemisia, Chrysothamnus and Atriflex.
Carnegie Institution of Washington, Pub. No. 326. See also Clements, An Ecologic View of the Species Question. Amer.
Nat., vol. 42, 1908, pp. 253-264.
jg GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
ported by the evidence drawn from the methods of evolution or the record of phylogeny. To the student of evolu-
tion, the genus represents a certain characteristic portion of the line or field of specialization, and its existence is
as definite as that of the species which constitute it. . . As a consequence of the unrestricted play of personal opinion,
not infrequently aided by bias or carelessness, present-day taxonomy contains genera of every possible quality. Many
of these disappear completely when the test of evolution is applied to them (p. 6).
In paleontology, more than in neontology, genera are not uniform in differentiation; one stock
will vary but little while another will do so extensively. The genera with but one or a few species
will practically take care of themselves, but in those with a great number of species it is desirable to
name all the determined genetic lines, since evolution is the -process and taxonomy the method of
marking the phylogenetic lines of descent.
It is clearly recognized that the making of new genera is purely a matter of personal judgment at the present
time. . . There is no general agreement as to criteria, methods, or results, and the importance of evolution as
the one safe guide is rarely if ever considered. A knowledge of the genus as a whole, especially when it
includes exotic species, is too often lacking, and little or no thought is given to the phylogeny of the genus and its
sections in relation to genera of the same evolutionary stock. . . It would seem desirable to make rather more of
sections as records ... of specialization within the generic stock (pp. 8-9).
PALEOECOLOGY
The paleontologist should study his specimens and species primarily in the light of the field to
learn their environmental and biotic relations, since the strata of their entombment are the habitats
of fossils. We hold with Clements" that the habitat is
the motive force in the life processes of plants and animals, both as individuals and as communities. . . Ecology
deals primarily with processes and is inherently and universally dynamic . . . quantitative in method, beginning with
the habitat in which measurements are relatively simple, and running through individual and community responses
in which they are difficult (p. 369).
As paleontologists we should, therefore, be primarily interested in the habitat of fossils and of
our faunas, since organisms are "the end forms of responsive processes." In other words, it is seem-
ingly the environment in the main that brings on the organic responses seen in the development and
evolution of fossils; accordingly the paleoecology and the time factor of our faunas should be con-
sidered in addition to the morphology, in the making of species and genera.
In paleontology we have, it is true, but a small part of the whole of the habitat or of the bios,
and therefore it is "puzzling to understand how the demands of ecology can be met in a field where
processes have ceased. The readiest answer, and a fairly complete one, is afforded by the princtple
of uniformity of processes [italics ours], the use of which has made modern geology possible"
(p. 370). Accordingly we paleontologists can learn much from the ecologists, but most from the
entombing strata and the associations of the fossil faunas.
In the paleoecology of marine faunas, the main factors in conditioning the local biotas are the
interrelations of temperature, currents, nearness to shore, and nature of sea bottom; depth, chemical
content, and clarity of water; prevalence of bottom-living flora, nature of floating life, presence of
oxygen as food, penetration of sunlight, and interaction of life.
HOMCEOMORPHY
What has long been known as "parallel development" has had but scant notice among Anierican
students of brachiopod ancestry, Beecher'" being about the only one to pay attention to this principle
of mimicry of outer form; among the ammonites, however, the factor has been used a great deal
since its introduction by Alpheus Hyatt and its later acceptance by J. P. Smith, In Europe, Buck-
" Scope and Significance of Paleo-ecology. Bull. Geol. See. America, vol. 29, 1918, pp. 369-374.
^''C. E. Beecher, Some Correlations of Ontogeny and Phylogeny in the Brachiopoda. Amer. Nat., vol. 27, 1893,
pp. 599-604.
PRINCIPLES OF MORPHOGENESIS 17
man" applied the principle of parallel development for many years and chiefly among the Jurassic
ammonites and brachiopods; and his work and now ours show that external characters are not always
reliable for generic and phyletic studies. The application of this principle to the genera heretofore
described often plays havoc not only with them, but above all with our notions of their genetic
relationships.
This phenomenon of parallel development Buckman has called homceomorphy. It refers to
species nearly alike so far as superficial appearance is concerned, but unlike when particular structural details are
closely examined. It is the phenomenon of similarity in general with dissimilarity in details, [or] the tendency of
different genetic stocks to pass, quite independently, through similar phases of development . . . There is a ten-
dency among Jurassic Brachiopoda for independent non-plicate species to become multiplicate . . . and in the
Rhynchonellida: for the multiplicate (costate) to become spinous {A catithothyris) , and in certain cases a spinous
species may, with age, retrogress to lose spines.
The various species of different stocks may cither produce these developmental characters more or less con-
temporaneously, in which case such forms are called isochronous homaeomorfhs, or they may produce the char-
acters at different dates — a later form simulating an earlier one — in which case they are called heterochronous
homoeomorfhs (1901, pp. 231-233).
In the Jurassic of the Cotteswold district of England, in rocks of about the same date, there are
five independent developments of the same character among species of Terebratulidas. In nearly
related stocks much excuse may be made for errors in identification, but when such errors occur in
different families whose internal structural details are quite distinct, then "the confusion of two species
of these families under one name becomes serious" (p. 239). In fact, among the Jurassic terebra-
tulids and rhynchonellids, homoeomorphs are so common that "they may be said to form veritable
'traps' in the matter of identification" (p. 262).
Extraordinary homoeomorphs occur among the lobate terebratulids {Pygofe, Antinomia,
Pygites) and these are set forth by Buckman in his paper of 1906.
When Hall and Clarke prepared their monograph, the perplexing feature of homoeomorphy was
not clearly understood, consequently some genera were made on the basis of external form alone.
It has been found in the present work that no one character, either internal or more especially
external, can be relied upon in the identification of a genus, but that a genus must be character-
ized by a combination of these features. Among the orthids there have been convergences either
toward other orthid families or toward the external form of other groups. Productorthis of the
early Ordovician may be cited as a conspicuous example in its resemblance to the productids of the
late Paleozoic. There are three genera that ape the external form of Skenidium (Skenidioides,
Mystropkora, Hesperorthis? (merope)), and no fewer than seven have the external form of Piono-
dema (Mimella, Hemipronites, Doleroides, Deltatreta (some species)), Finkelnburgia, Schizopho-
rella, and early Schizophoria). _ .
Of interest in this connection is the accelerated development of the Ordovician Clitambonitids
of European Russia. Early species took the outside features of Strophomena, as in Gonambonites,
and some of these later aped forms of Hebertella. Hemipronites is much like a Pionodema, and
Vellamo has essentially the form of Hesperorthis. This diverse development occurred in a relatively
short time, and the whole stock perished with the Ordovician.
"S. S. Buckman, Homitomorphy among Jurassic Brachiopoda. Proc. Cotteswold Nat. Field Club, vol. 13, 1901,
^^' Brachiopod Homoeomorphy: Pygofe, Antinomia, PygiUs. Quart. Jour. Geol. Soc., London, vol. 62, 1906, pp. 433-454.
Brachiopod Homoeomorphy: Sfirijer glaber. Ibid., vol. 64, 1908, pp. 27-33.
PART III. MORPHOLOGY OF THE ORTHOID SHELL
The Orthoidea, to be described in more detail later, are a prolific stock of primitive Protremata
which persisted, according to our present knowledge, from the middle part of the Lower Cambrian
to the end of Permian time. They are rather primitive brachiopods, certainly the simplest of the
"articulate" stocks, and are characterized by more or less strongly developed interareas in both
valves. Primitively the delthyrium was covered by a deltidium, but in later progressive stocks this
structure was lost and the delthyrium was unmodified except for lateral plates or sporadic apical
plates.
This large suborder may be divided into two superfamilies on the basis of the shell structure,
whether fibrous and endopunctate or fibrous and impunctate. With these superfamily characters go
definite internal structures that are described in later pages.
Most of the Orthoidea described in this volume were, at one time or another, classified under
the generic term Orthis. Even as late as 1892, the date of Hall and Clarke's great revision, not
more than thirteen orthoid genera were in use. These authors showed that Orthis (1828) had
become a "dump" genus, and that it embraced at least 13 groups of shells with orthoid features,
besides 10 other old or new genera with related forms. They further blazed the way toward a
correct genetic understanding of Paleozoic genera, a method that has been followed ever since and
one that has guided us in turn in the present revision. Schuchert (1897) regarded Hall and Clarke's
"groups of Orthis" as genera, and in the Bibliography of Schuchert and LeVene (1929) there are
catalogued as of July 1928 52 accepted genera of orthoids. In the present volume we recognize
103 genera or subgenera (29 are new) constituting the superfamilies Orthacea, Clitambonacea, and
Dalmanellacea. These statistics show also the accelerated rate at which students of brachiopods are
discerning the genetic ramifications of the orthoids.
We believe that the present arrangement shows genetic relationships more clearly than here-
tofore and that our classification is more natural. But it can not be final as yet, and as years pass,
greater refinement in paleontologic and stratigraphic practice, along with the making of additional
collections from old fields and new, will enlarge our knowledge and tend to alter our scheme. We
hope, however, that our fundamentals are sound and that time will fill in either the details of the
scheme here presented or that of nature, since after all we are striving to learn nature's ways of
creation.
MORPHOLOGY OF THE EXTERIOR
ORIENTATION OF THE SHELL
In citing directions in or on a brachiopod shell, we shall use the terms dorsal and ventral, and
anterior and posterior (pedicle end). When discussing or figuring the posterior of a brachiopod, we
place the ventral valve down, as this is the correct biological orientation in the living animal. The
terms ventral and dorsal, therefore, indicate the vertical direction. In other words, these directions
are at right angles to the plane of the commissure, which is oriented by us in a horizontal direction.
The terms anterior and posterior, on the other hand, define directions parallel to the plane of the
commissure. These terms can therefore be applied with precision regardless of orientation, and thus
enable us to avoid the ambiguous terms front and back, down and up.
In describing the shape, contour, or profile of a shell, the writers are following Thomson and
Buckman in giving preference to the dorsal valve. This leads to the use of an unfamiliar term for
some shells which are commonly called concavo-convex, as Dinorthis; according to our usage this is
a convexo-concave shell. No matter which valve be taken for reference, any precise nomenclature
must recognize a convexo-concave stage as well as a concavo-convex one. For the sake of uniformity,
then, we have adopted the scheme used by these two authorities on Mesozoic, Cenozoic, and Recent
brachiopods.
MORPHOLOGY OF THE ORTHOID SHELL 19
COMMISSURES
When viewed from the front or anterior, the line of contact of the two valves is primitively
straight but in most derived genera it is more or less undulated. The same holds for the lateral com-
missure. Buckman has analyzed the flexures of the anterior commissure in Mesozoic rhynchonellids
and terebratulids, and has named nine stages developed out of the primitive straight or recti marginate
one. Among the orthids only two of the Buckman stages can be recognized, namely the sulcate and
uniplicate ones; both of these are the simplest of the modifications of the rectimarginate stage. In
the sulcate stage there is a single sulcus in the dorsal valve and a fold in the ventral, as seen m Aula-
cella, Enteletim, or Parenteletes. This type of commissure is rather uncommon. In the uniplicate
stage, these conditions are reversed and there is a single fold on the dorsal valve and a sulcus m the
ventral one. This is the more common condition and is well exhibited by Platystrofhia.
The conclusion that a fold and sulcus, or what amounts to trilobation, may have been developed
to facilitate the passage of the incurrent and excurrent streams of water used in the aeration of the
mantle and for food-gathering was advanced by Orton.
The tendency to develop a fold and sulcus is inherent in most Orthoidea but in some of them,
for example Hebertella, there is little stability as to which valve shall receive the sulcus. In some
stocks there is a marked reversion of the fold and sulcus, as in Eridorthis and Thiemella.
The common condition of the lateral commissure is a more or less strong flexmg toward the
dorsal valve. This is true of Valcourea and many other forms. The primitive condition is an
unflexed lateral commissure. A ventrally flexed lateral commissure is rare.
CONVEXITY
In the Cambrian, most shells are normally biconvex, as is the first shell growth in all brachi-
opods, and here it is also usual to find the ventral shell the more convex and the deeper. In later
forms the reverse condition is, however, of common occurrence and is independently originated over
and over again. . . ,. , . ,• • 4.1- * *u»
The great majority of brachiopods, viewed in longitudinal section, are biconvex, in that the
external curvature of both valves is convex, with the ventral the more so and therefore deeper than
the dorsal This common condition is called the lenticular or biconvex phase hy Buckman. More
rarely it is the dorsal shell that is more convex, and such forms can be described as dorsi-biconvex.
Resupination is a condition that has been reported commonly in the orthids, but unfortunately
the term has never been defined with any precision. Some authors regard brachiopod shells as
resupinate when the ventral valve has less volume than the dorsal. Atryfa wou d be a fine example
of such "resupination," but this is not what the term apparently meant originally. As applied by
Hall and Clarke, it embraces such shells as have the ventral valve concave and the dorsal convex.
According to this view, Valcourea and Strofhomena would be two unrelated examples of resupina-
tion However, there is a marked difference between Valcourea (and all other convexo-concave
orthids) and Strofhomena in the manner of the reversion of convexity in the ventral valve. In the
young stages of Strofhomena the ventral shell is convex and may carry a low fold; the dorsal valve
is essentially flat and may be gently sulcate. In later stages, however, the dorsal shell becomes
strongly ventricose and the ventral one deeply concave. In the convexo-concave stage of the
orthids, on the other hand, as in Valcourea and Hebertella, the dorsal valve never has the incipient
flat stage as seen in Strofhomena, and this affords an easy external way of distinguishing a stropho-
menid from an orthid homoeomorph. Consequently in this work we are restricting the term resufma-
tion to the condition seen in Strofhomena and its allies, while the other condition among orthids
may be called fseudoresupination.
^ Orton. J. H., On Ciliary Mechanisms in Brachiopods and some Polycha:tes. Jour. Marine Biol. Assoc., U. K.,
new ser., vol. 10, 1914, pp. 283-311.
20
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
INTERAREAS
According to Buckman/ the word area should be retained for general use, but interarea might be
used for "the area lying between the apex and the posterior line of valve-j unction — the cardinal
margin when there is a hinge, but at any rate the posterior margin."
Interareas, or what were formerly called cardinal areas, are usual in most of the members of
the order Protremata and especially in its most primitive stock, the Orthoidea. True interareas are
VEA/T/f'AL
^j
-■"
Anacline OrthocUne ApsacUne CatacUne Proclcne
(^ ^
fx
f^ypercline
An a c line Ort/iocCcne
Apsacllne
DORSAL
Fig. 1. — Diagram to show various positions of the interarea with relation to the plane of the commissure.
at times also well developed in the Telotremata, but never in the Atremata or Neotremata. When
a similar structure is present in the two last named orders it is due to holoperipheral growth or to
subsequent internal thickenings of the posterior margins, and in both these instances it is termed a
■pseudointerarea.
The interareas are, then, the plane or slightly curved surfaces of the palintrope, which is a
shelf, growing antero-ventrally or antero-dorsally according to the valve, and representing the pro-
gressive growth track of the hinge-line or plane of articulation. In describing or discussing the inter-
Brach. Namyau beds, 1917 (1918), p. 453.
MORPHOLOGY OF THE ORTHOID SHELL 21
area the writers consider the length of said surface to be in the same direction as the length of the
valve. The width of the interarea is the width of the hinge-line. The length of the interarea is thus
seen to be perpendicular to the width or perpendicular to the hinge-line. Ordinarily the ventral
interarea has the greater length.
An interarea may be plane or more or less markedly concave. It may be striated parallel to
its length or to its width or both, most interareas having striae of one kind or another. The hori-
zontal stris are commonly growth-lines; the vertical stria: may represent the growth tracks of acci-
dental irregularities that make, as it were, "teeth" along the hinge-line. More uncommonly the
interareas may be ornamented by fine elevated lines passing obliquely across the surface from the
beak, as in Polytcechia and Deltatreta (see pi. 6, fig. 14).
Another important feature of the interareas is their inclination from the plane of the commis-
sure, which may cause important modifications of the muscle marks, the dental plates, and the
cardinalia. When studying the inclination of the interareas the ventral valve is placed by us below
the horizontal and the beaks (arbitrarily) on the observer's left. The plane of the commissure is
then horizontal and the dorsal valve is up. In this orientation the following positions may be
observed :
Ventral valve: (a) anacline — ^between vertical and horizontal — ex. Orthis s. s.; (b) orthocline —
interarea horizontal — ex. Archceorthis ; (c) apsacline — between horizontal and vertical, 90°-180°
from erect vertical — ex. Hesperorthis; (d) catacUne — bent down 90" from the horizontal — ex. some
species of Clitambonites; (e) frocUne — interarea bent more than 180° from the vertical — ex. Din-
orthis {Retrorsirostra). In the dorsal valve the anacline, orthocline, and apsacline conditions are
recognized, and in addition, a hyfercline condition in which the interarea is rotated in an anterior
direction more than 90° (see t. fig. 1).
This nomenclature has the advantage of enabling the observer to state precisely the average or
individual inclination of either interarea, or, if he desires to be more specific, the number of degrees
subtended by the interareas or by either interarea and the horizontal. For example, one may define
a certain interarea as 30° apsacline.
Of interest in connection with the interareas is the presence of a narrow triangular space on
either side of the delthyrium or notothyrium. One side and the base of the triangle are formed by
the delthyrial margin and the hinge-line, respectively. The other side is defined by a line running
from a point outside of the tooth in the ventral valve, or the socket in the dorsal valve, to the beak.
This line represents a suture marking the progressive growth of the tooth and socket; it is the line
between new shell deposited on the tooth or in the socket against the old shell of the hinge-line
during the growth of the valve. In the Strophomenacea a similar triangular space has been called
the "secondary area," but in these shells, Derbyia, Orthotetes, etc., the outer or suture line is never
correlated with either the teeth or the sockets. It is very doubtful, then, if this better known and
much discussed secondary area of the Strophomenacea can be homologized with the similar-appearing
structure in the orthoids.
DELTIDIUM
Modifications of the delthyrium (deltidium). — ^The deltidial covering has for many
years received much attention from taxonomists, and the kind of covering is now thought to deter-
mine the order to which the different groups of brachiopod shells belong. The deltidium' is an arch
^According to Hall and Clarke (Pal. N. Y., vol. 8, pt. I, p. 189, footnote), "The term deltidium was proposed by
von Buch for the triangular flate which, in many articulate genera, covers more or less completely the space between the
outer margins of the dental ridges. This plate he describes a composed of two pieces which may either completely sur-
round the foramen {deltidium amflectens), bound it on its lower side {deltidium sectans), or the parts may be separated
for their entire length by the foramen (deltidium discretum). These component parts of the deltidium take their origm
from the margins of the triangular cavity beneath the beak, but in some genera, particularly in Strofhomena, Sfirijer, and
their allies, there is still another form of shelly plate which grows from the apex downward, and to this the term peudo-
deltidium was applied by Bronn. Among recent writers there has been considerable laxity in the use of these terms and it
is very doubtful if they can be applied with precision." _ , , .,.
In the present work we have preferred to follow Hall and Clarke, Beecher, and others in using the tenn deltidium,
applying it, however, to the cover composed of a single piece which restricts the delthyrium of the Protremata.
22 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
built with its piers against the angle formed by the palintrope and the dental plates. The piers are
usually buttressed against the track or axis formed by the growth of the tooth (see D, PI. A). The
attachment is strengthened by adventitious deposit laid over the whole inner surface and along the
sides of the dental plates and usually concealing all sutural contacts. Externally the interarea and
deltidium appear to be continuous and a suture is rarely visible unless the deltidium is somewhat
broken in. Shells having lateral plates in addition to the deltidium, however, commonly show
suture lines (see below) where the lateral plates overlap the deltidium. In the Clitambonitidas,
and in the older Billingsellidse as well, it is not uncommon for the deltidium to carry an axial stif-
fening along its inner surface. Hence the deltidium is a distinct plate, deposited in all probability
by the mantle, and is not a part of the palintrope or cardinal area. It is therefore not homologous
with the homoeodeltidium, as stated by Walcott and Schuchert — a change of opinion of very great
significance in classification.
In Hesferorthis the deltidium, or "apical plate" as it has commonly been called, is truly an arch
as in Clkambonitesy and its piers are also built against the sides of the delthyrial cavity. Since
Hesferorthis commonly has in addition lateral plates or extensions of the palintrope over the margins
of the delthyrium, the deltidium rarely is arched above the interarea. On the other hand, the del-
tidium of Hesferorthis has been homologized with the apical plate of Sfirifer. In S. arenosus and
many other forms of the genus Sfirifer {sensu lato), the so called apical plate is a callosity filling
the back end of the notothyrial cavity but rarely if ever attaining the level of the interarea. It is not
a deltidium as in Hesferorthis, and accordingly the various structures are not homologous, although
they probably serve the same purpose, that of pedicle attachment.
In a few of the punctate orthids or Dalmanellacea, apical plates have been noticed. They are
especially well developed in the Schizophoriidas and Parmorthis, but in no wise do they suggest a
deltidium as defined above. The structure is not an arch, but a flat plate flush with the interareas.
In Pionodema the anterior portion of the plate is concentrically lined and bevelled sharply below
the level of the interarea, suggesting that this small structure served the same purpose as the pedicle
callist. Mystrofhora areola also has a flat plate, but here it lies beneath the level of the interarea.
The deltidium may or may not be perforate at the apex. In some species of Billingsella there
is a minute perforation barely large enough for the passage of a hair. The resemblance of this apical
foramen to that seen in the Strophomenacea has been urged as one link of kinship between the two
groups. There are, however, no other anatomical or stratigraphic grounds to support this supposi-
tion, but whenever this apical foramen occurs it is assumed either to have functioned for the protru-
sion of a pedicle, reduced in these forms to a mere thread, like the byssal threads in some lamelli-
branchs, or to have furnished passage for the anus.
In one large group of shells, the Clitambonacea (pi. A, fig. 3), there is commonly a conspicu-
ous apical foramen which undoubtedly served for the passage of the pedicle. Distinct scars of pedi-
cle attachment have been observed in Deltatreta on the under surface of the deltidium and the floor
of the delthyrial cavity. In CUtambonites and Estlandia marginata, the foramen is sealed at matur-
ity by shell substance deposited within it (see pi. 8, fig. 8). This clearly means the loss of a func-
tional pedicle in later mature life.
Function of the deltidium. — The function of the deltidium in all brachiopods is as yet not
clearly understood, since our studies do not embrace the Strophomenacea wherein this structure has
its best development. From the fact that the deltidium is present in the oldest and most primitive
forms, we must conclude, however, that it had some functional importance to the brachiopod possess-
ing it. In the geologically younger species, where the deltidium is almost uniformly absent, life
without the structure was obviously possible. At first it appears difiicult to understand the value of
a structure such as the well developed deltidia in the Strophomenacea, where, by their forward
growth, the pedicle opening will be constricted more and more, and in some forms no opening at
all will be left for the protrusion of the pedicle {Strofheodonta of the strophomenids) ; whereas
in other genera the deltidium has been resorbed or not allowed to grow by a thickened and therefore
more vital pedicle. This problem is of great interest, and may be solved when the great line of
deltidium-bearing shells, the Strophomenacea, are restudied from this point of view.
Among the Orthacea we note, however, the interesting fact that in some species of Valcourea
MORPHOLOGY OF THE ORTHOID SHELL 23
the deltidium is a normal and well developed structure, while in other species of the same genus it
is completely wanting. In the species without a deltidium, there is a well marked pedicle callist or
triangular scar which probably is the seat of pedicle attachment (see pi. 10, figs. 19, 22, 24). This
evidence appears to indicate that there is some connection between the deltidium and the pedicle. It
has been observed, further, that in orthid species having a deltidium, such as I lesperorthts tricen-
aria, Dinorthis szveetieyi, Valcourea, and others, the adductor and diductor muscles occupy the entire
delthyrial cavity, but in these forms there is no vestige of a pedicle attachment. Hence if there was
a functional pedicle, it must have been attached to some portion of the deltidium. These observations
were anticipated years ago by Winchell and Schuchert,* who clearly expressed the same views, as
follows:
In all the species of Orth'u observed when a pedicle muscle [callist] is present a deltidium is absent; but
where this plate is developed the muscle [callist] is rudimentary. This evidence leads the writers to the conclu-
sion that the pedicle muscle is attached to the bottom of the valve in the apex of the delthyrium when the del-
tidium is wanting, but when it is developed the muscle is then more or less attached to the deltidium.
In shells provided with a deltidium of the Deltatreta type, and having a prominent foramen,
it has been determined, at least for Deltatreta, that there is a well marked, even conspicuous pedicle
callist in the apex of the delthyrial chamber. Punctate shells are usually not provided with a del-
tidium, but when an apical plate is present, as in Pionodema, its position in the valve and the lack of
any visible scar of pedicle attachment on the floor of the delthyrial cavity make it clear that this plate
served for pedicle attachment.
Lateral plates. — In many genera, especially those of the Orthidas, there are lateral plates
which restrict the delthyrium. Such are prominent in Glossorthis (pi. 4, fig. 28) and Ptycho-
pleurella (pi. 6, fig. 9). Perhaps the best example is Glossorthis, in one specimen of which the right
plate has been fractured slightly, emphasizing the suture line. In Hesferorthis the ventral shell has
not only these lateral plates but likewise a small deltidium, showing the close connection of these
different parts of the same structure secreted by the mantle. These lateral plates strongly resemble
deltidial plates in manner of growth and position. They apparently grow inward and forward by
marginal deposits of the mantle, since they show successive growth-lines as in deltidial plates. They
have, however, never been observed to meet and in this respect are not unlike incomplete deltidial
plates of certain of the Rhynchonellacea and Terebratulacea. These observations appear to us very
important as bearing on the source of deltidial plates in the order Telotremata.
Less well developed plates of the sort described above occur also among the Pentameracea and
they have received considerable attention by other students of brachiopods. Hall and Clarke describe
them in several genera, and Kozlowski has gone so far as to place the Pentameracea in the Telotre-
mata because of their presence in that group.
MODIFICATIONS OF THE NOTOTHYRIUM (CHILIDIUM
AND CHILIDIAL PLATES)
In the dorsal valve the covering of the notothyrium is termed the chilidium. This structure is
usually absent in post-Cambrian orthids but occurs sporadically (probably as re-developments) or in
modified form in later genera. The usual type, seen in Vellamo, is a convex, perforate arch built
with its piers against the margin of the notothyrium and with the suture line of contact commonly
healed or grown over so that the interarea and chilidium appear continuous. The outer surface of
the arch is marked by convex lines or thin lamella; of growth. On the under side of the chilidium
the attachments to the sides of the notothyrium are strengthened by callus deposit laid over the points
of contact and along the walls of the notothyrial cavity. In many species of the Clitambonitidas
the posterior surface or edge of the cardinal process is attached to the under or anterior surface of the
chilidium. This type of notothyrial covering occurs throughout the Billingsellidas and Clitambom-
tidse. It is also present in some genera of the hesperorthid tribe.
*GeoI. Minnesota, vol. 3, pt. 1, 1895, p. 422.
24 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
In endopunctate orthid shells modifications of either the delthyrium or notothyrium are of
uncommon occurrence. Only one instance of a true deltidium is known and that is in Kayserella,
which stands unplaced in the Orthacea. A chilidium is also known in Heterorthis (see pi. 20, fig.
19). It is strongly convex and arches over the carinate postero-dorsal portion of the carinate median
lobe of the cardinal process. The only suggestion we can offer in regard to its function is that it serves
for protection of the muscle attachments on the cardinal process.
Of unusual form and interest is the umbrelliform chilidium of Productorthis (see pi. 4, figs.
15, 16). This plate has its origin in the growth of two discrete plates along the notothyrial margins.
These grow dorsally to the dorsal surface of the cardinal process, uniting and expanding into a cir-
cular plate that hangs over the distal end of the process like a small umbrella. Here again the
function may be one of protection for the muscle attachments.
In some orthids there occurs an incomplete chilidium or what may be termed chilidial plates.
These are low plates projecting posteriorly from the notothyrial margins and forming low walls on
each side of the notothyrium. These chilidial plates are commonly thickened by callus deposit on
the interior and cemented firmly by the spread of callus covering all points of contact. Chilidial
plates characterize Nicolella, Deltatreta, Pomatotrema, and Planidorsa.
From the above, it appears that the sporadic reappearance of the chilidium and chilidial plates
in late forms cannot have a direct genetic linkage with the older genera wherein these structures are
of continuous development 5 the former suggest, rather, atavistic returns of primitive features. In
the Clitambonitidse, where the normal genera possess a chilidium, its persistent absence in other forms
must mean a progressive change of considerable significance in establishing species and genera, for
example in A-pofnatella.
MORPHOLOGY OF THE VENTRAL INTERIOR
ARTICULATION
Genuine articulation is well developed in all of the Orthacea of the Cambrian, and its origin is
therefore to be sought in the most primitive order, Atremata.
In the orders Atremata and Neotremata the two valves are held in apposition by muscles, but
in the Protremata and Telotremata they are held in place by teeth and sockets and sometimes by
other articular devices that together act as hinges. In many forms the brachial process or brachio-
phore also assists in locking the valves, since it articulates with the tooth of the ventral valve and
helps to prevent lateral motion.
It will be shown directly that the tooth of the ventral valve in Orthacea bears a socket on its
posterior surface and a fossette on its inner and dorsal face. The accessory socket of the posterior
surface receives a small denticle on the outside of the socket of the ventral valve and the tooth fits
into the dorsal socket. On the other hand, it will be shown in the discussion of sockets that the
crural fossette receives the carinate or expanded posterior edge of the brachiophore. Accordingly,
we see that the brachiophore is as important in the articulation of these brachiopod shells as the tooth
^n.Q socket.
Teeth. — ^Teeth and dental plates are unknown in the inarticulate orders Atremata and Neotre-
mata, but ventral teeth with their dorsal sockets are present in all the Cambrian genera of the
Orthacea, though they appear to be very rudimentary in Kutorgina, thought to be the most primitive
genus of the articulate order Protremata. On the other hand, dental plates are not always present in
the older Cambrian genera (absent in Nisusia), but later on they make their appearance and are then
usually present.** , r , • c u a }
The teeth or articulating apophyses are situated immediately laterad of the margins ot the del-
thyrium, or, in a few genera, at the intersection of the delthyrial margin and the hinge-line. When
viewed from the posterior, the teeth are roughly triangular in outline, the apex of the triangle being
"sWalcott, Camb. Brach., 1912, p. 310.
MORPHOLOGY OF THE ORTHOID SHELL 25
directed toward the delthyrium. The teeth are considered to extend vcntrally as far as the ridge
bounding the crural fossette (see below) on the inner face of the tooth. The progressive forward
growth of the tooth produces a thickening under the palintropc along the dclthyrial margin, and
likewise a triangular area on each side of that margin. This small area is bounded on the inside by
the delthyrial margin and on the outside by a more or less well defined suture line connecting the beak
with a small socket in the outside, posterior face of the tooth. These narrow triangular spaces usually
can be easily differentiated from the remainder of the interarea by the difference in color. In punc-
tate shells the palintrope is punctate, but the dental area is impunctate. In a cross section of the
palintrope the triangular area is also three-sided and is supported by the dental lamells.
The teeth of Rhipdomella vary from the usual type described above. They form the margin
of the umbonal cavity and rest on the floor of the valve with little or no supporting plates, and
project dorso-laterally as blunt points.
Sockets. — There are sockets in both valves which receive articulating processes from the oppo-
site shell. In the ventral valve there are two kinds of sockets associated closely with the teeth:
(1) Accessory dental sockets in the postero-lateral face of the teeth (see t. fig. 2); and (2) a crural
fossette or crural socket" on the inner face of the teeth.
1 . The accessory socket in the tooth of the ventral valve is located in the postero-lateral sur-
face of the tooth next to the hinge-line and on the outside margin. It articulates with a small
SfS
Y^r.. 2. — Diagram showing the ventral interarea of Vdcourea, with accessory sockets in the teeth {Acs).
apophysis or tooth situated on the outside of the dental socket of the dorsal valve. This accessory
articulation is common throughout the Orthoidea and in strophomenids, spiriferids, etc.
2. The crural fossette is a more or less deep groove, usually defined by an oblique ridge, located
in the inner face of the tooth just ventrad of the delthyrial margin. Not uncommonly the fossette
is not sunk deeply beneath the surface of the tooth but is made by a small subtriangular plane sur-
face defined by an oblique ridge, a type frequently seen in the family Orthidx. The function of the
crural fossette is to articulate with the carinate, or, in some genera, expanded postero-ventral edge or
face of the brachiophore. In Hesperorthis the fossette is small, but the oblique ridge defining it is
prominent. In the articulation of this shell each tooth fits into the socket which is located outside
the brachiophore; it extends into the socket a distance equal to the plane or sunken face of the
crural fossette, while the oblique ridge rests on the posterior or postero-ventral edge of the brachio-
phore. It follows then that the brachial apparatus of the orthid plays an important role in the artic-
ulation of the shell, a role no less important than that of the teeth and sockets.
The crural fossette of Parmorthis (pi. 21, fig. 10) is developed to a remarkable degree. It is
an elongate, deep groove extending nearly to the floor of the valve and terminating in a deep socket.
The oblique groove receives the postero-ventral edge of the crural base, and the socket at the end
of the groove articulates with a slight expansion near its ventral extremity.
Dental plates. — Beneath each tooth there are as a rule two more or less strong plates divid-
ing the space beneath the overhanging palintrope into three chambers, two lateral ones and a central
one the delthyrial cavity. These plates have been most commonly termed "dental lamellae" or
"dental plates." Thomas calls them "delthyrial supporting plates" and Fredericks speaks of them
as "lamellae apicales." We prefer to remain by the older terms "dental plates" or "dental lamella."
"The term crural fossette ("fossette crurale") was used first by Kozlowski (Bib. Univ. Lib. Polon^, A, 1927, fasc.
17, p. 8, fig. 1).
26 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Thomas'' challenged the general conception that these plates gave support to the teeth. He says:
As to the function of these plates there appears to be greater reason for regarding them as supports of the areal
portion of the pedicle valve than as dental supports. It is certain . . . that they are not in all cases directly con-
nected with the teeth, while the connection in other instances need not necessarily imply the primary function of
dental support. The delthyrium is situated at the weakest part of the areal portion and the plates are developed
along its lateral margins and adjacent to the deltidium. This is just the position where one would expect a strength-
ening of the valve to take place. It seems preferable, therefore, to call such "dental" lamellae the "delthyrial
supporting-plates."
It has been the experience of the writers that in the Orthacea these lamellse are invariably con-
nected with the teeth. Thomas' argument that these plates support the palintrope at its weakest
point is not conclusive, because there are many strophomenoid genera with long interareas that have
no dental supports reaching the floor of the valve, and among the orthids the oldest known genus,
Nisusia, is also without them. Furthermore, shells having broad overhanging palintropes, such as
Hesferorthis and Plectorthis, are commonly provided with thin, delicate, short dental plates of the
receding type, but shells with shorter palintropes and more ventricose valves have ponderous dental
plates, e. g., Orthis s. s. and Archworthis. Where these lamellae are present, they undoubtedly serve
the double function of supporting the teeth and the palintrope.
Dental plates may be described as receding when they extend as ridges under the teeth and
the palintrope, and finally attain the floor of the valve near the apex only. Examples of this type
are common in American orthids such as Hesferorthis and Schizoramma. The dental plates are
called advancing when they slope forward and are continued around the lateral margins of the muscle
field as more or less well defined ridges, as in Schizofhoria. The term obsolete may be applied to
dental plates when the lateral umbonal cavities have been so filled by adventitious testaceous matter
as to obliterate them. This condition is common in old shells, so that the observer, if he does not
take the precaution to examine interiors of young specimens of the same species, may fall into the
error of describing the particular species or genus as possessing no dental plates. Such an error was
made by Hall and Clarke* in their definition of Orthorhynchula, which they say is without dental
plates. The young of that genus, however, are provided with well developed receding dental
lamellas.
SPONDYLIUM
History of the term. — The term spondylium (from the Greek word for vertebra) was pro-
posed by Hall and Clarke (1892) in their discussion of Clitambonites. They say of Pronites
adscendens Pander:®
On the interior of the valve the dental lameUae are very strongly developed, converging and uniting in the
median line before reaching the bottom of the valve; thus forming a spondylium [a spoon-shaped plate], which
with the deltidium encloses a conical subrostral vault . . . This term will apply with equal propriety to the similar
plate existing in the pedicle-valve of other brachiopods, e. g. . . . PentameruSy Camarella [Camarophona, etc.].
Later these authors add:^"
It has become evident since the introduction of the term that these processes in the two valves [spondylium
and cruralium of Pentamerus] , though similar in aspect, are similar neither in origin nor function, and it becomes
necessary to modify the application of this term. Hence it is proposed to restrict the term spondylium to the plate
existing on the pedicle- valve, and to the plates of the brachial valve, whether united or discrete, the name
cruralium will be applied. .
The spondylium is an area of muscular implantation. In its early or incipient condition it is evident that it
originates from the convergence and coalescence of the dental lamellae, and forms a receptacle for the proximal
portion of the pedicle, and for the . . . pedicle muscles. In Clitambonites and Pentamerus, where it attains its
'Mem. Geol. Surv. Gt. Brit., Pal., vol. 1, pt. 2, 1910, pp. 100-101.
«PaI. N. Y., vol. 8, pt. 2, 1893, p. 181.
•Op. cit., pt. 1, p. 234.
"Pt. 2, pp. 331-332, 335 footnote, 341.
MORPHOLOGY OF THE ORTHOID SHELL 27
greatest development, it bears all the muscles of the valve, the central adductor, and the lateral diductor scars being
often clearly defined, while the posterior portion of the plate is still reserved for the attachment of the pedicle, if
functional. In the pentamcroids the median septum of the pedicle-valve supporting the spondylium, is formed in
a similar manner by a continuation and coalescence of the dental plates, and wherever the median supporting septum
exists in this group, it will probably be found to have this composition. Median and lateral septa, however, in the
valves of the Brachiopoda, have a highly diverse origin in different cases. In most instances, except where bear-
ing spondylia, they are evidently of muscular origin and surfaces of muscular attachment, as shown in Spirifrrina.
[The spondylium is of early manifestation.] It appears in a highly developed state in conjunction with the
unmodified deltidium [delthyrium], first in Protorthis, of the Cambrian, then in PoLytoechla, Syntrofhia, Clitam-
honites and ScenUium, of the early [Ordovician] and later Silurian and of the Devonian.
Schuchert" formerly held that the spondylium
probably had its origin in an excessive deposit of testaceous matter about the bases of the powerful adductors,
diductors, and pedicle muscles. Growth of the individual necessitates the progressive anterior movement of the
muscles, and when these are large there is but little or no space left between or outside of them for the viscera and
genitalia, which are therefore crowded farther and farther anteriorly. This condition naturally produces constant
pressure of the genitalia against the anterior base of the forming spondylium, and since pressure causes resorption
or diverts testaceous deposition, it follows that these organs will gradually produce cavities for their relief beneath
this plate.
This explanation certainly appears true for the platform in the atrematous Trimerellidas, but it
is now apparent that this is not the way the thin, plated, true spondylia of the Clitambonitidae and
Pentameridas were made. It is clear that what Schuchert was describing is the origin of what is
now called the sessile spondylium (spondylium discretum) so well developed in the Billingsellidas.
Hall and Clarke give the correct function for the true spondylium when they say that it is "an
area of muscular implantation," originating from the convergence and coalescence of the dental
lamellae, and uniting either with a median septum or with the floor of the shell, but their further
statements about its making, in connection with the deltidium, a pedicle-sheath that had its first
stimulus of growth in the prodeltidium is, as we now see, wrong. What Schuchert and the older
students of brachiopods did not see is that the muscle-bearing platforms of the Trimerellidas, the
spondylia of Clitatnbonites and Pentamerus, and the cella of Merista are not homologous structures,
since, as we now know, all are of independent origin, arising in different ways though functioning
more or less alike. Sessile spondylia (spondylia discreta) are common in the Middle and Upper
Cambrian, but true spondylia are not present until late in Cambrian time and are chiefly character-
istic of the Ordovician and Silurian, while the cella type of muscle plate is of Middle and Upper
Ordovician origin, appearing first in Cyclospra and Dayia.
What Schuchert in 1 897 regarded as the primitive attached spondylium (= sessile spondylium),
Walcott in 1912 called the pseudospondylium, and states that it occurs in PNisusia, "Billingsella"
Eoorthisy Finkelnburgia (free in front) and Huenella (free at the sides). The sessile or "pseudo-
spondylium" of Eoorthis
appears in Orthis ... of the Ordovician and later faunas, probably as a reversion from a free spondylium [here
Walcott, as we now know, is clearly wrong]. On the line of descent to Protorthis the pseudospondylium becomes
a free spondylium and continues on through Syntrophia and Clarkella into the Ordovician and Silurian Pentameridas
and Clitambonitidx.'^
Walcott asked Ulrich to comment on the kinds of spondylia, and this he did as follows." The
term spondylium, he says,
applies only to the t}'pical free or medially supported umbonal camera or spoon . . . and corresponds to a ventral
muscular area which is raised above the floor of the valve and formed by the convergence and union of the dental
plates . . . The manner in which the spondylium is att.iched to the bottom of the valve is so variable that the
feature does not seem to be of more than generic consequence.
Ulrich then points out the great variability in a number of genera.
" Bull. 87, U. S. Geol. Surv., 1897, pp. 99-101.
"Walcott, 1912, p. 307.
"In Walcott, 1912, p. 308.
28 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Kozlowski^* has recently made a detailed study of the spondylium in the Pentameracea and has
reached some striking conclusions. He has shown that there are two types of spondylia in the Pen-
tameracea as constituted by Schuchert in 1913. One of these types, in which the spondylium is sup-
ported by a simple septum, he calls the "spondylium simplex," and thinks it originated from a
pseudospondylium by lateral crowding of the ovarian bodies and consequent resorption of the deposit
forming the base of the pseudospondylium. The Clitambonacea are characterized by this type of
spondylium and Kozlowski finds this superfamily to be more closely related to the orthids than to
Pentamerus. In his conclusion we concur, having arrived at the same opinion independently but
using different criteria as well, namely, the pallial and ovarian impressions and the cardinalia.
Characteristic of the second group — the Pentameracea — is the "spondylium duplex." In this
type the spondylium is elevated on a septum which is clearly composed of two parts thought to have
been produced by the squeezing of the two dental plates together due to lateral pressure from the
ovarian bodies. This type of spondylium is common to the pentamerids, but the cardinalia are much
more characteristic than is a spondylium duplex which is known in many other genera.
Present views and definitions. — We may add that the dental lamellse and the floor of the
valve between them are in many genera bound together by a chamber called the delthyrial cavity, and
in most of the orthids the floor of this space is the seat of attachment of the various muscles. In
other orthid genera the dental plates converge and unite with each other medially on the floor of
the valve, or are supported by, and fused with, a median ridge before attaining the shell floor,
forming an elevated spoon-shaped structure. It is to the latter type of muscle platform that the term
spondylium is now restricted. In rare instances among the oldest brachiopods {Protorthis) the dental
lamellae unite to form a freely suspended spoon without the intervention of a median septum. These
various types of muscle platforms may be briefly defined as follows:
1 . Discrete spondylium. — This, Kozlowski's spondylium discretum, designates the condition
in which the dental lamellae converge but slightly and extend directly to the floor of the valve, but
never become united. This type of muscle cavity occurs in PoramboniteSy Huenella, and a host of
other orthid shells. It is not a spondylium, but the structure does suggest how the genuine spondylia
arose, namely, by the complete convergence and union of the dental plates above the floor of the
valve, and their support by a median septum standing on the floor of the shell.
2. Pseudospondylium. — This term was introduced by Walcott^^ for "the rudimentary spon-
dylia attached directly to the inner surface of the valve, as in BilUngsella." In all the species listed
under the genus BilUngsella in the present work the dental lamellae do not converge but extend
vertically to the floor of the valve and conform in all essentials to the type of muscle platform
called by Kozlowski the spondylium discretum. In some species, however, the anterior portion of
the muscular area is elevated on a callosity. This shell thickening within the delthyrial cavity and
its connection with the dental lamellae make it appear that these plates are united but in reality they
are discrete, resting on the floor of the valve. It is to this type of muscle platform that we propose
to limit the term pseudospondylium.
Pseudospondylia are excellently exhibited in Glossorthis (see pi. 4, figs. 9, 12), Linoporella
(see pi. 18, figs. 13, 14, 18), and Finkelnburgia (see pi. 13, figs. 6, 11). In these genera the callus
beneath the muscle attachments is extended from the floor to the inside face of the dental lamellas.
Anteriorly the callus is thick and in Finkelnburgia is extended forward as a low ridge. Specimens of
Linoforella kindly loaned by Dr. A. H. Westergaard of Stockholm show a complete series from
the young stage with discrete dental lamellae and unthickened muscle attachments to a condition in
which a typical pseudospondylium with a median ridge has been developed. This series is illustrated
on plate 18.
Pseudospondylia are naturally more developed in old or late mature shells, as young individuals
do not deposit much callus. Since, therefore, the pseudospondylium is a feature of mature shells
only, it is obvious that it has a minor value in the taxonomy of the Brachiopoda.
"Pal. Polonica, 1919, pp. 122-125.
"Camb. Brach., 1912, p. 295.
MORPHOLOGY OF THE ORTHOID SHELL 29
3. Spondyloid. — This term is suggested for a structure simulating a spondylium in form
but produced by the deposition of adventitious testaceous substance on and about the clental lamellx,
swelling them laterally until union is effected. This type of structure is well exhibited in Poram-
bowtes. In late mature or gcrontic individuals of this genus, adventitious shell has been deposited
on the dental lamellx and on the floor of the valve in front of them, and may be produced forward
sufiicicntlv to simulate a median ridge or septum. In old shells this structure so closely resembles
the spondylium in pentamerids that Noetling and subsequent workers have been misled into the con-
ception that the thickening of the dental plates in Poratnbonites is a spondylium.
4. Free spondylium. — Here the dental plates converge and unite to form a spoonlike muscle
platform that hangs suspended in the ventral valve, since it is not supported by a median septum as
in the typical forms of spondylia. This type is exceedingly rare, being known in Protorthts of the
Middle Cambrian, and the younger genera Holorhynchus and Cymbidium.
5. Spondylium or spondylium simplex. — The term spondylium has customarily been
applied to the spoon-shaped muscle platform formed by the convergence and union of^^the dental
lamellx with a median septum, regardless of the structure of the septum. Kozlowski, however,
has shown that the spondylia are differently constructed and are therefore polyphyletic m origin, and
has consequently defined several kinds. He shows that the spondylium in Skenidmrn and Cluatnr-
bonhes is different in origin from that in the Pentameracea. In Clitambonites the spondylium is
formed by the union of the dental plates with a simple median septum (euseptum), the whole
forming one piece. To this type of spondylium he gave the name spondylium simplex. As this is
the simplest type of supported spondylium, we may call it spondylium and drop the limiting word
simplex. , , ^,. , • • j j • i
The spondylium is one of the characteristics of the subfamily Clitambonitidae and is seen also
in the Syntrophiidas and Skenidiidx.
6. Duplex spondylium. — The above type of spondylium is in decided contrast to that in the
Pentameracea (Conchidium), in which the supporting septum is actually double and composed of two
united vertical plates. To the latter type Kozlowski has applied the name spondylium duplex, and it
appears not to occur in any genus of the Orthoidea," but is characteristic of the pentamerids, where it
is associated with a definite kind of crural apparatus. ■ r . j
In its evolution, Kozlowski believes that the spondylium simplex has arisen from the pseudo-
spondylium. The genital organs are thought to have resorbed the testaceous deposit about the base
of the dental plates and under the muscle attachments. The resorption has gone so far as to leave
a rather narrow septum underneath the seat of muscle attachments. This is, in its essentials, precisely
the same idea held by Schuchert in 1897.^^ The spondylium duplex, however is considered by
Kozlowski to have originated in a different manner, i. e., through lateral crowding by the sexual
glands, which has pushed the dental lamellx gradually together.
SEPTA
Vertical septa are usually not conspicuous features of the ventral interior, but in sonie genera
rather prominent ridges or septa are developed in connection with the musculature, deltidium, and
pedicle attachment. Such ridges usually have value in species making but only rarely have they
generic significance. . . , ,,
In shells wherein a pedicle callist or a deltidium is present, it is not uncommon tor a small
septum to extend forward from the callist or deltidium for a short distance, dividing the back ends
of the diductor scars. This ridge is commonly formed in old shells and is the result of deposition of
adventitious shell between the muscles. Such septa are, however, of little taxonomic significance.
" 1929, pp. 122-126. ..,.,, l j .
"The writers have not seen a thin section of the spondylium of EnteUtella and lU detailed nature can not be deter-
mined from Likarev's figure.
"Op. cit., pp. 99-100.
30 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
In shells having a spondylium there may be other septa in addition to the median one. This is
true notably of Gonambonites, Clarkella, and Y angtzeella, in which the lateral septa probably play
a secondary part in the support of the spondylium. In Clarkella the several lateral accessory septa
appear to be excessively developed ovarian ridges, and such are common among the syntrophiids and
orthids.
A few genera that have greatly developed diductor scars, especially where these wrap about and
enclose the adductor scars, as in Rhipidomella, may develop short, low septa in front of the latter
impressions j the septa then separate the antero-median extremities of the diductor scars. These
septa are also of no special taxonomic value.
A few genera are provided with a broad and low median ridge which, besides dividing the
diductor impressions, also bears the adductor muscles. This type of septal ridge is seen best in the
Schizophoriida;, in which its development can be traced from a low ridge in Pionodema and the early
Schizophorias to a high septum in Orthotichia and Enteletes. The same kind of median septum is
also seen in certain stocks of the dalmanellids such as Cariniferella, and in these the ridges likewise
bear the adductor muscles.
There is an interesting development of a median ventral septum in Parenteletes. Here the
dental plates are similar to those of Enteletes, but are more widely divergent. The median septum,
however, has its origin a short distance anterior to the apex, continuing forward and increasing in
height in the same direction. But at the anterior end of the septum, just at the point of origin of
the shell fold (ventral), there is a small inverted V-shaped chamber, here termed the cella;^^ this
chamber evidently acts as an arch to support the dorsal septum above the inner sulcus produced by
the external fold. The septum in this genus is further distinguished from that of Enteletes by its
expanded, rounded dorsal edge.
MUSCULATURE
By means of muscles, brachiopods are enabled to open and close their valves, and to a limited
extent to protrude and retract the pedicle and to adjust the position of the shell. In the articulates
there are three sets of muscles: the diductor s, which by contraction open the valves; the adductors,
which by contraction close the valves; and the fedicle muscles (including the adjustors), which by
contraction "serve to alter or adjust the position of the animal as a whole by turning it in various
directions.""" All of the muscles traverse the visceral area. The attachment of the muscles to the
valves leaves as a rule well marked scars. The diductor muscles which attach to the cardinal process
are distinguished as the principal or anterior diductors, while the much smaller pair are the accessory
or posterior diductors; the latter are seen in the ventral valve as two small scars posterior to the
adductors. In most fossil brachiopods it is only the anterior diductor and the adductor scars that are
impressed.
According to Thomson,^^
The pedicle-muscles serve partly to attach the pedicle to the shell, and partly to retract the pedicle or to allow
the shell to erect itself. They consist of an unpaired muscle [unknown as such in orthids, where they are always
paired] running from the ventral side of the pedicle to the ventral valve, where it determines a transversely elon-
gated scar lying posteriorly of the other scars, and, in addition, two pairs known as the dorsal and ventral adjustors.
The dorsal adjustors are attached to the hinge-plates or other similar structures in the dorsal valve . . ., while the
ventral adjustors form two scars in the ventral valve lying outside the adductor-scars. The pedicle-muscles, not
being relatively very strong, do not form strong scars, the median unpaired muscle making the strongest.
In the Orthacea the ventral muscle field begins small, and progressively expands in later forms.
Hall and Clarke saw this long ago, saying:^*
The entire muscular system on the ventral side of the body, is, in primitive forms, inserted upon the base of
the pedicle [delthyrial] -cavity. This is apparent from a study of such a shell as Orthts callactis, where it is per-
fectly clear that no muscular bands were attached to the pedicle-valve outside the limits of this strong and con-
^° From the Latin word for small or extra room.
^"Parker and Haswell, Text-book of Zoology, vol. 1, 1921, p. 358.
"Brach. Morph., 1927, p. 30.
"Pal. N. Y., vol. 8, pt. 2, 1894, p. 338.
MORPHOLOGY OF THE ORTHOID SHELL 31
densed posterior area, which is but a sessile spondylium. [In some shells] the original contents of the pedicle-cavity
may be represented by enormous muscles whose scars extend almost to the anterior margin of the valve, as in
Hipfarionyx and Rhip'uiomella.
The detail of the muscle-scars in brachiopods is usually difficult to determine, because of the
poor preservation of the inner surface, or because of the thinness of the shells. Furthermore, as the
animals grow larger, the muscles migrate forward, leaving more or less elongate tracks widening
toward the front. On the other hand, the tracks do not always afford the detail of the muscles
because the mantle later on covers up the posterior portions of the tracks as migration continues. It
is therefore not uncommon that a doubt may be entertained as to what the actual marks represent in
detail. To cover these various aspects of the muscle-scars we deem it best to adopt the following
terms from Buckman :"*
1 . "Muscle-mark — any mark indicating muscular attachment.
2. "Muscle-track — the course down the valve shown by successive muscular attachments.
3. "Muscle-scar — more or less defined areas representing the ultimate muscular attachment."
In general, when the preservation is favorable, four sets of muscle impressions may be distin-
guished in the ventral valve, as follows: (1) the principal or anterior diductors, (2) the adductors,
(3) the adjustors, (4) the accessory or posterior diductors. Of these four sets, the first three are
usually visible, but the accessory diductor scars are rarely to be seen, and in some instances the
adjustors are not determinable.
( 1 ) Anterior diductor muscles. — ^The diductor impressions are always the largest scars in
the ventral valve. In the early impunctate genera, their tracks and scars are usually rather narrow
and straight, and never enclose the adductor impressions at the front. In later genera, such as
Dinorthis s. s.y DinorMs (Pl^siomys), and Rhipdomella, the diductor scars enclose the adductors.
(2) Adductor muscles. — When the actual adductor scars are visible they are usually hemi-
elliptical in outline and separated by a low ridge which may be single or double. In some genera the
adductor impressions can not be determined, but their position is marked by a linear track. In a few
genera, such as Platystrofhia, Mcewanella, and Productorthis, there is no trace whatever of either
the scars of attachment or the tracks. In other genera (Schizophoria, Orthotichia, and the Entele-
tinae), the adductor muscles were borne on a high vertical septum, consequently their marks are not
recorded on the shell.
(3) Adjustor or pedicle muscles. — These muscles are not always clearly defined on the
valves and have not been determined in all genera of the Orthoidea. The position of these mus-
cles, however, is always outside of, and posterior to, the diductors at the base of the dental lamella,
or they are more or less elevated on the side of these plates. As would be expected from their posi-
tion, these muscle impressions are usually elongate, and rarely present the semi-flabellate outlme
commonly seen in the diductor scars. The adjustor scars are the most variable of the muscle mark-
ings and in this work little reliance has been placed on them in the establishment of genera. Where
good material is available, however, they may be of some use in the making of speaes.
In their great work on brachiopod genera. Hall and Clarke"' have applied two terms to the set
of muscles we are calling adjustors. In the text of the discussion of DinorMs they refer to these
muscles as "adjustors," but in the legend to Plate V, where this genus is figured, they call them
"posterior diductor muscles." We prefer to use the term adjustor muscles because these scars have
precisely the same position in reference to the diductors as in Recent genera. Furthermore, the pos-
terior diductor scars in living forms are located just posterior to the adductor impressions. Similarly
situated scars can occasionally be seen in Paleozoic shells and their presence lends support to our
usage of the term adjustor. It must be admitted that similarity of position does not prove homology
of the muscle-scars in question, but in the absence of more definite knowledge of the soft parts of
these Paleozoic shells, we can only compare the structures in the older genera with those in the
Recent forms.
"Brach. Namyau beds, 1917 ( 191 8), p. 90.
»« Pal. N. Y., vol. 8, pt. 1, p. 195.
32
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
(4) Accessory diductor muscles. — In Laqueus and other terebratulid genera there is an
accessory diductor set located immediately posterior to the adductor scars. From the presence of
such marks in these recent shells it might be suspected that homologous muscle patches should
occupy a similar position in the orthids. Such scars have been described by Sardeson^' in Dalman-
ella emacerata, in which they are located just posterior to the adductors and between them and the
pedicle callist, hence in precisely the same position as in Laqueus. In shells like Dinorthis sub-
quadrata and Rhifidomella there may be a corresponding set of muscles associated with the adduc-
tors, although these were not clearly seen by us.
According to our interpretation of this set of muscles as adjustors, there can be no correspond-
ing set of scars on the dorsal valve, since these muscles are here attached to the pedicle.
PALLIAL AND GENITAL MARKINGS
The mantle (or certain of its layers) is folded upon itself at various points, enclosing cavities,
or fallial sinuses, which contain the body fluids and frequently portions of the genital organs.
Pallial markings. — The markings of the main pallial trunks are often seen in the Cambrian
Figs. 3-5. — Ventral pallial and ovarian markings. 3, Orthis s. s.; this type characterizes the family Orthidae as here
described. 4, Schizoramma, in which the markings are essentially the same as in Orthis and Hesferorthis. 5, Dinorthis
(PUsiomys) subquairata (Hall) ; notice here that the main trunks extend from the anterior of the diductor scars. In the
ventral valve the pallial trunks in all orthoid brachiopods begin at the same place.
genera of Atremata {Obolus, Lingulobolus, Lingulella, Bicia, Dicellomus) and of Neotremata {Obol-
ella, Acrothele, Botsfordia, Acrotreta). Accordingly these markings should be common among the
Cambrian Orthacea, and so they are. They are especially well seen in BilUngsella.
In living brachiopods, according to Thomson,^'
The pallial sinuses take the form of great trunks, entering the mantle-lobes from the coelome, and generally
branching repeatedly towards the margins. The disposition of the sinuses varies considerably in different groups,
and it is probable that these characters have at least super family value in classification.
The pallial marks have been found of great use in defining some of our families.
In general, the pallial markings of the ventral valve are rather simple as regards the main
trunks. Their general arrangement is foreshadowed in the Cambrian genera of the Billingsellidas in
the two prominent trunks which radiate antero-laterally from the forward ends of the diductor scars,
thence splitting and diverging toward the front and sides of the valve. One of the anterior branches
of each trunk swings dorsally and runs nearly parallel to the lateral margin. The other, shorter
branches extend inward and may or may not unite near the mid-line of the valve (see pi. 1, fig. 10).
^'Amer. GeoL, vol. 19, 1897, p. 93.
»«Brach. Morph., 1927, p. 11.
MORPHOLOGY OF THE ORTHOID SHELL
33
In the Orthidas and Clitambonitidas the two main trunks are clearly visible but instead of being
widely divergent as in the Billingsellidas they extend forward near the mid-line of the shell, being
separated by a narrow septum only (t. figs. 3, 4; pi. 2, fig. 18; pi. 6, figs. 18, 26; pi. 8, fig. 10).
At the front they may or may not diverge. In the higher families of the Orthoidea such as the
Dinorthidse and Plectorthida: the pallial markings are more complicated but of the same fundamental
pattern. In Plcesiomys (see t. fig. 5; pi. 10, fig. 26) the main trunks are short and rather narrow,
diverging from the antero-lateral extremities of the diductor scars. The main trunks branch almost
immediately after their inception, sending one trunk posteriorly and another antero-medially. Each
of these subsidiary trunks gives rise to minor branches toward the front and sides of the shell. In
Mhnella (see t. fig. 6; pi. 12, fig. 20) the general arrangement of the trunks is on the plan of
D'morthis, but details of the branching are different. Orthostrophia (t. fig. 7) has the two diverg-
ent trunks of the Dinorthidx which branch into subsidiary trunks, but in addition has one or two
minor trunks extending forward from the adductor tracks. These may actually be branches from the
main trunks in front of the diductor impressions, but no lines of contact were observed.
In the Dalmanellidaj the two main trunks are visible in many of the genera, extending forward
from the diductor impressions. The branching of the main trunks into subsidiary rami is more or less
complicated (t. fig. 8; pi. 17, fig. 22).
^^.<«'<
Figs. 6-8. — Ventral pallial markings. 6, Mimella mdonica (Willard). 7, Orthostrofhia aff. O. Urofhomenoides
(Hall), in which they are of the same type as those of Dinorthis and Mimella. 8, Dalmanella ignota Sardeson: Pc, pedicle
callist; da'», accessory diductor scars; /la!;, adjustor scars; i4, adductor scars; Z)», diductor scars.
Genital or ovarian markings.— In living brachiopods the genital glands (brachiopods are
dioecious) are, according to Thomson,^
rather thick, convoluted bands . . . varying somewhat in size . . . There are four glands in each animal, two on
the ventral and two on the dorsal side . . . The glands in some genera are bound down to the shell by muscular
ties, which give the shell a pitted appearance, the so-called ovarian impressions.
These markings are usually dissimilar on either valve, and in some Orthacea are not observable
at all. • L u 1 1
Genital or ovarian markings consist usually of more or less reniform areas m the umbo-lateral
portions of the valve bounded by the main trunks or the posterolateral branches of the pallial sinuses.
Within the reniform areas are elevated ridges radiating from the umbonal cavities. These probably
represent attachments of the ovarian bodies. Reniform ovarian areas are most promment in the
Orthidse and Clitambonitidx, but in many genera these markings are not represented by reniform
areas but by wavy ridges or by pustules that are aggregated in the umbo-lateral spaces.
"Brach. Morph., 1927, p. 13.
34 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
MORPHOLOGY OF THE DORSAL INTERIOR
NOTOTHYRIAL PLATFORM
The interarea of the dorsal valve in most genera of the Orthoidea is centrally cleft by a tri-
angular opening called the notothyrium, which lies opposite the delthyrium of the ventral valve j both
have been described in a previous section of this memoir. Beneath the margins of the notothyrium
is a cavity, the notothyrial cavity, which is deep or shallow depending on the degree to which the
floor has been built up by deposition of shell substance. The floor of this cavity is commonly built
ventrally from the floor of the valve by the accretion of testaceous substance, producing a swelling
within the walls of the cavity. To this swelling the term "platform" has recently been applied"* but
that term has already been used for the elevated muscular platform of the Trimerellida; (see p. 9).
To avoid using this term for two very diff^erent str uctures we here suggest the designation notothyrial
platform.
DENTICLES AND SOCKETS
Denticles. — Teeth for the main articulation of the valves occur only in the ventral shell, but
accessory processes fitting into the sockets in the posterior face of the teeth of the ventral valve occur
in most of the genera. These are here called denticles. They are usually wider than long and are
located on the outside wall of the socket. This accessory apparatus makes for rigidity in articulation
(t. fig. 2).
Sockets. — The socket which receives the tooth of the ventral valve in articulation is always
located between the inner shell wall and the outer face of the brachiophore. The simplest type of
socket occurs in the Billingsellidas, Orthidas, and Dalmanellidas, in which it is merely the cavity
between the brachiophores and the inner wall of the valve. This may or may not be slightly exca-
vated beneath the palintrope, or into adventitious shell matter laid on the wall of the valve.
A second type of socket is that which is found in the Plectorthidas, Wattsellidas, and Schizopho-
riida:. In these families the socket is defined by a small concave plate (fulcral plate) joining the
brachiophore to the wall of the valve (see pi. 22, fig. 25).
CARDINALIA
The articulating apparatus, the brachial supports, and the cardinal process are together known
as the cardinalia. Until recently this structural ensemble has been little used in the construction of
genera and families. Hall and Clarke in their study of Orthis gave little attention to the brachial
supports and cardinal process, and accordingly did not see the significant differences between Hebert-
ella, Dinorthisy Orthis, Plectorthis, and Dalmanella, differences pointed out in the present work.
The cardinalia are intimately bound up with the brachia and the musculature of the brachiopod and
consequently are important structures.
CARDINAL PROCESS
Nothing in the nature of a cardinal process is ever seen in the inarticulate orders Atremata and
Neotremata. Such first appears among the Orthacea of the Cambrian, but at no time in this period
can it be said to be strongly developed, and even in certain of the primitive genera it is a linear ridge
that may be absent in some species of the same genus. In Kutorgina no cardinal process is known,
and one may be present or absent in Nisusia and Jamesella. In the late Cambrian a cardinal process
is of sporadic occurrence in nearly all of the genera."^
The cardinal process is located on the notothyrial platform in the mid-line of the shell. It may
be a simple, linear, more or less thickened ridge, or it may be a far more complex structure and then
^^ Bancroft, B. B., Mem. and Proc. Manchester Lit. and Philos. Soc, vol. 72, 1928, p. 175.
"Walcott, Camb. Brach., 1912, p. 306.
MORPHOLOGY OF THE ORTHOID SHELL 35
divisible into two parts: (1) the shajt or anterior element, and (2) the myofhore or posterior part,
the seat of attachment of the diductor muscles. The shaft is usually extended forward for some dis-
tance or may merge with a median ridge. Rarely is the shaft much abbreviated (R/iipidomella).
The head or myophore may be expanded, multilobate, and crenulated, or it may be compressed
laterally so that the actual muscular attachment takes place at the thinned posterior extremity of the
process (see pi. 1 7, fig. 26). In some of the later genera, such as Schizophoria, the process, which in
young shells has much the same form as in R/iipidomella,
becomes absorbed and thus narrowed with age making a thin and sharp ridge; concomitant with this change is
the formation, in the delthyrial [notothyrial] cavity, of one, two or even three minor ridges on each side of the
original process, so that in old shells the posterior face of the process appears to be multilobate.'"
Accessory ridges are also present in some species of Schizoramtna (see pi. 5, fig. 14).
The following nine types of cardinal process have been observed in the Orthacea:
(1) The Orthis type, which consists of a thin ridge situated in the middle of the notothyrial
platform and usually extending its whole length. This ridge is generally thicker at its base; it
may or may not be expanded toward the front. Scars of muscular attachment may actually be
Fig. 9. — Diagram showing features of the cardinalia. My, myophore of the cardinal process; sh, shaft of same; Den,
denticle on outside wall of socket, which articulates with accessory socket in ventral tooth ; SA, so called secondary area.
observed in some genera on the ridge, but they do not appear to be restricted to it, since in some
species (see pis. 2 and 5) distinct muscle marks can be observed on the notothyrial platform at the
base of the process. The development of a vertical ridge naturally increases the area of muscle
attachment and so strengthens the pulling power of the diductor muscles. The Orthis type of cardi-
nal process is the most primitive structurally and the earliest chronologically. Its first appearance
is in the Middle Cambrian and it characterizes the Billingsellidas, Orthids, and Clitambonitida:. So
far as our knowledge goes, this type of cardinal process is absent in punctate Orthoidea. A few punc-
tate genera (Harknessellinas, Heterorthinx) have a cardinal process that simulates the Orthis type,
but in all examples it can be shown to be a modified lobate or Dalmanella type.
(2) The Productorthis type (see pi. 3, fig. 11; pi. 4, fig. 1 5), a unique and very unusual varia-
tion from the ordinary kinds seen in the Orthoidea, which has been developed as an adaptation to the
productoid form of the shell. The dorsal valve is nearly flat and the cardinal process rises abruptly
from a posterior thickening of the shell and is directed posteriorly, extending for some distance
beyond the margin of the hinge-line. The shaft is strong and thick, the myophore a compressed
region on the postero-dorsal face of the shaft, clearly showing the diductor scars.
(3) The Dinorthis type (see pi. 9, figs. 3, 20), characteristic of the Dinorthidas, in which the
shaft is short and stout. In mature shells having this type of cardinal process, the median ridge
appears not to be a continuation of the shaft of the process but is given off rather from the anterior
end of the notothyrial platform. The shaft is subelliptical or suboval in section. In young mature
shells the myophore is likewise oval or elliptical in plan, usually dilated slightly laterally, and
clearly divisible into a right and left half l)y a more or less elevated ridge (Pla-siomys) or depression
(Dinorthis) running along the long axis of the ellipse. Each half ellipse is strongly wrinkled by
arcuate ridges running backwards to the margin of the myophore.
In shells having this type of cardinal process, age modifications introduce notable changes in
size and shape. In PliFsiomys the shaft may be totally obliterated by enlargement of the notothyrial
'"Hall and Clarke, Pal. N. Y., vol. 8, pt. I, p. 212.
36 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
platform as successive depositions of adventitious substance are laid upon it. The plan of the myophore
may become distinctly oval or even subcircular, the central ridge becoming more elevated especially
at the antero-ventral extremity. Such modifications result in a cardinal process not unlike that found
in some of the Dalmanellidas. In Dinorthis, wherein the two crenulated halves are divided by a
depression, the ventral portion of the cardinal process may become distinctly bilobed, the lobation
being produced by posterior growth of the cardinal process through the gradual enlargement of the
lobes with increasing age. The slight depression dividing the crenulated halves of the myophore is
not obliterated during growth.
(4) The Hebertella type, which is not unlike the preceding in its initial stages, having a short
shaft confined within the notothyrial cavity and having the muscle attachment on its dorsal extremity.
It differs, however, in having the myophore in late stages impressed into the sides of the shaft. In
very youthful forms the muscles may be borne on the dorsal surface of the shaft as in the Dinor-
thidas, but with increasing age the muscle attachments are sunk below the surface of the sides of
the shaft. In old forms the myophore may appear as a rather slender septum crenulated on its sides
and mounting a more or less stout shaft. In gerontic forms the muscle attachments may be sunk
into the shaft at the dorsal portion of the cardinal process, but the ventral portion may be expanded
and bulbous. This type has been observed in Plectorthis, Doleroides, and other members of the
Plectorthidse (see pi. 11, figs. 4, 17, 23, 26). It has not, however, been definitely noted in Platy-
strofhia, in which the cardinal process is not uncommonly considerably resorbed and in some instances
reduced to a mere remnant.
(5) The Dalmanella type, common to many endopunctate shells. Primitively the cardinal
process has a short shaft and a distinctly lobate myophore. The latter may be either bilobate as in
Heterorthina (pi. 17, fig. 32) or trilobate. The cardinal process of these shells is distinctly progres-
sive, since all the diductor attachments are on the myophore. Usually there are clearly visible four
distinct scars, but it is not uncommon for the middle two to be coalesced and in some instances
elevated above (in a posterior direction) the outer two, and in that event the myophore is distinctly
trilobate. In other forms the inner and outer set are combined, making a bilobed myophore. This
bilobation may be expressed in the shaft, and with progressive posterior growth of the myophore
there is left anteriorly a depression or cleft in the shaft (see pi. 1 7, fig. 32). As far as our researches
have gone, these variations of the posterior portion of the cardinal process have no generic value, nor
are they always constant in the same species.
Old-age thickening of the cardinalia, and of the cardinal process in particular, produces riotous
growths. Such are seen commonly in Dalmanella meeki and another type occurs in Levenea sub-
carinata and Isorthis perelegans. In D. meeki and other dalmanellids the myophore may become so
enlarged as to fill the notothyrium completely. In Levenea and Isorthis the anterior portion of the
ventral lobe of the myophore may be produced forward along the shaft as a distinct process, giving to
the whole structure the appearance of a fly's head with "tongue" or proboscis protruded.
There are several modifications of the Dalmanella type of cardinal process which should
be mentioned, since they are distinct enough to mark groups of shells. These are:
(6) The Rhipidomella type, in which the shaft has its greatest extension in a ventral direction
(at right angles to the plane of the commissure) and is scarcely developed anteriorly. The myophore
is commonly large. The greatest development of this type of cardinal process is found in Platyorthis
planoconvexa, in which it is remarkably robust (see pi. 19, fig. 24).
(7) The Parm^orthis visbyensis type, in which the myophore is like that of Dalmanella but has
been revolved 90° so that it is parallel to the plane of the commissure and is distinctly visible in
dorsal view. The shaft is essentially obsolete, as the brachiophore plates and the cardinal process
have become fused. This modification is no doubt developed to allow a greater pull of the muscles
on the myophore (see pi. 21, fig. 8).
(8) The Heterorthis type (pi. 20, fig. 20), in which the median lobe of the myophore is elon-
gated posteriorly at the expense of the lateral lobes, producing thereby a carinate ridgelike structure
on the cardinal process. In molds of the interior this type appears to be a simple ridgelike cardinal
process, but in well preserved specimens the primitive lobation is apparent.
MORPHOLOGY OF THE ORTHOID SHELL 37
(9) The Pionodettta or Schizophoria type, in which the shaft is delicate, the myophore may or
may not be lobate in front, while the muscle attachment is near the dorsal portion of the myophore,
leaving an unoccupied portion ventrally. Here the muscle attachments are not uncommonly deeply
sunk so that the myophore simulates the Hebertella type. Finally, in Schizo-phoria the cardinal
process may be resorbed and its place occupied by low ridges (pi. A, fig. 14).
BRACHIOPHORES OR BRACHIAL APPARATUS
In previous works treating of the Protremata, little attention has been paid to the calcified
brachial apparatus, and in consequence the classificatory value of these structures has been almost
completely overlooked. In the present studies we produce some new knowledge regarding these
parts in the most primitive families of the Protremata, and have used these structures, in combina-
tion with the other parts of the shells, to prove relationships of genera hitherto unsuspected. To
facilitate more detailed description, it is necessary to have a new terminology defining the various
parts of the cardinalia.
The simple brachial apparatus of the orthids has usually been termed the crura, but it is not yet
established that these processes are homologous with the crura of the rhynchonellids or the "crura"
of the terebratulids and spirifers, which continue unbroken into the descending lamellae of the loops
or spires. In the usual Paleozoic rhynchonellid, the crura are long curved processes borne on the
inside of a socket plate or crural base. In the orthids, on the other hand, the structures commonly
termed the crura are also the "socket plates," since they bound the sockets. Furthermore, these so
called crura in many of the orthids actually have elongate processes which extend into the valve pre-
cisely as do the crura of rhynchonellids. In separated valves these processes are commonly broken
off as is also the case among the rhynchonellids, but in a few orthids the entire brachial apparatus has
been preserved (see pi. 5, fig. 24).
Among the orthids, we propose to apply the term brachiofhore to the structures on either side
of the notothyrium which bound the sockets and to which were attached the elongate brachiofhore
processes; to the latter in turn was fastened the lophophore. In some genera the brachiophores are
supported dorsally by plates, and to these the name brachiofhore flates or suf forts is given. It will
be seen from the above that the brachiophore or so called crus of the orthid is evidently homologous
with the crural base or socket plate of the rhynchonellid, rather than with the crus of the latter.
Our terms are applicable only to the more primitive or orthoid stage of development of the brachia,
and among these shells there are several types of brachiophores as follows:
(1) Eoorthis-Billingsella tyfe (see pi. 1, figs. 19, 25). — Since the brachiophore in these forms
is derived from that of the most primitive of the Cambrian orthids, it naturally should be of the
simplest type. The brachiophore is a flat blade with its inner margin flush with the margin of the
notothyrium and lying obliquely under its anterior surface. The dorsal palintrope thus overlaps the
posterior or outer surface of the brachiophore. The socket is the space between the sloping outer face
of the brachiophore and the palintrope. In the Billingsellidas, Nisusiidas, and Protorthidas the
sockets are narrow and slitlike, and the brachiophore is supported along its anterior surface by the
swelling of the notothyrial platform (pseudocruralium of Walcott) which extends laterally under the
anterior surface of the brachiophore. This type of brachial process may have evolved into the one
seen in the Orthidas (Orthinae, Hesperorthina;), Dinorthidas, and Clitambonitidas.
(2) Orthis-Hesferorthis tyfe (see pi. 2, fig. 10; pi. 4, fig. 21; pi. 5, fig. 24).— This type is
not unlike the previous one but is more advanced. The brachiophores were more efficient, since they
had a greater antero-ventral extension. In this type the brachiophore is an elongate blade or rod,
occasionally grooved along the inner face as in Hesferorthis, unsupported except for the addition of
shell substance under the anterior face during the growth of the notothyrial platform. The brachial
processes of the Russian Orthis callactis-calligramma group are very close to those of Billingsella and
Eoorthis in their simplicity. On the other hand, the brachiophores of Hesferorthis are advanced,
being grooved along the inner face and in well preserved shells terminated by an elongate process
or point. The Orthis type of brachiophore is present in several genera in various modifications
brought about by deposition of adventitious material. This is best seen in Glyftorthis, in which the
notothyrial platform simulates that in Hebertella.
38
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
(3) Clitambonites ty-pe (see pi. A, fig. 7^ pi. 8, fig. 6; t. fig. 10). — Here the brachiophores
are simple blades or flattened rods, but are supported in a unique manner. Shell matter of the noto-
thyrial platform is built up conspicuously under the cardinal process and is extended laterally for a
considerable distance, forming, with the prominent median ridge and chilidium, an anchor-shaped
structure. However, the original or youthful brachiophore is in some specimens clearly distinguish-
able from the adventitious shell matter. This type of brachial apparatus occurs in Clitambonites,
Vellamo, Gonambonites, Estlandia, Hemipronites, Deltatreta, and Pomatotrema; also in certain shells
referred to the Plectambonitidse, as Plectambonites s. s., Plectella, and Ingria.
Another modification of the clitambonitid type is visible in Productorthis, in which the brachio-
phores are at first of the primitive flat blade type, but in later growth adventitious shell is laid down
inside and outside of them and likewise around the distal end of the blade, forming cuplike structures.
This type, in a somewhat modified form, also occurs in certain dalmanellids, totally obscuring the
original brachial apparatus (see pi. 4, fig. 1 5).
(4) Plectorthis-Hebertella type (see pi. 11, figs. 4, 26). — Here the brachiophores are sup-
ported by concave plates which unite with the floor of the valve on each side of or beneath the
Fig. 10. — Estlandia marginata (Pahlen). Diagram showing brachiophores in place supported by a
lateral swelling of adventitious substance.
cardinal process. The socket is defined, not by the outer face of the brachiophore, but by a small
concave plate called the fulcral plate^^ located between the outer face of the brachiophore and the
wall of the valve. This type of brachial apparatus characterizes the Plectorthidas and Finkeln-
burgia (see pi. 13, fig. 16). It is foreshadowed hy Orusia {•wKich.isve.vy close, to Finkelnburgia) in
which the brachiophores are supported by subparallel plates. In young Plectorthis the brachiophore
plates are commonly discrete but in older forms they unite beneath the cardinal process or with
a median septum.
(5) Skenidioides type. — This is a modification of the Plectorthis brachial apparatus, and proba-
bly is derived out of that of Finkelnburgia. The brachiophores are very long and the supports are
concave, uniting with a high median septum to form a cruralium. The sockets are defined by con-
cave fulcral plates.^" This type is not confined to the impunctate orthids but occurs also in Linopor-
ella (see pi. 10, figs. 8, 10, 12).
(6) Schizophoria type (see pi. 23, figs. 7, 8, 21 ; pi. 24, fig. 3). — Here the brachial apparatus
simulates that of Hebertella, but differs chiefly in having vertical or widely flaring and never con-
vergent brachiophore supports. The brachiophores are rather long and shaped like the tusk of a boar.
The sockets are defined by fulcral plates (see pi. 23, figs. 18, 21 ). This type is seen to perfection in
Pionodema, Schizophoria, and Enteletes, and characterizes the Schizophoriidas.
In the (7) Dalmanella type (see pi. 17, figs. 2, 31 j pi. 18, figs. 23, 29), the brachiophores are
flattish divergent blades placed obliquely to the vertical. The socket is formed by the outer sloping
^1 Cooper, Jour. Pal., vol. 4, 1930, p. 371.
^^ See Ko7.1owski, Pal. Polonica, pt. I, 1929, p. 48, t. fig. 5, for illustration of this type.
^^ Cooper, op. cit., p. 374.
MORPHOLOGY OF THE ORTHOID SHELL 39
face of the brachiophore, fulcral plates being absent. The brachial apparatus is supported by adven-
titious shell substance only, deposited on the inside surface of the brachiophores and under the antero-
dorsal edge. This gives, in old shells, a cuplike appearance. This type of brachiophore is best seen
in Leveuea, Dalmanella, Cannijerella, etc.
(8) Parniorl/iis type (see pi. 21, figs. 3, 13). — The brachiophores here are supported by short
divergent plates and the socket is defined by a concave fulcral plate. This type is found in Parmorthis,
Mendacella, etc.
(9) Watisella type (see pi. 22, figs. 9, 22, 23, 25, 29). — Like the preceding except that the
brachiophore plates are subparallel or convergent and unite with the median ridge. Fulcral plates
are present.
(10) Heterorthts type (see pi. 20, figs. 19, 20). — In this group the brachiophores are dalman-
ellid-like, but supported by a deposit of adventitious substance speading from the notothyrial
platform and the floor of the valve under the dorsal edge of the brachiophore. This is clearly a
modification of the Dahnanella type and is seen also in Smeathenella^ Reuschella, and Harknessella.
In Rhipidomella and its allies, support of the brachiophores is by means of adventitious substance from
the floor of the valve, which unites with the dorsal edge of the brachiophore; here, too, there also is
not uncommonly a rather long sharp crural process extending from the brachiophore.
CRURALIUM AND PSEUDOCRURALIUM
A cruralium is not often seen in the Orthoidea, but some stocks have developed it, as the Skeni-
diidas, Mystrophoridse, and Linoporellidse. Some of the Plectorthida; have a sessile cruralium. In
the Billingsellidas and Orthidse a pseudocruralium is not uncommon; it is the same structure that we
have called notothyrial platform.
SEPTA
The dorsal valve of the Orthoidea is almost never without some sort of axial thickening to
strengthen the valve between the adductor muscles. This thickening is usually in the form of a low
broad ridge, as in Hesperorthis (see pi. 4, fig. 17), and rarely takes the form of a narrow septum.
In a few families and genera the median septum forms a prominent partition which divides the
valve into equal halves. Such is the case in the Skenidiidse, and also in Mystrophora, where the
septum is so high as nearly to reach the inner surface of the ventral valve.
The median ridge of most orthids is clearly the homologue of the median septum of the
Rhynchonellacea, and in the Paleozoic these shells are scarcely ever without an axial thickening.
Aberrant genera such as Porambonites and Lycophoria are unique in not possessing a median septum.
MUSCULATURE
The individualization of the musculature of the dorsal valve is fraught with the same difficul-
ties as that of the ventral valve. In well preserved specimens there are usually the distinct scars of
eight muscles, but in a few species two additional scars are distinguishable. Most prominent and
usually best preserv^ed are the four (in many genera six) adductor scars produced by the bifurcation
of the two ventral adductor muscles as they pass from the ventral to the dorsal side. These form a
field of variable outline usually located near the center of the valve and anterior to the notothyrial
platform. These two pairs are almost invariably divided longitudinally by the median ridge and
are usually separated transversely by smaller, less prominent ridges at a greater or lesser angle to the
median one, thereby dividing the field into quadrants. The pair immediately in front of the noto-
thyrial platform are the posterior adductors, and the pair farther forward arc the anterior adductors.
In many genera the anterior adductor impressions are clearly divisible each into two parts (nota-
bly true in Prodtu tort his y see pi. 3, fig. 1 1 ), so that there are evidently six scars in the adductor field.
This third "adductor" set may represent adjustor muscles whose ventral attachments are on the
pedicle and are thus not recorded by a corresponding set of impressions on the ventral valve. It is
possible also that the adductor muscles trifurcate in their passage from the ventral to the dorsal valve.
Derby** early directed attention to the presence of six adductor scars in the dorsal valve of
"BuU. CorneU Univ., vol. 1, pt. 2, 1874, p. 30.
40
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Orthotichia {Orthis (?) morganiana Derby). This writer, however, was mistaken as to the true
number in that genus. It is shown under Orthotichia, and also in our discussion of Schizofhoria,
that the posterior adductor scars migrate laterally, leaving a rather prominent space occupied by the
low median ridge only. It is this space that Derby took to be the scars of a third pair of muscles.
The diductor impressions of the dorsal valve are located either on the myophore of the cardinal
process or on the floor of the notothyrial cavity on either side of a linear cardinal process or septum
as in Hes'per orthis and Dolerorthis. In genera with a cardinal process of the Orthis type, it has been
possible to distinguish definitely only one pair of muscles, placed on either side of the process.
There is, however, a possibility that there were actually two pairs, one attached to the sides of the
process and the other to the notothyrial platform next to the process. In shells with the Dalmanella
type of cardinal process it is clear that there were two pairs of muscles attached to the myophore, as
shown clearly in the quadrilobation and trilobation of the latter.
PALLIAL MARKINGS
Our study of the Orthoidea shows that a definite pattern for the pallial sinuses of the dorsal
valve is fairly prevalent. In the early forms such as Finkelnburgia, Syntrophioides, Syntrophia,
Billingsella, and other related genera, the pallial markings in general have a radial arrangement, the
trunks generally taking their origin between the adductor impressions both on the sides and in the
Figs. 1 1-15. — Dorsal pallial markings. 1 1, Orthis rotunda (Pander). 12, Schiozophoria. The usual condition in the
orthoid dorsal valve is a lateral trunk extending from the space between the anterior and posterior adductors, and two
trunks from the anterior end of the median ridge between the anterior adductor scars. These two trunks bifurcate immedi-
ately, giving rise to four. Cf. t. figs. 13, Isorthis; 14, Levenea; 15, Heterorthis clytie (Hall).
front. In later forms the radial arrangement is lost but the trunks originate at essentially the same
point. In Schizophoria and Isorthis two trunks take their origin medianly between the left and right
adductor sets. These extend for a short distance and then bifurcate at or near the front of the
anterior adductor scars. The four resulting branches may extend directly anteriorly as in some
species of Schizophoria (t. fig. 12), or may run obliquely as is more usual. In addition to these
trunks and their subsidiary branches, a lateral trunk originates between the anterior and posterior
adductors, and extends directly laterad as in Isorthis and Levenea (t. figs. 13, 14). In some species
MORPHOLOGY OF THE ORTHOID SHELL 41
of Schizophoria the low transverse ridge dividing the anterior adductors from the posterior ones is
oblique, being directed antero-laterally; in such the lateral pallial trunks extend in the same direc-
tion as the adductor ridge, thus giving rise to six subparallel trunks.
Our studies show that in the present state of our knowledge not much taxonomic importance
can be attached to the dorsal pallial sinuses, because of the absence of marked variation, and also
because of the rarity of specimens in which they are preserved.
MICROSTRUCTURE OF THE SHELL
The orthid shell of the Middle Ordovician, as shown by Sardeson,^" consists of two calcareous
layers as follows: (1) an outer, thin, first or primary, non-fibrous layer that grows at the margin of
the shell only. It grows at an equal rate along the whole hinge, and elsewhere around the periphery
at an increasingly greater rate toward the front. It is this first layer that determines the general
outline and convexity of both valves, the folds and sulci and the plications. Sardeson erroneously
calls this primary calcareous layer the "epidermis," but in living brachiopods the thin chitinous
outer skin has long been known as the epidermis or periostracum and it covers the whole of the shell.
Such an epidermis undoubtedly also existed in the ancient brachiopods, but all trace of it has been lost
in fossilization. It is to this external chitinous skin that the term epidermis should be restricted, and
Sardeson's "epidermis" is the thin lamellar layer mentioned on an earlier page.
(2) Sardeson next points out that inside the primary lamellar non-fibrous layer there is a much
thicker one composed of prisms or fibres of calcite, which are directed obliquely forward and inward
with respect to the whole shell. They are based against the lamellar layer and terminate upon the
inner surface of the valves. The growth of this fibrous shell matter is not at the edge of the valves
but upon the whole inner surface, and it is deposited by the mantle proper. This fibrous layer
thickens the valves more and more, obliterates the plications and other inequalities, and often thickens
the articulating and brachiophore structures. When the shell is endopunctate, it is this fibrous layer
that is perforate, due to the shell's growing around the minute and threadlike papillce on the outer
surface of the mantle and adhering to the inner surface of the outer non-fibrous lamellar layer.
Young^" has also shown that in the genus Productus there are two layers, the inner one being
punctate (now known not to be true) and the outer impunctate. Kozlowski, however, points out
that other strophomenids are not punctate. Young also observed a similar condition in Eichwaldia
and Chonetes. In the impunctate genera it is probable that a similar condition exists, that is, there is
an outer calcareous layer growing only at the margins of the shell which determines the external
sculpture of the valves, and this is covered on the inner surface by the main mass of the fibrous or
prismatic shell. In punctate shells the primary shell matter of teeth, dental plates, apical plates, etc.,
is impunctate. The deltidium is said to be impunctate in punctate shells.^^
In Cambrian shells Walcott reports a shell structure different from those of later periods.
According to him, the billingsellids and other Cambrian shells that he sectioned appear to have a
granular structure throughout. To the writers, this granular shell structure, restricted to the Cam-
brian, always appeared anomalous. Therefore we sectioned a specimen of B. Undstromi from the
Paradoxides zone of Sweden, and it proved to have a fibrous structure. Indeed, the fibers are clearly
visible in the specimen with a low-power hand lens (pi. 29, fig. 12). We have also rephotographed
one of Walcott's sections of B. coloradoensis and this too proved to be fibrous (pi. 29, fig. 13). The
photograph of this thin section was enlarged about 30 times, whereas Walcott used an enlargement of
50 to 100 times. We believe that this latter enlargement is too great and unduly emphasizes the
fractured condition of the mineralized shell. Furthermore, we found no evidence of puncta; in any
"Amer. Geo!., vol. 19, 1897, pp. 92-93.
=»In Davidson, Brit. Foss. Brach., Suppl. to Carb. Brach., vol. 4, 1874, pp. 296-302.
'" In regard to this statement, the writers wish to say that they have studied but one punctate shell which has a del-
tidium {Kayserella), and unfortunately the one specimen studied was too mineralized to show whether or not the deltidium
was punctate. Beecher's statement that the deltidium is impunctate in punctate shells loses force in the light of Kozlowski's
recent work (1929), in which the latter shows that the supposed puncta: of the Strophomenacea are in reality granula:
formed by rods of crystalline substance in the shell. Since the Strophomenacea are (excluding the Clitambonitida:) the chief
deltidium-bearing shells, the anomaly emphasized by Beecher may after all not prove to be so important as he thought.
42 GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
of the Cambrian shells studied, nor could we find any in Walcott's sections, although they are
reported in Billingsella, Huenella, and Syntrofhia. All of the billingsellids and other Cambrian
articulates that we studied have the essential structure of Orthis and Clitambonites. There is there-
fore no reason to suspect that the shell structure in the oldest genera is different, and our evidence
favors the view of a uniform shell nature and growth of the orthids since early Cambrian time.
Furthermore, we find no punctate (endopunctate) shells in the Cambrian and Ozarkian, and this type
of shell is first seen in the dalmanellids (of the Chazy), which probably had their origin in early
Ordovician time (Canadian).
Since brachiopods were first studied, investigators have noticed minute perforations in the inner
and outer surfaces of the test. The present observations show that these perforations are of two
main sorts and that they may be grouped into two divisions, as follows:
ExopuNCTiE. — Pores of this type are readily visible on the unabraded exterior, i. e., in the outer
lamellar layer. They do not, however, penetrate far into the interior of the shell substance and
never pass completely through the fibrous test. Such pores are especially well exhibited by Pauror-
this and have frequently been mistaken for true punctas (endopunctse). They are also visible in
Valcourea, Doleroides, Hebertella, Rhipidofnella, and many other genera. In occurrence the
exopuncta; are sporadic within a genus and they are not confined to shells of the "impunctate" type.
In Valcourea, Doleroides, and some other genera, the exopunctse appear as perforations in tiny
granules on the ribs.
Endopunct^. — These are pores that are found only in the fibrous layer of the test, extending
from the inside but never appearing on the surface when the outer lamellar layer is present. On the
inside they are common to the whole surface of the shell, but when the shell is costellate the pores
are concentrated into rows toward the exterior.
VALUE OF PUNCTATION IN TAXONOMY
Some European authors regard the endopunctje as important in the establishment of species
among living terebratulids and other punctate shells. Since the size and arrangement of the pores
is quite uniform, when the same portions of different shells are compared, a difference in pattern is
believed to be of specific value. The idea has not, however, found application in this country.
Among the orthids, punctation is of great generic value, since certain types of internal structure
may be correlated with the endopunctas. The oldest known endopunctate shell occurs in the Middle
Ordovician (Chazy) but from the internal structure of some Lower Ordovician (Beekmantown)
genera, this type of punctate shell must occur at least that early. It appears evident at this time
that the punctate forms arose out of impunctate ones, but whether the punctate stock, once arisen,
remained persistent, or whether punctation was invented many times, has yet to be determined j it
would appear that both views are tenable.
OLD-AGE CHARACTERS
An important feature of the inside of a brachiopod shell is the internal thickening, which is a
consequence of age, since the mantle continues to secrete shell matter throughout life. This addition
of extra testaceous substance may so alter the internal features, muscle fields, and cardinalia in old
individuals as to suggest other genera than the one actually under observation. In the ventral valve
the chief alterations are in the obsolescence of the dental plates and the development of a pseudo-
spondylium. Hall and Clarke record the lack of dental plates as one of the generic features of
Orthorhynchula, but in young shells of O. linneyi and in O. ottawaensis (Bills.) there are prominent
dental lamellae. The development and importance of the pseudospondylium and spondyloid are
discussed under Glossorthis, Linoforella, Porambonites, and other genera having this feature.
In the dorsal valve, adventitious tissue is commonly utilized for the support of the brachio-
phores, as is well exhibited in the Clitambonitidas (see figures of Estlandia). We have laid chief
stress in classification, however, upon the primary or youthful structures, and these have guided in
making our family groupings. The different modes of deposition of extra shell matter are useful in
some instances in showing relationships, but are more often deceptive.
PART IV. THE GENERA OF THE SUBORDER ORTHOIDEA
The supcrfamily Orthacea erected by W'alcott and
Schuchert in 1908 has grown to large proportions in
the way of genera. Among these the presence of
an impunctate (m.ay be exopunctate) or a punctate
(alwa}'s endopunctate) shell is now seen to be of much
significance in taxonomy, and the genera of the old
division "Orthacea" are now known to be separable,
on the basis of punctation and certain internal features
of the shells, into three superfamilies, namely, ( 1 )
Orthacea as here restricted, (2) Clitambonacea (for-
merly included in the Pentameracea), and (3) Dal-
manellacea. Out of the Orthacea came the (4)
Syntrophiacea, which may have given rise to the (5)
Pentameracea; both are now included in the new
suborder Pentameroidea. All of these superfamilies are
impunctate with the exception of the Dalmanellacea,
which are internally punctate (endopunctate).
As the superfamilies Orthacea, Clitambonacea, and
Dalmanellacea are closely linked genetically and have
an external expression in common, i. e., transverse
shells with wide hinge-lines, more or less prominent
interareas, and usually open delthyrium, it is desirable
to combine them into a new suborder, Orthoidea. On
the other hand, the Syntrophiacea and the Pentamer-
acea tend more and more with time to lose their orthid
ex-pression and to become elongate and rostrate shells
with decidedly different cardinalia, and accordingly are
combined into the new suborder Pentameroidea.
Therefore when we write "orthids," we refer to
Orthacea, dalmanellids = Dalmanellacea, clitamboni-
tids = Clitambonacea, syntrophiids = Syntrophiacea,
and pentamerids = Pentameracea. "Orthoids," on
the other hand, refers to the Orthoidea, and "Penta-
meroids" to the Pentameroidea.
The suborder Orthoidea ranges, so far as known,
from the Lower Cambrian to the close of the Permian,
whereas the Pentameroidea begin in the Upper Cam-
brian and die out with the Devonian.
Ulrich^ in discussing the musculature of the
Ordovician orthoids in comparison with those of the
Cambrian, foreshadows the classification developed in
this book when he says that a "natural division" of the
orthoids into two families is possible as follows:
(1) Ventral muscular area small, obovate or obcordate;
adductors reaching front margin of area (Orthis s. s.
[^ Hesferorlhis], Plectorthis, Platystrophia, Hebertelta,
Orthostrofhia, Dalmanella [the only genus that we do not
include in the impunctate superfamily. This is the fore-
shadowing of our superfamily Orthacea, now seen to be
most e.isily distinguished on the basis of an impunctate
test]) . . . (2) Ventral muscular area large, bilobed or
elliptical; adductors proportionately small and more or
less completely inclosed anteriorly by the flabellate diduc-
tors {Heterorlhisy Plttsiomys? defiecta group, Dinorthis
[the last two genera we think are out of place here and
are best referred to the Orthacea], Bilobiles, Rhifidom-
ella, Schizofhoria, Orlholichia), [This division includes in
the main our Dalmanellacea.]
Superfamily ORTHACEA Walcott and Schuchert 1908
The evolution is thought to be as shown in Table 1 .
Primitive Orthoidea of early Cambrian time. A
prolific stock with the test always impunctate (we do
not agree with \V^alcott's observations to the contrary).
Shells usually multicostellate, rarely costate and even
more rarely smooth or nearly so; nearly always with
more or less prominent interareas in both valves, and
wide hinge-lines; deltidia and chilidia sporadic; with
a simple cardinal process except in primitive genera,
where there is none; spondylia rarely developed,
pseudospondylia not uncommon.
Range: Earliest Cambrian into Devonian.
Includes the families:
Nisusiids
Protorthidje
Billingsellidse
Eoorthidae
Orthidse
Dinorthidae
Porambonitidae
Lycophoriidse
Finkelnburgiids
Plectorthids
Skenidiida:
' In Walcott, Camb. Brach., 1912, p. 308.
Family NISUSIID^E Schuchert and Cooper
1931
(Nisusiinx Walcott and Schuchert 1908, Wal-
cott 1912, Schuchert 1929)
The most primitive of the known Protremata and
Orthacea, having a well developed deltidium with an
apical foramen in the genotype, but no dental plates.
Shell probably very thin. In the dorsal valve there is a
chilidium, and the brachiophores are rudimentary and
similar to those of Eoorthh or Bilimgsella. No cardi-
nal process is present in Nisusin, and a rudimentary one
only in Jamesella.
The family embraces the genus Nisusia, and for the
present Jamesella is also placed here, though its origin
remains unknown.
44
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Table 1
Porambonitidae
Dinorthidx
Plectorthidas
Lycophoriidse
Orthidae
Skenidiidx
'Eoorthidae
Protorthidae
Discussion. — Walcott has always regarded Nisusia
as the most primitive known representative of the Pro-
tremata, it being also the oldest member of this order,
and to this we agree, with the statement that it appears
to be the progenitor of the Orthacea. Nisusia appears
late in the Lower Cambrian and vanishes with the
Middle Cambrian. Jamesella is a European stock of
another origin and of the later Cambrian. Possibly
out of Nisusia came Protorthis of the Middle and
Upper Cambrian, while the older Loperia is of another
genetic line. As yet we do not know the origin of
Swantonia of the Lower Cambrian, unless it be out of
Nisusia, and this doubt is due to lack of knowledge of
the dorsal interior. Since Swantonia has no spondylium
it may not be an orthid at all, and hence it is not at
all certain that this genus gave rise to the Syntrophiacea.
Walcott says that Swantonia may have been the pro-
genitor of both the syntrophiids and Protorthis^ but in
this we can not concur.
= Camb. Brach., 1912, p. 320.
Genus NISUSIA Walcott 1905, emended
PI. l,figs. 16, 20
Walcott, Proc. U. S. Nat. Mus., vol. 28, 1905, p. 247;
Camb. Brach., 1912, p. 725, pi. 100, figs. 1-lj,
2-2c, t. fig. 6.
Genoholotype : Orthisina festinata Billings 1861,
Pal. Foss., vol. 1, p. 10, figs. 11-12.
Description. Exterior. — Subquadrate to semi-
oval, unequally biconvex, with the dorsal valve the
more convex. Hinge-line straight, usually as great as,
or greater than, the greatest width of the shell; car-
dinal extremities usually acute, anterior commissure
faintly uniplicate; ventral sulcus shallow; ventral
interarea broad, strongly apsacline to procline; del-
tidium well developed, strongly convex, but only par-
tially covering the delthyrium, perforated at the apex.
Dorsal interarea anacline, notothyrium more or less
well developed. Chilidium present. Surface costel-
late, crests of costellas provided with prominent spines
GENERA OF THE SUBORDER ORTHOIDEA
45
in the genotype and other species. Micro-structure of
the shell not definitely known, probably fibrous,
impunctate.
Ventral interior. — Delthyrial cavity obsolete; teeth
very rudimentary; dental plates absent, ventral muscle-
scars not visible.
Dorsal interior. — Notothyrial cavity very shallow;
notothyrial callosity confined, without a cardinal proc-
ess, and not produced forward as an axial ridge or
thickening. Brachiophores bladelike thickenings along
margins of notothyrium. Adductor scars appearing
as two divergent, elongate impressions anterior to the
notothyrial callosity.
Geological range. — Late Lower and early Mid-
dle Cambrian.
American Species'
Billingsella Jberla (Walcott) 1888
B. festinata (Billings) 1861
B. transversa (Walcott) 1886
Nisusia burgessensis Walcott 1924
? BUlingsella bivia Walcott 1912
? B. orientalis (Whitfield) 1884
? Nisusia (Jamesella) amii Walcott 1905
? N. (J.) erecta Walcott 1905
?A'. (y.) /o»»" Walcott 1908
? iV. (y.) nautes (Walcott) 1905
? Af. (y.) sfencei (Walcott) 1905
? iV. (y.) utahensis Walcott 1905
Distinguishing characters. — The genus Nisusia
is characterized especially by the biconvex profile of the
valves, the well developed deltidium with apical per-
forations (in the genot)'pe), a chilidium, a lack of
dental plates and of a cardinal process, and very primi-
tive cardinalia. Walcott (1912) regarded it as the
most primitive of known Protremata.
Discussion. — Since Nisusia is the oldest known
articulate brachiopod of the Cambrian, it has great
taxonomic importance. Accordingly the species of the
genus have, perhaps, the most primitive structure. The
valves are biconvex, the dorsal having as a rule greater
convexity. The ventral valve has a prominent sulcus
and the surface of the shell is marked by costelL-e which
increase both by intercalation and by bifurcation. In
the genot)'pe and some of the other species the crests
of the costellx are provided with prominent spines.
This spinose surface Walcott considered as the dis-
' Generic designations used in these lists are taken from
the following sources:
For American species prior to 1897, Schuchert, Bull. 87,
U. S. Geol. Surv., 1897.
For Cambrian species from 1897 to 1912, Walcott,
Mon. 51, U. S. Geol. Surv., 1912.
For American Ordovician and Silurian species from
1897 to 1915, Bassler, Bull. 92, U. S. Nat. Mus., 1915.
Other species are, in the main, cited under their original
generic designation.
tinguishing feature between Nisusia and Jamesella,
but it appears to be of doubtful generic importance,
since the generic characters should be mainly the more
fundamental internal ones.
The intcrareas are well developed on both valves
and somewhat extravagantly on the ventral one. The
elongate ventral interarea, combined with the promi-
nent deltidium, might lead one to suspect that he was
dealing with a member of the Clitambonitida;, but this
is not true. The deltidium is strongly arched, especi-
ally at the wide end, and does not cover the del-
thyrium completely. The arching is greatest at the
open end of the deltidium, the margin of which is
strongly concave toward the beak. The apex of the
ventral shell in all specimens of A^. jestinata (Bills.) is
broken, suggesting that there was an open foramen
which is now filled with matrix, hence the destruction
of the beak in internal molds. In any event, the
actual margin of the foramen was not observed. It is
well to emphasize again that the deltidium of Nisusia
is well developed, since one might expect the del-
thyrium in so primitive an articulate brachiopod to be
a completely open one. We therefore see that in this
very early development of the deltidium and chilidium
there is great value in classification, as first pointed out
by Beecher.
The interior of the ventral valve shows surprisingly
few characters, but this may be due to the thinness of
the valves. Walcott says that these shells have "dental
plates that extend outward, also inward, forming on
the inside a shallow spondylium." We saw no such
structures in the specimens studied, and in our opinion
Nisusia does not possess a pseudospondylium, or any
structure even remotely similar to a spondylium, nor
do dental plates occur in the genotype, A^. jestinata.
If such plates were present, the internal molds would
show as indentations or tracks representing the position
of the plates. Squeezes, however, do show slight thick-
enings along the delthyrial margins, which may indi-
cate incipient dental plates or the growth tracks of the
teeth. The explanation of all this is that Walcott's
reference to dental plates (pi. 100, fig. If) and a
pseudospondylium in A^. jestinata was inadvertently
made on a dorsal valve. The cardinalia of Nisusia
do, in some degree, resemble a cruralium (see his p.
728), and his "spondylia" in Nisusia may have been
incorrectly identified in dorsal valves. Traces of mus-
culature occur rarely in the ventral molds, but are too
faint to make out their nature.
The internal morphology of the dorsal v.ilve of
Nisusia, like that of the ventral valve, is misunderstood.
Walcott has described a cruralium, but it may be ques-
tioned whether this structure exists in any of the Cam-
brian genera. The brachiophores are flattened plates
like those of BUlingsella or Eoorthis, making the noto-
thyrial margin, and are supported by adventitious shell
deposit that extends from the floor of the notothyrial
cavity. These plates are situated oblique to the dorsal
46
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
direction, and the margins of the interarea overlap
them, leaving a long groove on their outer side which
serves as the dental sockets. A chilidium is present in
several species, but there is no cardinal process. The
only evidence of the adductor tracks is tvi^o elongate,
divergent depressions just anterior to the notothyrial
callosity.
From the above it is evident that it has been neces-
sary wholly to revise Walcott's list of species referred
to Nisusia, with the result that but four are left unques-
tionably by us in this genus. N. comfta (Tate) of
South Australia varies widely from Nisusia in the shape
of the valves. It is syntrophiid in form and suggests
A^. oriens Walcott 1924. Both these species should be
referred to another genus.
Genus JAMESELLA Walcott 1905
PI. 1, fig. 24
Walcott, Proc. U. S. Nat. Mus., vol. 28, 1905, p. 252;
Camb. Brach., 1912, p. 731, pi. 101, figs. 1-lh.
Genoholotype. — Orthis ferfasta Pompeckj 1896,
Jahrb. geol. Reichs. Wien, vol. 45, pp. 515-516, pi.
15, figs. 15-18.
Description. Exterior. — Transversely subquad-
rate; hinge-line straight, cardinal extremities usually
obtuse. Lateral profile subequally biconvex. Fold and
sulcus not stabilized. Ventral interarea long, curved,
strongly apsacline; delthyrium open or covered by a
convex deltidium. Dorsal interarea short, moderately
anacline; notothyrium open. Surface usually multi-
costellate. Microstructure of shell unknown.
Ventral interior. — Delthyrial cavity deep, dental
plates rudimentary ( ? ) ; muscle area wide ; adductor
track subtriangular, longer than the diductor scars;
diductor impressions wide, attached on the sides of the
delthyrial cavity; pallial depressions on the outside
margins of the diductors, but their anterior continua-
tions are not visible.
Dorsal interior. — Notothyrial cavity moderately
deep, brachiophores billingselloid, dental sockets small;
cardinal process linear or rudimentary; adductor scars
unknown.
Geologic range. — Walcott (1912) says that
Jamesella occurs in the Lower Cambrian, but the
actual deposits having the conglomerate pebbles with
fossils are of Middle Cambrian time. The genus is
very poorly known and none of the American species
referred to it conforms to the structure of the geno-
type. As here redefined, Jamesella is restricted to the
Middle Cambrian of Bohemia, most of the American
Lower Cambrian species placed here by Walcott being
better referred doubtfully to Nisusia.
European Species
Nisusia {Jamesella) kuthani (Pompeckj) 1896
TV. (7.) ferfasta (Pompeckj) 1896
N. (j.) fer-pasta macra (Pompeckj) 1896
N. (J.) ferfasta subquadrata (Pompeckj) 1896
Distinguishing characters. — Walcott distin-
guished Jamesella from Nisusia chiefly by the absence
of external spines in the former. More fundamental,
however, are the presence of pronounced muscle-scars
showing a rather wide adductor track, and the rudi-
ments of pallial marks similar to those usually seen in
Billingsella. In the dorsal valve the cardinalia are
billingselloid, so far as can be determined from squeezes
of the genotype specimens. The interior characters are
those rather of Middle Cambrian than of Lower
Cambrian time.
Family PROTORTHID^ Schuchert and
Cooper 1931
Primitive specialized Orthacea with a very short free
concave plate, evidently a free spondylium; there are
no dental plates nor is there a deltidium or chilidium;
the cardinalia are like those of Billingsella, and a car-
dinal process is absent.
The family embraces Protorthis Hall and Clarke
and Loperia Walcott, both of the Middle Cambrian of
New Brunswick and Nova Scotia.
Discussion. — Walcott (1912, p. 317) thinks that
Protorthis arose in the Lower Cambrian out of the
stock that gave rise to Nisusia, and to this we agree.
Genus PROTORTHIS Hall and Clarke 1892
PI. 1, figs. 12, 14
HaU and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 231,
pi. 7a, figs. 14-21.
Walcott, Camb. Brach., 1912, p. 738, pi. 99, figs. 1-lg.
Genoholotype. — Orthis billingsi Hartt 1868, in
Dawson, Acad. Geology, 2d ed., p. 644, fig. 223.
Description. Exterior. — Shell usually small, thin-
shelled, transversely subquadrate or semicircular, hinge-
line straight, usually equal to the greatest width of the
valves; cardinal extremities angular; lateral profile
subequally biconvex. Ventral interarea long; delthy-
rium open. Dorsal interarea short; notothyrium open.
Surface multicostellate. Microstructure fibrous?,
impunctate.
Ventral interior. — Teeth small, delthyrial cavity de-
fined by a free spondylium, probably for pedicle mus-
cle attachment. Muscle-scars not visible on spoon or
floor of valve.
Dorsal interior. — Notothyrial platform very shallow,
confined and without a cardinal process; chilidium
absent; brachiophores like those of Billingsella, short;
median ridge absent.
Geologic range. — Middle Cambrian of New
Brunswick.
GENERA OF THE SUBORDER ORTHOIDEA
47
Species
BillingseUa billingsi (Hartt) 1868
B. latourensis (Matthew) 1886
B. quacoensi4 {M.M\\ev;) 1886
? Eoorthis /uutingsensis Walcott 1905
P. (?) hunnehergensis and P. wingi of Walcott can
not be placed in any Cambrian genus. P. helcna and
P. l/Fvis of the same author may be syntrophiid.
More recently, Walcott'' has also referred two
Ordovician shells, P. tones and P. porcias, to this genus.
Neither has a free spondylium or any structure ap-
proaching it. Furthermore, both species are compos-
ite, including representatives of Archceorthis and prob-
ably of Tafia.
Distinguishing characters. — Protorthis extern-
ally resembles Eoorthis with its rather large costells,
but the unsupported short spondylium of the ventral
valve is an important feature in its identification.
Discussion. — The preservation of the New Bruns-
wick Middle Cambrian Protorthis is not good. The
specimens occur in a soft and much distorted shale and
accordingly are much crushed. It is, however, possible
to distinguish, in molds of the interior, rather small
teeth for articulation of the valves, and thickenings
along the delthyrial margins which are the tracks of the
forward growth of the teeth.
The most interesting and important internal feature
in Protorthis is the very short and small spondylium
that hangs free in the delthyrium. Hall and Clarke'
say correctly that the cardinal area "is transected by a
broad delthyrium which is closed below by a concave
plate apparently produced by the union of the dental
lamelLx, which are not continued to the bottom of the
valve." In Protorthis the spondylium is variable in
length ; in some species it is a narrow shelf under the
posterior lateral margins of the delthyrium, and in
others it is a spoon-shaped plate two-thirds the length
of the delthyrium. Since the function of the true
spondylium is to furnish attachment for the diductor
and adductor muscles, one should expect to find scars
on the spoonlike plate. No such scars have been seen
on the spondylium, nor have definite scars been dis-
covered on the floor of the valve beneath the spondyl-
ium. Evidence is therefore lacking as to the function
of this peculiar structure. Such a plate as this is un-
known elsewhere among the orthids. Among the
pentamerids a free spondylium is known and its origin
can be traced to the resorption of the median support-
ing septum. Such an origin can not be maintained for
the spondylium of Protorthis because there is no known
spondylium-bearing (with a median septum) ancestor
< Smiths. Misc. Coll., vol. 67, no. 9, 1924, pp. 503,
504.
'Pal. N. Y., vol. 8, pt. 1, 1892, p. 231.
from which it could have been developed. Further-
more, the orthoid brachiopods older than Protorthis
were not provided with dental lamells. It is here sug-
gested that in Protorthis we have one of the earliest
developments of dental plates, but in this instance the
dental lamella: grew toward each other and united
instead of growing directly ventrally to the floor of
the valve.
The morphology of the dorsal valve of Protorthis is
not unlike that of Nisusia and BilUngsrlln, since the
former has very primitive cardinalia and a cardinal
process is wanting. No definite evidence of the mus-
culature is known.
It has been customary, since the publication of Prot-
orthis by Hall and Clarke, to say that it has a punctate
shell. The evidence for this statement is found in the
presence of fine papillx on the molds of the exterior or
interior. Although papilla? are suggestive of punctje,
a thin section of the shell in the Schuchert Collection
fails to reveal true puncta; (endopunctas). On the
other hand, as no Cambrian articulate brachiopod is
definitely known to have a punctate shell (endopunc-
tate), it is hardly to be expected that Protorthis has
such.
Protorthis is unlike any other known genus and
therefore appears to be an early specializing stock
which gave rise to no other groups.
Genus LOPERIA Walcott 1905
Walcott, Proc. U. S. Nat. Mus., vol. 28, 1905, p. 287;
Camb. Brach., I9I2, p. 744, pi. 99, figs. 5-5j.
Genoholotype. — Protorthis (Loprria) dougald-
ensis Walcott 1905.
Description. Exterior. — Outline subquadrate,
hinge-line straight, cardinal extremities obtusely sub-
angular; lateral profile resupinate. Ventral interarea
long, strongly apsacline; delthyrium open. Dorsal
interarea short, procline or faintly anacline; notothy-
rium narrow, open. Surface multicostellate. Micro-
structure probably fibrous impunctate.
Ventral interior. — Precisely as in Protorthis.
Dorsal interior. — Crural bases very short, nototh)'-
rial platform small, bearing a very low, thick cardinal
process. Median elevation low.
Geologic range. — Middle Cambrian. Only
known species, L. dougaldensis Walcott of Cape
Breton, Canada.
Distinguishing characters. — Loperia is charac-
terized by the same internal features as Protorthis, but
differs in having a strophomenoid lateral profile or con-
vexo-concave shell. The ventral valve has strong
teeth and a free spondylium, but no clear evidence of
musculature was seen on it. In the dorsal valve, the
48
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
cardinalia are more strongly developed and there is a
low thick cardinal process; nothing of muscle marks
was seen.
Discussion. — Walcott states that the shell of this
genus is punctate, and the evidence is based on the pres-
ence of papillae on the internal and external molds. If
these indicate endopunctas, they should be confined to
the internal molds; besides, they are coarser than is
common for punctas in punctate shells. We can not
explain these supposed pores either as fortuitous or as
anatomical features. We incline toward the former
Family BILLINGSELLID^ Schuchert 1893
Primitive costellate Orthacea, usually with a deltid-
ium and chilidium; there is no spondylium, since the
dental plates remain discrete, but there may be a pseu-
dospondylium. The ventral muscles are clearly differ-
entiated into broad adductor and well marked diductor
tracks. Ventral pallial sinuses widely divergent. In
the dorsal valve the brachiophores are short, flat,
oblique plates, placed under the palintrope. Cardinal
process present or absent ; when present, a simple ver-
tical plate. As now constituted, the family has but
the one genus, Billingsella.
Discussion. — Hall and Clarke* say that Billingsella
"may have served as a point of departure for the
Orthidas and Strophomenidae." Walcott'' is correct in
saying that the general resemblance of the Cambrian
eoorthids to certain Ordovician Protremata is striking
and the lines of descent suggestive. This is seen not
only in the family Billingsellidae, but as well in its
descendants the Finkelnburgiida:, Plectorthidas, Or-
thidas, and the Clitambonacea and Syntrophiacea.
The Strophomenacea are structurally foreshadowed
here, but these apparently did not originate directly out
of the Billingsellidas but out of one of the later families,
probably the Orthidas, during the Lower Ordovician,
since the earliest known forms occur in the Middle
Ordovician (Chazy). In this work we have not taken
up a revision of the Strophomenacea for want of time,
and must leave it to others.
Billingsella, as here defined, could, theoretically,
have given rise to the Clitambonacea, a group now
known to be closely related to Orthis. This super-
family is provided with pallial markings exactly like
those of Orthis (see pi. 8, fig. 10). Furthermore, the
Clitambonitidas and Deltatretidas retain the primi-
tive deltidium and chilidium so well developed in
Billingsella.
«Pal. N. Y., vol. 8, pt. 2, p. 355.
' Camb. Brach., p. 300.
Genus BILLINGSELLA Hall and Clarke 1892
PI. 1, figs. 6, 10, 13, 19, 21, 25, 27; pi. 29,
figs. 12, 13
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 230,
pi. 7, figs. 16-19, pi. 7a, figs. 7-9.
Walcott, Camb. Brach., 1912, p. 7+9, pi. 85, fig. 1, t.
figs. 6, 66.
Genoholotype. — Orthis fefina Hall 1863, N. Y.
State Cab., 16th Rept., p. 134, pi. 6, figs. 23-27.
Description. Exterior. — Subquadrate or semi-
circular in outline, ventral valve subquadrate, dorsal
valve usually transverse; hinge-line straight; cardinal
extremities usually rectangular or obtusely angular,
occasionally acute; lateral profile unequally biconvex;
anterior commissure faintly sulcate ; ventral palintrope
very long, orthocline or moderately apsacline; delthy-
rium wide, more or less covered by a convex deltidium
which in some species is perforated at the apex by a
small aperture. Dorsal palintrope shorter than the
ventral, strongly anacline, notothyrium wide, partially
covered by a convex chilidium. Surface multicostellate.
Microstructure fibrous, impunctate.
Ventral interior. — Teeth prominent and large, with
strong sockets on their outer margins; dental plates
strong, oblique to the vertical and widely divergent;
musculature prominent and scarcely ever making a dis-
tinct pseudospondylium ; diductor tracks widely diver-
gent; adductor track forming a central triangular scar
that is often more or less prominently elevated in front.
Pallial marks prominent, consisting of two pairs of
divergent, narrow sinuses, originating at the anterior
margin of the diductors and extending forward about
three-fourths the length of the valve, where they fork.
In the center of the valve they define an elongate
pentagonal area and laterally they bound a subreniform
space. At the anterior margin innumerable secondary
sinuses extend radially toward the margin.
Dorsal interior. — Brachiophores widely divergent,
short, and with imperfectly defined sockets appearing
as shallow cups outside the crural bases. Brachiophore
bases usually somewhat obscured by adventitious shell
grown about them, forming a prominent thickening in
the notothyrial cavity and extending forward a short
distance as a median axial thickening. Cardinal process
a simple ridge between the diductor scars; adductors
elongate ; elliptical scars diverging from the prominent
pits anterior to the notothyrial platform; a radial pallial
mark extending with slight convexity from the anterior
end of each adductor impression.
Geologic range. — Mainly Middle Cambrian to
uppermost Cambrian. There is also an undescribed
species in the lower Ozarkian of North America.
American Species
Billingsella ? affalachia Walcott 1905
B. color ado ensis (Shumard) 1860
B. holtedahli Walcott 192+
GENERA OF THE SUBORDER ORTHOIDEA
49
B. nutjor Walcott 1905
B. flualflla WiXcon 1905
B. strUlj Walcott 1905
Orthii fefina Hall 1863
Clitambonites flanus retroflexus Matthew 1896 (looks much
like B. linJstromi)
European Species
Billingsella lindstromi (Linnarsson) 1876
Distinguishing characters. — The important
distinguishing features of B'dlingsella are the subquad-
rate outh'ne and biconvex lateral profile; ortho- or
slightly apsacline, elongate and plane interareas; large
teeth with low supporting lamcll<-e; prominent muscle
marks with elongate adductor track; strong pallial
trunks; primitive cardinalia; and the presence of a
deltidium and chilidium.
Composition of genus. — Before we proceed with
the generic discussion, it should be said that Walcott in
1912 referred 20 species and 1 variety to Billings-
ella — a rather heterogeneous lot — and of these 14 are
found in North America, the remainder in Norway
and Sweden (3), Wales (1), Bohemia (1), and
China (2). Of these 21 forms we leave but 8 (?7)
in Billingsella (7 in America and 1 in Sweden). Of
the other 13, 2 are referred doubtfully to Ntsusia
{hivia and orientalis), 3 to Oligomys {exforrecta and
rugosicostata of Sweden and hicks't of Wales), 1 to
W'tmanella {highlandensis) , 1 to Bohemiella (romin-
geri) and 1 (5. dice Walcott) to Deltatreta; this
leaves 5 unplaced for want of knowledge of their
interior characters. It is at once apparent, therefore,
that our characterization of BiUingselln is narrower
and more precise than that of Walcott.
Discussion — It is important, therefore, to define
precisely the morphology of B'dlmgsella, since the mem-
bers of this genus and especially the genotype, together
with B. coloradoensis (Shum.), have been widely fig-
ured and variously interpreted. Externally Bdlingsella
is distinctly subquadrate in outline, but more peculiar is
the very long interarea, wide delthyrium, and, in the
genotype and B. coloradoensis at least, the prominent
apically perforated deltidium. The deltidium is a dis-
crete convex plate, but usually less convex than Wal-
cott figures it on his plate 85, figure In, a figure which
unfortunately has been republished very widely; it is a
normal delthyrial covering that is apically perforate,
and in situation and size this aperture recalls that seen
in the deltidium of RafinesquirM or Strofhometui more
than that of the Clitambonitida:. Further, the del-
tidium of Bdlingsella is clearly an arch built with its
piers fastened to the inside of the walls of the delthy-
rial cavity just below the delthyrial margins of the
interarea.
In the ventral valve the internal structures are dis-
tinctly orthoid or clitambonitoid. The dental plates are
widely divergent, obliquely cemented to the floor of
the valve, and at their anterior ends are continuous
with the teeth. The pseudospondylium, when devel-
oped, is a callus under the muscle attachments, and
none of the species here referred to Bdlingsella has
excessive thickenings at the posterior end. Walcott
mentions such structures only in B. dice (pp. 749,
754), B. orientalis (p. 307), B. exporrecta (p. 307),
and B. highlandensis (p. 307), but all of these species
are referred by us to different genera. In Kozlowski's
opinion,* Billingsella has rudimentary spondylia, but the
type of dental plates and muscle area corresponds to
his spondylium discretum, which, however, is in reality
not a spondylium.
The ventral musculature of Bdlingsella is essentially
orthoid in plan and its most important characteristic is
the elongate adductor track which expands as it grows
forward and is usually slightly elevated on a low callus
at its anterior end. The diductor tracks are shorter
and continuous with the pallial trunks. Positive evi-
dence of adjustor marks is lacking, as in Orthis s. s.,
Hesperorthis, Nicolella, etc. These muscles may have
been confined to the dental plates, where they are not
visible, or may have been united with the diductors.
The ventral musculature of several species presents
some variations from the normal type. In B. resseri
and B. trempealeauetisis (both of Ira Edwards MS.),
the diductor tracks unite for nearly the whole length
of the delthyrial cavity, restricting the adductor track
to a small subpentagonal scar at the antero-median
sides of the diductor marks. A similar arrangement is
suggested in B. highlandensis (a Wimanella) and
Wimanella simplex (see Walcott, pi. 87, fig. 4b, and
pi. 89, fig. 2d).
One of the striking characters of Billingsella, and
one which has been exploited considerably, is the prom-
inent ventral pallial marks usually called "vascular"
markings. These consist of two more or less strongly
impressed, subparallel, narrow depressions, originating
at the front ends of the diductor scars and extending
antero-laterally. Near the front of the shell the sub-
parallel trunks fork, the outer branch curving back-
ward and extending nearly parallel to the periphery
of the shell and terminating near the cardinal extrem-
ity. The inner sinuses run obliquely toward the middle
of the shell, where they either die out or unite at the
mid-line, forming an elongate pentagon. Near the
front margin many subsidiary branches radiate from
the main channel. Pallial marks similar to those of
Billingsella are also common to other Cambrian shells,
and this fundamental type can be seen, with variations,
in all higher genera.
The cardinalia are very distinctive and exceedingly
important from a taxonomic point of view. The
brachiophores are flattened plates set obliquely beneath
the interareal margins of the notothyrium. They are
"Pal. Polonica, vol. 1, 1929, p. 128.
50
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
supported by a prominent callosity or swelling in the
notothyrial cavity (the pseudocruralium of Walcott),
which is extended forward no farther than the middle
of the valve as a low axial thickening. Articulation
is accomplished by the sloping inner surface of the
ventral tooth which rests on the slanting outer surface
of the brachiophore. The cardinal process is a simple
linear ridge, a septum between the diductor muscles,
and serving also partly for muscle attachment ; but the
chief seat of attachment appears to have been on the
notothyrial callosity.
The dorsal musculature of Billingsella is rather
obscure, but there appear to be four adductor impres-
sions, the posterior pair being located in the pits imme-
diately anterior to the notothyrial platform and being
somewhat larger than the anterior pair.
Family EOORTHID^ Schuchert and Cooper
1931
Orthacea wholly without deltidia and chilidia, so
far as known, and with or without a cardinal process.
Though not yet well understood, the family is now
considered to embrace the following genera:
Wimanella Walcott
Eoorthis Walcott
Otusia Walcott
Bohemiella Schuchert and Cooper
Oligomys Schuchert and Cooper
The genetic lines are thought to be about as shown
in Table 2.
Table 2
Otusia
Eoorthis
Oligomys
Wimanella
Bohemiella
NiSUSIIDiE
Unfortunately most of the species of the Eoorthidae
are not well understood internally, due to their poor
preservation or to lack of material. Nearly all of the
specimens come from limestone and accordingly most
of them are exfoliated, and but rarely are the interiors
of the valves nicely weathered out, as is so commonly
the case with many of the brachiopods of the Ordovician
and later periods. Finally, we know the American
shells best, and the European and Chinese species are
regretfully few in number. On the other hand, the
brachiopods of the American Lower Ordovician
(Canadian) are almost unknown, and here are to be
expected the connecting links between the genera of
the Cambrian and the later Ordovician. Under these
circumstances a final classification of the Eoorthidae
along well determined genetic lines is yet to come, and
when it does, the phyletic lines into the Orthids and
Clitambonitida2 will be better established.
Genus WIMANELLA Walcott 1908
Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 98, pi. 10,
fig. 2; Camb. Brach., 1912, p. 745, pi. 89, figs. 2-2e,
t. fig. 64; Smiths. Misc. Coll., vol. 67, 1924, pi. 1 1 1,
figs. 2-4.
Genoholotype. — Wimanella simplex Walcott
1908, an almost characterless species. Our presenta-
tion is based on the genotype and Billingsella (==
Wimanella) highlandensis (Wale).
Description. Exterior. — Thin-shelled. Outline
subquadrate to subsemicircular; hinge-line straight;
cardinal extremities obtusely or acutely angular; lateral
profile subequally biconvex; ventral interarea longer
than dorsal; delthyrium open; notothyrium narrow,
open. Surface covered by fine concentric growth-lines
and obscure costellas.
Ventral interior. — Delthyrial cavity shallow, diduc-
tor scars large, tapering anteriorly, separated dorsally
by a low ridge, which forks anteriorly about the adduc-
tor impression; pallial trunks prominent.
Dorsal interior. — Crural plates short; axial ridge
low, extending forward to about the middle of the
valve. Cardinal process apparently absent.
Geologic range. — Lower and Middle Cambrian
of North America.
Species
Orthis ? highlandensis Walcott 1886
Wimanella ? anomda'W Aeon 1905
W. borealis Walcott 1924
W. Shelby ensisWilcoXl \9Q^
W. simflex Walcott 1908
Distinguishing characters. — The name Wim-
anella may serve for Lower and Middle Cambrian
nearly smooth or very finely ribbed billingsellids of the
type of W. simplex Walcott. As stated by Walcott
(1912), the genus was to embrace the older and
smooth shells of the Billingsellidse, but a study of all
of his species of Wimanella at the U. S. National
Museum shows the presence of faint radiating lines in
shells conspecific with the genotype and in the actual
types. Obviously, then, the characterization of this
GENER.A OF THE SUBORDER ORTHOIDEA
51
genus as strictly smooth Billingscllid.T has little generic
value. However, the name will be useful for the
oldest Eoorthid.T, having finely costellatc shells with
interiors that approach the features of Billingsrlla.
Discussion. — In choosing Wimanclla simplex as
the genotype, Walcott unfortunately selected an almost
characterless shell. The material from Montana oc-
curs in a soft shale, and since the forms are rather
thin-shelled they are b.adly crushed and show little of
the morphology. This is particularly true of the type
specimen (see pi. 89, fig. 2 of Walcott 1912). The
most important clue to the ventral morphology of these
shells is furnished by a specimen referred to W. simplex
(Ibid., pi. 89, fig. 2d), in which the ventral muscula-
ture consists of two large diductor tracks, closely adja-
cent at the posterior of the shell but divergent at the
front. In the space between the antero-median mar-
gin of the diductor tracks is a low suboval elevation
corresponding probably to the adductor impressions.
This is exactly the same musculature as shown by the
type of Bilitngsclla htghlatiAensts (see Ibid., pi. 87, fig.
4b). Here the adductor impression is not shown be-
tween the diductors but is actually present in the speci-
men from which the figure was drawn. This species
also has prominent ventral pallial trunks as in BUllngs-
elloy is likewise very finely ribbed, and seems to cor-
respond well with the concept of Wlmanella described
in this paper.
Wlmanella horealls Walcott is another finely costel-
late species and this one too is said to have faint pallial
marks, although they do not show on Walcott's fig-
ures (1924, pi. Ill, fig. 2). The writers have ex-
cluded Wlmanella harlanensls (Wale.) from this
genus, since its structure, especially in the musculature
of the two valves, relates it to Syntrophla and Clark-
ella. The placing of Wlmanella tnyoensls Walcott
among the articulate brachiopods is questionable.
Genus EOORTHIS Walcott 1908
PI. 1, figs. 23, 26, 28
Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 102; Camb.
Brach., 1912, p. 772, pi. 91, figs. 1-ls, pi. 92, figs.
2-2d, 3-3e, t. fig. 7.
Genoholotype. — Orthls remnlchaW'mzhcW 1886,
Geol. Surv. Minn., 14th Ann. Rept., pp. 317-318,
pi. 2, fig. 7.
Description. Exterior. — Shell subquadrate to
transversely subelliptical ; hinge-line straight, cardinal
extremities usually obtusely angular; lateral profile
subequally biconvex; anterior commissure sulcate;
dorsal sulcus marked most clearly on the middle and
dorsal part of the valve; ventral interarea broad,
slightly curved, apsacline; delthyrium wide and not
covered by a deltidium. Dorsal interarea short, ana-
cline; notothyrium wide, not closed by a chilid-
ium. Surface multi- to fascicostellate. Test fibrous,
impunctate.
Ventral Interior. — Delthyrial cavity shallow; teeth
strong; dental plates strong, receding, continued
around the lateral margins of the muscle field as a
low ridge. Musculature orthoid, diductor scars tri-
angular, adductor track median, expanding in front.
Dorsal Interior. — Notothyrial cavity shallow ; brach-
iophores consisting of flattened oblique plates attached
to the roof of the valve on the surface of which the
interarea rests, the whole forming the walls of the
notothyrial cavity. The sockets are narrow and shal-
low (see pi. 1, figs. 23, 28). Notothyrial platform
of adventitious shell crowded under the brachiophores
to support them; cardinal process a simple ridge ex-
panded toward the front. Median ridge wide and
strong.
Geological range. — Upper Cambrian to Ozark-
ian of North America.
Species
Eoorthis in» Centralblatt f. Min., etc., 1922, pp. I23-12+.
*° (Translation) The original specimen of Platystrofhia
bijorata, which is located in Berlin, is a fairly well pre-
served example about 22 mm. wide, 16 mm. long, and
13.5 mm. thick. In the sinus [sulcus] it has 5 equally
strong, undivided ribs, on the fold there are 6. On the
lateral slopes one counts 9 sharp ribs on both valves. About
the beak all of the ribs disappear; the sulcus in that place
is shallow and at the delthyrium it passes into a small swell-
ing, on which the ribs do not go; so far as can be seen,
these appear simultaneously and none is favored. On the
fold the ribs develop by division.
this study he stated that the "presumptions arc strongly
in favor of its [the genotype of Platystrofhia^ being
biplicate [bicostate]" (p. 18), and accordingly he
restricted the term bijorata to bicostate forms. If
Dietrich's determination of the genotype as a tricostate
form be correct, it is evident that the bicostate species
of "bijorata," will need to be replaced by new specific
names.
Cumings' splendid monograph on the "Morpho-
genesis of Platystrofhia" gave the first careful analysis
of the genus. It was in this paper that the supposed
marked difference between the American and Euro-
pean Platystrophias was first indicated. These ideas
have been extended and elaborated by McEwan. Ac-
cording to Cumings, three divisions may be distin-
guished as follows: (1) uniplicate, (2) triplicate, and
(3) biplicate. Since in the present work the term
plication is restricted to a major undulation of the shell,
such as a fold or the undulations of the shell in
Enteletes, we here suggest that these terms be altered
to unicostate, tricostate, and bicostate. The three
groups may then be defined as follows:
( 1 ) Unicostate grouf. — Here there is one costa in
the sulcus and two on the fold at the end of nepi-
onic development, and this condition continues then
throughout life.
(2) Tricostate grouf. — In this group the primary
costa of the unicostate condition remains unmodified
throughout life, but in the early neanic stage a costa
is implanted on each slope of the sulcus. Simultane-
ously the two primary costae of the fold bifurcate.
The tricostate group is merely a modification of the
unicostate one but it is convenient to continue the two
groups for their stratigraphic value. Under the tri-
costate group McEwan recognizes three subgroups:
(a) low-fold, (b) high-fold, and (c) Ponderosa.
(3) Bicostate grouf. — Here the median costa of
the sulcus of the early neanic shell bifurcates, and
simultaneously a costa is implanted between the two
primary costa: of the fold. Four subgroups are recog-
nized by McEwan but a comprehensive study of the
European forms would doubtless demonstrate the need
for more subdivisions.
Cumings has shown that the nepionic shell of
Platystrofhia has the sulcus in the dorsal fold and a
fold on the ventral. In the neanic stage, however, the
costs bounding the sulcus become elevated to form a
fold, and with this change the median rib of the dorsal
valve is depressed to form the lone costa of unicostate
shells. From this fundamental unicostate type the
tricostate and bicostate groups have evolved.
According to McEwan and Cumings, divergence
of the tricostate and bicostate stocks must have taken
place in early Ordovician or Upper Cambrian time,
this because the modification of "the plications [costae]
of the fold and sinus [sulcus] takes place before the
shell has reached a length of 1 mm." The tricostate
group is thought to have diverged "from the ancestral
68
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
stock much later than the biplicate [bicostate] group"
as the uniph'cate condition remains till the shell has
reached a length of 1.2 to 1.5 mm. (p. 391).
Platystrophia first appears in the European Middle
Ordovician (Kuckers formation, Brandschiefer) in well
organized bicostate and tricostate species, P. dentata
and P. lynx. In the Schuchert Collection is a lot of
P. dentata labelled as "probably Echinosphjerites lime-
stone." If this horizon be correct, it pushes the first
appearance down into lower Middle Ordovician or
about the time of the Black River in America. These
Echinosphasrites limestone specimens are bicostate forms
and would not afford notable support to McEwan's
theory concerning the origin of the group. The
Kuckers may be upper Black River in age but is more
probably lower Trenton. According to McEwan
(p. 400), "a uniplicate species was found to occur
in the Jewe [Trenton], and one specimen was
found which occurred in the Upper Ordovician (F^)
[Lyckholm or uppermost Trenton]." The unicostate
group therefore appears to be a rather insignificant
assemblage. Both Cumings and McEwan maintain
that the bicostate group is the dominant one in Europe.
The foreign species are so poorly known that it is as
yet difficult to know what is the dominant group in
the way of species, but it is a fact that after their origin
the bicostate group held the European ground occupied
from the Middle Ordovician into the Middle Silurian.
In North America, however, the situation is just the
reverse, the tricostate group holding its ground through-
out the Middle Ordovician and into the Middle
Silurian.
McEwan's table (pp. 402-404) indicates the first
appearance of Platystrophia in North America in Black
River time (Decorah shale of Wisconsin). Hall and
Clarke,-^ Winchell and Schuchert,^^ Ruedemann,^^
and Schuchert^* all have reported Platystrophias from
the Chazy but neither McEwan nor Cumings^^ could
find any evidence to substantiate these reports. There
may also be some doubt as to the precise age of the
form P. extensa McEwan, said to have come from the
Decorah shale. This formation has recently been sub-
jected to a critical survey by G. Marshall Kay,"^ who
comes to the conclusion that the upper or Ion member
of the Decorah is actually lower Trenton in age. Kay
reports P. extensa McEwan from this member (upper
Ion, Prasopora faunule. Church, Iowa) in company
with P. trentonensis McEwan. This is the only ho-
rizon from which he has Platystrophia and it is there-
fore probable that the specimen from the Decorah of
Wisconsin is from the Ion member and actually lower
" Pal. N. Y., vol. 8, pt. 1, 1892, p. 202.
" Geo!. Minn., vol. 3, pt. 1, 1895, p. 456.
^^N. Y. State Mus., Bull. 49, 1902, p. 25.
" U. S. Geol. Surv., Bull. 87, 1897, p. 309.
^''Amer. Jour. Sci. (4), vol. 15, 1903, p. S.
^*Jour. Geol., vol. 37, 1929, pp. 639-671.
Trenton in age. This would be in agreement with the
remarks made above on the European section.
In North America the first Platystrophias to appear,
barring the one mentioned above, are bicostate forms
in the lower Trenton and one unicostate species, P.
uniplicata McEwan. If the so called Black River
form be considered lower Trenton in age, then the
three groups appear in North America almost simul-
taneously and fully standardized. The unicostate
group is represented here by one known species only.
After lower Trenton time the bicostate group is, so
far, unknown in the American Ordovician until the
topmost formation, the Gamachian (Ellis Bay) of
Anticosti, is reached. From this time on the bicostate
group is dominant in American Silurian strata and a
very few rare tricostate individuals are to be found in
the early Silurian.
A recent table of suggested correlations by Ulrich^^
places the Wierland group, of which the Echino-
sphasrites limestone and Kuckers are a part, as upper
Chazy in age. This would make the European species
antedate the American forms and would be rather sug-
gestive, although not final evidence, of a European
origin of the genus. The important point, however,
is not the precise age of their appearance but the fact
that, when Platystrophias are present for the first time,
the three groups come together, fully organized.
The appearance of Platystrophia in early Trenton,
Black River, or late Chazy time is suggestive that the
ancestor of the group should be sought in rocks of
Chazy age. McEwan has prophesied a unicostate pro-
genitor, from which the bicostate group diverged first,
followed by the tricostate group.
Both Cumings and McEwan have turned to the
Upper Cambrian faunas as being the possible source of
Platystrophia. Cumings found in Orusia lenticularis
(Wahlenberg) "a form that possesses in the adult
practically all of the nepionic characters of Platystro-
phia" (p. 5). Taking only external characters, this
form could have evolved the exterior of Platystrophia,
and internally it has subparallel, discrete brachiophore
plates, not unlike those of Platystrophia. It is possible,
of course, that crowding of the bases of these toward
each other could produce the condition seen in Platy-
strophia, but the early appearance of Orusia and its
short stratigraphic range make it unlikely that it is the
direct ancestor, although it may have been in the
general line.
Cumings has also pointed out the external similari-
ties between Platystrophia and Plectorthis, as follows
(pp. 11-12):
In some respects the adult Plectorthis plicatella resem-
bles the neanic Platystrophia. If the fold and sinus be
disregarded (and in some Trenton forms of Platystrophia
these are surprisingly inconspicuous), the neanic Platy-
strophia is almost a Plectorthis. There is little doubt that
" U. S. Nat. Mus., Proc., vol. 76, 1930, p. 73.
GENERA OF THE SUBORDER ORTHOIDEA
69
when the nepionic shell of PUctorthis is discovered it will
be found to be quite indistinguishable from the nepionic
shell of Pljtsstrof.) thakil trifida Salter 1865
? O. (D.) annamitica Mansuy
Placed from the
literature
American Species of PljEsiomys
Dinorthis Columbia WWson 1927
D . if higenia CWiW'mgs) 1862
D. meedsi (Winchell and Schuchert) 1892
D. meedsi arctica Schuchert 1900
D. meedsi germana (Winchell and Schuchert) 1892
D.rockymontana'^'^soxi 1927
D . subquadrata (Yi^V^) 1847
D. transversa Willard 1928
D.ulrichi Foerste 1909
Orthis anticostiensis Shaler 1887
GENERA OF THE SUBORDER ORTHOIDEA
95
European Species of Pl/Esiomys
Orthis {Dinorthis) fabellulum carrickensis Rccd 1917
O. infijia Salter
O. fore at a McCoy 1 846
O. Solaris von Buch
O. (D.) striato-costata Salter 186S
O. \d.) suiJirisa Salter 1865
American Species of Retrorsirostra
Dinorthis carUyi (Hall) 1860
D. carleyi insolens Focrste 1909
D.retrorsa (Salter) 1858
Anticosti Species of Pionorthis
Dinorthis carUtona Twenhofel 1928
Orthis sola Billings 1 866
Distinguishing characters. — Dinorthis is char-
acterized chiefly by its convexo-concave profile, svib-
quadrate and anteriorly bilobate plan of the ventral
muscle field, Or?/;w-type brachiophores, crenulated
myophore, and pallial sinuses. From Orthis s. s. it
differs in its contour, musculature, and pallial markings.
Discussion. — Dinorthis of the Dinorthidae and
Dolerorthis of the Orthidas form an interesting homoe-
omorphic pair, but the two can be distinguished readily
by their internal features. The ventral musculature of
Dolerorthis is hke that of Orthis s. s. and never has the
adjuster scars developed to any marked degree. The
most important difference, however, is to be seen in
the pallial and ovarian impressions of the two genera
(see pi. 5, fig. 20, and compare with pi. 10, fig. 24).
The pallial marks of Dolerorthis are of the Orthis type,
two subparallel trunks given of? from the anterior ends
of the diductor tracks and extending directly anteriorly.
They are separated by a narrow septal ridge and bound
ovarian impressions which occupy nearly the entire sur-
face of the interior lateral spaces. In Dinorthis, on
the other hand, the ventral pallial trunks are divergent
and the ovarian impressions are greatly reduced.
There is so much variation in the external contour
and profile of Dinorthis that several distinct subgenera
may be separated as follows:
1 . D. fectinella — Dinorthis s. s.
2. D. suhquadrata — Plwsiomys
3. D. carleyi — Retrorsirostra
4. D. sola — Pionorthis
(1) Dinorthis fectinella (pi. 9, figs. 2, 5) is the
type of the genus and as well of the subgenus Dinor-
this s. s. Its costate exterior differentiates it from
the multicostellate exterior of Plwsiomys.
(2) D. suhquadrata (pi. 9, figs. 3, 20; t. fig. 5)
t}'pifies the subgenus that was designated Plirsiomys by
Hall and Clarke, and embraces the many species listed
above.
(3) The D. carleyi subgenus (pi. 9, figs. 21-23),
now termed Retrorsirostra, is characterized by its
strongly prodine ventral palintrope and deeply concave
ventral valve. In the ventral valve the muscle field
is square in front and commonly elevated on a thicken-
ing of adventitious shell. The tribe is common in the
Upper Ordovician of North America and Europe.
(4) Another subgenus of Dinorthis is characterized
by Orthis sola Billings, referred by Twenhofel"' to
Rhipuiontella; it may be called Pionorthis (Gr. fion,
fat) in allusion to its biconvex profile (see pi. 9, figs.
4, 6-9, t. fig. 18). D. carletotia Twenhofel and an
unnamed species from the Upper Ordovician of the
Bighorn formation belong to this subgenus.
The name Dinorthis was used first by Hall and
Clarke, who considered its most important characters
to be its reversed convexity, subquadrate muscle im-
pressions, deltidium, and peculiar cardinal process.
The same authors also proposed Plcesiomys, which fol-
lows the description of Dinorthis and is characterized
by having muscle-scars like those of Dinorthis but an
exterior similar to that of Hebertella. It is clear from
Fig. 18. — Diagram showing the ventral musculature of
Dinorthis {Pionorthis) sola (Billings).
their descriptions that they had O. calligramma in
mind when differentiating Dinorthis and were more
mindful of the external resemblances of Plirsiomys to
Hebertella than of the internal similarities of Dinorthis
and PlcFsiomys.
In the description of the interiors of Dinorthis and
Plirsiomys, Hall and Clarke emphasized exactly the
same features for both of their genera. This is also
borne out by later studies. In an examination of a
large series of these shells the present writers have been
unable to find any internal generic distinction between
the two. Therefore to individualize Dinorthis and
Plwsiomys external characters only are available. But
here, too, there is considerable diflficulty in the way of
a precise definition of the two genera. It was the con-
tention of W^inchell and Schuchert that there was a
gradation between the external characters of Orthis
fectinella (genotype of Dinorthis) and O. suhquad-
rata (genotype of Plirsiomys). This contention they
embodied in the following words :^*'
"Mem. 154, Geol. Surv. Canada, 1927 ( 1928), p. 181,
pi. 17, figs. 10, 11.
"Geol. Minn., vol. 3, pt. 1, 1895, p. 421.
96
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
From O. ■pectinella we pass to the variety sweeneyi,
which is a local variation of it. Associated with the latter
are specimens in which the strong plications begin to divide
near the anterior margin. At the base of the Galena shales
the strong simple, plicated forms become rarer, while those
with more numerous striae prevail. Upon reaching the
strata containing Clitambonites diversa Shaler, provision-
ally known to the survey as Galena shales, the numerously
striated form, here described as O. meedsi, is the only one
found. Ascending into the Galena formation for thirty or
forty feet more we find O. meedsi still exhibiting a tend-
ency to increase the number of its striae [costella:] , and
finally assuming characters (variety germana) which attain
their greatest development in O. subquadrata of the Hudson
River [Richmond] formation. The change from O. fec-
tifiella to O. subquadrata is thus completed.
Consistent with this argument they placed Plcesiomys
in the synonymy of Dinorthis and the same relationship
was continued by Schuchert in 1897 in the Synopsis
of American Fossil Brachiopoda.®^ It is, however,
doubtful that such a gradation between D. fectinella
and Plcesiomys subquadrata actually exists because in
the Chazy (possibly Black River) of Tennessee the
Dinorthis s. s. of that region are already showing a
marked divergence toward Pla-siomys. The D. trans-
versa, D. quadriflicata, and D. interstriata all have
interstitial or dichotomous ribs. Furthermore, the P.
ifhigenia of the Black River and P. ulrichi of the
Trenton are well established species agreeing in form
and ornamentation with O. subquadrata.
There is still another angle at which this problem
of the distinction between Dinorthis and Plcpsiomys
may be viewed, and that is, that D. fectinella and
related forms represent the culmination of a trend
which went in the direction of simplification of ribs.
If this be true, some early Pleeslomys would be the
ancestor of Dinorthis.
The value of the name Pleeslomys has been variously
interpreted. In 1911 Raymond^^ found it "best to
retain the name Pleeslomys for the present, and apply
it to such forms as O. subquadrata and O. flatys [our
Multlcostella, described farther on], in which the sur-
face is not coarsely plicated, but is covered with stria-
tions [costellas] which increase by bifurcation and im-
plantation." In 1913 Schuchert^^ regarded Dinorthis
as a subgenus of Pleeslomys, but later reversed the
relationship.
It has been shown above that internally Dinorthis
and Pleeslomys are inseparable and should be regarded
as forming a single genus. But if the suggested evolu-
tional trend toward the simplification of ribs in Dinor-
this be correct, it would be desirable to continue the
usefulness of Pleeslomys by considering it as of sub-
generic value. On nomenclatorial grounds Dinorthis
" Bull. 87, U. S. Geol. Surv., pp. 215, 308.
^*Ann. Carnegie Mus., vol. 7, no. 2, p. 239.
^° Zittel-Eastman Text-book of Paleontology, 2d ed.,
vol. 1, p. 382.
has priority over Pleeslomys because it appears first in
HaU and Clarke's book. Accordingly we suggest that
Dinorthis be the generic name under which the whole
assemblage of these related brachiopods be designated,
and to bring out the tribal relationships we propose that
this genus be divided into five subgenera as defined
on an earlier page.
Subgenus MARIONELLA Bancroft 1928
PI. 8, figs. 16-18
Bancroft, Mem. and Proc. Manchester Lit. and Philos. Soc,
vol. 72, 1928, p. 181, pi. 2, figs. 13-16.
Genoholotype. — M. typa Bancroft 1928.
Description. Exterior. — Dinorthids of medium or
small size, subelliptical in outline; hinge-line straight;
cardinal extremities rounded. Lateral profile con-
vexo-plane to convexo-concave. Anterior commissure
faintly sulcate, sulcus shallow; ventral fold low, ob-
scure. Interareas short, the ventral one apsacline, the
dorsal orthocline. Ornamentation finely multicostellate.
Ventral Interior. — Delthyrial cavity shallow; dental
plates strong, flaring, continued as ridges about the
periphery of the muscle field. Muscle area and pallial
markings as in Dinorthis.
Dorsal interior. — Notothyrial platform shallow;
brachiophores of the Orthls type as developed in Dinor-
this; cardinal process slender, simple, adductor field
small.
Geologic range. — The single known species, M.
typa, comes from the Middle Ordovician of Wales.
Distinguishing characters. — Marlonella differs
from Dinorthis s. s. and Pleeslomys only in its much
finer ornamentation and "the frequent, but not uni-
versal, presence of a narrow (sharply pinched up)
ventral mesial fold" (p. 181).
Discussion. — The genus was first placed by its
nomenclator as a member of his subfamily Harkness-
ellinse, but this reference appears to us wrong. Ban-
croft in a letter tells us that he now believes Marlonella
to be a subgenus of Dinorthis. Specimens sent by him
to us are molds of the interior and exterior which give
no information regarding the structure of the shell,
whether punctate or impunctate. Our presumption is
in favor of an impunctate test because the other internal
features fit best with this type of shell, for example the
simple cardinal process.
Characteristic dinorthid features occur in both valves
as follows: In the ventral, the musculature and pallial
markings are typical (see pi. 8, fig. 17). The car-
dinalia are of the orthoid type. In young forms the
crenulated myophore of the cardinal process is not
visible in the narrow slots of the internal molds.
Marlonella is a parallel development to Pleeslomys,
evolved probably from the British Dinorthis. No shells
exactly like it are known in North America, and be-
cause of this independent development it deserves at
least subgeneric designation.
GENERA OF THE SUBORDER ORTHOIDEA
97
Genus VALCOUREA Raymond 1911
PI. 10, figs. 16, 19-23, 27-29; t. fig. 2
Raymond, Ann. Carnegie Mus., vol. 7, 1911, p. 239, pi.
35, figs. 15-19, pi. 36, fig. 1, t. fig. 12.
Genoholotype. — Pltrslomys strophomeno'utes Ray-
mond 1905, Amcr. Jour. Sci. (4), vol. 20, p. 370.
Description. Exterior. — Shells strophomcnoid,
hingc-linc wide and straight, cardinal margins rarely
suhmucronate or subauriculate, commonly deflected;
lateral profile strongly convexo-concave, anterior com-
missure broadly uniplicate or faintly sulcate ; dorsal
sulcus shallow, in some species obsolete at the front;
ventral palintrope broadly triangular, apsacline to cata-
cline or slightly procline, delthyrium open or closed by
a deltidium; dorsal intcrarea shorter than the ventral
one, orthocline or apsacline, notothyrium partially or
completely covered by a chilidium; ornamentation
multicostellate, fine elevated threads in the interspaces
and crossing the ribs. Test fibrous, internally impunc-
tate; costells e.xopunctate.
Ventral interior. — Delthyrial cavity shallow, teeth
strong, with accessory sockets (see t. fig. 2) ; crural
fossettes oblique, deep; dental supports strong in young
shells, obsolete in adults; cavities deep in juvenile
individuals. Muscle area subpentagonal, wider and
moderately bilobed in front; diductor tracks oblique,
elongate, expanded in front; adductor tracks small,
thin, elongate; adductor scars elongate, semielliptical;
adductor track linear, enclosed by the diductor scars in
front; adjuster scars prominent, situated at the base
of the dental plates, as in Dinorthis. A small septum
may be located at the base of the pedicle callist, or of
the deposit under the deltidium. When a deltidium
is absent a well marked pedicle callist is present. Pal-
lial markings similar to those of Dinorthis, umbo-lateral
spaces marked by radiating elevated ridges indicating
the position of the ovarian bodies.
Dorsal interior. — Notothyrial cavity shallow; car-
dinalia confined to about the anterior one-fifth of the
length of the valve, brachiophores forming the margin
of the notothyrium, short, supported by a shell thick-
ening beneath; sockets shallow, bounded by the slop-
ing face of the brachiophore and an accessory tooth on
the hinge margin. Cardinal process large, having a
prominent shaft, and a crenulated myophore as in
Dinorthis; chilidium present; median ridge short,
extending as a rule approximately one-third the length
of the shell.
Geologic range. — Middle Ordovician (Stones
River to Black River), chiefly of North America.
American Species
Dinorthis deflecta (Conrad) 1843
D.loricula (Hall and Clarke) 1892
D. recta (Conrad) 1843
D. (Valcourea) strofhomenoides (Raymond) 190 5
Strofhomena venlrocarinata Butts 1926
Valcourea magna, n. sp.
European Species
? Orthis grandis (Portlock)
Discussion. — The name Valcourea was proposed
by Raymond for "impunctate orthids with reversed
valves, strophomenoid habit, well developed deltidium,
simple cardinal process, and finely striated [costellate]
surface." It was differentiated from Plrrsiomys by its
finer ornamentation and the presence of a deltidium
throughout life. These orthids form a very remark-
able convergence toward the genus Strofhomenn.
They may be distinguished therefrom, however, by
several important features: Externally they may be
distinguished by the resupinate form of Strophomena
and the lack of this feature in Valcourea. It is true
that the relative convexity of the valves in the latter is
reversed, that is, the dorsal valve has the greater con-
vexity. However this may be, the umbo of the dorsal
valve of Valcourea is always convex and there is a
distinct beak. In Strophomena, on the other hand,
there is scarcely any dorsal beak and the umbo is
decidedly concave. It is the change in convexity from
concave at the umbo to convex in the middle and
front of the dorsal valve that distinguishes Stropho-
mena. The external convergence of Valcourea toward
Strophomena is not carried to such a degree that the
shell is resupinate, although its convexity is reversed.
In the ventral valve the subquadrate plan of the mus-
cle field of Valcourea readily separates the two genera.
The forked cardinal process of Strophomena is a fea-
ture unknown in any orthid. Another difference is to
be seen in the deltidia, that of Strophomena being
apically perforate and that of Valcourea lacking a
foramen.
Internally, Valcourea and Dinorthis (Pla-siomys)
are very similar, differing only in minor details of the
pallial markings and ventral musculature. In the
latter the diductor scars, although distinctly lobate in
front, are not so strongly lobate as those of Valcourea,
and the adjustors are much less divergent. The most
notable difference, however, occurs in connection with
the adductor impressions. Between the diductors of
Valcourea is a double ridge which extends to the apex
of the reentrant between the diductor lobes. Upon
this double ridge are situated the adductor scars which
together form an elongate suboval or lanceolate im-
pression, widest toward the front. The adductor
scars of Valcourea are situated at the front of the mus-
cle field; this contrasts with the same impressions in
PliFsiomys, which are located in the middle or at the
back end of the field. The pallial impressions of
Valcourea are much like those of Pla-siomys, but differ
in being less distinctly impressed and less broken up
into subsidiary rami along the front margins. Fur-
thermore, the ovarian radial ridges are larger and
more distinctly marked in Valcourea.
98
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Valcourea appears to be best represented in the lower
Middle Ordovician of North America where the genus
first appears in the Stones River group and is last seen
in the Black River. The range is short but the species
are widely spread during this time. In Europe one
species, Orthis grandis Portlock, seems to belong in this
association. Valcourea is contemporaneous with D'm-
orthts s. 5. and PlmsiomySy but dies out long before
either of these tribes.
Valcourea magna, n. sp.
PI. 10, figs. 16, 20, 27-29
Shell large, wider than long, convexo-concave to
convexo-plane ; dorsal valve having a faint sulcus
which is lost toward the front of the shell. Ventral
interarea long, strongly apsacline. Delthyrium open.
Surface multicostellate, costellae crossed by fine ele-
vated concentric lines. Ventral muscle field bilobed in
front, pentagonal in outline. Pallial marks as in
Dinorthis.
This species is the largest of all the Valcoureas and,
so far as known, does not have a deltidium. The con-
cavity of the dorsal valve is less than is usual in other
species.
Measurements of the holotype, Cat. No. 779, Schu-
chert Collection, Yale University:
Length Thickness
37 mm. 17 mm.
Width
47 mm.
Horizon and locality. — Ordovician (Simpson),
Criner Hills, Oklahoma.
Genus MULTICOSTELLA Schuchert and
Cooper 1931
(Lat. multiy many; costella, small rib)
PI. 8, figs. 19,22,23,27; pi. 15, fig. 12
Schuchert and Cooper, Amer. Jour. Scl. (5), vol. 22, 1931,
p. 244.
Genoholotype. — Orthis ( ? ) saffordi Hall and
Clarke 1892, Pal. N. Y., vol. 8, pt. 1, pp. 217, 340,
pi. 5 A, figs. 38-40.
Description. Exterior. — Shells semielliptical, an-
terior margin convex; lateral margins convex or
straight; hinge-line wide and straight; cardinal ex-
tremities angular or obtuse; lateral profile subequally
biconvex; anterior commissure rectimarginate to sul-
cate; fold and sulcus absent, faintly or strongly devel-
oped; interareas nearly equal in length, the ventral
usually slightly longer; ventral interarea apsacline,
umbo convex, delthyrium open; dorsal interarea or-
thocline or faintly anacline; umbo very gently con-
vex, usually sulcate. Ornamentation multicostellate,
interspaces with elevated growth-lines; test fibrous,
impunctate.
Ventral interior. — Delthyrial cavity shallow; teeth
small; dental plates strong, advancing; small pedicle
callist in the apex; crural fossettes shallow, oblique;
muscle area nearly one-third the length of the shell,
about as long as wide, bilobed in front; diductor scars
elongate, expanded in front; adductor tracks elon-
gate; adjustor scars short, narrow, slightly expanded
in front. Elevated, elongate oblique lines occupy the
lateral spaces next the cardinal cavities.
Dorsal interior. — Notothyrial cavity shallow; sock-
ets shallow; brachiophores stout, blunt, supported by
the thickening of the notothyrial platform; cardinal
process stout, myophore crenulated ; median ridge low,
short; adductors not deeply impressed on the shell.
Geologic range. — Middle Ordovician (Chazy)
of North America.
Species
Dinorthis flatys (Billings) 1859
Plusiomys brevis Willard 1928
P. «/07z^d/?ibonites, as Kozlowski has done, but
the dorsal valve shows departures too radical to justify
this reference.
In the dorsal valve, the cardinalia and the muscle
impressions are the chief structures of interest. The
"cardinal process," so called, consists of four distinct
parts: (1) the chilidium, (2) the cardinal process
proper, (3) the brachiophores, and (4) the "crura."
( 1 ) The chilidium is a thick, subcircular plate lying
over the base of the cardinal process, bent ventrally
on both sides and also dorsally at the front end. It
reminds one much of the chilidium of Productorthis
(see pi. 4, fig. 16).
(2) The cardinal process is more difficult to indi-
vidualize. At its front end it is crescentic or lunate
in outline, and extends under the ventral beak. In
some specimens its ventral surface bears a rather deep
groove. However, the process is clearly single, never
being bifid at its front end as in Derbyia, Triflesia, or
Meekella. In other words, the cardinal process,
although much modified, is essentially orthoid.
(3) The brachiophores show as obscure plates con-
vergent toward the roof of the valve and possibly
uniting at their bases. These have been crowded
together and have fused with the cardinal process at
their posterior extremities (see pi. 14, fig. 30). The
sockets are deep and excavated into the shell substance,
and bear a small tooth on the outer wall above the
excavation noted before. The curved posterior ex-
tremity of the tooth fits into the excavation and the
small tooth articulates with the deep socket on the
posterior face of the ventral tooth.
(4) The crura are long processes extending from
the brachiophores on each side of the cardinal process.
They have a slight hollow groove toward their dorsal
ends and appear as folded plates.
The taxonomic position of Lyco-phoria is difficult to
express. Lahusen would place it with the Stropho-
menida:, but in current classification it has been allied
doubtfully with the Parastrophininas. Kozlowski^^
would place it with Poramhonites in the Porambon-
itidffi. Strophomenoid affinities are said to occur chiefly
in the cardinal process, which, according to Hall and
ClarkeV^ section is described as strongly bifid. How-
ever, the writers have been unable to find a bifid car-
dinal process. If Hall and Clarke's section were cut
obliquely across the beaks so as to bevel the cardinal
process transversely or obliquely, the tapering of the
antero-ventral ends of the ventral groove would give
the appearance of a bifid process. None of Lahusen's
figures, nor any of the excellent interiors in the Schu-
chert Collection, give any indication of a bifid cardinal
process. Hall and Clarke thought that the cardinal
structure allied this genus to the orthids but that
"Atrypa micella adds to these orthoid features the
cardinal process of a streptorhynchoid, like Triplecia
and Mimtdus, thus presenting another point of tan-
gency between these shells and the pentameroids."
Schuchert has persistently classified this genus, al-
though with a query, with the pentamerids, allying it
always with the Parastrophininas. However, there is
no pentamerid feature in Lycophoria save the biconvex
valves. Kozlowski placed it in the Porambonitidas,
referring this family to the Telotremata. It has been
shown — and a glance at the figures (pi. 14) will con-
firm this — that no characteristic pentameroid features
occur in Lycophoria. Furthermore, we have removed
the Porambonitidae from this association and referred
them to the Orthacea. The same reference, but as a
separate family, is suggested for the genus now under
consideration, since it shows orthoid features in the
ventral interarea, open delthyrium, and discrete dental
plates. In the dorsal valve it has been shown that the
cardinalia have developed, by growing inwardly and
fusing with the brachiophore supports, a cardinal
process and chilidium. These features could be devel-
oped by the lateral crowding of such cardinalia as are
seen in Productorthis, but we are not holding that
Lycophoria descended from that genus.
The dorsal valve of Lycophoria thus forms a con-
vergence toward the type of cardinalia so well known
in Meekella and Derbyia of the Carboniferous. Lyco-
phoria and Productorthis of the Middle Ordovician
are therefore two stocks that have independently orig-
inated characters that are re-developed in other stocks
{Derbyia and Productus) in the Pennsylvanian.
"Pal. Polonica, vol. 1, 1929, p. 131.
" Pal. N. Y., vol. 8, pt. 2, pi. 62, fig. 5 3.
GENERA OF THE SUBORDER ORTHOIDEA
107
Superfamily CLITAMBONACEA Schuchert 1929, emended
Specializing and terminal Orthoidca probably devel-
oped out of the Billingsellidx and retaining as a rule
the primitive features of deltidia and chilidia, here much
enlarged, and developing either pseudospondylia (more
rarely) or spondylia simplex. Test impunctate.
deltidia and cardinalia as in Vellamo and Clitambomtes,
but without spondylia and with discrete chilidial plates
that may be remnants of chilidia.
This small family of two genera is restricted to the
Lower Ordovician (upper Canadian) of the United
Tables
Of European origin and later dispersion
to North America
Clitambonitin^
Vellamo
DELTATRETIDiE
Polytoechia
Deltatreta
Pomatotrema
» Estlandia
Hemipronites
BiLLINGSELLIDiE
Ingria
Range, throughout the Ordovician and rarely in the
Silurian.
The phylogeny of this small superfamily is believed
to be as shown in Table 8.
Family DELTATRETID^E Schuchert and
Cooper 1931
Primitive Clitambonacea that probably originated in
the Billingsellid.-c. Largely orthoid in expression, with
States and Canada. It forms a morphologic connec-
tion between the orthids on the one hand and the large
family Clitambonitida on the other. It includes the
two genera Deltatreta Ulrich and Pomatotrema Ulrich
and Cooper.
Internally the dorsal valves are like those of Vellamo
and Clitambonites, but there are chilidial plates instead
of a chilidium. In the ventral valve there is no spon-
dylium, but in old shells of both genera there may be
a pseudospondylium. The deltidium of both genera is
exactly like that of the Clitambonitidae.
108
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Genus DELTATRETA Ulrich 1926
PI. 6, figs. 10, 11, 13-15, 19, 30
Ulrich in Butts, Geol. Surv. Alabama, Spec. Rept. No. 14,
1926, p. 100, pi. 18, figs. 1-+ (no description and
no type selected).
Syn. Deltorthis Ulrich, in Poulsen, Meddel. om Gronland,
Bd. 70, 1927, p. 297, pi. 20, fig. 4.
Genolectotype. — Deltatreta fillistriata Butts
1926.
Description. Exterior. — Resembling Pionodema
externally, subelliptical, hinge-line straight, usually nar-
rower than the greatest shell width; cardinal extremi-
ties obtusely subangular. Lateral profile unequally
biconvex, the ventral valve usually having the greater
convexity. Anterior commissure rectimarginate. Ven-
tral palintrope long, curved, moderately or strongly
apsacline; delthyrium closed by a strongly convex
deltidium which is perforated near the apex by a large
foramen like that of Vellamo and the Clitambonitidas.
Dorsal interarea short, anacline ; notothyrium partially
closed by discrete chilidial plates. Surface multicostel-
late; shell structure fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep ; teeth
strong, crural fossettes prominent ; dental plates strong,
extending directly to the floor of the valve, defined by
deep umbonal cavities. Muscle marks strongly im-
pressed on a callus which grows under them and
spreads about the inner bases of the dental plates, form-
ing an incomplete pseudospondylium. Diductor scars
elongate, situated near the base of the dental plates,
not extended in front of the adductor track, the latter
occupying the space between the adductor impressions
and in mature and old shells continued forward as a
low ridge. Lateral spaces marked by subreniform
ovarian impressions as in Orthis s. s. and Hemipronites.
Dorsal interior. — Cardinalia confined to the vicinity
of the hinge. Cardinal process orthoid, a linear
septum. Brachiophores orthoid, supported by lateral
swellings of adventitious shell exactly as in Vellamo
and Clitambonites.
Geologic range. — Lower Ordovician (Canadian)
of the United States and Canada.
Species
D. fillistriata Butts 1926
D. two n. spp. Ulrich MS.
Billingsella dice Walcott 1 90 5
Discussion. — The combination of characters in
this interesting early Ordovician shell unites features
seen in the later Orthidx and the Clitambonitidae.
Orthoid features are the ovarian markings and discrete
dental plates, clitambonitoid ones are the apically per-
forate deltidium and the brachiophores supported by
lateral extensions of adventitious shell as in Vellamo.
We will first describe in detail the morphology of
this genus and then discuss the peculiar nomenclatorial
questions involved in the choice of a genotype. Ex-
ternally Deltatreta has the appearance of Pionodema
in both outline and profile and the shell is finely multi-
costeUate with the ventral palintrope curved and apsa-
cline as in the last named genus. The ventral inter-
area is marked by fine, elevated lines parallel to the
posterior margins of the shell. Such elevated lines are
also characteristic of Polytcechia. Deltatreta is unlike
the later Pionodema in its possession of a perforate del-
tidium. Such a deltidium is unknown so far in any of
the punctate shells such as Pionodema. The deltidium
of Deltatreta is strongly convex, decidedly like the
same feature in Clitambonites, and unlike that of Bill-
ingsella since the apical foramen is very large, and not
uncommonly the foraminal margins are flexed or
turned outward.
In the ventral valve the musculature and pseudo-
spondylium are variable, depending on the age of the
specimen. In young shells there is no vestige of a
pseudospondylium, the adductor and diductor tracks
are rather wide, and there is a prominent pedicle callist
showing the inner attachment of the pedicle (see pi. 6,
fig. 30). In old shells the space occupied by the
adductor field is strongly elevated on adventitious shell,
which is not uncommonly prolonged forward to the
middle of the valve as a thick median ridge (pi. 6,
figs. 13, 15). The latter may nearly completely cover
the floor of the delthyrial cavity, forming a rather
prominent pseudospondylium. The floor of the lateral
spaces and umbonal cavities is marked by low radiating
ridges, probably markings of the attachments of the
ovarian bodies. In one specimen (see pi. 6, fig. 15)
the ovarian impressions are subreniform as in Orthis
s. s. or Hesferorthis. The palintrope and dental plates
are not unlike the corresponding structures in Hes-per-
orthis. The palintrope is long, and the teeth are placed
considerably outside of the delthyrial margins. They
are rather small but have prominent crural fossettes.
The deltidium develops as in Hesperorthis and Clitam-
bonites. It is an arch built with its sides attached to
the ventral surface of the narrow flange of the palin-
trope which overhangs the delthyrial margins. The
scar of pedicle attachment is not confined to the callist
at the apex but can be traced on the sides of the dental
plates and on the ventral surface of the deltidium; on
the dental plates its margin runs from the antero-
lateral extremity of the callist as a low ridge in an
antero-dorsal direction, nearly parallel with the sloping
edge of the dental plates, and then passes to the ventral
surface of the deltidium some distance behind the
foramen.
The dorsal valve is usually less convex than the
ventral and has a shorter palintrope, and the notothy-
rial cavity is rather narrow and shallow. The noto-
thyrial platform is inconspicuous and bears a simple
cardinal process which is typically orthoid. The brach-
GENERA OF THE SUBORDER ORTHOIDEA
109
iophores arc likewise orthoid and supported by adven-
titious shell deposited on their inner and dorsal surfaces.
This adventitious material may be extended laterally
for some distance (see D. dice (VValcott)) so that the
cardinalia of Deltatretn resemble markedly those of
Citttimhonites. The median ridge given off from the
notothyrial platform extends nearly to the middle of
the valves as is usual in orthoid shells. The sockets
are the cavities formed by the envelopment of the
brachiophores by adventitious substance and by the
sloping outer face of the brachiophore.
Deitatreta, like many orthoid brachiopods, possesses
an incomplete chilidium composed of two discrete chi-
lidial plates. These are low, extending from the mar-
gins of the notothyrium, and covering its sides; they
are extensions built on the edges of the brachiophores
along the delthyrial margins and strengthened by ad-
ventitious shell deposited on the inner face of the
brachiophores. The specimens at hand are not favor-
ably enough preserved to show the dorsal musculature.
This discussion of the genus Deitatreta has been pre-
pared from material loaned by Dr. E. O. Ulrich and
the U. S. National Museum. The specimens are all
from the upper Canadian of Alabama and Oklahoma.
We also include in this genus Billingsella dice Walcott,
found in the drift near St. Albans, Vermont, which is
very close to Deitatreta^ n. sp. (see pi. 6, fig. 1 5 ) from
northeast of the Wichita Mountains, Oklahoma.
Turning now to the nomenclatorial difficulties, the
first use of the name Deitatreta was by Ulrich in a
faunal list prepared by him for Purdue and Miser,'*
the name appearing as "Deitatreta of. electro Billings"
and unaccompanied by any description or figure. This
citation is then clearly a nonien nudum and as such has
no standing.*"
In 1926 Butts used Deitatreta as of Ulrich for
shells collected in Alabama and Oklahoma. Two
species were named and both were accompanied by
illustrations and one of these has a short statement of
Ulrich's conception of the genus. Since no type has
ever been definitely designated for Deitatreta, we here
select D. fillistriata Butts. This species has been chosen
instead of D. elegantula Butts which appears first in
the report (page 99, in reference to the figures on
plate 18), because there is no characterization of the
latter species and in addition it is clearly not typical
of Deitatreta according to the views expressed for D.
fdlistriata and as indicated by Ulrich's specimens in
Washington. In the plate legend (pi. 18, figs. 1-4
[p. 100]) for D. fillistriata, Butts states clearly that
"U. S. Geol. Surv., Geol. Folio 202, 1916, p. 5.
"* The recent Schuchert-LeVcne catalogue cites the geno-
type as "D. cf. electra Ulrich ? = Orlhis electra Billings,"
with bibliographic reference to the last named species.
Since, however, the name as written by Ulrich is a doubt-
ful identification, it can not be held that he intended to
place Billings' species as the type of the genus. See Rules
of Nomenclature, Art. 30, 11 e^.
Ulrich has proposed the name Deitatreta for shells
having a deltidium. Hence D. elegantula, which has
no deltidium, is obviously not typical of Deitatreta as
conceived of by Ulrich. We refer it doubtfully to our
new genus Paurorthis.
Genus POMATOTREMA Ulrich and Cooper,
n. gen.
(Gr. pntna, cover; trciiia, hole)
PI. 16, figs. 14-16, 18-21,23, 26,31
Genoholotype. — p. muralis Ulrich and Cooper,
n. sp.
Discussion. — On plate 16 the writers figure a shell
that has been known as "Orthisina" grandcrva, being
first referred to Orthisina and later by Hall and Clarke
to Billingsella. However, it does not belong to either
of these, but is of a new genus which is not uncommon
in the Lower Ordovician. We had provisionally re-
ferred this species to Tafia, but after the junior author
had studied interiors of the genotype, Taffia planocon-
vexa, at Washington (unfigured by Butts) he found
that the group under consideration {Pomatotrema) has
nothing to do with Taffia as figured by Butts. It was
Ulrich's intention to affix the name Taffia to shells
similar to if not identical with O. granda-va, but in the
Alabama report unfortunately T. flanoconvexa was
figured and this of course fixed the genotype of Taffia.
Being so established, Taffia is not congeneric with
Orthisina gratidcrva, but is a member of the family
Orthidas.
The junior author discovered the differences be-
tween Taffia and Pomatotrema after he had removed
from Yale University to the U. S. National Museum,
and after he had agreed to collaborate with Dr. E. O.
Ulrich in a study of the Ozarkian and Canadian
brachiopods. Consequently the new genus Pomato-
tre7na born by the above union bears as its author the
names Ulrich and Cooper, with P. muralis Ulrich and
Cooper as the genoholotype. The following discus-
sion of the genus is based on material in the U. S.
National Museum and the figured specimens from
Newfoundland in the Schuchcrt Collection at Yale.
Distinguishing characters. — Plano-convex in
lateral profile, with perforate deltidium, chilidial plates,
and subparallel or vcntrally convergent dental plates.
Pomatotrema muralis Ulrich and Cooper, n. sp.
PI. 16, figs. 15, 20
Shell small or medium-sized, nearly as wide as long,
cardinal extremities nearly a right angle. Ventral
interarea long; delthyrium longer than wide, covered
by a prominent convex deltidium which is apically per-
forate as in Vellamo. Notothyrium partially closed by
chilidial plates. Surface multicostellate, about 3 cos-
tellae to 1 millimeter at the front of the shell. Dental
no
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
lamellx strong, adductor field lanceolate, enclosed by
the subcrescentic diductor scars. Pallial trunks as in
Orthis s. s.y bounding subreniform ovarian impressions.
In the dorsal valve the brachiophores are simple rods
supported by lateral growths of shell substance as in
Vellamo. Cardinal process simple. Adductor field
subflabellate, anterior scars the smaller. Inside the
margin of the valve is a thick subperipheral rim.
To this genus also belong Orthisina grandwva Bill-
ings, and Clkatnhonites semiconvexus Poulsen.
Horizon and locality. — Ordovician (Cana-
dian), SW 14 Sec. 2, T 1 S, R 1 W, about 4 miles
east of Hennepin, Oklahoma.
Genus POLYTCECHIA Hall and Clarke 1892
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 239, pi.
7a, figs. 26-30, t. figs. II, 12.
Horn. Waagenia Hall 1889.
Genoholotype. — Hemifronkes aficalis Whitfield
1886, Bull. Amer. Mus. Nat. Hist., vol. 1, p. 300,
pi. 24, figs. 1-5 (non Orthis? apicalis Billings).
Original description. — Shell small, subtrihedral in
contour. Hinge-line straight, about equaling the diameter
of the shell. Pedicle-valve with a high, nearly vertical car-
dinal area marked with oblique striations parallel to the
lateral margins. Delthyrium covered by a narrow, convex
plate; the presence of a foramen not determined. On the
interior the dental lamellx are widely separated, and
descend along the umbonal cavity for a short distance verti-
cally, thence bending sharply inward and meeting at a low
angle in the median line; thus forming, with the del-
tidium, a conspicuous subrostral vault. This inner spoon-
shaped plate, spondylium, is supported by a stout median
septum, and two smaller lateral septa, which meet it at the
lines of angulation ; the former of these extends for the
entire length of the plate, while the latter is free from the
accessory septa near its anterior edge. The umbonal cavity
of the valve is thus divided into five chambers, and in the
lateral chambers there is still another septum, lower than
the rest and not extending to the spondylium. The
brachial valve is shallow and depressed-convex, with a nar-
row cardinal area. The delthyrium is very broad with a
partially developed covering, the dental sockets are widely
separated, the crural plates narrow and nearly parallel to
the hinge-line. The cardinal process is simple, linear and
quite prominent, and at its union with the crural plates is
a subtriangular thickening which is supported by a low
median septum. Surface covered with fine, elevated, radiat-
ing strise, without evidence of median fold and sinus.
Geologic RANGE. — Canadian (Beekmantown) and
Chazy?
American Species
Hemifronites aficalis Whitfield 1886
Polytoechia symmetrica Butts 1926
P. ? oaiensi's Butts 1926
Discussion. — The multicamerate apical ventral in-
terior of this genus is characteristic of it, and shows
a convergence toward similar structures in Gonambo-
nkes s. s. and Clarkella. The genus, however, can
not be placed in the Syntrophiidae because of its ex-
ternal sculpture, shape of the valves, and internal
features of the dorsal valve, which are evidently close
to those of Vellamo or Deltatreta. The presence of a
deltidium and chilidium are further features linking
this genus intimately with the Clitambonitids or
Deltatretidas.
Polytcechia appears to be an American genus only,
and for this reason its relationships to Clkanibonkes s. s.
are doubtful. The ensemble of the shell ornamenta-
tion, profile, etc., suggest Deltatreta, and were it not
for the multicamerate apex it would definitely belong
here. The position we assign the genus is tentative.
Family CLITAMBONITID^ Winchell and
Schuchert 1893
Divergent specialized Protremata derived out of the
Orthacea, having well developed deltidia and chilidia.
In the ventral valve the muscles are usually borne on
a spondylium simplex. In the dorsal valve the car-
dinalia are of the Orthis type, supported by lateral ad-
ventitious shell growths. Ventral, pallial, and ovarian
markings essentially the same as those of Orthis.
Discussion. — The members of the Clitambonitidas,
prolific in variable individuals, have until recently been
classified in the Pentameracea, but Schuchert in 1929^'
made them the basis of a new superfamily, the Clitam-
bonacea. This he did when he saw that the stock
had a genetic origin independent of the Pentameracea,
as is plainly shown by their different type of spondylia.
It is true that the Clitambonacea are closely related to
the Orthidje, but as they are not in the main line of
brachiopod evolution, being a specializing stock, and
since most of them have peculiar deltidia and as a rule
strong chilidia, and more or less well developed simple
spondylia, it is thought advisable to recognize these
tendencies and to separate them from the Orthacea as
another superfamily, Clitambonacea.
Ventral valve, — The chief points of departure from
the usual orthid structure in the Clitambonitidas are
in the spondylium and deltidium. The former is a
spoon-shaped plate usually resting on the floor of the
valve at its posterior end but elevated on a median
septum at the front end. In a few forms the septum
may be absent or may be so abbreviated as to be virtu-
ally absent. The junction of the upper ends of the
spondylium with the under side of the palintrope is
marked by a distinct suture at which the growth-lines
of the inner surface of the spondylium end abruptly.
The delthyrial margin is an elongate triangular area
"Foss. Cat., Pars 42, p. 15.
GENERA OF THE SUBORDER ORTHOIDEA
111
sloping slightly vcntro-latcrally and formed by the
inside surface of the teeth as they grow forward. It is
to this surface that the deltidium is attached.
The upper surface of the spondylium is marked by
concentric lines which represent periods of no growth.
Superimposed upon these are longitudinal lines which
are taken to represent traces of muscle markings. No
signs of muscle attachment occur anywhere in the valve
except on the inner surface of the spondylium, making
it evident therefore that the function of this structure
was one of muscle anchorage. However, the indi-
vidual muscle marks have not been ascertained. In
one specimen were seen four divergent longitudinal
ridges on the upper surface of the spondylium. The
strongest two are at the bottom, with the other ones
some distance on the sides.
It is deduced from the above that the adductor
muscles occupied the central part of the spondylium
over the median septum, and the diductors and adjus-
ters were located laterally on the sides of the spondy-
lium. The scar of attachment of the pedicle was
probably located at the rear. In Hemipronites a slight
callosity at the apex indicates the scar of pedicle attach-
ment. Deltatreta has a prominent pedicle callist at
the apex.
The septum consists of a single piece (euseptum)
and is usually prolonged to the middle of the valve
or beyond. To this ensemble, consisting of a spoon-
shaped plate and euseptum, Kozlowski*" has applied
the name spondylium simplex.
The deltidium of the Clitambonitids is always a
convex plate covering the delthyrium. Its sides are
buttressed against the upper surface of the ridge formed
by the growth of the teeth and are strengthened further
by deposits of callus on the sides of the teeth (pi. 7,
fig. 14), and in some forms on the walls of the spon-
dylium. The upper layer of shell on the interarea
appears to be continuous with the outer surface of the
deltidium.
The deltidium in these forms is usually perforate
and far less commonly imperforate. Usually there is
a large foramen located near the apex, which suggests
that this opening functioned, at least during life, as the
pedicle opening. However, in some genera and species
the apical foramen was sealed at or before maturity,
thus doing away with this structural feature (see pi. 8,
fig. 8). The apical foramen is especially well devel-
oped in VellamOy and here appears to have persisted
throughout life, at least in the Trenton forms. Many
of the specimens from Minnesota have an elevated
flange or rim about the foramen and from its position
at the apex it would appear that the deltidium is formed
around the pedicle by the mantle.
In the ventral valve the ovarian and pallial impres-
sions, where visible, are similar to those of Orth'ts and
Hesperorthis. As shown in Hemipronites, a pallial
" Pal. Polonica, vol. I, 1929, p. 124.
sinus extends from the outside extremities of the spon-
dylium in the position of the diductor tracks, along
each side of the median ridge, bending abruptly later-
ally at the front (see pi. 8, fig. 10). These sinuses
bound subreniform ovarian areas marked by elevated
wavy ridges exactly as in the Orthidx. In some
genera these markings arc much less distinct but in
all they strongly suggest direct affiliation with the
Orthidae.
Dorsal valve. — The pattern of the dorsal valve in
most of the genera is alike. The brachiophores are
flattened or rodlike divergent plates forming the mar-
gins of the notothyrium and extending laterally into
the visceral cavity of the valve. In adults the noto-
thyrial platform is greatly thickened by adventitious
shell which extends laterally onto the inner surfaces
of the brachiophores and around their dorsal surface.
This gives the brachiophores the appearance of being
laterally prolonged plates when actually they are short
and hidden within the extra testaceous matter. The
postero-lateral face of the brachiophore, however,
always forms the inner wall of the socket, while on
the outer wall a denticle can usually be seen which
articulates with the socket in the postero-lateral face
of the tooth.
The chilidium is formed similarly to the deltidium.
It is a convexly arched plate built against the sides of
the notothyrium and cemented by deposition of adven-
titious shell under the brachiophores and under the
anterior side of the chilidium. Not infrequently adven-
titious deposit is laid on the ventral surface of the
brachiophore and continuously with the front margin
of the chilidium. The precise function of the chilidium
is, at present, not known, but it may be of use to the
animal in protecting the muscle attachments on the
myophore of the cardinal process.
The musculature of the dorsal valve is like that seen
in Orthis, Hesperorthis, and other orthids. There are
four adductor scars divided centrally by a stout median
ridge and horizontally by ridges at right angles to the
median elevation. The median ridge, its lateral ridge,
and the continuous curved ridges of the chilidium and
lateral thickenings under the anterior face of the brach-
iophores give the appearance of an anchor when the
shell is inverted with the posterior toward the observer.
This analogy was emphasized by Pahlen*^ in his study
of the genus Orthisina. The anterior pair of adduc-
tors are not uncommonly divisible into two separate
scars, as in Productorthis.
The cardinal process is simple, orthoid in structure,
and may be continued posteriorly so as to unite with
the inner surface of the chilidium. Pallial markings are
usually not clearly visible in the dorsal valve. Most
shells show two oblique ridges extending antero-later-
ally from the adductor pits to a little beyond the
anterior margins of the muscle field.
" Mem. .Acad. Imp. Sci. St. Petersb., 7th ser., vol. 24,
no. 8, 1877, p. 7.
112
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Affinities. — Kozlowski^* has recently shown that
the spondylium of the pentamerids, such as Pentamerus
and Conchidium, has had a different origin from that
of Clitambonites and Skenidium. The polyphyletic
origin of this peculiar muscle platform is clear evidence
of the separate origin of the two groups. Kozlowski
has pointed out that the prominent development of the
deltidium and chilidium in the Chtambonitidffi sug-
gests a close relationship with the Strophomenacea, but
the presence of an orthoid cardinal process and other
features of the Orthidas shows stronger affinities with
the Orthacea. Before Kozlowski's paper appeared in
this country, the writers had also come to the conclu-
sion that the Clitambonitidas were primitive, aberrant,
and specialized orthids. We saw this relationship in
the ventral pallial and ovarian markings, the simple
septum-like cardinal process, the Orthis-Wke brachio-
phores and adductor field. We now know that the
presence or absence of a deltidium or chilidium is in
itself not of such great significance as was formerly
believed, since these features appear spasmodically in
many of the later genera and families. However, an
important feature of the clitambonitid deltidium is its
prominent apical foramen. Kozlowski has looked with
probable correctness to the Billingsellidae as the ances-
tral stock of the Clitambonitidas, and in this we agree,
since the Billingsellida: have all the necessary structures
by which such a transition could be accomplished.
The writers also independently of Kozlowski saw
the need of separating Skenidium and its allies from
the Clitambonitidae. Skenidium has no deltidium or
chilidium, and in this respect is very specialized. The
internal differences, and especially the nature of the
cardinalia, link Skenidium with the Plectorthids rather
than with the Clitambonitidae. Skenidioides, probable
progenitor of Skenidium, undoubtedly originated in
Finkelnburgioy since the cardinalia of the latter are like
those of the Plectorthidae.
Opik*^ also points out that the Clitambonitidae in
structure are foreign to the Pentameracea and places
them close to his new family Plectambonitidae. The
latter family has, however, a closer relationship to the
Orthacea than to the Strophomenacea, as is shown in
the nature of the cardinal process and other internal
structures, and it is not unlikely that more study will
establish it as an aberrant and terminal division
of the Orthacea. We consider the Clitambonitidae
as special developments, probably from the same ances-
tral stock, namely, the billingsellids.
The large family Clitambonitidae is divisible into
the following subfamilies:
Plectellinae Opik
Clitambonitina Schuchert and Cooper
Gonambonitinse Schuchert and Cooper
"Op. cit., pp. 122-125.
*' Acta et Comment. Univ. Tartuensis, A, vo]. 17, pt. 1,
1930, p. 60.
Subfamily PLECTELLIN^ Opik 1930
The Plectellinae are primitive Clitambonitidae with-
out spondylia, which apparently gave rise to the special-
izing Clitambonitidae of Europe.
In his splendid monograph on the Estonian Pro-
tremata, Opik*^ has proposed a family Plectambonitidae
which he defines as follows (in translation) :
This family embraces all Strophomenacea with a simple
cardinal process and strophomenoid habit, thus with con-
cavo-convex or convexo-concave shells. All others, with a
double cardinal process, form the family Strophomenidse.
Heretofore the members of our new family have been
combined with the Rafinesquinina: and were placed near
the beginning of this subfamily.
Opik divides his new family into three subfamilies,
the Plectellinje, Plectambonitinae, and Sowerbyellinae.
We shall concern ourselves here chiefly with the Plect-
ellinae, which we believe are very close to the Del-
tatretidae in structure. The Plectambonitinae and
Sowerbyellinae in their simple cardinal process show re-
lationships with orthoid brachiopods rather than with
the Strophomenacea where they have persistently been
classified. Here again external form appears to have
been the chief guide in classification.
Within the Plectellinae Opik places Plectella Laman-
sky, Ingria Opik, and PaltFostrofhomena Holtedahl.
He believes in the uniqueness of Plectella and in this
he has the support of Kozlowski, who maintains this
to be a good genus. Schuchert (1929)*' unites
Plectella with Plectamhonites Pander, but in this the
two European authors do not concur. In our study of
these genera we are wholly dependent upon the litera-
ture and hence our conclusions may be in error. We
regard Palceostrofhomena as a possible member of the
Dinorthidae, close to Valcourea. The two remaining
genera are characterized by having a chilidium and an
imperforate deltidium. Fine radial lines mark the out-
side of the shells and there is no spondylium. In the
dorsal valve of both Plectella and Ingria the cardinal
process is orthoid, not plectambonitoid. In other
words, it does not form a tentlike structure as in
Sozverbyella. Furthermore, the brachiophores are
orthoid as in Deltatreta and are supported by lateral
extensions of the notothyrial platform as in Vellamo
and other Clitambonitina. It is our contention, then,
that these shells are aberrant Clitambonitidae, without
spondylia. Development of the Plectambonitinae and
Sowerbyellinae may have come from this line. In
America, Plectella and Ingria find their nearest rela-
tives in Deltatreta and Pomatotrema. These two
genera differ from the Plectellins in the presence of
an apical foramen and incomplete chilidium only, all
other structures being in agreement.
*" Acta et Comment. Univ. Tartuensis, A, vol. 17, pt. 1,
1930, pp. 55-58.
" Foss. Cat., Pars 42, p. 98.
GENERA OF THE SUBORDER ORTHOIDEA
113
Subfamily CLITAMBONITIN,-E Schuchcrt and
Cooper 1931
(^ Orthisinin.T Waagcn 1884)
The typical and most prolific subfamily of the
Clitambonitida?, having a spondylium simplex. Em-
braces the following genera:
Cl'ttamhonites Pander
Vellamo Opik
Clinambon, n. gen.
Eitlattd'm Schuchert and Cooper
Hemipronites Pander
Pahlenella Schuchert and Cooper
Apomatella Schuchert and Cooper
Species (the first thirteen of Pander 1830)
Proniles aduenden?*
P.dta
P. convexa
P. excelsa
P. humilis
P. la/a
P. oblonga
P. flana
P. fracefs
P. frarufia
P. rotunda
P. tetragona
P. transversa
Orthisina schmidtiVMcn 1877
? Orthisina concava Pahlen 1877
Genus CLITAMBONITES Pander 1830
PI. 7, figs. 17, 19-23,26
Pander, Beitr. Geogn. Russ. Reiches, 1830, p. 7U, pi. 17,
fig. 6.
Syn. Proniles Pander, Ibid., p. 71, pi. 17, fig. 6.
Syn. Orthisina D'Orbigny, Compt. Rend., Acad. Sci. Paris,
vol. 25, 1847, p. 267.
Genolectotype (Dall, and Hall and Clarke). —
Pronites adscendem Pander 1830.
Description. Exterior. — Shell semielliptical,
hinge-line less than the greatest width of the valves;
lateral profile biconvex or convexo-concave; dorsal
valve convex; ventral valve usually subpyramidal;
anterior commissure rectimarginate, dorsal valve sul-
cate in youth only. Ventral interarea the longer,
strongly apsacline to procline; deltidium prominent,
rarely perforate; dorsal interarea the shorter, usually
anaciine; chilidium well developed. Surface multi-
costellate, commonly imbricate and spinose. CostelL-E
crossed by elevated concentric lines of growth. Test
fibrous, impunctate.
Ventral interior. — Provided with a spondylium sim-
plex which is as wide as long or longer than wide, the
sides usually flexed inward and the base usually flat.
The median septum extends to about the middle of the
valve. The musculature was evidently confined to the
upper or inner side of the spondylium, the adductors
probably at the base, the diductor and adjuster scars
(if any) on the sides.
Dorsal interior. — Notothyrial cavity small, cardinal
process linear, brachiophores orthoid, supported by
lateral extensions of the notothyrial platform, forming,
with the median septum, an inverted "anchor." Ad-
ductor field quadripartite; anterior adductor set the
larger.
Geologic range. — Lower and Middle Ordovi-
cian of Europe.
Discussion. — The features best characterizing
Clitambonites are (1) the subpyramidal ventral valve,
(2) the convex dorsal valve; (3) the inclination of
the ventral interarea; and (4) the external ornamen-
tation. The ventral exterior is usually slightly convex
or nearly flat, but in one exceptional species (C. con-
cava) it is concave. The ventral interarea is usually
catacline or decidedly procline, the angle from the hori-
zontal being not uncommonly more than 80', but
it may also be very strongly apsacline. The dorsal
valve is always more or less strongly convex, always
less deep than the ventral one, with the greatest con-
vexity usually located at the middle of the valve.
The most striking external feature of Clitambonites,
however, is the sculpture, which sets it apart at once
from Vellamo, the shell of the former being strongly
lamellose, each interval of growth making a distinct
layer ("like steps or roof-tiles," Hall and Clarke, p.
236), and the costella produced forward as flanges,
so that there is a costellate border about the margins
of the shell when they are viewed from the inside,
somewhat as in A try pa (see pi. 7, figs. 19, 20). This
condition is approached in Vellamo by V. squamata,
but in that form there are differences in the spondylium
and external form that prevent its being placed in
Clitambonites.
The deltidium of Clitambonites is typical of all this
family, namely, wide and highly convex and perfor-
ated by a large pedicle foramen. It is interesting to
note, however, that the foramen in the apex of mature
shells is rarely visible, being sealed up during early
maturity. It is not uncommon that the internal sur-
face of the deltidium is strengthened by a longitudinal
'■' Verneuil (Geology of Russia) placed all of Pander's
species of Proniles except P. oblonga under the name Orlhis
adscendens. From our present point of view, it seems
apparent that \'crneuil never understood Pander's discrim-
inating work, and due to his great influence unjustly sub-
merged many of the species and generic concepts of the
earlier investigators.
114
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
thickening or low septum. The spondylium is sessile
at its posterior extremity but is elevated on a septum
in its median portion and free at the front end. The
umbonal cavities commonly have some filling but never
to the degree shown by Vellamo diversa from Anticosti.
It was Hall and Clarke^* who revived Pander's
" Klitamhonites" as a generic term, and restricted the
name, as they thought, "pretty nearly" to Pander's
term Pronites. They, however, did not appreciate the
features of Gonambonites, nor of the tribe of Orthisina
verneuili which has been recently made the genotype of
the genus Vellamo by Opik.
Genus VELLAMO Opik 1930
PI. 7, figs. 5, 8-11, 14-16, 18, 24, 25, 27-32;
pi. 29, figs. 8, 14
Opik, Acta et Comment. Univ. Tartuensis, A, vol. 17, pt. 1,
1930, p. 212.
Genoholotype. — Orth'ts verneuili Eichwald 1841,
Urwelt Russlands, II, p. 51, pi. 2, figs. 3-5.
Description. Exterior. — Shell narrowly semi-
elliptical, hinge-line straight, as wide as or wider than
the total width of the shell; cardinal extremities usu-
ally acutely angular. Lateral profile piano- to slightly
concavo-convex; anterior commissure rectimarginate
to broadly sulcate. Ventral palintrope long, strongly
apsacline to catacline but never procline. Dorsal pal-
intrope shorter, anacline. Deltidium perforate in ma-
ture forms, with the apical foramen sealed in old in-
dividuals. Surface coarsely costellate, the costellse
being crossed by fine elevated lines of growth. Test
fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep, teeth
strong, forming a thickening along the sides of the del-
thyrial margin; crural fossettes shallow. Spondylium
slightly depressed so that it is usually wider than high;
median septum low but long, extending nearly to the
front margin. Internal lateral spaces marked by irreg-
ular granules.
Dorsal interior. — Notothyrial cavity small, shallow,
divided into two chambers by the cardinal process.
Brachiophores orthoid, supported by lateral growths
anteriorly, formed by the swelling of notothyrial plat-
form. Median ridge thick and broad, extending to the
front of the muscle area; sockets shallow; adductor
field quadripartite, the anterior set being the larger
and divided from the posterior pair by low ridges at
right angles to the median ridge. An oblique pallial
ridge is given off from the antero-lateral extremities
of the anterior adductor scars. Internal surface
marked by low granules.
Geologic range. — Middle and Upper Ordovician
(Chazy to Richmond).
«" Pal. N. Y., vol. 8, pt. 1, 1892, p. 233.
American Species
Orthisina diversa Shaler 1865
Clitatnbonites americanus Whitfield 1877
C diversa altissima WincheU and Schuchert 1 893
C. rogersensis Foerste 1910
C. ruedemanni Raymond 1 92 1
C. trentonensis Raymond 1 92 1
aff. C. multicosta (Hudson)
European Species
Orthisina adscendens Davidson (Brit. Foss. Brach., vol. 3,
pt. 7, p. 278) (non Pander).
O. comflectens 'Wivcid.n 1907
O. emarginata Pahlen 1877
O fyramidalisYztii&n X'iill
O. squamata Pahlen 1877
O. verneuili wesenbergensis Pahlen 1877
Orthis verneuili Eichwald 1841
Clitambonites comflectens albida Reed 1917
C. humilis Fuchs
Skenidium grayitiT>a.vi6i&on 1883
S. shallochiense Davidson 1883
Vellamo farva Opik 1930
V. fyramidalis arcuato Opik 1930
V . fyramidalis fahleni Opik 1930
V . fyramidalis simflex Opik 1930
K. wWwjOpik 1930
Distinguishing characters. — Vellamo is char-
acterized externally by the wide hinge-line, apsacline
palintrope, concavo- to plano-convex profile, and non-
imbricate shell sculpture.
Discussion. — From the above it is apparent at once
that Vellamo differs in important details from Clitam-
bonites. In the former the palintrope is usually long,
flat or curved noticeably, as a rule moderately or
strongly apsacline, and only very rarely catacline.
Clitambonites altissimus and C. trentonensis among
American species have nearly catacline pahntropes.
Vellamo differs further from Clitambonites in not
possessing the strongly lamellose or frilled ornamenta-
tion. The surface sculpture is like that visible in the
umbonal region of Clitambonites as pointed out by
Opik. The type of ornamentation in Clitambonites is
approached in Vellamo only by Orthisina squamata
Pahlen, which is placed here because of internal
similarities.
Internally it is difficult to define any substantial
difference between the two genera. The spondylium
of Vellamo is usually wider than long and this de-
pressed appearance is in contrast to the elongate or
narrow one of Clitambonites. Inside the dorsal valve
the fundamental structures of the two genera are essen-
tially the same, the only perceptible variations being in
a rather thicker notothyrial platform in Vellamo and
the flange-like border around the internal margin of
Clitambonites. Opik points out further that the chi-
lidium of Vellamo is relatively short and wide and the
muscle-scars generally wider and shorter, but there
appears to be little generic value in these features.
GENERA OF THE SUBORDER ORTHOIDEA
115
The deltidium of Vellamo appears to be formed in
precisely the same manner as that of Clitamhonites,
but at maturity the apical foramen is not sealed as in
the latter genus though it is closed in old-age specimens.
Clittimbomtfs appeared first geologically (Kunda),
and died out with the Middle Ordovician. Vellamo,
on the other hand, appeared later (Chazy) and en-
dured through the rest of the Ordovician.
Genus CLINAMBON. n. gen.
(Gr. klino, bend, and amhon, umbo)
PI. 8, figs. 24, 28
Genoholotype. — Anomites anomala Schlotheim
1822, Nachtnige, p. 65, pi. 14, fig. 2.
Description. Exterior. — Subquadrate in outline,
valves very unequal, the ventral one pyramidal, the
dorsal flat and elongate. Anterior commissure unipli-
cate. Ventral interarea strongly procline, longer
than the dorsal one. Interarea of the dorsal valve
unusually long; chilidium wide and strongly arched.
Deltidium perforate in young shells but foramen sealed
in old ones. Valves multicostellate as in Vellamo.
Ventral interior. — There is a prominent spondylium,
the sides of which are infolded at the front, giving a
pinched-in effect. The median septum is short.
Dorsal interior. — Exactly as in Vellamo except that
the structures are greatly overdeveloped. The cardinal
process is fused to the ventral border of the ponderous
chilidium. Median ridge short. Notothyrial platform
ponderous and lateral thickenings greater than in any
other member of the Clitambonitidas. Brachiophores
flat blades clearly visible near the sockets.
Geologic range. — Middle Ordovician (Jewe and
Kegel, Do) of Estonia. The genotype is the only
known species.
Discussion. — The unusual development of the
dorsal interarea and the ponderous chilidium are fea-
tures which set this shell aside from Vellamo. The
ornamentation is like that of the latter genus, and the
appearance in the geologic column comes long after
the disappearance of Clitamhonites, indicating relation-
ships with Vellamo rather than any other group of the
Clitambonitinx.
Genoholotype. — Orthisina marginata Pahlen
1877, Mem. Acad. Imp. Sci. St. Petersh., 7th ser.,
vol. 24, no. 8, p. 33, fig. 8, pi. 3, figs. 11-15, pi. 4,
figs. 1-3.
Description. Exterior. — Sub-strophomenoid to
hebertelloid in lateral profile and outline; ventral
interarea longer than dorsal, usually strongly apsa-
cline. Deltidium having an apical foramen; chi-
lidium complete. Surface multicostellate. Test fibrous,
impunctate.
Ventral interior. — Delthyrial cavity deep; teeth
large; spondylium supported at the front by a promi-
nent median septum and laterally by low, very short
septa. Muscle attachments confined to the spondy-
lium. Adductor and diductor tracks linear. Sub-
peripheral rim low, but prominent.
Dorsal interior. — Notothyrial cavity shallow ; noto-
thyrial platform swollen, with prominent thick lateral
extensions which support the brachiophores. Median
ridge strong; brachiophores orthoid; cardinal process
simple, cemented to the under surface of the chilidium.
Subperipheral rim prominent; adductor field large,
with the muscle attachments commonly elevated.
Geologic range. — Middle Ordovician (Kuckers)
of Europe.
Species
Orthisina marginafd Pahlen 1877
O.f'yro/! Eichwald 18+0
O.volborthi Pahlen 1877
Gonambrinltes marginatus asfer Opik 1930
G. marginatus magnus Opik 1930
G. fanderi'd'^W. 1930
Hemifronites carrickensis Reed 1917
H. thomsoni Reed 1917
? G. infiexa Pander 1830
Discussion. — Estlandia differs from Gonambonites,
which it resembles and with which it has usually been
associated, in having an apical foramen, median septa
in both valves, and a complete chilidium. The orna-
mentation of Estlandia and its internal structure, how-
ever, suggest relationship with Vellamo. As in the
Orthidas, Dinorthid.x, and other groups, it is reason-
able to expect a convexo-concave stage of development.
Estlandia appears, then, to be a convexo-concave stage
of Vellamo, of rather short geological range and local
development.
Genus ESTLANDIA Schuchert and Cooper
1931
PI. 8, figs. 6, 8, 9; t. fig. 10
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 245.
Gonambonites (pars) Opik, Acta et Comm. Univ. Tartu-
ensis. A, vol. 17, 1930, pp. 222-227, pi. 19, figs. 229-
236, 248; pi. 20, figs. 236-239; t. figs. 24, 25.
Genus HEMIFRONITES Pander 1830
Pi. 8, figs. 10-15
Pander, Beitr. Gcogn. Russ. Reiches, 1830, pp. 71, 74,
pi. 3, fig. 14, pi. 18, fig. 6, pi. 28, fig. 22.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 238,
figs. 9, 10.
Genolectotype (Dall). — H. tumida Pander
1830,
116
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Description. Exterior. — Shell rotund to sub-
semielliptical, strongly biconvex; hinge-line straight,
usually narrower than the total width of the shell;
cardinal extremities obtusely angular or rounded. An-
terior commissure rectimarginate; dorsal sulcus obso-
lete or only faintly impressed. Ventral interarea longer
than the dorsal, curved, apsacline ; delthyrium closed
by a deltidium which is usually imperforate in adults.
Dorsal interarea short, orthocline to faintly apsacline
or anacline ; chilidium prominent. Surface finely mul-
ticostellate ; test fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep, spondy-
lium longer than wide, sessile posteriorly but supported
by a low septum in front, the septum being continued
forward nearly to the front margin. Adductor ( ? )
track occupying the central depressed portion of the
spondylium, diductor ( ? ) tracks on each side at the
base and partially on the sides of the dental plates.
Interior lateral spaces covered by subreniform ovarian
markings. Subparallel pallial impressions bounding the
inner margins of the ovarian markings and separated
by the median septum.
Dorsal interior. — Notothyrial cavity and sockets
shallow, brachiophores orthoid, short, blunt, and sup-
ported as in Gonamhonttes. Cardinal process a linear
ridge on the thick notothyrial platform. Median ridge
strong, extending to the middle of the valve. Anterior
adductor impressions elongate, separated from the
shorter posterior pair by a narrow ridge at right angles
to the median elevation. Lateral spaces occupied by
pallial and ovarian markings.
Geologic range. — Lower and Middle Ordovician
of northwestern Europe.
European Species (of Pander 1830 except
where otherwise stated)
H emifronit es i^jualis
H. dta
H. brevis
H. circularis (pi. 16, B, is same figure as H. maxima)
H . ex f ansa
H. lata
H . latissima
H. maxima
H. obtitsa
H. orbicularis
H. feralta
H . ferlata
H . ■prominens
H. rotunda
H. sfherica
H. transversa
H. tumida
Orthis hemifronites Von Buch 1 840
O. radians Eichwald
? H. globosa (pi. 16, B, fig. 6). This is the same figure as
H . elongata and both have the appearance of a
hycofhoria
? H. tenuistriata WeWcr 1907 (China)
Distinguishing characters. — Hall and Clarke
used the name Hemifronites for shells with tumid,
subequally convex valves, hinge-line narrower than
the greatest width, the greatest thickness of the ventral
valve not at the beak, the surface finely multicostellate,
and the deltidium non-perforate.
Discussion. — Hemifronites differs from its nearest
relative Clitamhonites s. s. in several important char-
acteristics. It is usually subequally convex, the ventral
palintrope is never procline, and the deltidium is im-
perforate. This contrasts strongly with Clitamhonites
in which the ventral valve is usually subpyramidal,
and the deltidium perforate at least in early maturity.
The ornamentation of Hemifronites is also different
in being much finer and in lacking the strong concen-
tric lamellje or frills of Clitamhonites.
Internally there is also considerable variation be-
tween Hemifronites and Clitamhonites. In the ven-
tral valve of the former, to judge from H. tumida,
the spondylium is sessile for most of its length but at
its front end it is elevated on a low septum or ridge
which extends nearly to the front margin. The walls
of the spondylium are slightly convex inward and
converge rapidly, forming a narrow floor at the base
of the structure. This type of spondylium contrasts
with that of Clitamhonites in which it is sessile only at
the posterior and is elevated on a rather high septum.
The front end of the spondylium of Clitamhonites is
free and the floor rather wide.
One of the specimens in the Schuchert Collection
(Cat. No. 369; see pi. 8, fig. 10) shows markings on
the spondylium that can be interpreted only as the
muscle impressions. Homologizing these marks with
similarly situated scars in orthids, the writers believe
that the central linear track represents the position of
the adductor muscles. This track occupies most, but
not all, of the narrow floor of the spondylium. It is
bounded on each side by low ridges. The diductor
impressions are thought to be narrow linear tracks
located outside the ridges bounding the adductor track
at the line where the dental plates unite with the
septum. The impressions of these tracks are also visi-
ble for a short distance on the inside surface of the
central lamellae. They are marked oS by scarcely
perceptible ridges along the margin of the muscle track.
Adjustor muscle impressions were not definitely
determined.
Ovarian markings of irregular elevated lines are
also well exhibited in the same specimen. These are
subreniform areas such as are so common in Orthis,
Dolerorthlsy Paurorthls, etc. The shallow grooves
separated by the median ridge and bounded by the
ovarian impressions are taken to represent the two
main trunks of the pallial marks, homologous to the
two sinuses extending from the anterior ends of the
diductors of Orthis, Bllllngsella, etc. It is therefore
evident from the above that the important internal
GENERA OF THE SUBORDER ORTHOIDEA
117
shell features of H r mi promt rs differ from those of
Ort/iii s. s. only in having a spondylium.
The dorsal interior of Hfmipronitfs is likewise dis-
tinctly orthoid. The brachiophores arc rather flat
plates, divergent and oblique to the vertical. The
space between the sloping outer face of the brachio-
phore and the wall of the valve forms the socket. The
brachiophores are supported and usually nearly en-
gulfed by adventitious shell of the notothyrial plat-
form, but never to the extent seen in Vrllnrrio. The
median ridge is rather high and extends to the middle
of the valve. The posterior diductors are smaller than
the anterior pair which are elongate and elliptical.
Finally, the whole interior of the valve outside the
muscle field is marked by elevated, irregular radiating
ridges, and there can be no doubt that the spaces
between some of these represent pallial sinuses although
no definite system could be discerned.
Verneuil'" united nineteen of Pander's species under
Von Buch's name Orthis hem'tpronites. This is an-
other example of Verneuil's "lumping" attitude and
his failure to understand Pander's ability in species
making. There can be no doubt that many of
Pander's species of Hem'tpronites are insufficiently
drawn, but even so, it must be said that all of his nine-
teen forms can not be put into one species. There is
great need for a critical revision of the species occurring
in the "Glauconite" horizons by someone thoroughly
familiar with the local stratigraphy of these shells.
Opik has referred Pander's species H. maximus to
the genus Clitambonites. A large specimen in the
Schuchert Collection (Cat. No. 365), however, agrees
with Pander's figure (pi. 16, B, fig. 5) except in the
arching of the ventral palintrope, and it shows all the
characteristics of /fron/Ve^ (see pi. 8, figs. 12, 13).
We believe, therefore, that Opik has not figured H.
maxima of Pander but actually has a new species not
referable to Hemipronites but with a shell surface
which relates it to Vellamo squamata.
Genus PAHLENELLA Schuchert and Cooper
1931
(After Pahlen, in recognition of his fine work on
Orthisina)
PI. 7, figs. 1-4
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 245.
Genoholotype. — Orthis trigonuln {ex parte)
Eichwald 1840, Sil. Schicht. Esthland, I, p. 148;
Pahlen, Mem. Acad. Imp. Sci. St. Petersb., 7th ser.,
vol. 24, no. 8, 1877, p. 46, pi. 4, figs. 22-24.
Description. Exterior. — Semiclliptical, hinge-
line straight ; cardinal extremities acute; lateral profile
concavo-convex; anterior commissure sulcate; ven-
' Geology of Russia, vol. 2, Paleontology, 1845, p. 205.
tral valve provided with a prominent fold. Ventral
palintrope the longer, moderately apsaclinc; dcltidium
perforate. Dorsal intcrarea nearly obsolete, hyper-
cline. Surf.ice coarsely multicostellate. Test fibrous,
impunctate.
Ventral interior. — Teeth prominent, crural fossettes
deep; spondylium short, supported by a low septum
which is not, however, produced forward beyond the
anterior end of the spondylium (sec pi. 7, fig. 2).
Dorsal interior. — Notothyrial cavity nearly obsolete,
brachiophores as in Clitambonites and Gonamhonitrs.
Cardinal process, along with the median ridge and
notothyrial platform, fused with a sessile shield-shaped
plate of adventitious shell underneath the muscle field.
Posterior adductor scars the smaller.
Geologic range. — Lower Ordovician (lower
Biii^ or Kunda formation) of western Russia. Only
known species the genotype.
Discussion. — In this interesting little shell there are
several features that set it apart from the rest of the
Clitambonitidas. Externally the concavo-convex pro-
file is not in itself unique, but this, when combined
with a prominent ventral fold and a corresponding
dorsal sulcus, makes an aggregate of characters suffi-
ciently distinct for generic discrimination. Internally
there are additional striking variations in each valve.
In the ventral valve, the spondylium is supported on a
septum so low as to give it the appearance of being
sessile; the septum is furthermore very short and in
this is very unlike the long ones in Clitambonites.
In the dorsal valve, the development of an elevated
adductor field is a convergence toward the type of
structure seen in Leptelloidea Jones. The disc is
shield-shaped and produced anteriorly into a short
process, while the pattern of the muscle marks does
not recall those of Clitambonites.
Genus APOMATELLA Schuchert and Cooper
1931
(Gr. a, without; potiia, cover)
PL 7, figs. 6, 7, 12, 13
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 245.
Genoholotype. — Orthisina ingrica Pahlen 1877,
Mem. Acad. Imp. Sci. St. Petersb., 7th ser., vol. 24,
no. 8, p. 48, pi. 2, figs. 18-21.
This name is suggested for the small Orthisina
ingrica Pahlen which is devoid of a deltidium and
chilidium. This loss of important features is a con-
vergence toward the Orthida: and appeared mther
early in this genus of the Clitambonitida;. The ventral
valve is subpyramidal, with a catacline or procline inter-
area. Internally the spondylium is short and elevated
upon a high septum. The interior of the dorsal valve
was not observed. The exterior is multicostellate.
118
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
The genotype is the only known species and comes
from the Canadian (Walchow) in the vicinity of
Leningrad.
Subfamily GONAMBONITIN^ Schuchert and
Cooper 1931
Aberrant Clitambonitids having a strophomenoid or
substrophomenoid profile and a sessile spondylium
(pseudospondylium). Dorsal and ventral median
septa are lacking. In the species studied by us the del-
tidium is imperforate.
The subfamily embraces only the one genus,
Gonamhonites Pander.
Genus GONAMBONITES Pander 1830
sensu lato
PI. 8, figs. 1-5, 7, 20, 21, 25, 26
Pander, Beitr. Geogn. Russ. Reiches, 1830, p. 77, pi. 3,
fig. l,pl. 16a, fig. 3, pi. 28, fig. 15.
Opik, Acta et Comment. Univ. Tartuensis, A, vol. 1 7,
pt. 1, 1930, pp. 220-222.
Genolectotype (Schuchert and LeVene). — G.
lata Pander.
Description. Exterior. — Shell strophomenoid or
substrophomenoid in appearance, semielliptical ; hinge-
line wide and straight, cardinal extremities acutely
angular; lateral profile convexo-concave; lateral com-
missure flexed dorsally; anterior commissure slightly
sulcate, there being a faint sulcus in the dorsal valve.
Ventral interarea the longer, plane, strongly apsa-
cline; dorsal interarea short, apsacline to anacline.
Deltidium imperforate in G. -planus; notothyrium
closed by a chilidium. Ornamentation multicostellate.
Shell substance fibrous, impunctate.
Ventral Interior. — Delthyrial cavity deep; teeth
small; spondylium (.'' pseudospondylium) sessile and
strengthened on each side by a short lateral septum or
several septa.®^
The muscles were attached to the upper surface of
the spondylium. The adductor tracks are linear.
Diductor and adjustor scars can not be differentiated
but the combined marks are situated on the sides of the
dental plates. Subperipheral rim low.
•^ A note in regard to the spondylium (?) of G. flanus
will be of interest. This is sessile and strongly suggests the
pseudospondylium common to Finkelnburgia and Linofor-
ella. The extra "supporting plates" are directly ventral to
the dental plates and may actually be a continuation of
them, and the floor of the spondylium may therefore be
composed of callus. We had before us no very young shells,
from which the true character of the spondylium could be
ascertained. Should this ventral muscle field prove to be
a pseudospondylium, the relationship of Gonamhonites
flanus to the Clitambonitina: may prove to be still more
remote than we had suspected.
Dorsal interior. — Notothyrial cavity shallow or ob-
solete; notothyrial platform swollen and extended
laterally; chilidium and cardinal process protruding
above the interarea. Cardinal process thin, linear;
brachiophores orthoid, supported by lateral extensions
of the notothyrial platform (see pi. 8, fig. 7). Sockets
shallow. Adductor field subflabellate ; median ridge
obsolete or rudimentary. Subperipheral rim low.
Geologic range. — Lower Ordovician (Canadian)
of Europe (Walchow (Bn) for G. -planus Pander).
Species. — We offer here no list of species because
we had available for study very few forms of Gonam-
botntes. Of G. planus there was an abundance of
material, but we had no specimens of G. latus. We
had specimens of "G." inflexus and G. excavatus
Pander but these do not agree morphologically with
G. planus, from which our description was made up.
We will not re-assign Pander's species from his figures
or descriptions because both are rather inadequate and
mistakes would be inevitable.
Discussion. — The old genus Gonamhonites has
been regarded by most writers as a synonym of
Clitamhonites and was so placed by Hall and Clarke
in 1892. Dall in 1877 listed G. lata, Pander's first
species, but never selected a type. Schuchert and
LeVene (1929), following Dall's lead, selected G. lata
as the type of the genus. A little later Opik (1930)
made a critical study and revision of the genus and
selected as the type G. planus Pander. Opik's selec-
tion unfortunately can not stand as Schuchert and
LeVene's choice has precedence.
In the description of Gonamhonites presented above,
we have based our remarks on G. planus for two
reasons: (1) This is the only material we had avail-
able, G. latus being entirely lacking from the Schu-
chert Collection; and (2) Verneuil (Geology of
Russia) placed G. latus in the synonymy of G. planus.
It is a known fact that Verneuil took liberties with
Pander's work that would be unheard of to-day, and
it is very probable that some of the shells placed by
him under G. planus deserve recognition as indepen-
dent species. From Pander's figures of G. latus, there
is to us a strong superficial resemblance to G. inflexus,
a species that clearly is not a Gonamhonites. If it is
shown by subsequent workers that G. latus has affinities
with G. inflexus, a wholly different interpretation of
the genus will be required, and it may be found neces-
sary to set off G. planus as an independent generic
group on the basis of its unusual spondylium (pseudo-
spondylium) and non-perforated deltidium.
In the absence of material, we feel obliged to follow
Verneuil's interpretation of G. latus as a probable
synonym of G. planus, although we feel strongly that
Verneuil as a rule took many liberties. On this basis
we are justified in regarding "G. planus" as a "cotype,"
as it were. Therefore, as explained under Estlandia,
we were forced to make a new genus for shells differ-
ing very widely from Gonamhonites as described above.
GENERA OF THE SUBORDER ORTHOIDEA
119
Superfamily DALMANELLACEA Schuchert and Cooper 1931
Progressive and terminal Orthoidca, probably de-
rived out of the Orthidx, and most easily character-
ized by their endopunctate test and a primitively
bilobed cardinal process.
Embraces the following families:
Dalmanellida: Schuchert
Wattsellidx Schuchert and Cooper
Bilobitid.-e Schuchert and Cooper
Mystrophoridx Schuchert and Cooper
Rhipidomellidas Schuchert
Heterorthid.T Schuchert and Cooper
Schizophoriida- Schuchert
Linoporellida: Schuchert and Cooper
Tropidoleptidae, n. fam.
tion. We shall not be surprised, however, if someone
points out that punctation had more than one origin.
Punctation once introduced, the superfamily shows
shell variations similar to those of the Orthacea, a
superfamily that arose in the Cambrian, dominated the
Ordovician, and vanished with the Devonian. The
Dalmanellacea, on the other hand, arose early in the
Middle Ordovician (first ones known in the Chazy),
differentiated greatly in the late Silurian and early
Devonian, spread over most of the world, constantly
throwing off new genera, and yet apparently died
out with the Permian.
The genetic relations seem to be as shown in
Table 9.
Table 9
MYSTROPHORIDiE
DaLMANELLID/E
Proschizophoria
BiLOBITIDiE
Bilobites
Aulacella
Heterorthina
ORTHIDiE
Discussion. — As is seen in the definition of the
Dalmanellacea, we lay the superfamily characteristics
in the endopunctate shell and the beginning of a bilobed
cardinal process. We further are forced to assume
that the punctate shell started in a single species of the
Orthacea, but unfortunately do not know in which of
the older families this tendency originated, since in
none of this superfamily is there any endopunctate
species or genus. It is this utter lack of endopuncta-
tion among the Orthacea that leads us to our assump-
Family DALMANELLIDA Schuchert 1929,
emended
(=Dalmanellin2e Schuchert 1913)
Progressive and terminal Dalmanellacea in which
the ventral muscle field is bilobed in front, diductor
scars not enclosing the adductor impressions. Brachio-
phores simple, bladelike, without fulcral plates.
120
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Geologic range. — Ordovician to close of
Devonian.
The family has the following genera:
Dalmanella Hall and Clarke
Car'inijerella Schuchert and Cooper
Aulacella Schuchert and Cooper
Proschizofhoria Maillieux
Levenea Schuchert and Cooper
Heterorthina Bancroft
Genus DALMANELLA Hall and Clarke 1892
PI. 17, figs. 2-5, 7, 10, 13, 19-27, 29-31, 33;
t. fig. 8
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, pp. 205,
223, pi. SB, figs. 27-39.
Sardeson, Amer. Geol., vol. 19, 1897, pp. 91-111.
€yn. Onniella Bancroft.
Genolectotype (Schuchert and Cooper). — Or-
this testudinaria Hall and Clarke {non Dalman) 1892,
pi. 5B, figs. n-?,\=Orthl5 rogata Sardeson 1892,
Bull. Minnesota Acad. Nat. Sci., vol. 3, p. 331, pi. 5,
figs. 1-4.
Description. Exterior. — Subcircular to subquad-
rate; hinge-line straight, narrower than the widest
part of the shell; cardinal extremities rounded ; lateral
profile piano- to very unequally biconvex; anterior
commissure sulcate, the sulcus usually being pro-
nounced; ventral fold faint or prominent. Ventral
palintrope longer than the dorsal, apsacline, beak in-
curved; delthyrium open. Dorsal interarea short,
anacline, notothyrium closed by the cardinal process.
Ornamentation fascicostellate, having prominent ele-
vated growth-lines in the interspaces. Test fibrous,
punctate.
Ventral interior. — Delthyrial cavity deep, teeth
stout; crural fossettes deep; dental plates strong,
flaring somewhat anteriorly; muscle field bilobed in
front; diductor scars elongate, usually extending a
little anterior to the front end of the adductor track;
adjustor scars situated at the base of, or on the sides
of, the dental plates, usually narrow, elongate. Ad-
ductor track linear, narrow or wide. Pallial sinuses
consisting of a main trunk directed slightly antero-
laterally, taking its origin at the anterior ends of the
diductor impressions. It trifurcates shortly after its
origin, one trunk being directed antero-medially, one
antero-laterally, and a third secondary sinus extending
directly laterally. These secondary trunks break up
into subsidiary rami toward the margin.
Dorsal interior. — Notothyrial cavity completely
filled by the cardinal process; brachiophores simple,
divergent, bladelike plates, subtrigonal in plan, sup-
ported only by adventitious shell deposited about the
cardinal process and on the inner side of the brachio-
phore. Cardinal process short, myophore trilobate or
multilobate; median ridge low, extending nearly to
the front or terminating at the front margin of the
muscle field. The latter small, suboval or subcircular
in outline; anterior adductor scars the larger, separ-
ated from the posterior pair by low ridges at right
angles to the median elevation.
Geologic range. — Middle Ordovician (Chazy)
to Silurian.
American Species
Orthis corfulenta Sardeson 1892
O. emacerata Hall 1860
O. futilis Sirdeson 1897
O. «^«o/a Sardeson 1897
O.meeki M\]\eT 1875
O. niultisecta Meek 1873
O. porrecta Sardeson 1897
O. rogata Sardeson 1892
Dalmanella bassleri Foerste 1909
D.resufinata Raymond 1921
D. whittakeri Raymond 1921
? Orthis tersa Sardeson 1892
European Species
Dalmanella navis Opik 1930
Onniella avelinei Bincioh 1928
O. broggeri Bancroft 1928
O.reuschi Bancroft 1928
Distinguishing characters. — ^The members of
this genus are to be recognized chiefly by the plano-
or nearly plano-convex profile, fascicostellate ex-
terior, bilobed ventral muscle area, and primitive
brachiophores.
Discussion. — Hall and Clarke suggested the name
Dalmanella, first using it as the "Group of Orthis
testudinaria" under the genus Orthis. These authors
distinguished thirteen group names under the old genus
Orthis, but they never designated these "groups" as
genera or subgenera. In describing Dalmanella as the
"Group of Orthis testudinaria Dalman" they had be-
fore them American shells which they correlated with
Dalman's species. The group included, however, a het-
erogeneous lot from which several genera have already
been split. We will show that Orthis testudinaria
Dalman non Hall and Clarke actually belongs to a
group which is pretty much restricted to the Upper
Ordovician and early Silurian and is totally distinct
from the American Ordovician Dalmanellas with
which Hall and Clarke obviously dealt in their descrip-
tion of the group. This situation then brings up an
intricate nomenclatorial problem as to what the geno-
type of Dalmanella really is. If one adheres strictly
to the rules of nomenclature, he would say that Hall
and Clarke chose O. testudinaria of Dalman and the
European species should therefore constitute the type
of the genus. This would, however, restrict one of
our commonest names to an heretofore obscure divi-
GENERA OF THE SUBORDER ORTHOIDEA
121
sion of dalmancllids, namely, Wattsella Bancroft, rep-
resented, among others, by two species, D. edgeivood-
frisis Savage and D. trstudinarM Dalman, both of
early Silurian age. Obviously the confusion caused
by so designating the genotype for a group of shells
that Hall and Clarke never had in mind would be
unjust to those two authors, and would offset any
advantage obtained by classifying the biological
properties.
Looking at the nomenclatorial problem in another
way, it can be justly contended that Hall and Clarke
did not have before them typical examples of Dalman's
Orthis testutiifwria, but American shells that had from
the beginning been erroneously identified as this
species."" Therefore O. testudhwria of American
authors in general and specifically of Hall and Clarke
is not the same as O. testudinana Dalman of Sweden.
Accordingly, one of the several species figured by Hall
and Clarke under this name can be selected as the type
of the genus, and we now select as the genotype of
Dalmanella the specimens illustrated by them on plate
5B, figures 27-31, which are of Sardeson's Orthis
rogata.
It may be objected by "legalists" that this pro-
cedure is invalidated by Schuchert's having named
O. testud'mnria Dalman as the genotype of Dalmanella
in his work of 1897,*' a procedure in which he was
followed by many others. This objection is granted
willingly and would be valid if O. testudinaria Dalman
were a native American shell, as pointed out before.
Schuchert et al. never questioned Hall and Clarke's
identification of the species; it was then the order of
the day everywhere to identify similar shells as O. testu-
dinaria Dalman throughout the Ordovician. It can be
contended, further, that the followers of Hall and
Clarke, by using their name unchallenged, did not
alter the instability of the identification.
In further support of the contention that Hall and
Clarke did not base their group discussion on O. testu-
dinaria Dalman is the excellent work of Sardeson
(1897) in which he describes as new species Dal-
manellas usually referred to O. testudinaria. He
says (p. 106):
None of the above described species are like, or similar
to, Dalman's figures, and to the best of my knowledge, there
is ample room for preference of Meck's view, that our forms
may none of them be identical with those described as
Orthis testudinaria by Dalman, or those identified with that
species in England.
'- We have learned from Doctors Reeds, Croneis, and
Rucdcmann, curators of the Hall material in the American
Museum of Natural Histor\', the Walker Museum of the
University of Chicago, and the New York State Museum,
respectively, that there are no specimens of O. testudinaria
Dalman in these collections from Borcnshult, the type
locality.
»' Bull. 87, U. S. Geol. Surv., 1897, p. 199.
Raymond"^ corroborates this statement in the re-
mark that ". . . . no one seems to have proved that the
real Dalmanella testudinaria is found in America."
The present study, moreover, shows that Dalman's
species actually has an internal structure totally distinct
from that of D. testudinaria Hall and Clarke = D.
rogata (Sardeson) and is deserving of a different
generic designation.
Onniella Bancroft (pi. 17, figs. 1, 6, 8, 9, 11, 12,
18) has essentially the same internal structure as Dal-
vianella (emend.), but differs chiefly in being more
transverse and having a somewhat different ornamen-
tation. We do not consider these external details of
generic value and therefore place this genus in the
synonymy of Dalmnnella (emend.). Should Paleon-
tology progress to the point where ribbing characters are
considered of value in genus making, it would probably
be found that Dalmanella meeki will also conform to
the characters of Onniella.
Dalmanella emacerata and D. ignota are among the
few Paleozoic brachiopods in which nearly the full
complement of muscle-scars has been observed (see pi.
17, figs. 19, 22). Sardeson figures (his pi. 5, fig. 6,
of ignota) a specimen showing, besides the diductor,
adductor, and adjuster scars, two small accessory
diductor scars. The specimens that Sardeson studied
are now in the Schuchert Collection and there can be
little question as to the presence of these marks although
they can not be seen so clearly as the figures would
indicate. They are not isolated but are continuous
with the diductor scars. They may actually represent
the back end of the diductor impression rather than
separate and special scars. The adductor marks, as in
many other genera, are individually semielliptical but
together form an elliptical or oval impression super-
imposed over the adductor track.
In the dorsal valve the brachiophores have no fulcral
plates and this differentiates the true Dalmanella from
Wattsella and Idiorthis of the Wattsellidas, at least so
far as the dorsal valves are concerned. The simple,
bladelike brachiophores may become spoonlike by the
development of adventitious tissue on their inside sur-
face, and then they become attached to the dorsal sur-
face of the valve; the true brachiophore plate may in
that event be almost completely obscured. A common
mature and old-age condition is a growth of shell sub-
stance over the cardinal process, both shaft and myo-
phore ; and in extreme instances the adventitious shell
may completely fill the notothyrial cavity and encroach
on the brachiophores.
Dalmanella tcrsa is diflncult to place, since its ex-
terior and cardinalia are much like those of Rhipidom-
ella. Furthermore, in the ventral valve the diductor
scars show a marked tendency to enwrap the adductor
field. The species is thus intermediate between Rhipi-
domella and Dalmanella, and is believed to indicate
the probable origin of Rhipidomella.
"Geol. Surv. Canada, Bull. 31, 1 92 1, p. 14.
122
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Genus CARINIFERELLA Schuchert and
Cooper 1931
(Lat. carina, keel; and jerre, to bear)
PI. 18, figs. 9-12, 15, 16
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 246.
Genoholotype. — Orthis carinata Hall 1843,
Geol. N. Y., Rept. Fourth Dist., p. 267, fig. 1, as
figured by Hall and Clarke (1892).
Description. Exterior. — Transversely semicir-
cular, margins rounded, cardinal angles obtusely
rounded; hinge-line narrower than the greatest width
of the shell; lateral profile convexo-concave to une-
qually biconvex; anterior commissure sulcate; fold nar-
row, subcarinate; sulcus deep, narrow ; ventral inter-
area short, apsacline, beak not prominent, incurved,
umbo low, convex, and sulcate. Ornamentation mul-
ticostellate, with elevated growth-lines covering the
whole surface. Test fibrous, punctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong; dental plates thick, nearly obsolete in adults;
muscle field bilobed in front; diductor scars elongate,
expanded anteriorly; adductor track linear, not en-
closed in front by the diductor scars. Aggregate
adductor scar elliptical. Adjuster scars narrow, diver-
gent, short, placed posterior to the diductor impres-
sions. Short pallial sinuses extending antero-laterally
for a short distance in front of the diductor scars.
Dorsal interior. — Cardinalia confined to the imme-
diate vicinity of the hinge, sockets deep, oblique; brach-
iophore plates widely divergent and extending verti-
cally to the floor of the valve, without fulcral plates;
cardinal process very small, shaft short, myophore
trilobed; median ridge low, extending to the anterior
margin of the muscle area where it merges into the
fold produced by the ventral sulcus. Muscle area
small as a whole, not extending to the middle of the
shell. Adductor scars separated by horizontal ridges;
anterior adductors the smaller.
Geologic range. — Upper Devonian.
American Species
Orthis carinata Hall 1843
DalmaneUa carinata efsilon Williams 1908
D.elmiraW\\Yi3.m.% 1908
Z). /io^a Williams 1908 {non Hall 1867)
D. Virginia Williams 1908
D. Virginia beta Williams 1908
European Species
Carinijerella dumonti (Verneuil)
Distinguishing characters. — The distinctive
features of this genus are the convexo-concave profile
of the shell, the aberrant sharp fold and the corre-
sponding deep, narrow sulcus, the Dalmanella-WVt ven-
tral musculature, the strongly divergent brachiophore
plates, and the small muscle area of the dorsal valve.
Discussion. — The members of this new genus have '
been referred variously to Schizophoria and Dalman-
eUa. Schuchert referred them to the former in 1897,
but in 1908 Williams®^ restudied the different species
and concluded that their affinities placed them in clos-
est association with DalmaneUa. The combination of
characters displayed by this group, however, necessitates
the creation of a special designation for them.
The ventral musculature is similar to that of Dal-
maneUa and Schizophoria in the anterior bilobation,
but the adjuster scars are much shorter and more
oblique, and the median ridge (euseptoid) common to
the Upper Devonian Schizophorias is not well devel-
oped. Instead of being strongly elevated and con-
tinued in front of the diductor scars as a ridge, it is
divided in Carinijerella and forms a distinct V in front
of the diductors. Williams considers this forked
septum an important character of the genus "Dal-
manellt^' although it is by no means common to all
the "species."
In the dorsal valve the variations of this genus from
Schizophoria are most readily perceived in the nature
of the cardinalia and the musculature. The brachio-
phore plates are widely divergent, bladelike, attached
directly to the inner surface of the valve. The sockets
are wide and elongate and are not defined by a fulcral
plate as is so characteristic in Schizophoria. The mus-
cle area is rather small, but the fact that the individual
scars are separated by a horizontal ridge contrasts with
Schizophoria in which the scars are separated by an
oblique ridge. In this respect Carinijerella resembles
the genus Proschizophoria most closely. The adductor
scars of Schizophoria, furthermore, are usually larger
and somewhat flabellate. Pallial markings are very
indistinct in most of the specimens, but when visible
show the same elements common in the genus Levenea.
There is a lateral trunk extending slightly obliquely
from the ridges separating the adductors and another
pair extends forward from the antero-median ex-
tremity of the anterior adductors. In Carinijerella
dumonti the anterior trunks bifurcate near their point
of origin so that there are four trunks originating in
the same points as the pallial sinuses of Levenea. Car-
inijerella is evidently an Upper Devonian branch of
the Dalmanellidas, aberrant chiefly in its external form.
Genus AULACELLA Schuchert and Cooper
1931
(Gr. atihx, furrow)
PI. 19, figs. 7, 8, 10, 11, 13
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 246.
Genoholotype. — Orthis eijelensis de Verneuil
1850, Bull. Soc. Geol. France, 2d ser., vol. 7, p. 25.
^^ Proc. U. S. Nat. Mus., vol. 34, pp. 38-41.
GENERA OF THE SUBORDER ORTHOIDEA
123
Description. — This genus externally resembles
Rhipuiomi-lltt and Th'u-nicUa hut has a well marked
fold on the ventral valve and a sulcus on the dorsal
which are not reversed in the young stages. Internally
the arrangement of the ventral muscle-scars is similar
to that of Rhipuiotiiflla in the imprisonment of the
adductor field by the diductor scars. The diductor
impressions are never broadly flabellate as in Rh'tpi-
domi-lla and the adjustor marks are usually clearly
visible as in CannijereUti. Furthermore, the diductor
impressions are separated by a low ridge which is
forked much as in Cnriniferrlta. This is a feature
never shown by Th'tetnflla or Rh'tfuiomrlla in which
the median ridge is always direct and unforked.
In the dorsal valve the cardinalia are ponderous and
Strongly resemble those of Cnriniferelln and Rhifi-
domdla but are totally unlike those of Thicmella which
are delicate and confined. In our classification Aulac-
ella is placed in association with Dalmnnella and
C artntjerella because of the close similarity of the
ventral musculature and dorsal cardinalia.
The only known species is the German Orthis
eifelensis.
Genus PROSCHIZOPHORIA Maillieux 1911
PI. 19, figs. 25, 26, 30, 32
Maillieux, Bull. Soc. Beige Geol., Pal., d'HydroL, vol. 25,
1911, p. 177, pi. B, fig. I.
Genoholotvpe. — Orthis fersonata Zeiler 1857,
Verb. Nat. Hist. Ver. Bonn, vol. 14, p. 48, pi. 4,
figs. 9-11, emend. Kayser 1892, Jahrb. k. Preuss.
Geol. Landesanst., for 1890, p. 98, pi. 11, figs. 3-5,
pi. 12, figs. 1-4.
Description. Exterior. — Like Schizophorin, shell
large and thick.
Ventral interior. — Delthyrial cavity deep; teeth
large; dental plates thick and strong, continued as
ridges for some distance around the margins of the
diductor scars; muscle area large, cordate, wider than
long; diductor scars large, divergent, not enveloping
the adductor scars in front; adductor impressions
forming two semielliptical impressions, together making
an oval scar; the adjustor scars elongate marks on
the outside of the diductor impressions.
Dorsal interior. — Cardinalia ponderous; brachio-
phores as in Carinijerella, divergent; sockets deep;
shaft of cardinal process a stout linear ridge, rounded
ventrally and continued forward nearly to the anterior
ends of the adductor scars; adductor impressions sub-
equal, separated from each other by low ridges at right
angles to the median ridge.
Geologic range. — Lower Devonian (Coblenz-
ian) the only known species being the European
P. personata (Zeiler).
Distinguishing characters. — This genus diflFers
from Schizophoria, which it most closely resembles, by
the cordate ventral muscle area. The ventral adduc-
tor ridge so prominent in Schizophoria is lacking here.
In the dorsal valve the adductor scars are subequal in
size and separated by a horizontal ridge at right angles
to the median elevation. The prominent cardinal
process without expanded myophorc is another signifi-
cant variation from Schizophoria.
Discussion. — The name Proschizophoria was not
happily chosen, as this genus is neither the earliest of
the Schizophorias nor is it the progenitor of the group.
The structure of the dorsal valve obviously relates it to
Carinijerella and the Devonian representatives of the
Dalmanellidx. Neaverson*" places Orthis provulvaria
Maurer in this genus, but its dorsal valve has the
musculature and pallial markings of Schizophoria,
Genus LEVENEA Schuchert and Cooper 1931
PL 18, figs. 19-23,25-32; t. fig. 14
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 246.
Genoholotvpe. — Orthis subcarinata Hall 1857,
10th Rept. N. Y. State Cab., p. 43, figs. 1, 2.
Description. Exterior. — Subquadrate to subcir-
cular in outline, hinge-line narrower than the greatest
shell width ; cardinal extremities rounded ; lateral pro-
file unequally biconvex to plano-convex; ventral inter-
area longer than dorsal, apsacline; delthyrium open.
Notothyrium closed by the cardinal process. Surface
multicostellate. Test fibrous, punctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong, located at the angle of the delthyrial and hinge
margins. Crural fossettes deep. Dental plates strong
in the young, obsolete in old forms, thickened on the
inside to form the fossette. Muscle field pentagonal
in outline ; diductor tracks deeply impressed, elongate ;
adductor track wide, elevated, shorter than the diduc-
tor marks. Adjustor tracks located on the sides of the
dental plates, strongly impressed. Pallial markings as
in Isorthis and Schizophoria.
Dorsal interior. — Brachiophore plates blades like
those of Dalmanella ; cardinal process prominent, shaft
short or obsolete, myophore lobate; adductor field sub-
circular or widely elliptical; adductor scars subequal.
Pallial markings similar to those of Isorthis (see t.
fig. 14).
Geologic range. — Silurian to Middle Devonian.
American Species
Orthis lenticularis Vanuxein 1 842
O. quadrans Hall 1861
O. subcarinata H.1II 1857
Dalmanella macra Dunbar 1920
D. subcarinata Dunbar 1919 (non Hall)
? Orthis concinna Hall 1859
? O. solilaria Hall I860
"" Stratigraphical Palaeontology, 1928, p. 256.
124
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
European Species
Orthis canaliculata Lindstroni 1860
Distinguishing characters. — Levenea is most
like Isorthis in all except cardinalia, but differs in its
unequally biconvex or plano-convex lateral profile, and
pentagonal ventral muscle field. This genus is close
to Isorthis in its ventral interior but differs in hav-
ing less widely divergent pallial markings. In the
dorsal valve it differs still more strongly from Isorthis
in not having a fulcral plate, or as elongate an
adductor field.
Discussion. — Of special interest in Levenea is the
remarkable deposition of adventitious shell, especially in
the dorsal valve about the various structures of the car-
dinalia. Shell matter is laid on the inside surface of
the brachiophores and extends around their dorsal face
to the wall of the valve. The socket is a deep excava-
tion in this adventitious shell and in some specimens
may simulate a socket-plate (see pi. 18, figs. 19, 21,
29). This support of the brachiophore plates is exactly
the same as that seen in Dalmariella s. s. The cardinal
process is usually rather small and bilobed, without a
pronounced shaft. In old forms a secondary shaft is
produced forward over the median ridge. In such
specimens the process has the appearance of a fly's head
with proboscis protruded.
This genus is named for Miss Clara Mae LeVene,
in recognition of her assistance in the preparation of
this monograph: first, by long-continued bibliographic
work on the brachiopods, begun in connection with
the second edition of Zittel-Eastman in 1913, and
carried on to form the basis for the Schuchert-LeVene
generic catalogue of 1929; and second, by editorial
revision and other work accompanying the transforma-
tion of the hand-written manuscript into the present
printed volume.
In the dorsal valve the cardinalia are similar to those
of Dalmanella. The brachiophore plates are bladelike,
divergent, supported by adventitious shell, which forms
a rather thick notothyrial platform. The cardinal
process is small, the shaft short, the myophore lobate.
The adductor field is somewhat shield-shaped with
individual scars subequal.
Discussion. — Heterorthtna differs from Heterorthis
in lacking the widely divergent diductor scars in the
ventral valve, and the thickened ridges parallel to the
anterior margins. The deposition of adventitious shell
about the cardinalia takes more the form of that seen
in Dalmanella rather than that of Heterorthis. In the
latter the brachiophore plates are thickened at their
dorsal and distal extremities, the thickening being pro-
longed as curved margins around the adductor field.
The cardinal process of Heterorthis is also different
from that of Heterorthtna. The myophore of the
former is elongated ventrally and the median lobe
drawn out posteriorly into a rather sharp carina. The
lateral lobes are reduced to small ridges or bosses. In
Heterorthina, on the other hand, the process is small,
bilobed, and cleft in front, as seen commonly in Dal-
manella. No trace of a heterorthoid chilidium was
seen in Heterorthina. The internal structure of the
genus relates it more closely to Dalmanella than to
Heterorthis, and for this reason we are placing it in
the family Dalmanellidae.
Geologic range. — Upper Ordovician of Europe
and possibly of the Ohio Valley.
European Species
Heterorthina frteculta Bancroft 1928
Orthis ellipoides Barrande 1 847
American Species
? Dalmanella jairmountensis Foerste 1909
Genus HETERORTHINA Bancroft 1928
PL 17, figs. 17, 28, 32; pi. 18, figs. 1-8
Bancroft, Mem. and Proc. Manchester Lit. and Philos.
See., vol. 72, 1928, p. 59.
Genoholotype. — H. frtpculta Bancroft 1928.
Description. — Externally the shells of this genus
resemble Heterorthis in outline, but the dorsal valve,
instead of being flat or concave, is very gently convex
and bears a shallow sulcus. The surface is rather
finely multicostellate. In the ventral valve the teeth
are short and flaring and their anterior ends are con-
tinued forward as low ridges along the outer margins
of the diductor scars. The muscle area is long, extend-
ing nearly to the middle of the valve or a little beyond.
It is strongly lobate in front, the diductor scars are
elongate with subparallel sides, and their anterior ends
extend in front of the elongate adductor track. Adjus-
ter marks were not seen.
Family WATTSELLID^ Schuchert and
Cooper 1931
Progressive and terminal Dalmanellacea originating
in the Dalmanellida, with subcircular or shield-shaped
shells, cordate ventral muscle field, and fulcral plates
defining the sockets.
Geologic range. — Upper Ordovician to Lower
Devonian.
Embraces the following genera:
Wattsella Bancroft
Resserella Bancroft
Horderleyella Bancroft
M endacella Cooper
Idiorthis McLearn
Parmorthis Schuchert and Cooper
Fascicostella Schuchert and Cooper
GENERA OF THE SUBORDER ORTHOIDEA
125
The genetic relations of the Wattscllida: appear to
be as shown in Table 1 0.
Genus WATTSELLA Bancroft 1928
PI. 22, figs. 9, 13, 14, 17-29
Bancroft, Mem. Proc. M.inchester Lit. and Philos. Soc.,
vol. 72, 1928, p. 55, pi. 1, figs. 1-5.
Genoholotype. — Watisella wattsi Bancroft 1 928.
Description. Exterior. — Subcircular, hinge-line
straight, narrower than the greatest width of the shell;
cardinal extremities rounded; lateral profile unequally
biconvex, the ventral valve .ilways with the greater
Table 10
Fascicostella
Parmorthis
Idiorthis <■
Mendacella
> Horderleyella
Resserella
Dalmanellio^
convexity. Anterior commissure rectimarginate to
faintly sulcate. Dorsal sulcus shallow, deepest posteri-
orly; ventral fold conspicuous only at the posterior.
Ventral palintrope longer than the dorsal, curved, apsa-
cline, beak incurved, umbo strongly convex. Dorsal
palintrope short, faintly anacline, beak inconspicuous;
umbo sulcate, delthyrium and notothyrium open. Sur-
face multicostellate ; shell fibrous, punctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong; crural fossettes deep; dental plates sharp,
divergent, commonly continued forward as a ridge on
the lateral periphery of the diductor scars. Muscle
area subcordate, more or less gently bilobed in front.
Adductor track linear, squarish in front. Diductor
scars elongate, rounded in front, and narrowing
behind; adjustor scars not separable.
Dorsal interior. — Cardinalia prominent, brachio-
phores elongated into slender points, extending nearly
directly ventrally; brachiophore supports triangular in
side view, convergent, and uniting with the median
ridge; sockets defined by a small fulcral plate. Car-
dinal process small; shaft slender, and only defined
in the sp.icc between the brachiophore supports; myo-
phorc lobed. Median ridge prominent, extending to
the middle of the valve; muscle area oval, widest in
front. Anterior adductor scars the larger.
Geologic range. — Upper Ordovician into early
Silurian.
American Species
Dalmdnella edgezvooJensis Savage 1913
Shells of this genus are common in eastern North America
and are now parading as Dalmanella tesludinaria
European Species
Orthis tesludinaria Dalman 1828
Terebratula miguis Sowerby 1839
Watisella wattsi Bancroft 1928
? W. multiflicata Bancroft 1928
Distinguishing characters. — This genus differs
from Dalmanella in its more cordate muscle area, the
subparallel brachiophore supports which converge dor-
sally to meet the median ridge, the presence of fulcral
plates defining the socket, and the exceedingly long
tenuous brachiophores.
Discussion. — In restricting Dalmanella to shells of
the type of Orthis rogata Sardeson, which Hall and
Clarke mistakenly identified as Orthis testudinarta
Dalman, the writers have left the European dalman-
ellid group without a proper generic name. Bancroft's
recently proposed Wattsella has a structure identical
with that of Orthis testudinarta Dalman and must
therefore include that species. Bancroft laid generic
value on the differences in the cardinalia of the dal-
manellids and based several genera on their variations.
The cardinalia of Wattsella, as well as the ventral
musculature, are strikingly different from those of
Dalmanella as restricted by us. In the latter genus
the diverging brachiophores are typically bladelike, and
are never provided with fulcral plates defining the
socket. In Wattsella, on the other hand, the brachio-
phore plates converge dorsally to meet the outside
margins of the median ridge. It is these plates that
make the parallel slots in internal molds (see pi. 22,
fig. 20). The median ridge extends to the middle of
the valve, is low and wide. The cardinal process is
normally rather small, with a short shaft and trilobcd
myophore which in its lateral lobes in adults or old
forms may be extended anteriorly some distance.
When such is the case, it gives this structure the appear-
ance of being fissured. In some specimens the median
lobe may be extended forward along the shaft as in
Isorthis, so that the cardinal process simulates in form
the head of a bee or fly.
In mature forms of Wattsella, as in most other
genera of the Dalmanellacea, adventitious shell is
deposited about the brachiophore plates. In the genus
126
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
under discussion, this secondary shell is deposited mainly
between the brachiophore plates in connection with the
cardinal process, but in Orthis testudinarta Dalman
from Borenshult, Sweden, the brachiophores are
swollen on the inside at their junction with the median
ridge and a very noticeable amount has also been
deposited in the cavities between the brachiophore and
the fulcral plates. If this deposition were carried to
its extreme, the fulcral plates would be obliterated and
the cardinalia would simulate those of Dahnanella,
Levenea, and other genera of the Dalmanellidas.
In the ventral valve the differences are not so strik-
ing. However, the diductor scars are not so long and
flexuous, and the muscle impressions as a whole are
more heart-shaped than in Dalmanella.
Wattsella is abundant in the Upper Ordovician of
England and Wales and in the early Silurian of
Sweden in strata previously regarded as Ordovician.
In the United States, it is known for the first time in
the early Silurian (Edgewood limestone of the Alexan-
drian series) of Illinois and Missouri. This is a strik-
ing fact which lends strength to the assertion made in
the discussion of Dalmanellay namely, that shells having
the structure of Orthis testudinarta Dalman are as yet
unknown in the North American Ordovician. In the
Silurian of Arisaig some of the specimens referred by
McLearn*' to Dalmanella elegantula actually belong
to Wattsella. It is not improbable that some of the
Silurian dalmanellids from Anticosti referred to D.
testudinarta by Twenhofel will prove to be Wattsellas
when the interiors are studied. Further, many of the
"Dalmanellas" collected by Williams in the Silurian of
Maine prove to belong to Bancroft's genus.
Genus RESSERELLA Bancroft 1928
PI. 17, figs. 14-16
Bancroft, Mem. Proc. Manchester Lit. Philos. See, vol. 72,
1928, p. 54.
Genolectotype. — Orthis canalis Sowerby 1839,
in Murchison, Sil. Syst., pi. 13, fig. 12a.
Description. — Externally, Resserella (as here
restricted) forms a very precise homoeomorph of Dal-
manella as described in this memoir. The valves are
unequally biconvex, the dorsal being flatly convex and
the ventral rather strongly so. There is a shallow
sulcus on the dorsal valve that is defined from the
vicinity of the beak to the anterior margin. The beaks
and the interareas have the same features exhibited by
Dalmanella s. s. The external surface is multicostel-
late as in the American shells.
Inside the ventral valve the identity with Dal-
manella is carried out to the form and lobation of the
muscle area. In the dorsal valve the cardinalia of
mature shells are identical with mature Dalmanella.
"Geol. Surv. Canada, Mem. 137, 1924, pp. 53-54.
In Resserella the adductor impressions of the dorsal
valve are subequal and form a rather circular pattern.
Discussion. — From the above i^ will be seen that
the interior and exterior of Resserella and Dalmanella
are very close if not identical in mature shells. For
this reason we had regarded Resserella as a synonym
of Dahnanella (restricted) in the early phases of our
work. However, in correspondence with Mr. Ban-
croft, he has assured us that there is a very close
relationship between Resserella and Wattsella, to be
seen in the presence of fulcral plates in the early
growth stages of the former. If these fulcral plates
exist in Resserella, we admit the validity of the genus.
We have not seen such plates in the material available
to us and must accept Bancroft's statement.
The recognition of Resserella as a distinct genus
does not invalidate our genus Parmorthis, based on
Dalmanella elegantula, which Bancroft places in his
Resserella. The type selected by Bancroft for his
genus is Orthis canalis of Sowerby. As originally
described, this species was composite, including within
it Ordovician and Silurian specimens. On the basis of
the latter, Davidson made Sowerby 's species a synonym
of Orthis elegantula Dalman. The specimen from
the Ordovician, however, according to Sowerby's fig-
ures and remarks (pp. 630, 640), is different from the
Silurian forms, which clearly belong to "Dalmanella"
elegantula (Dalman) and were so referred by David-
son. On the other hand, specimens sent us by Mr.
Bancroft prove to be of the larger Ordovician form,
and it is on this shell and not on the "elegantula" type
that Resserella is based.
Resserella as thus restricted consists of shells that are
more circular as a rule than those of Parmorthis. Fur-
thermore, the species of the latter genus have a rather
definite ribbing system unknown in Resserella, con-
sisting of a rather prominent median fascicle in both
valves that is so well developed in some of the species
as to produce a flattened or smooth portion in the
middle of the valves at the front. On the interior,
however, the diiTerences between Resserella and Parm-
orthis are still more pronounced. In the ventral
valve the strong arching of the beak produces a very
deep delthyrial cavity and strong dental plates, much
thicker than those of Resserella. Moreover, the ven-
tral muscle field of Parmorthis is not decidedly lobate
as is the corresponding area in Resserella. Inside the
dorsal valve the differences are equally striking. In
Resserella as known to us there is no prominent thick-
ening produced laterally along the periphery of the
adductor field, whereas this same area in Parmorthis
has a very distinctive shape shared only by the closely
related Fascicostella. Here the adductor area is elon-
gate and the anterior impressions are triangular. An-
other very important difference between the two
genera is the striated teeth and sockets of Parmorthis,
which are very rare in the whole brachiopod class.
It is clear, therefore, that Resserella and Parmorthis
GENERA OF THE SUBORDER ORTHOIDEA
127
are quite distinct. There are also notable differences
between Rrsscrella and Wattsflla, particularly in the
ribbing characters. We are, however, willing at pres-
ent to accept Mr. Bancroft's statement regarding the
relationships of these two genera in the absence of
specimens of immature Resserella.
Genus HORDERLEYELLA Bancroft 1928
PI. 22, figs. 30, 32-35
Bancroft, Mem. Proc. Manchester Lit. Philos. Soc., vol. 72,
1928, p. 178, pl. 1, figs. 15-18.
Genoholotype. — H. fUcata Bancroft 1928.
Description. Exterior. — Shells rather small, sub-
semielliptical or subquadrate in outline; hinge-line
straight, cardinal extremities obtuse. Lateral profile
subequally biconvex. Anterior commissure sulcate, sul-
cus shallow; ventral fold subcarinate. Interareas sub-
equal, ventral one apsacline, dorsal anacline. Ventral
umbo rather strongly convex, dorsal umbo gently
convex. Surface strongly fascicostellate. Test prob-
ably punctate.
Ventral interior. — Delthyrial cavity rather deep;
dental plates short and strong; muscle area short, sub-
pentagonal; diductor impressions subtriangular. Ad-
ductor impression linear, occupying a depression formed
by the posterior extension of the fold. Pallial impres-
sions unknown.
Dorsal interior. — Notothyrial cavity shallow, brach-
iophores long, brachiophore plates convergent dorsally
and uniting with the median ridge. Sockets defined
by fulcral plates.
Geologic range. — Ordovician of England and
Wales. The species are : H. flicnta Bancroft, H. n. sp.
Discussion. — This genus was originally placed by
its author in the Harknessellinae, but it appears to us
to belong nearer Wattsella, since its brachiophores are
supported by convergent plates and there is a fulcral
plate bounding the socket. From Wattsella it differs
in the greater convergence of the brachiophore sup-
ports, which do not appear as parallel slits in internal
molds.
Genus MENDACELLA Cooper 1930
(Lat. mendax, lying)
PI. 22, figs. 1-5, 8
Cooper, Jour. Pal., vol. 4, 1930, pp. 377, 380, pl. 36,
figs. 2, 16-18 (uteris), also figs. 6, 9 {mullochiensis).
Genoholotype. — Orthis uheris Billings 1866,
Cat. Sil. Foss. Anticosti, p. 42.
Description. Exterior. — Similar to Rhifidomella
but with the valves subequally convex. The ventral
valve is always the larger of the two.
Ventral interior. — Delthyrial cavity moderately
deep; teeth large; dental plates strong, subparallel or
divergent, continued forward as ridges on the outer
margins of the diductor scars. Muscle area bilobed in
front; diductor scars long and narrow; adductor
ridge wide or narrow, carinatc or flat, never extended
to the front of the diductor scars. Adjuster scars
small or large, narrow. Pallial markings not observed.
Dorsal interior. — Cardinalia confined ; brachio-
phores stout, bluntly pointed, slightly divergent; sock-
ets deep, defined by a small concave fulcral plate.
Cardinal process small, shaft slender, not extending
anterior to the ends of the brachiophore plates, myo-
phore expanded lobate; a low broad median ridge
extending from the ends of the brachiophore plates
nearly to the middle of the valve. Adductor scars
subequal, separated in some species by low ridges at
right angles to the median ridge.
Geologic range. — Upper Ordovician and early
Silurian.
American Species
Orthis tequivalvis Shaler 1865 ^ O. uheris Billings 1866
Rhifidomella rhynchonellijormis (Shaler) 1865
Schizofhorella arisaigensis McLearn 1924
? Rhifidomella circulus (Hall) 1843
? R. lenticularis Foerste 1903
? R. tenuilineata Foerste 1913
European Species
Orthis minuscula Barrande
O. mullochiensis Davidson (Sil. Brach., p. 221)
Distinguishing characters. — This genus is dis-
tinguished especially by the Dalmanella-Wke. character
of the interior and the Rhipidomella-Vke exterior. Ex-
ternally, however, it differs from Rhipidoinella in hav-
ing the ventral valve usually the larger. Internally the
variations of the muscle-scars, dental plates, and car-
dinalia from those of Rhipidomella are striking. The
muscle area does not have the broadly semiflabellate
diductor scars enclosing the oval adductor ones. The
diductor impressions of Mendacella are quite direct and
narrow, and ordinarily only slightly divergent; they
have a rather strong resemblance to the same scars in
Dalmanella.
Discussion. — There is some variation in the ventral
musculature between the various species placed by us
in this genus. In M. uheris from the Ellis Bay forma-
tion (late Ordovician) the diductors are frequently
separated by a low wide ridge, but in the same species
from the Silurian Gun River formation the ends of the
diductors are separated from each other by a very
narrow ridge only. The other Silurian species such as
M. arisaigensis and M. mullochiensis all resemble the
Silurian M. uheris in this respect. There is also a vari-
able development of the adjustor scars within the same
species and in different species.
128
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
From the structure of the cardinalia with its moder-
ately divergent brachiophore plates, strengthened by
fulcral plates, it is to be deduced that Mendacella is
more closely related to Wattsella and Parmorthis than
to Dalmanella and its allies.
Genus IDIORTHIS McLearn 1924
PI. 21, figs. 34-38
McLearn, Geol. Surv. Canada, Mem. 137, 1924, p. 56,
pi. 3, figs. 19-24, pi. 4, figs. 1-4, pl. 28, fig. 10.
Genoholotype. — /. matura McLearn 1924.
Description. Exterior. — Suborbicular, hinge-
line narrow, cardinal extremities rounded ; lateral pro-
file piano- to concavo-convex, the dorsal valve usually
convex at the umbo but flat or concave in front of the
middle. Anterior commissure slightly sulcate ; ventral
interarea the longer, curved, apsacline ; beak incurved ;
delthyrium open. Dorsal interarea short, anacline.
Ornamentation multicostellate. Test punctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong; dental plates thick, divergent, continued as
ridges around the periphery of the diductor scars.
Muscle field cordate, occupying nearly half the length
of the valve. Diductor scars large, irregularly sub-
triangular, longer than the adductor track which is
elongate, rectangular; adductor scars elliptical; ad-
juster scars not visible, or very narrow and situated at
the base of the dental plates.
Dorsal interior. — Cardinalia ponderous, brachio-
phores and their supporting plates not separable, sub-
parallel or slightly divergent. Cardinal process tri-
lobed, its shaft obscured by the median ridge which is
thick and clavate posteriorly but tapers to a point
toward the front and terminates at the margin of, or
just in front of, the anterior end of the muscle field.
Muscle area reduced by the encroachment of the crural
base supports which have forced the posterior adduc-
tors "up on the truncated anterior face of the crural
lamella, which, expanding laterally, curve around the
postero-lateral borders of the greatly enlarged and
almost circular anterior adductor scars" (McLearn).
Geologic range. — Early and } Middle Silurian.
American Species
Idiorthis ovila McLearn 1924
/. matura McLearn 1924
European Species
? Orthis eJgelliana (Salter MS.) Davidson (Sil. Brach.,
p. 228)
Distinguishing characters. — These are the ex-
tremely large ventral muscle area, strong divergent
dental plates, subparallel arrangement of the brachio-
phore supports, large size and structure of the median
ridge and cardinal process, and nature of the dorsal
musculature. These characters are combined with a
concavo-convex exterior.
Discussion. — Idiorthis most closely resembles
Wattsella in the internal structure of the valves. The
ventral muscle field is obcordate as in the former
genus, with a rather wide adductor track. In the
dorsal valve the brachiophore plates, situated on each
side of the median ridge, are subparallel. The sockets
appear to be defined by small socket-plates. The
encroachment of the adductor muscles upon the front
ends of the brachiophore supports in the type specimens
is due to their being gerontic individuals. This fact
also accounts for the peculiar structure of the cardinal
process and the median ridge. Accordingly it is our
view that Idiorthis as now understood is an old-age
stage of Wattsella, but in the absence of young speci-
mens this can not be proved.
Idiorthis has not been identified outside of the Arisaig
section but McLearn has suggested a resemblance of
Orthis edgelliana Salter to its genotype.
Genus PARMORTHIS Schuchert and Cooper
1931
(Gr. farmey shield)
PL 21, figs. 1-16, 29
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 246.
Genoholotype. — Orthis elegantula Dalman
1828, K. Svensk. Vet. Akad. HandL f. 1827, p. 117,
pl. 2, fig. 6.
Description. Exterior. — Suborbicular, elongate
elliptical or shield-shaped in outline; margins convex,
front margin frequently slightly produced; hinge-
line narrower than the greatest shell width; cardinal
extremities rounded; lateral profile plano-convex, ven-
tral valve ventricose, dorsal valve with a shallow sul-
cus; ventral interarea strongly curved, slightly apsa-
cline, umbo swollen, beak strongly curved; dorsal
interarea short, anacline, beak nearly obsolete; del-
thyrium usually open, notothyrium closed by the car-
dinal process. Multicostellate, rarely fasciculate. Test
punctate.
Ventral interior. — Delthyrial cavity deep; teeth
ponderous, crenulated on the inner surface; crural
fossettes deep; accessory socket large; dental plates
strong, vertical, subparallel or only slightly divergent;
muscle area confined to the delthyrial cavity; adduc-
tor track usually narrow, linear, slightly elevated;
diductor scars triangular, not extended appreciably an-
terior to the adductor track, covering the walls of the
delthyrial cavity; adjustor impressions narrow; a
slight median thickening extends anteriorly from the
adductor track, and on each side of this ridge and
GENERA OF THE SUBORDER ORTHOIDEA
129
closely adjacent to it, a pallial trunk runs forward
nearly to the anterior margin.
Dorsal interior. — Cardinalia confined; brachio-
phores large, divergent, bearing long blunt points given
off from the inside antero-ventral part; sockets very
deeply defined on the inner side by the sloping crenu-
lated outer face of the crural base and a small concave
fulcral plate which unites the brachiophore to the
floor of the valve. Denticle large; muscle area elon-
gate-oval in outline; anterior adductors the smaller;
peripheral ridges low; cardinal process small, bilobed
or trilobed, shaft produced forward to the line of divi-
sion between the diductors, where it is cleft.
Geologic range. — Silurian.
American Species
Dalmanella concavoconi'exa Twenhofel 1928
D. ip-ingfelJemis Foerste 1917
D. wildroneniii Foerste 1917
Parmorthis crassicostata, n. sp.
? Orihis media Shaler 1865
European Species
On his basalis Dalman 1828
O. eUgantulj Dalman 1828
O. visbyensis Lindstrom 1860
Distinguishing characters. — This genus is dis-
tinguished externally by its plano-convex contour,
strongly inflated ventral valve, and peculiar ornamen-
tation. Internally, the stout brachiophores with their
blunt processes, oval muscle area, unusual articulating
apparatus with its crenulated teeth and sockets, and
ventral muscles and pallial sinuses all combine to indi-
vidualize the genus. From Dalmanella s. s., Parmor-
this is differentiated by its more inflated ventral valve,
different ornamentation, differently shaped ventral
muscle area, divergence of the brachiophore plates at
their junction with the floor of the valve, and possession
of a concave fulcral plate. It differs from Isorthis in
not possessing a complicated pallial system and in cer-
tain details of the cardinalia.
Discussion. — There is a feature of the ornamenta-
tion of these shells which is characteristic. In the
sulcus of the dorsal valve there is usually a concentra-
tion of costellae due to the accelerated appearance of
secondary and tertiary ribs. This frequently produces
a nearly smooth or nearly plane area in the front of
the sulcus that is ordinarily elevated as a slight fold in
its center. There is a corresponding smooth area in
the median portion of the ventral valve which is com-
monly depressed slightly below the general level of
the shell. Thb peculiarity occurs in nearly all of the
species studied.
The articulation of Parmorthis is unusual for the
strength of its parts and their specialization. It is the
only genus known among the orthids (except Trofid-
oleptus, now placed in the Dalmanellacea) that possesses
ci cnulated teeth and sockets. The details of the articu-
lation are described on page 25.
Noteworthy also in this genus is the occurrence of a
small deposit of secondary shell in the apex of the del-
thyrium. This has nothing whatever to do with a
deltidium, being merely an apical callus such .is occurs
commonly in some spiriferid genera. In the dorsal
valve the brachiophores not uncommonly bear elon-
gate, bluntly pointed processes on their inner dorsal
and distal extremities. If these and similar processes
occurring in the same position in other orthid genera
could be homologized with the crura of the rhyncho-
nellids, it would be possible to prove that the brachio-
phores in reality are the same as the crural bases.
"Dalmanella" visbyensis (Lindstrom) shows an in-
teresting variation from the usual type of Parmorthis.
In this form the ventral beak is more strongly arched
than is usual, actually overhanging the dorsal interarea.
Along with this variation goes a concave dorsal valve.
Within the dorsal valve the myophore of the cardinal
process is directed backward (posteriorly and dorsally)
so far as to be visible from the dorsal side. Seen from
the inside, one perceives that the inner margins of the
shaft and the brachiophore plates are grown together.
Orthis elegantula Dalman differs importantly from
our Dalmanella and from Resserella. In Dalmanella
the ventral muscle field is lobate and the pallial mark-
ings widely divergent, whereas in Parmorthis the ven-
tral pallial markings are closely appressed and sub-
parallel, and the muscle area is never lobate and is
confined to the delthyrial cavity. In the dorsal valve
important differences also occur. The adductor field
of Parmorthis is elongate, and in our Dalmanella it is
subcircular. Further, the sockets of Parmorthis are
defined by concave fulcral plates, which are lacking in
Dalmanella. These differences we regard as of sufl^-
cient importance to separate the two genera and place
them in different families.
Parmorthis crassicostata, n. sp.
PI. 21, figs. 4, 5
Shell rather small, subcircular, of the type of P. ele-
gantula but having rather coarse ribs, there being about
34 to the valve. Measurements of the holotype:
length, 9 mm.; width, 9 mm.
Holotype, Cat. No. 913, Schuchert Collection, Yale
University. Silurian (Niagaran), Martin's Mills,
western Tennessee.
Genus FASCICOSTELLA Schuchert and
Cooper 1931
(Lat. jasc'uy bundle; costella, a little rib)
PI. 22, figs. 6, 7, 10-12, 15, 16, 31
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 246.
130
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Genoholotype. — Orthis gervillei Defrance 1827,
Diet. Sci. Nat., vol. 51, p. 152.
Description. Exterior. — Dalmanelloid, subcircu-
lar to subquadrate; lateral profile piano- to slightly
concavo-convex; anterior commissure rectimarginate
or sulcate ; sulcus on the dorsal valve shallow ; ven-
tral interarea curved, beak incurved; dorsal interarea
anacline; ornamentation strongly fascicostellate, the
chief distinguishing feature of the genus.
Ventral and dorsal interior. — Essentially the same
as in Orthis elegantula Dalman (^PartTiorthis).
Geologic range. — Upper Silurian ? to Lower
Devonian of Europe, with the following species:
Orthis dorsoflicata Beclard
O. gervillei Defrance
O. sedgwicki D'Archiac and Verneuil
Discussion. — Fascicostella is distinguished from all
other Dalmanellacea by its peculiar ornamentation,
since it has the greatest development of fasciculation
seen in any orthid. Internally the species most closely
resemble Parmorthis elegantula of Gotland. How-
ever, the hinge-line is proportionately wider and the
cardinal extremities less rounded and the ventral valve
never so ventricose. The ventral musculature is like
that of P. elegantula, but has larger adjustor scars.
The pallial sinuses are also like those of the Gotland
species in being closely together, subparallel, and sepa-
rated by a narrow, low ridge. The anatomy of the
dorsal valve agrees closely with that of P. elegantula.
The close similarity of the internal anatomy of Fasci-
costella to that of Parmorthis elegantula suggests that
the genus had its origin in that form. Fascicostella
seems to be localized in the Lower Devonian of
Europe, except for Kozlowski's report** of "Dalman-
ella" gervillei in the highest Silurian of Poland
(Borszczow).
Family BILOBITID^E Schuchert and Cooper
1931
Aberrant, specialized Dalmanellacea originating in
the Dalmanellidas, having an emarginate anterior mar-
gin, narrow hinge-line, and a deep sulcus in each valve.
The only genus is Bilobites Linnasus, extending
from the Upper Ordovician into the early Middle
Devonian of Europe and North America.
Genus BILOBITES Linnaeus 1775
Linna:us, Syst. Nat., ed. Miiller, vol. 6, 177S, p. 325.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 204,
pi. 5B, figs. 11-14.
Syn. Diccelosia King 1850.
Genoholotype. — Anomia biloha Linnaeus 1767,
Syst. Nat., 12th ed., p. 1154.
Description. Exterior. — Small, bilobed, anterior
margin emarginate, hinge-line narrower than the
greatest width of the shell; lateral profile unequally
biconvex; anterior commissure broadly sulcate. Ven-
tral interarea the longer, curved, apsacline, umbo
swollen, sulcate, beak incurved; dorsal interarea short,
anacline, beak projecting slightly, incurved; surface
multicostellate ; shell coarsely punctate.
Ventral interior. — Umbonal cavity deep ; teeth
strong; dental plates thick and rather obscure; muscle
area bilobed, thickened along the margins; divided
centrally by a sharp ridge corresponding to the external
sulcus; diductor scars semiflabellate, divergent, not
enveloping the adductor impressions; adductor scars
borne on the central ridge, obscure; adjustor scars
obscure.
Dorsal interior. — Cardinalia thick, brachiophores
ponderous, long, bladelike, widely divergent; sockets
shallow; cardinal process thick; myophore bilobate,
crenulated on its posterior face, its shaft extended for-
ward and merging with the median ridge formed by
the impression of the external sulcus on the inside of
the shell.
Geologic range. — Upper Ordovician (White-
house group of Girvan; Richmondian of Gaspe,
Quebec); widely in the Silurian; Lower Devonian
(New Scotland, United States) and early Middle
Devonian (Bohemia, Ggi).
American Species
Bilobites acutilobus (Ringueberg) 1888
B.bilobus (Linna:us) 1767
B. indentus Cooper 1930
B. varicus {Cor\r3iA) 1838
European Species
Bilobites bilobtts (Linnasus) 1767
B. verneuilianus Lindstrom
Orthis dimera Barrande
Discussion. — External form most readily distin-
guishes Bilobites from all other genera of the Dal-
manellacea. Internally the ventral musculature and
cardinal process are decidedly dalmanelloid. The
brachiophores appear to be modified dalmanelloid,
bladelike, and suggest an origin out of Dalmanella.
Beecher®" has figured a deltidium perforated at the
apex in young Bilobites, but such a structure has not
been observed in any of the mature forms studied or
in any other punctate shell. If this actually exists only
in the young of Bilobites, it is one more crumb of evi-
dence that a delthyrium covered by a deltidium is
actually the primitive condition in early brachiopod
Pal. Polonica, vol. 1, 1929, p. 70.
'Studies in Evolution, 1901, p. 402.
GENERA OF THE SUBORDER ORTHOIDEA
131
growth stages, as is so forcibly indicated by the occur-
rence in the early Cambrian of Nisusi/i and the later
Billingsellidx with their covered delthyria.
Beecher'"" has suggested the derivation of BUob'ttes
"from a radicle haying, in many respects, the charac-
ters of the group represented by PLitystrophia bijorata.
This statement has been construed by Cumings and
others as "a virtual demonstration of the derivation of
BUob'ttes from Platystrophia." Beecher and Cumings
showed the external resemblances between the nepionic
stages of the two genera, but the former merely pointed
out that the two may have come from a platystrophoid
radicle. This is true from the standpoint of exteriors,
but certainly the internal features of Bilobiies and
Platptrofhia are diverse. On an earlier page it has
Genus MYSTROPHORA Kayser 1871
PI. 16, figs. 1-5; t. figs. 20, 21
Kayser, Zeits. deut. geol. GcscU., vol. 23, 1871, pp. 612-
614, pi. 13, fig. 5.
Genolectotype (Williams and Breger 1916). —
Orthis areola Quenstedt 1871, Petref. Deutschl., p.
589, pi. 57, fig. 27.
Description. Exterior. — Transversely subquad-
rate to subsemicircular in outline; cardinal extremi-
ties obtuse or angular; lateral profile plano-convex;
anterior commissure sulcate, sulcus deep, ventral fold
low, marked by a median costella. Ventral palintrope
long, strongly apsacline, beak slightly curved; del-
^ ^ ^ Aor Op. cit., p. 404.
'"Amer. Jour. Sci. (4), vol. 15, 1903, p. 40.
thyrium usually open but may be closed at the apex
by callus. Dorsal interarea short, plane, anacline;
notothyrium partially closed by the cardinal process.
Surface finely multicostellate ; shell fibrous, punctate.
Ventral interior. — Delthyrial cavity deep; dental
plates low, divergent. At the apex between the dental
plates there is a flat callus deposit, probably for pedicle
attachment. The cavity beneatli this is usually com-
pletely filled by punctate shell substance.
Dorsal interior. — Notothyrial cavity deep; cardinal
process with a long shaft and lobate myophore. Brach-
iophores elongate, pointed. Brachiophore supports con-
vergent and uniting with a median septum, which is so
high as to divide the shell into two chambers. Muscu-
lature unknown.
Geologic range. — Middle Devonian.
European Species
Orthis areola QncnUcil 1871
O. deshayesi Rigaux 1873
Scenidium jallax GUrich 1 896 | p^^yication not seen
S. folonkum Ourich 1 896 )
Distinguishing characters. — The name My-
strophora has usually been regarded as a synonym of
Skenidium, despite the fact that its author showed that
some of the shells to which he applied the name were
132
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
actually punctate. Mystrofhora, however, differs so
strongly from Skenidium in other details that it could
easily have been determined as generically distinct with-
out the aid of punctation. The lobate cardinal process,
together with the punctation, at once establishes
Mystro-phora as a dalmanellid. It differs further from
Skenidium in the ventral valve, which has no spondy-
lium; instead, the divergent dental plates are attached
directly to the floor of the valve. In the apex, grow-
ing to the inner sides of the dental plates, is a flat plate,
probably for pedicle attachment, similar to that seen
occasionally in Schizofhoria and other members of the
Schizophoriidas.
Discussion. — In describing Mystrofhora, Kayser
did not definitely designate a genotype. Underneath
Fig. 21. — Mystrofhora areola (Quenstedt). Section
about 2 mm. from the beak, showing relations of apical
plate and dental lamellae, x ca. 12.
the heading "Subgenus Mystrophora" is placed a refer-
ence to Quenstedt's figures. At the end of his discus-
sion, he names as typical species "M. Lewisii Davids."
from the Silurian and "M. areola Quenst." in the
order here given. Kozlowski^"' makes the suggestion
that if future work on Skenidium and Mystrophora
should prove the former to be punctate, the name
Skenidium could be used for the punctate species and
Mystrophora with "M. lewisii" as the type for the
impunctate group. In the absence of definite informa-
tion one way or the other, he includes both punctate
and impunctate forms under Skenidium.
It is clear from Kayser's text that he regarded
Orthis areola as the type of his subgenus. This view
was also held by Williams and Breger,^*"* who say,
"The type of Mystrophora was Quenstedt's Orthis
areola." Schuchert and LeVene'"* more recently cite
Quenstedt's species as the type, and it is so regarded in
the present study.
Williams and Breger evidently considered Mystro-
phora a subgenus of Dalmanella in describing D. (M.)
elevata. Their species is clearly a dalmanellid, and
probably a Wattsella if one can depend on the ventral
musculature.
Mystrophora is an aberrant and specialized dal-
manellid paralleling Skenidioides in its internal dorsal
"^Tal. Polonica, vol. 1, 1929, pp. 46-47.
"' U. S. Geol. Surv., Prof. Paper 89, 1916, p. 61.
"* Foss. Cat., Pars 42, 1929, p. 86.
Structure, but this feature has not yet evolved into the
large hinge-plate of Skenidium.
Genus KAYSERELLA Hall and Clarke 1892
PI. 16, figs. 7, 8, 10
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 259,
figs. 15-17.
Genoholotype. — Orthis lepida Schnur 1853, Pal-
aeontogr., vol. 3, p. 218, pi. 45, figs. 9a, b.
Description. Exterior. — Dalmanelloid, subcircu-
lar in outline; hinge-line narrower than the greatest
width of the shell; cardinal extremities obtuse; lateral
profile unequally biconvex, the ventral valve with the
greater convexity; anterior commissure rectimargin-
ate; dorsal valve provided with a shallow sulcus.
Dorsal interarea long, nearly plane, strongly apsacline,
beak very gently curved; delthyrium with elevated
margins, partially covered by a convex deltidium;
dorsal interarea short, anacline, notothyrium closed by
the cardinal process and narrow chilidial plates. Sur-
face multicosteUate. Shell punctate.
Interior. — There was only one specimen of this
genus in the Schuchert Collection, and sections of it
proved disappointing because the shell is greatly min-
eralized. However, a few points regarding the in-
ternal structure were obtained. The delthyrial cham-
ber is deep and surrounded by adventitious shell, which
is also connected with the deltidium. Dental plates
were not observed. In the dorsal valve the brachio-
phores are long, but the brachiophore plates could not
be seen. The cardinal process is lobate as in other
dalmanellids. Anterior to the cardinalia the median
septum is extended so as nearly to touch the inner wall
of the ventral valve, giving exactly the same appearance
as in Mystrophora.
Geologic range. — Middle Devonian of Germany.
Discussion. — It has been customary for taxonomists
to consider Kayserella a streptorhynchid, but, as
Kozlowski'"^ has pointed out, the shell is punctate
exactly as in Dalmanella. This excludes the genus at
once from Streptorhynchus and its allies, since, as this
author has also shown, the Strophomenacea all have
impunctate shells. Furthermore, the cardinal process
is clearly dalmanelloid and not strophomenoid. These
two characteristics, then — endopunctate shell and or-
thoid cardinal process — are sufficient to place Kayser-
ella among the Dalmanellacea.
The genetic relations of the genus are not yet clear,
but as it is best to refer it, on the basis of our present
imperfect knowledge, to the family with which it most
closely agrees, we place it provisionally with the
Mystrophoridae, though it probably does not belong
here. We lay least family value on the sporadic reap-
pearance of the deltidium and chilidium, and most on
the internal features and the dalmanelloid exterior.
10" Pal. Polonica, vol. 1, 1929, p. 89.
GENERA OF THE SUBORDER ORTHOIDEA
133
Family RHIPIDOMELLID^ Schuchcrt
1913, emended
(=partim Rhipidomellinse Schuchert 1913)
Subcircular, progressive, and terminal Dnlmanella-
cea with broad flabellate diductor scars, completely
enclosing the elliptical adductor field in front. Brach-
iophores short, without fulcral plates.
This large family begins in the early Silurian and
dies out in the late Permian. It embraces the follow-
ing genera:
RhipiHomcUa Oehlert
Perditocard'tnia Schuchert and Cooper
Plijtyorthis Schuchert and Cooper
Thiemella W^illiams
11.
The genetic relations seem to be as shown in Table
Table 11
Thiemella
Platyorthis
Rhipldomella-
-> Perditocardinia
Dalmanella (D. tersa ?)
Genus RHIPIDOMELLA Oehlert 1890
PI. 19, fig. 3; pi. 20, figs. 22-24, 26, 27
Oehlert, Jour. Conch. (3), vol. 30 [38], 1890, p. 372.
Horn. Rhifidomys Oehlert 1887.
Genoholotype. — Terehratula mtchelim L'Eveille
1835, Mem. Soc. Geol. France, vol. 2, p. 39, pi. 2,
figs. 14-17.
Description. Exterior. — Subtrigonal to circular,
anterior margin not uncommonly emarginate, hinge-
line narrow; lateral profile unequally biconvex, the
brachial valve having the greater convexity, with the
ventral one concave at the front in many species; an-
terior commissure faintly uniplicate or rectimarginate ;
in some instances a sulcus on each valve; ventral
interarea the longer, curved, apsacline, umbo swollen
or gently convex, beak incurved; dorsal interarea
greatly reduced, ortho- to apsacline; delthyrium open,
notothyrium usually closed by the cardinal process or
partially by chih'dial plates; surface multicostellate,
hollow costcUx- numerous. Fibrous, punctate.
Ventral intrrior. — Delthyrial cavity shallow; dental
plates abbreviated, teeth strong, divergent, elongate;
a broadly curved ridge extending from the bases of the
low dental plates around the margin of the muscle
field; muscle field large, flabellate, not confined to the
delthyrial cavity, occupying from one-third to five-
sixths the length of the valve and usually deeply im-
pressed; diductor scars semiflabcllate, separated from
each other by a sharp or low broad ridge, completely
enclosing the adductor scars, which form an elliptical
patch just anterior to the pedicle callist; adjustor scar
commonly discernible on the outside of the diductor
scar; pedicle callist occupying the delthyrial cavity.
Dorsal interior. — Cardinalia confined, sockets wide,
deep, without concave fulcral plates; brachiophores
long, bluntly pointed, supported by adventitious sub-
stance deposited beneath their anterior edge; sharp
processes or points on the ends of the brachiophores
have been interpreted as crura; cardinal process large,
myophore commonly ponderous, lobatc; shaft short.
Median ridge extending to the middle of the shell.
Muscle field quadripartite, the posterior scars the
larger. Ovarian and pallial impressions occupying the
area of the shell not covered by the muscle marks.
Geologic range. — Silurian (Clinton) to close of
Permian.
American Species
Rhifidomella aha (Hall) 1863
R. altiroslris Mather 1915
R. arkansana Girty 1911
R.assimilis (Hall) 1859
R. burlingtonensis (HiW) 1858
^. guadrata Bancioh 1928
Subfamily HARKNESSELLIN^ Bancroft
Heterorthidae having biconvex valves, coarser orna-
mentation than is usual in the Heterorthinje, a promi-
nent fold on the ventral valve and an equally promi-
nent sulcus in the dorsal. Embraces the following
genera:
Harknessella Reed
Reuschella Bancroft
Stneathenella Bancroft
Genus HARKNESSELLA Reed 1917
PI. 20, figs. 6-10
Reed, Trans. Roy. Sec. Edinburgh, vol. 51, pt. 4, 1917,
p. 862, pi. 11, figs. 3-7.
Genoholotype. — Orthls vespertlllo Sowerby 1839,
Sil. Syst., pi. 20, fig. 11.
Description. Exterior. — Shell generally small or
medium in size, usually subquadrate in outline; hinge-
line straight; cardinal extremities acute or more rarely
obtuse; lateral profile unequally biconvex, the dorsal
valve usually having the greater convexity; anterior
commissure sulcate; sulcus deep, ventral fold usually
low but prominent. Ventral interarea longer than
the dorsal, apsacline; umbo gently convex. Dorsal
interarea prominent, moderately anacline, umbo gently
convex. Surface costellate to fascicostellate. Shell
punctate.
"" Mem. and Proc. Manchester Lit. .ind Philos. Soc,
vol. 72, 1928, p. 69.
'"'Syst. Sil. Boheme, vol. 5, pt. 1, pi. 66, fig. II, 11a
and I 4.
Distinguishing characters. — Harknessella is
distinguished by the contour and profile of the valves,
the subquadrate form being rather unusual in punctate
shells. In the ventral interior the muscle-scars are
dalmanelloid and in the dorsal the cardinalia suggest
those of Heterorthls. This structural ensemble, com-
bined with a fascicostellate exterior, makes a combina-
tion unique among the Dalmanellacea. The external
form is similar to that of Carinlferella of the Upper
Devonian.
Discussion. — The greatest morphologic interest is
in the dorsal valve and in the cardinalia. As stated
above, the greatest similarity is with Heterorthls. In
Harknessella the brachiophores are rather long, extend-
ing dorso-ventrally. They are unsupported except for
adventitious shell deposited on the inside and along the
dorsal edge, which unites them to the valve. This is
similar to the condition in Heterorthls, but in Harkness-
ella there is a much greater development of the noto-
thyrial platform. This is usually swollen about the
inside surfaces of the brachiophores, and in some in-
stances the platform is nearly flush with the ventral
edge of the brachiophores. In front of the notothyrial
platform are two deep indentations separated by the
median ridge; it is in these pits that the posterior
adductor muscles were lodged. The cardinal process
is distinctly lobed as in all Dalmanellacea but the shaft
may be so swollen as to hide or obscure the original
lobation. In one undescribed species the cardinal
process is delicate, with a slender shaft but an expanded
and lobed myophore.
The distinction between Harknessella and Smeath-
enella and Reuschella is rather difficult to see if one
deals with either the actual shell or a wax replica
thereof, but in internal molds is not so troublesome.
GENERA OF THE SUBORDER ORTHOIDEA
139
In HarknessflLi (see pi. 20, fig^. 8, 9) the base of the
brachiophores and their supporting tissue are triangular
in plan, with the antero-lateral extremity of the tri-
angle somewhat drawn out. The adductor pits are
represented by two posteriorly directed acute lobes on
each side of a median depression. Other differences
are discussed farther on.
Harktu-sscUa is not uncommon in the Middle Ordo-
vician (Caradocian) of the British Isles but is so far
unknown in North America.
Subgenus REUSCHELLA Bancroft 1928
PI. 20, figs. 11-15
Bancroft, Mem. and Proc. Manchester Lit. and Philos.
Soc., vol. 72, 1928, p. 180, pi. 2, figs. 9-12, t. fig. 5.
Genoholotype. — R. semiglohata Bancroft 1928.
Description. Exterior. — Shells commonly rather
large, subquadrate in outline, hinge-line straight, car-
dinal extremities acute; lateral profile unequally bicon-
vex or convexo-concave, the dorsal valve having the
greater convexity. Anterior commissure more or less
strongly sulcate; dorsal sulcus deep in young stages,
obsolete or prominent in old stages; ventral fold sub-
carinate. Ventral interarea the longer, strongly apsa-
cline ; dorsal interarea anacline or orthocline. Umbos
gently convex. Surface costellate to fascicostellate.
Shell punctate.
Ventral interior. — Delthyrial cavity shallow; teeth
strong; dental plates stout, flaring, rather short, con-
tinued as ridges on the lateral margins of the muscle
area. Muscle field pentagonal in outline, gently
bilobed in front. Adductor field linear, strongly im-
pressed; diductor scars elongate, tear-shaped. Adjus-
ter scars rather large. Pallial markings unknown.
Dorsal interior. — Notothyrial cavity obsolete, as it
is filled completely by the notothyrial platform and the
cardinal process; brachiophores bladelike as in Heter-
orthis, cemented to the valve in front by adventitious
substance. Sockets deep; cardinal process with a
lobate myophore, shaft slender or swollen. Adductor
impressions occupying troughs bounding the median
ridge.
Geologic range. — Middle Ordovician (Caradoc-
ian-post-Harnage) of the British Isles, with the follow-
ing species:
Reuse hella bilobata (Sowerby) 1839
R. horderleyensis Bancroft 1928
R. semiglobataBancioh 1928
Discussion. — Reuschella differs from Harknessella
in its coarser ornamentation and in details of the car-
dinalia. Bancroft's description of this genus was made
entirely from internal molds, and the distinctions from
Harknessella that he points out and figures appear very
slight. From specimens kindly sent to us by Bancroft
we could discern no fundamental differences in the
cardinalia. We recommend therefore that Bancroft's
genus be considered a subgenus of Harknessella.
Genus SMEATHENELLA Bancroft 1928
PI. 20, figs. 1-5
B.incroft, Mem. and Proc. Manchester Lit. and Philos.
Soc., vol. 72, 1928, p. 177, pi. 2, figs. 1-5.
Genoholotype. — S. hamagensis Bancroft 1928.
Description. Exterior. — Shell rather large, sub-
quadrate in outline; hinge-line straight; cardinal ex-
tremities usually obtuse; lateral profile unequally
biconvex or convexo-concave, the dorsal valve having
the greater convexity. Anterior commissure sulc.ite;
ventral fold strongly carinate. Interareas subequal,
ventral interarea apsacline, dorsal anacline; umbos
gently convex. Surface unequally costellate as in
Rafinesquina.
Ventral interior. — Delthyrial cavity confined, shal-
low; dental plates short and stout, muscle area rhom-
boidal in outline.
Dorsal interior. — Like Harknessella; notothyrial
cavity closed by the cardinal process and notothyrial
platform. Brachiophore plates slender, heterorthoid.
Sockets deep, median elevation corresponding to ex-
ternal large sulcus.
Geologic range. — Middle Ordovician (Carodoc-
ian) of the British Isles, with the single species S. har-
nagensis Bancroft.
Distinguishing characters. — Smeathenella is
very closely allied to Harknessella but differs in its
ornamentation, lateral profile, and in details of the
cardinalia. The ornamentation has been described by
Bancroft as "markedly Rafinesquinoid," that is, there
are coarser costells separated by many fine costellas.
This ribbing, in connection with a much less convex
dorsal valve than is usual in Harknessella or Reuschella,
will serve to distinguish the genus. Other differences
setting apart this genus from the other two are to be
found in the interior of both valves. The dental
plates are usually proportionally shorter and the mus-
cle field is smaller. In the dorsal valve the cardinalia
are more slender and the adductor pits not as deeply
excavated.
Family SCHIZOPHORIID^ Schuchert 1929
Progressive and terminal Dalmanellacea, probably
derived out of the Dalmanellidas,^"* having biconvex
or lenticular valves in the older formations and in the
younger growth stages, but in mature and old forms
with the dorsal valve usually larger than the ventral.
Surface ornamented by costellse, often hollow. In the
'"* PionoJema, earliest of the Schizophoriidx, appears
simultaneously with the DalmancUidx. It is therefore diffi-
cult at present to state with assurance what stock gave rise
to Schizofhoria and allies.
140
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
aberrant Enteleti'nae this ornamentation is superim-
posed over broad undulations or plicae. Shell fibrous,
punctate.
The ventral interior is especially marked by promi-
nent diductor scars, separated by a median ridge which
becomes more and more elevated in the more advanced
and geologically more recent genera. The dorsal
cardinalia consist of tusklike brachiophores having
widely divergent supporting plates; the cardinal process
is typically dalmanelloid; the dorsal adductor scars
are separated by an oblique ridge in the later forms.
The cardinalia, being alike throughout the family, are
its most significant feature. The dorsal pallial sinuses
consist usually of three pairs; the two inner ones,
given off at the anterior ends of the anterior adductor
scars, bifurcate immediately at their inception and ex-
Table 13
Enteletinae
Schizophoriinae ■
-> Isorthina:
tend to the front margin as four subparallel trunks.
The third pair is given off from the oblique ridge sepa-
rating the adductor scars and extends to the front
margin nearly parallel to the other sinuses. The inner
four trunks are usually the more prominent.
Geologic range. — Ordovician (Chazy) to
Permian.
The Schizophoriidas are subdivided into the follow-
ing subfamilies:
Schizophoriinffi Schuchert
Enteletinse Waagen
Isorthinas Schuchert and Cooper
The genetic relations appear to be as shown in
Table 13.
Discussion. — The Schizophoriidas is one of the
most easily recognized and longest lived families of
the Dalmanellacea. It has its inception in the early
Middle Ordovician (Chazy) with Pionodema as the
oldest representative of the family, starting with the
biconvex or lenticular shell phase. The passage from
Pionodema to Schizophoria appears to be almost im-
perceptible. In Pionodema the ventral septum is low
and long, being of the euseptoid type (Fredericks),
and is the place of attachment of the adductor muscles.
This septum increases in height during geological time
and attains its final development in Orthotichia and
Enteletes. In Pionodema the adductor scars are
clearly visible on the median ridge, and although in
the geologically higher forms no adductor scars are
visible on the floor of the valve, the presumption is
that they were also borne on the septum.
The cardinalia are nearly uniform throughout the
Schizophoriidae from Pionodetna to the last of the
Enteletes in the Permian. The brachiophores are
always shaped like the tusk of a boar, sharp and curved.
The supporting plates are widely divergent and al-
ways have a small fulcral plate defining the socket.
The cardinalia are perhaps the most distinctive struc-
tures in the whole group and their uniformity from
genus to genus throughout the range of the family is
a rather definite expression of the value of the cardinalia
as a family characteristic.
The modification of the dorsal musculature from
Pionodema to Orthotichia has some value in chrono-
logical stratigraphy. In Pionodema the adductor scars
have a quadripartite arrangement, the posterior scars
directly in back of the anterior pair and separated by
horizontal ridges. Later, however, in Devonian and
Mississippian times, the posterior adductors have migrat-
ed laterally and taken a position outside of and posterior
to the anterior pair. These scars, further, are rather
oval in outline instead of subcircular or quadrate as in
the earlier forms, and are separated by an oblique
ridge. The two oval scars one above the other pro-
duce a subflabellate appearance much like that of the
ventral valve of Rhifidomella. The lateral migration
of the posterior scars leaves a large central area occu-
pied only by the much reduced median septum. The
higher, more specialized forms such as Orthotichia,
Enteletes, Parenteletes, etc., continue the dorsal mus-
culature of the later Schizophorias.
Subfamily SCHIZOPHORIIN^ Schuchert 1929
Lenticular, or convexo-concave Schizophoriidae not
having numerous strong undulations or plicae developed
at the front end of the shell.
Geologic range. — Middle Ordovician (Chazy)
to Permian.
Embraces the following genera:
Pionodema Foerste
Schizophoria King
Orthotichia Hall and Clarke
Aulacophoria Schuchert and Cooper
The genetic relations are thought to be as shown in
Table 14.
In this subfamily we place Pionodema as the origi-
nating stock of the Schizophoriidae, this genus giving
rise to Schizophoria out of which came the culminat-
ing Orthotichia. Pionodema and Schizophoria form
interesting homoeomorphs with Schizophorella and
GENERA OF THE SUBORDER ORTHOIDEA
141
Hebertella of the Plectorthin.r. Schizophorclla is
the lenticular type of hebertelloid evolution, just as
Piotwderna represents the same phase in the develop-
ment of Sch'tzofhor'ut. The convexo-concave profile
of Hebertella corresponds to the similar shell form in
Schizophoria.
Genus PIONODEMA Foerste 1912
PI. 23, figs. 1-10, 12-14; pi. 29, fig. 1
Foerste, Bull. Denison Univ., vol. 17, 1912, p. 139.
Cooper, Jour. Pal., vol. 4, 19.30, pp. 369-382.
Horn. Bathyc Aulacophoria
->Enteletin«
Schizophoria *.
-^ ISORTHIN^E
' Pionodema
Description. Exterior. — Semi-oval or subglobose,
margins convex, cardin.-il extremities obtuse, hinge-line
slightly narrower than the greatest width of the shell,
lateral profile lenticular or globose, the anterior part
of the ventral valve becoming concave at the front;
anterior commissure unisulcate or uniplicate; ventral
interarea longer than the dorsal, gently curved, apsa-
cline, beak slightly incurved, umbo prominent; dorsal
interarea curved, orthocline, umbo convex, sulcate;
delthyria open or partially closed by an apical plate;
multicostellate, with hollow costellx; shell fibrous,
punctate.
Ventral interior. — Delthyrial cavity deep; teeth
small, triangular; crural fossettes oblique; dental
plates sharply defined, widely divergent, continued for-
ward as a slight ridge of adventitious shell for a short
distance along the lateral margin of the muscle area;
muscle area not confined to the delthyrial cavity,
longer than wide; diductor scars divergent, subsemi-
flabellate ; adductor impressions consisting of two elon-
gate semielliptical scars on a small ridge between the
diductors; adjustor scars elongate, situated at the base
of the dental plates. Apex closed by a small apical
plate, the front of which is bevelled slightly below the
level of the interarea. This plate clearly served for the
att.ichment of the pedicle. Ovarian impressions occupy
the umbo-lateral spaces.
Dorsal interior. — Cardinalia confined ; brachiophore
supporting plates not separable, vertical or nearly so,
divergent at their bases; brachiophores sharp, diver-
gent, shaped like a boar's tusk; sockets small, excavated
beneath the palintrope, defined by a small concave ful-
cral plate which also serves to bind the brachial appara-
tus to the wall of the valve; cardinal process very
small, expanded and bilobed posteriorly, its shaft being
extended forward to merge with the low median ridge
that extends forward nearly to the middle of the shell.
Muscle area very faintly impressed, anterior adductor
scars the larger.
Geologic range. — Early Middle Ordovician
(Chazy) to Upper Ordovician (Maysville).
American Species
Dalmanella bellula (Meek) 1873
Z). «>c«/r»Vw Stauffcr 1918
S. resufinoitles (Cox) 1857
5. sedalie?tsis Wellcr 1914
5. senecta Hall and Clarke 1 892
S. j/r«a/tt/d (Schlothcim) 1813
S.striatula tnarylanJ tea Clarke and Swartz 1913
S.swallovi (Hall) 1858
5. /«//«'<;««/ (Vanuxem) 1842
Rhifidomella iubelliftica (White and Whitfield) 1 862
Foreign Species
Schizofhoria beaumonti (Verneuil) 1849-1850
S.fragilis Kozlowski 1929
S. injracarbonica Janisevskij 1911
S. interstriata Janisevskij 1911
S. frovulvaria (Maurer)
S. resufinaia {MiiUn) 1809
S. resupinata lata Demanet 192 1-1923
S. resupinata rotundata Demanet 1921-1923
5. striatula (Schlotheim) 1813
S. fw/fijrw (Schlotheim) 1820
Distinguishing characters. — Schizophoria is
distinguished by its convexo-concave profile, the diver-
gent or subparallel diductor scars in the ventral valve
separated by a low median ridge (euseptoid) which
bears the adductor marks, and in the dorsal valve by
the widely divergent crural apparatus, characteristic
muscle marks, and pallial trunks. The adductor mus-
cles are separated by a curved, oblique ridge, a feature
which at once separates this genus from Proschizo-
phoria. The pallial marks consist of four or six sub-
parallel trunks. Schizophoria closely resembles Hebert-
ella externally, but the fundamental difference in shell
structure and cardinalia serves to differentiate them
immediately. The similarities and differences between
Orthotichia and the genus under discussion are pointed
out under the former genus.
Discussion. — Schizophoria is a long-ranging genus
and for this reason shows considerable variation in its
internal anatomy. In the ventral valve the variation
is seen in the musculature and the dental plates. The
diductor scars vary from subparallel and extremely
elongate in some species (S. vulvaria and S. beaumonti,
Lower Devonian of Germany) to widely divergent
and large or small (5. propinqua, S. provulvaria, and
S. niultistriata). In S. iowensis the muscle area is
obcordate and much like that of Hebertella. Occa-
sionally the adjustor scars are considerably developed,
144
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
with the result that the muscle area is notably ex-
panded in front and is a trapezium in outline. The
median ridge carrying the adductor scars varies from
thin to very wide and in a few forms (S. lowensls,
S. striatula) is extended forward beyond the anterior
margin of the muscle area. In some specimens of
Schizophoria from the Pennsylvanian the median ridge
has attained the profile and height seen in Orthotichia.
In the ventral valves of S. resufinata, there are two
palHal sinuses extending forward from the anterior
ends of the diductors and bowing outward in a con-
siderable curve.
In the dorsal valve there are some notable variations
in the musculature and pallial markings. In speci-
mens of the genotype, S. resufinata, the arrangement
of the adductor scars is nearly identical to that seen in
Orthotichia, with the exception that the anterior scars
are not in contact and that the space between the
longitudinal sets is not so great as in the latter genus.
In the early Schizophorias the muscle field is compact
and the right and left sets of adductors are in close
proximity, being separated only by a low median ridge,
but in the later forms the longitudinal sets migrate
laterally so that there is a notable space between them
occupied only by a remnant of the formerly large
median ridge. This lateral spreading of the two longi-
tudinal sets of muscles reaches its maximum in Orthoti-
chia. The generic difference between Orthotichia and
Schizophoria, therefore, is certainly not very great.
The pallial markings are usually well developed,
especially in the dorsal valve ; S. macjarlani shows the
common type. This species has four parallel trunks
extending anteriorly from the front margin of the
anterior adductors to the shell margin, scarcely branch-
ing during their passage. Rarely there are six of these
trunks, the two outside ones corresponding to the
lateral trunks of horthis. So deep are these sinuses in
S. macjarlani that they have impressed themselves
deeply in the shell, so that the slightest exfoliation of
the shell laminze shows these sinuses as ridges. The
so-called S. profinqua (Hall) has pallial markings of
the horthis type and has accordingly been placed with
that genus.
The earliest undoubted Schizophoria is S, senecta
from the Clinton of New York and probably also from
Port Daniel, Quebec. Therefore the group must have
its inception in the Ordovician, in Pionodema, whose
external resemblance to Schizophoria has already been
remarked upon. Furthermore, in the ventral valve of
Pionodema there is an incipient adductor ridge and the
structure of the cardinalia in the dorsal valve is identical
in every fundamental detail with that of Schizophoria.
Genus ORTHOTICHIA Hall and Clarke 1892
PI. 24, figs. 12, 15,22-24,27
Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, 1892, p. 213,
pi. 7, figs. 11-15.
Genoholotype. — Orthis ? morganiana Derby
1874, Bull. Cornell Univ., vol. 1, p. 29, pi. 3, figs.
1-9, 11, 34, pi. 4, figs. 6, 14, 15.
Description. Exterior. — Externally like Schizo-
phoria but usually more finely ornamented.
Ventral interior. — Umbonal cavity deep ; teeth
strong; dental plates strong, divergent, extended
nearly to the middle of the valve as high septal ridges
about the lateral margins of the muscle area; the
cavity defined by these plates is centrally divided by a
median septum, which takes its origin a short distance
in front of the apex, rising to its maximum height
a little in front of the ends of the dental plates, where
it is abruptly truncated. Diductor and adjustor scars
confined to the areas between the dental plates and
the median septum; adductor scars attached to the
sides of the median septum.
Dorsal interior. — Cardinalia strong; brachiophores
strong, tusklike, supported by strong plates that diverge
around the lateral margins of the muscular area; all
of these structures are intimately fused together; the
sockets are deep and are defined by a thin concave ful-
cral plate which unites the crural apparatus to the
palintrope. Cardinal process small, "multifid"; muscle
area quadripartite, the anterior adductors subtriangular
or irregularly oval, situated so that their antero-median
extremities are in contact, the posterior extremities
being divergent and separated by the expanded ex-
tremity of the low median ridge; the anterior adduc-
tor scars on the outside of and slightly posterior to the
anterior pair and separated from them by a narrow,
curved, oblique ridge. Anterior scars narrow sub-
parallel grooves separated by a low ridge. Pallial
markings as in Schizophoria.
Geologic range. — Pennsylvanian to Permian.
Distribution world wide.
American Species
Orthotichia morganiana (Derby) 1874
O. schuchertensis Girty 1903
O.kozLowskii King 1930 (= 1931)
? O. texana Girty 1928
Foreign Species
Orthotichia chekiangensis Chao 1927
O. free hi Fliegel
O.indica (Waagen) 1884
O. marmorea (Waagen) 1884
O. morganiana (Derby) 1874
O. morganiana chihsiaensis Chao 1927
Distinguishing characters. — Orthotichia is dis-
tinguished by the presence of three strong septal plates
in the ventral valve, the outer two being the divergent
dental plates; the inner or median ridge rises to a crest
at the front of the muscle area as in Enteletes and is
obliquely truncated. This genus most closely resembles
GENERA OF THE SUBORDER ORTHOIDEA
145
certain forms of Mississippian and Pennsylvanian Schiz-
ophorut but differs from them in the degree of devel-
opment of these plates. In Orthotkh'ui the dental
plates are always high and extend to the front of the
muscle area as high ridges. Some Pennsylvanian species
of Schizophorui approach Orthot'tch'ui in the accelerated
development of the median septum but in them the
dental plates have not attained the specialized character
of those in Orthotichla.
Discussion. — The dorsal valve has the general
characteristics of the Pennsylvanian Schizofhoria. The
posterior adductor scars are situated behind and out-
side of the anterior impressions, being separated by a
low oblique ridge that is antero-laterally directed. The
individual scars are rather elongate, tapering posteriorly
but expanded toward the front. This gives the mus-
cle-scars a flabellate outline where viewed in the
aggregate. It was Derby's idea'** that there were
six adductor impressions in the dorsal valve. The
smooth spaces on each side of the low median ridge
were interpreted as muscle-scars but there is no crenu-
lation or any other sign of muscle attachment in the
three spaces. Hall and Clarke*" also suggested a third
pair of dorsal muscles in Schizofhoria macfarlani.
The specimen to which they refer is an old obese shell
in the Schuchert Collection. What appear to be lateral
muscles are actually pits left by the incomplete cover-
ing up of the brachiophore apparatus by adventitious
shell.
Orthotichia structurally forms the passage between
Schizofhoria and Enteletes but this does not necessarily
mean that the latter actually developed out of Ortho-
tichia. Enteletes probably developed directly out of
the more plastic Schizofhoria, and Orthotichia may
then be a terminal branch of the Schizofhoria line.
Genus AULACOPHORIA Schuchert and
Cooper 1931
(Gr. aulax, furrow; fhoreein, to bear)
PI. 29, figs. 2, 5, 10
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 247.
Genoholotype. — Orthis keyserlingiana De Ko-
ninck 1843, Desc. Anim. Foss. Terr. Carb. Belgique,
p. 230, pi. 13, fig. 12.
Description. — Aulacofhoria is proposed for shells
having an interior like that of Schizofhoria but having
a deep sulcus on the dorsal valve and a strong fold on
the ventral one. Besides the genotype, two other
European species are placed in this genus, Enteletes
injracarbonica Janisevskij from the Lower Carbonifer-
ous of the eastern Urals in the vicinity of Khabarny
"" Bull. Cornell Univ., vol. 1, 1874, p. 30.
"'Pal. N. Y., vol. 8, pt. 1, p. 214.
and E. uralica Gorsky from the Middle Carboniferous
of the eastern slope of the Urals. Schizofhoria
{Enteletes?) mesoloba Janisevskij may be another
form belonging in this genus.
In the dorsal valve the brachiophore plates are
widely divergent as in Schizofhoria and Enteletes, and
the sockets are defined by fulcral plates as is usual in
the family. In the ventral valve the prominent dental
lamellae are subparallel but no prominent median sep-
tum was detected, such as occurs in Orthotichia or in
Enteletes. The ornamentation is very much like that
of Enteletes, much more so than like Schizofhoria.
Aulacofhoria thus occupies an intermediate position
structurally between Enteletes and Schizofhoria. It
differs from the former in being less ventricose and
inflated and in not possessing the prominent ventral
median septum. The great development of the median
septum in Enteletes, according to Gorsky, may be an
adaptation to the great inflation of the valves to accom-
modate the attachment of the adductor or closing
muscles.
Gorsky"* maintains that the type of structure shown
by Enteletes injracarbonica Jan. represents the earliest
phase of Enteletes. It is our idea, on the other hand,
that Aulacofhoria is a terminal offshoot from Schizo-
fhoria. We base this conclusion on the greater re-
semblance of the interior to Schizofhoria than to
Enteletes.
Subfamily ENTELETIN^ Waagen 1884
Aberrant, globular or strongly biconvex Schizo-
phoriidas that are usually strongly plicate in front,
or atavistically ? smooth.
Geologic range. — Pennsylvanian and Permian.
Embraces the following genera:
Enteletes Fischer de Waldheim
Enteletina Schuchert and Cooper
Parenteletes King
Enteletella Likharev
Enteletoides Stuckenberg
The genetic relations seem to be as shown in
Table 15.
Discussion. — The Enteletinx in their compara-
tively short life span have tried to adopt several of the
features developed in other groups by more tedious
routes of evolution. Parenteletes tried the cella or
camera of Mcrista. Enteletella developed a spon-
dylium for muscle attachment. Further, there was no
stability in the development of the fold and sulcus.
This trait is not unusual among the orthids but in the
Enteletinx a ventral fold became persistent in two
'" Bull. Cora. Geol. Leningrad, vol. 43, no. 9, 1927,
pp. 1184-1186, pi. 18, fig. 9.
146
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
stocks and therefore of use in the definition of two
genera along with other features.
The evolution of the Enteletinae is somewhat analo-
gous to that of the Derbyias and Meekellas which
lived at about the same time. In the last named
genus the shell also develops broad undulations at the
front as in Enteletes. It would be interesting to know
what conditions of ecology in the Pennsylvanian and
Permian seas could have produced such parallel devel-
opments in these two different stocks. Or is it an
expression of old age in these terminal stocks that
arose so far back in the Ordovician?
Table 15
Ente etina
Enteletes
Parenteletes
* Enteletella
Enteletoides
Schizophoria
Genus ENTELETES Fischer de Waldheim
1825
PI. 24, figs. 1-3, 5-10, 25
Fischer de Waldheim, Notice sur la Choristite, 1825, p. 6;
Oryct. Gouv. Moscou, 1830-1837, p. 144, pi. 24,
figs. 10-11 {choristites ^^ lamarcki) , pi. 26, figs. 6-7
{glaber).
Genoholotype. — E. chorhtltes Fischer de Wald-
heim 1825 =^Sfirifer lamarcki.
Description. Exterior. — More or less globular,
margins convex; hinge-line narrower than the great-
est width of the shell; cardinal extremities rounded;
lateral profile unequally biconvex, the dorsal valve
being the more convex; lateral commissure dorsally
deflected near the hinge; anterior commissure unipli-
cate; ventral interarea the longer, curved, apsacline,
beak strongly incurved, umbo swollen; dorsal inter-
area short, curved, orthocline to apsacline, beak
strongly incurved, umbo tumid; delthyrium open.
notothyrium partially closed by the cardinal process.
Surface finely costellate, and plicate anteriorly. Shell
fibrous, punctate.
Ventral interior. — Umbonal cavity deep ; teeth
strong ; crural fossettes oblique ; dental plates strongly
developed, advancing, slightly convergent or subpar-
allel; the space between these plates divided medianly
by a thin bladelike septum rising to an apex at its
anterior extremity, truncated sharply in front so that
it terminates in a line with the anterior termination of
the dental plates; muscle area compressed laterally;
diductors and adjustors confined to the narrow areas
between the dental plates and the septum, while the
adductors were probably attached to the latter.
Dorsal interior. — Cardinalia strong; brachiophores
strong, curved, supported by thin plates that are ex-
tended forward and around the lateral margins of the
muscle area as far as the anterior margin. Sockets
strong, defined by a socket-plate on the outside margin
of the socket; along the hinge-line a strong denticle;
cardinal process small ; muscle area like that of Ortho-
tichia, the anterior adductor scars large, subcircular;
the posterior adductors forming two small scars on the
outside of and slightly posterior to the anterior adduc-
tors and next the ridges from the brachiophore
supports.
Geologic range. — Middle Pennsylvanian to Per-
mian in many parts of the world.
American Species
Enteletes andii {T>'Oih\gnY) 1842
E.dumbleiGnxy 1908
E . hemiflicata ( H all ) 1852
E.leonardensis King 1930 (= 1931)
E.Uumbonus King 1930 (= 1931)
E.flummeri King 1930 (= 1931)
E. u'oljcamfensis King 1930 (= 1931)
E.wordensis King 1930 (= 1931)
Foreign Species
Enteletes contractus Gemmellaro 1 898
E. elegans G&cameAixo 1898
E. haugi Gemmellaro 1 898
E. hemiflicatus naia Fredericks 1923
E. kayseri Waagen 1 884
E . Itevissimus Waagen 1884
E. lamarcki Fischer de Waldheim 182 5
E. meridionalis Gemmellaro 1 898
E. microflocus Gemmellaro 1 898
E . oehlerti GemmcWiTO 1898
E . subiiquivalvis Gemmellaro 1898
E. tschernyscheffi Diener
E. waageni Gemmellaro 1898
? E. fentamera Eichwald
Distinguishing characters. — Enteletes is dis-
tinguished externally by its elliptical outline, globular
profile, and plicate anterior. Internally the subpar-
allel dental plates and sharp, crested median septum
GENER.A OF THE SUBORDER ORTHOIDEA
147
are diagnostic characters. From Orthotichia it differs
in the presence of the anterior ph'cations and in the sub-
parallelism of the dental plates. It differs from Entele-
t'tna and Parentcletes in having the fold on the dorsal
valve. EnteleteUa differs from this genus in the posses-
sion of a spondylium.
Discussion. — Waagen**^ proposed two groups of
EnteUtes: ( 1 ) the "ventrisinuate" group having the
fold on the dorsal valve; and (2) the "dorsosinuate"
group which has the fold on the ventral valve.
King^"" has recently separated the latter group as a
new genus called Parenteletes. The new generic
group is, however, not homogeneous and should be
further split into two groups on the basis of internal
structure. The term Enteletes, then, must be re-
stricted to shells of the E. lamarcki and E. hemiflicatus
type, which have the fold and sulcus in the usual
position. Specimens having a small sulcus in the fold
and a plication in the sulcus are not excluded from
Enteletes; this condition does not alter the uniplicate
character of the anterior commissure and is not con-
sidered of sufficient import for the separation of a
new group.
VVaagen*"^ suggested that Enteletes evolved from
Orthotichia by the development of plicas in the anterior
part of the shell, and this idea has gained quite general
acceptance. Enteletes is the culmination of a long
line of orthid evolution that began in Chazy time with
Pionodema. It appears in the Middle Pennsylvanian
and ranges through the Permian. By loss of the plicas
in late Permian time it is thought to have returned to
the ancestral Orthotichia-like condition, this atavistic
phase of Enteletes being termed Enteletoides by
Stuckenberg.
It is thought by the writers that Orthotichia, which
ranges from the Pennsylvanian to the Permian, is
probably a terminal stock of the Schizophoriidas and
may not have given rise to Enteletes. We suggest the
separate development of Enteletes out of Schizophoria
in the Pennsylvanian at about the same time as the
appearance of Orthotichia.
Gorsky'"^ has claimed the development of Enteletes
from Orthotichia by way of simply plicated stocks like
Aulacofhoria. We hold, rather, that Aulacophoria is
a side line out of Schizophoria, and one that probably
did not survive beyond the middle Pennsylvanian.
Genus PARENTELETES King 1931
PI. 24, figs. 11, 13, 14, 16, 18, 21, 26
King, Bull. 3042, Univ. Texas, 1930 (1931), p. 48, pi. 1,
figs. 16-20; pi. 2, figs. 1-3.
"• Mem. Geol. Surv. India, Pal. indica, ser. XIII, vol. 1,
pt. IV', fasc. 3, pp. 5 5 3-563.
'" Bull. 3042, Univ. Texas, 1930 (1931), p. 48.
"' Op. cit., p. 564.
122
Op. cit., 1927.
Genoholotype. — P. cooperi King 1931.
Description. Exterior. — Externally like Ente-
letes, but somewhat more transverse, dorsosinuate;
lateral profile unequally biconvex, the dorsal valve the
larger; anterior commissure sulcate ; ventral interarea
the longer, apsacline, beak strongly incurved, umbo
swollen, delthyrium large; dorsal interarea short,
curved, apsacline, beak strongly incurved, umbo tumid,
notothyrium wide. Surface multicostellatc and plicate,
rugose, with hollow costella-, the plica broad and
angular. Shell fibrous, punctate, the punctx arranged
in narrow radial rows.
Ventral interior. — Delthyrial cavity deep, teeth
elongate, sockets pointed; dental plates strong, sub-
parallel posteriorly but diverging strongly anteriorly;
area between them divided by a median septum which
originates very close to the apex, rounded on its dorsal
extremity, rising as it progresses forward to reach its
maximum height at the point where the anterior ends
of the dental plates die out. Here it is abruptly trun-
cated and its extremity forms the crest of a V-shaped
camera or cella, formed at the point where the internal
sulcus corresponding to the fold has its origin. Muscu-
lature as in Enteletes. A small plate for pedicle attach-
ment is in the apex.
Dorsal interior. — Cardinalia and musculature like
those of Enteletes.
Geologic range. — Upper Pennsylvanian and
Lower Permian of Europe and America.
American Species
Parenteletes cooperi King 1931
Foreign Species
Enteletes dieneri Schellwien 1900
E. suessi Schellwien 1892
E. suessi acuticosta Schellwien 1892
Distinguishing characters. — Parenteletes dif-
fers from Enteletes in having the fold on the ventral
valve, and in the possession of a V-shaped camera or
cella under the anterior portion of the median septum.
This internal character also serves to differentiate the
genus from Enteletina, which closely resembles it
externally.
King has shown that Parenteletes in America ap-
pears in geological time before Enteletes, and this
appears to indicate that the genus under discussion
evolved separately from Orthotichia or Schizophoria
and is not a modification of Enteletes. Girty'"^ and
Waagen'"'' have suggested that Parenteletes (the dor-
sosinuate group) developed out of an Enteletes having
'" U. S. Gcol. Surv., Prof. Paper 5 8, 1908, p. 290.
'" Mem. Geol. Surv. India, Pal. Indica, ser. XVIII,
vol. 1, 1887, p. 562.
148
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
a small sinus in the dorsal fold and a plication in the
sulcus, by enlargement of said plication. While this
is possible, the fact remains that Parenteletes was devel-
oped earliest. Furthermore, there is much more simi-
larity between Orthotichia and Parenteletes in the
divergence of the dental plates. Therefore the evi-
dence points to an independent development of the two
genera out of Orthotichia.
E. suessi, figured by Schellwien,^^^ we place in asso-
ciation with American species of Parenteletes, as it
shows, according to his figure, the same internal char-
acteristics as the American forms. ScheUwien re-
marked on the external similarity between E. suessi
and the Indian E. latesinuatus Waagen, but pointed
out the internal differences and on this basis separated
the two species; his figure shows the walls of the
camera uniting with the dental plates, but in American
forms these are discrete. There is a possibility that
the figure has not been drawn accurately.
The camera of Parenteletes is a remarkable con-
vergence toward the type of muscle platform in
Merista, Dayia, and Cyclosfira, although the one in
Parenteletes differs in bearing a median septum on its
crest.
Genus ENTELETINA Schuchert and Cooper
1931
PI. 24, figs. 17, 19, 20
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 247.
Genoholotype. — Enteletes latesinuatus Waagen
1884, Mem. Geol. Surv. India, Pal. Indica, ser. XIII,
vol. 1, pt. IV, fasc. 3, pp. 559-560, pi. 57, figs. 4-6.
Description. Exterior. — Externally Enteletina is
identical with Parenteletes but internally it has all of
the features of Enteletes. It therefore is essentially an
Enteletes with the fold on the ventral valve and com-
prises Waagen's division of "dorsosinuates." The
dental plates are not strongly divergent and there is a
crested median septum which does not have the peculiar
V-shaped camera so characteristic of Parenteletes.
The presence of this chamber, the function of which is
not understood unless it be for muscle attachment, is
therefore not a distinction between the Asiatic and
American and European "dorsosinuate" Enteletes.
The writers have selected Waagen's species E. late-
sinuatus to serve as the genotype, as both internal and
external characters of it have been admirably figured.
The Indian forms are all Upper Permian in age and
may represent a development from Enteletes by the
enlargement of plica5 in the ventral sulcus, such as sug-
gested by Waagen and Girty. (See under discussion
of Parenteletes.) We have placed in this genus only
"'Abh. k. k. geol. Reichsanst., Bd. 16, Heft 1, 1900,
p. 12, pi. l,fig. 18.
the Late Permian species of India, and do not include
here such Pennsylvanian and Lower Permian forms as
E. suessi and variety acuticosta and E. dieneri, since
their internal structure is clearly that of Parenteletes.
Enteletes globosus Girty, probably from the Word
of late Middle Permian age, is placed here provisionally
since its internal structure is not known.
Geologic range. — Permian of India and Texas.
Indian Species
Enteletes acutiflicatus Waagen 1884
E. jerrugineaWiigtn 1884
E. latesinuatus Wiigen 1884
E. fentameroiJes Waagen 1 884
E. suMirvis WiAgen 1884
American Species
? Enteletes globosus Girty 1908
Genus ENTELETELLA Likharev 1924
PI. 24, fig. 4
Likharev, Bull. Com. Geol., Leningrad, vol. 43, no. 6,
1924, pp. 719, 721, pi. 5, figs. 1-3.
Genoholotype. — E. nikschitschi Likharev 1924.
Description. — Enteletella has the external form
and ornamentation of a ventrisinuate or true Enteletes,
closely resembling E. microflocus Gemmellaro. It
differs internally from Enteletes, however, in the
possession of a spondylium. The dental plates unite
with the median septum in such a way as to enclose a
portion of it, which projects as a ridge for the attach-
ment of the adductors inside the spondylium. The
dorsal edge of this ridge is somewhat club-shaped, and
the lower part of the median septum remains free. The
dorsal valve is, in all respects, the same as that of
Enteletes. The genotype is the only species known.
Geologic range. — Lower Permian of northern
Caucasia.
Genus ENTELETOIDES Stuckenberg 1905
Stuckenberg, Mem. Com. Geol., n. sen, livr. 23, 1905,
pp. 59, 129, pi. 6, fig. 8, pi. 9, fig. 8.
Gorsky, Bull. Com. Geol., vol. +3, no. 9, 1927, pp. 1184-
1186, pi. 18, fig. 7 (subrossicus) .
Genoholotype. — E. rossicus Stuckenberg 1905.
Distinguishing characters. — Stuckenberg pro-
posed this name for shells having a convexo-concave
profile and multicostellate external ornamentation,
recalling Orthotichia in both of these characteristics.
According to that author the shell completely lacks
interareas. Internally the arrangement of the dental
plates and median septum is identical with that of
GENERA OF THE SUBORDER ORTHOIDEA
149
EnieUtes. In other words, this is essentially an
EnteUtes showing atavistic tendencies toward Ortho-
Uchia in the loss of the radial plications and globose
profile.
Discussion. — The absence of interareas, while not
impossible, is not convincing from the figures presented
by Stuckenberg, especially figure 8e of plate 6. Such
an arrangement of the dental plates and their connec-
tion with the lateral margins of the shell as indicated
suggests a wide hinge-line, and the latter presupposes
a palintrope. The shells of Orthotichia and Enteletes
are usually thin and very susceptible to crushing;
this may be the reason for the apparent lack of inter-
areas in Stuckenberg's specimens. Parallelism of the
dental plates would be an important clue to deter-
mining the ancestry of this form, but the figures of
the author are not specially convincing on this point
(see his fig. 8b, pi. 9). It may be questioned whether
an Enteletes that has atavistically lost its radial orna-
mentation would likewise lose its most characteristic
internal features and the globose contour of the shell
as well.
Schellwien has made much of the supposition that
many species now referred to Orthotichia may actually
represent atavistic Enteletes and for this reason he
referred all smooth forms having the internal struc-
ture of Enteletes to that genus, placing there even the
genotype of Orthotichia. It is important, if it can be
proved that atavistic forms of Enteletes actually exist,
that these be separated under a new designation and
not included in Orthotichia, which is essentially an
incipient or potential Enteletes. It is also important to
determine when these atavistic tendencies appear.
They may have appeared soon after the origin of the
genus, occurring several times during the Upper Penn-
sylvanian and Permian, or they may have been delayed
till near the end of the Permian, in which case the
matter is more simple. King (1931) maintains that
the Permian Enteletes, in large part, are more strongly
plicated than the Pennsylvanian species, and that the
forms with faint plications do not even resemble Ortho-
tichia in profile. If the atavism is actually carried to
the degree of the resumption of the convexo-concave
form of Orthotichia, the only reliable clue to the rela-
tionship of atavistic shells would be in the parallelism
of the septal plates of the ventral valve. The paral-
lelism of the plates in Enteletes is frequently more
apparent than real, and it is often difficult to evaluate
the degree of divergence that does exist. It will thus
be seen that it is extremely difficult to establish the
fact of atavism in these shells. It seems to the writers
that unless the atavistic tendencies are inaugurated in
the nepionic stage of Enteletes, Enteletoides should
have the globose outline and interior of the former
genus. If the return of the previous characters takes
place in the nepionic stage, all objections in regard to
profile in internal characters noted above lose their
force.
Another species referred here is Enteletoides sub-
rossicus Gorsky 1927, from the Middle Carboniferous
on Kamenka River, eastern Urals.
Subfamily ISORTHIN^ Schuchert and Cooper
1931
Divergent biconvex Schizophoriidae, having the ven-
tral musculature, cardinalia, and pallial markings of
Schizophoria. The only known genus is Isorthis
Kozlowski, probably derived out of early Silurian
Schizofhoria.
Genus ISORTHIS Kozlowski 1929
PI. 21, figs. 17-28, 30-33; pi. 23, figs. 15, 19;
t. fig. 13
Kozlowski, Pal. Polonica, vol. 1, 1929, pp. 29, 75, pi. 2,
figs. 24-41, t. figs. 16-18.
Genoholotype. — Dalmanella {Isorthis) szajno-
chai Kozlowski 1929.
Description. Exterior. — Transversely subellipti-
cal, hinge-line straight, narrower than the greatest
width of the shell; cardinal extremities rounded.
Lateral profile unequally to subequally biconvex; an-
terior commissure rectimarginate to faintly sulcate.
Dorsal sulcus shallow. Ventral palintrope longer than
the dorsal, curved, gently apsacline. Beak curved,
umbo swollen; delthyrium open. Dorsal palintrope
short, faintly apsacline or faintly anacline ; notothyrium
closed by the cardinal process. Ornamentation multi-
costellate. Shell fibrous, punctate.
Ventral interior. — Delthyrial cavity deep ; teeth
large; crural fossettes deep; dental plates strong in
young specimens, obsolete in old ones. Muscle field
deeply impressed, bilobed in front ; diductor scars elon-
gate, subparallel; adductor track elevated, usually nar-
row, adductor scars semielliptical when visible ; adjus-
tor scars located on the sides of the dental plates,
usually not clearly visible. Pallial markings promi-
nent, consisting of two main trunks extending antero-
laterally from the anterior end of each diductor.
Dorsal interior. — Brachiophores as in Schizophoria,
i. e., bladelike plates, with fulcral plates and usually
supported by adventitious shell (see below). Cardinal
process small, bilobed, trilobed, or multilobed, com-
monly modified by deposition of adventitious testaceous
deposit. Median ridge low. Muscle area subcircular
in outline, usually with thickened peripheries. Adductor
scars subequal in size. Pallial sinuses consisting of three
pairs of trunks as in Schizophoria; two originate at
the antero-medial ends of the anterior adductor scars
and extend anteriorly; a second set starts just outside
the former and extends antero-laterally. The third
150
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
set appears at the line separating the anterior and pos-
terior adductor sets, each trunk bifurcating into sub-
sidary ones (see discussion below).
Geologic range. — Late Silurian (upper Ludlow)
to Middle Devonian.
American Species
Dalmanella arcuaria Hall and Clarke 1 892
D.ferelegans (HaU) 1857
D. fygmtta Dunbar 1920
D.rockhousensis Dunbar 1920
Schizofhoria frofinqua (HaU) 1847
European Species
Dalmanella (/.) szajnochai Kozlowski 1929
Ortkis canalicula SchnuT 185 3 (1851?)
O. decifiens Barrande 1 847
O. loveni Lindstrom
O. neglecia Barrande 1 847
O. occlust Barrande 1847
O. tetragona Roemer 1844
O. irigeri Verneuil
Distinguishing characters. — Isorthis is distin-
guished from Dalmanella by its strongly biconvex
lateral profile, lack of prominent fold and sulcus, pecu-
liar ventral and dorsal musculature, and brachiophores
with fulcral plates.
Discussion. — The ventral musculature with its
elongate and divergent diductor impressions most
strongly resembles that of certain species of Schizo-
fhoria. The diductor tracks are deep and elongate and
are separated by a prominent ridge which carries the
adductor muscles. A strong pallial trunk extends an-
teriorly from the ends of the diductor impressions.
Branching of these primary trunks has not been
observed.
In the dorsal valve the cardinal process is small, but,
contrary to Kozlowski's statement, it has a lobate myo-
phore, as shown by /. canalicula (Schnur) and other
species placed in the genus. The pallial sinuses are
well shown in /. tetragona^ in which four trunks appear
to originate at the antero-median extremities of the
anterior adductor scars. In reality there are only two
main trunks but they bifurcate almost at their origin
and send out two secondary branches, one pair antero-
medially, the other antero-laterally. A second pair of
primary pallial sinuses is given off from the horizontal
elevation dividing the adductor scars. This trunk
bifurcates in about half the distance to the margin,
sending one branch antero-laterally, the other postero-
laterally. In makeup these sinuses are much like those
of Schizophoria, as seen in S. tuUiensis and S. senecta,
in which all the trunks originate at the same place as in
Isorthis, but since the shell ridge dividing the adductor
scars is oblique they extend toward the front in a sub-
parallel arrangement. Schizofhoria frofinqua (Hall)
has pallial markings exactly like those of Isorthis and
is therefore provisionally placed in that genus.
Of interest in Isorthis is the great development of
adventitious shell deposited upon the cardinalia and
in the vicinity of the dorsal muscular area. In some
instances primary structures are nearly completely
obscured.
Isorthis appears to be common in Europe, being
well represented in the Lower Devonian of Bohemia
and in the younger Eifelian of Germany. In America
it is common in the Helderberg (New Scotland)
(/. ferelegans, I. rockhousensis, I. fygmcea), and in
the Silurian of Tennessee it is represented by /. arcuaria.
Family LINOPORELLID^ Schuchert and
Cooper 1931
Aberrant, specialized Dalmanellacea, having a dor-
sal cruralium and a shell ornamentation recalling
Porambonites,
Geologic range. — Silurian, with the genera
Linoforella Schuchert and Cooper and Orthotrofia
Hall and Clarke.
Discussion. — The ventral musculature of Linofor-
ella is close to that of Pionodema and Schizofhoria.
In the dorsal valve, however, the convergence of the
brachiophore plates to meet a median septum is such
a radical departure from the usual structure of the
Schizophoriidae as to warrant the erection of a family
to recognize this variation. The schizophorioid ventral
muscles and the punctate shells indicate the probable
origin of Linoforella, but the presence of a cruralium
shows a distinct divergence from some stock as yet
unknown, but probably to be looked for among the late
Ordovician Schizophoriidae.
Genus LINOFORELLA Schuchert and Cooper
1931
PI. 18, figs. 13, 14, 17, 18,24,33
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 247.
Genoholotype. — Orthis functata Verneuil 1848,
Bull. Soc. Geol. France (2), vol. 5, p. 343.
Description. Exterior. — Semioval to subglobose,
margins convex; hinge-line narrower than the greatest
width of the shell; cardinal extremities rounded;
lateral profile subequally biconvex; anterior commis-
sure slightly sulcate; ventral interarea the longer,
curved, apsacline, beak strongly incurved, delthyrium
open; dorsal interarea anacline, beak incurved; sur-
face multicostellate, the striae being marked by a row
of coarse pits which do not perforate the interior shell
layer. Test fibrous, punctate.
Ventral interior. — Delthyrial cavity deep ; teeth
small, fossettes lacking; dental plates strong and
GENERA OF THE SUBORDER ORTHOIDEA
151
prominent, subparalkl, produced forward as prominent
ridges on each side of the diductor scars; a median
ridge extends from the front of the muscle area nearly
to the margin of the shell and is commonly extended
between the diductor impressions nearly to the apex.
Muscle field longer than wide; adductor scars borne
on the median ridge; diductor scars elongate, narrow;
muscle area thickened in front; irregular, wavy
ovarian markings occupying the lateral spaces. The
palintrope overhangs the delthyrial cavity.
Dorsal interior. — Cardinalia strong; notothyrial
cavity deep; brachiophores forming a thickening below
the notothyrial margin and terminating in short, blunt
points supported by stout plates that converge to meet
a median septum and thus make a cruralium; sockets
shallow, excavated in the margin of the hinge and the
outer face of the crural base, defined by an obscure
fulcral plate; cardinal process unique, consisting of an
elongate thickened myophore and a thin septum-like
shaft that is continuous with the median septum.
Median septum high, extended forward about half
the length of the valve. Muscle area elongate-oval,
divided by the median septum, commonly with an ele-
vated periphery. Elevated, wavy visceral markings
occupy the spaces outside of and posterior to the
muscle area.
Geologic range. — Middle Silurian or Gotlandian
(Niagaran).
American Species
Orthit functostriata Hall 1852
European Species
Orthis functata Verneuil 1 848
? O. turgida McCoy 1 85 I
Distinguishing characters. — Ltnoforella is
unique among punctate orthoid genera in the conver-
gence of its ornamentation toward the kind seen in
Porambonttes. There are, however, internal and ex-
ternal differences that when combined with the geolog-
ical occurrences separate the two genera. Externally
Linoporella has the outline and profile of Pionodema,
differing thus from Porambonttes, and internally the
ventral musculature, dorsal cruralium, and cardinal
process further serve to differentiate the two.
Discussion.— Hall and Clarke (ISgZ)'-" were
aware of this group of orthids, saying of O. functata
and O. punctostriata that they could not be placed in
their divisions of the old genus Orthis; they did not,
however, give them a generic name.
The internal features of Linoporella separate the
genus from all other Dalmanellacea. In the ventral
valve of young shells the dental plates are sharply
defined by deep umbonal cavities and extend directly
'^'Pal. N. Y., vol. 8, pt. 1, p. 217.
to the floor of the valve. In most specimens these
plates are prolonged along the floor of the valve as low
ridges. The diductor scars are semielliptical or semi-
oval in plan and are separated by a depressed adductor
ridge. The latter is low in the posterior of the shell
but is elevated to a sharp crest at a point just in front
of the anterior ends of the diductor scars, and then
descends to disappearance near the front margin.
Along the top of this ridge is a shallow, longitudinal
groove which usually does not extend anterior to the
crest. In older shells the front margins of the diduc-
tor scars are elevated on a low callus deposit which is
elevated forward and inward along the median ridge
and rises to disappearance at the crest. Posteriorly and
laterally the callus decreases in thickness to become
only a film on the sides of the dental plates and floor of
the valve. This callus is significant, however, because
it obscures the front ends of the dental plates and
produces a pseudospondyliurp. Careful observation of
old specimens will commonly show low extensions of
the dental plates into or beyond the callus and its
upturned anterior border. The delthyrial region of
Linoporella is another significant example of obsoles-
cence of primary structures (bases of dental plates in
this instance) by secondary deposit of shell. In this
tendency it also parallels Porambonttes, although the
degree to which the deposition is carried does not result
in structures that are precisely alike.
The dorsal interior is also unique in Linoporella,
being a convergence to that seen in Skenidio'tdes. The
brachiophores are elongate, toothlike, bluntly pointed
processes extending into the interior of the valve.
Their forward growth produces a thickening under
the palintrope which lies on them and extends over
the notothyrial cavity for a short distance. These
processes merge into discrete convergent plates which
unite near the floor of the valve with a sharp median
septum. In old shells the cavities between the brachio-
phore supports and the floor of the valve are filled up
with adventitious shell, causing the development of a
structure simulating a sessile cruralium. In reality,
however, in young shells the brachiophore supports in
their line of attachment with the septum curve ventrally
so that their anterior ends rise to a point on the summit
of the septum. The cardinal process has a simple shaft
that thickens toward the front and merges with the
median ridge to form a continuous septum, the thicken-
ing at the front of the cruralium being the only mark
of union of the two septa. The myophore in old shells
is a triangular thickening of the shaft at the posterior,
the compressed sides of the triangle bearing the crenu-
lations or marks of muscle attachment. The median
ridge usually extends to about the middle of the valve
as is usually the case in the orthids. The muscle field
is rather narrow, elongate oval, with the posterior
adductor scars the larger. Each anterior mark is
bipartite as in many other orthid genera. Elevated,
152
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
thickened margins similar to those occasionally seen
in Devonian Schizophoria are not infrequent in
Linoporella.
Linoforella is represented by a single species in the
Gotland of Sweden and by a closely related form in
the Niagaran of the United States. Reed^" states that
Orthis ■polygramma fentlandica Davidson has pits
between the costellae as in Linoporella, but all of the
figures indicated by him display neither the external
outline and profile nor the internal characters of the
genus under discussion. Hence we feel that this species
can not be placed in association with Linoporella.
Orthis turgida McCoy, on the other hand, has the
external outline and profile and most of the internal
features of the genus we are here proposing. David-
son's figures^^* show the cruralium exactly as it is in
Linoporella, and in the ventral valve (fig. 20a) the
muscle area is somewhat more expanded than is typical
in our genus. In the descriptions and figures, how-
ever, there is no mention of the external pits so charac-
teristic of L. punctata. However, we refer O. turgida
to Linoporella with a query because of the close similar-
ity of internal structure, which we consider of more
generic importance than the external ornamentation.
Discussion. — Orthotropia has been well figured
but never has been adequately described. Since the
genus was made known it has been erroneously classi-
fied among the Pentameracea, with which it has no
relationships. Orthotropia appears to be most closely
related to Linoporella, having in common with it a
pseudospondylium, a cruralium, and a simple orthoid
cardinal process (so far as could be determined from
the specimens studied).
The only known specimens of Orthotropia are in
the form of internal molds preserved in a hard dolo-
mite. This is the type of specimen that was available
to Hall and Clarke and also the kind preserved in the
Teller Collection at the National Museum. The ex-
ternal sculpture and the shell substance are therefore
unknown. This being the case, it has been impossible
to determine the exact relationships of Orthotropia to
Linoporella. Should the shell substance prove to be
punctate and the surface to have the characteristic
linoporellid pores, our genus must become a synonym
of Orthotropia. However, in the absence of this im-
portant information it has seemed best to designate the
group of Orthis punctata as a new genus.
Genus ORTHOTROPIA Hall and Clarke 1894
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1894, pi. 84,
figs. 3-7.
Genoholotype. — O. dolomitica Hall and Clarke
1894.
Description. Exterior. — Shell rather small,
hinge-line straight, narrow; cardinal extremities ob-
tuse. Lateral profile unequally biconvex, the ventral
valve having the greater convexity. Anterior com-
missure faintly uniplicate. Ventral interarea long,
apsacline; beak curved. Delthyrium probably open.
Dorsal interarea short, anacline; notothyrium open.
Nature of shell substance and external surface
unknown.
Ventral interior. — Dental plates prominent, discrete.
Muscle field elevated at the front end by a callosity
which forms a prominent pseudospondylium. Diduc-
tor tracks narrow; adductor field narrow, elevated
on a low ridge in old shells.
Dorsal interior. — Notothyrial cavity deep. Brachio-
phore plates convergent, forming a cruralium with the
median septum, which is thin. Adductor field suboval.
Cardinal process a simple ridge, possibly with expanded
myophore.
Geologic range. — Silurian (Racine dolomite).
The genotype is the only known species.
'"Trans. Roy. Soc. Edinburgh, vol. 51, pt. 4, 1917,
p. 857.
'2« Brit. Foss. Brach., vol. 3, pt. 7, pi. 32, figs. 19a, 20a.
Family TROPIDOLEPTID^, n. fam.
(Tropidoleptinas Schuchert 1896)
Genus TROPIDOLEPTUS Hall 1857
Hall, N. Y. State Cab., 10th Rept., 1857, p. 151, figs.
1,2; Ibid., 20th Rept., 1867, p. 280.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 302.
Genoholotype. — Strophomena carinata Conrad
1839, 3d Ann. Rept., N. Y. Geol. Surv., p. 64.
In this family there is a single genus, Tropidoleptus,
which, because of its anomalous structure, has been
buffeted about between the Strophomenacea and the
Terebratellidas of the Terebratulacea. It is not the
purpose here to redescribe the anatomy of Tropidolep-
tus; this has been done very adequately by Hall and
by Hall and Clarke. It is our purpose, however, to
make some suggestions regarding the taxonomic posi-
tion of the genus. The anomaly in Tropidoleptus is
the early appearance of what looks like a terebratelli-
form loop, and this character has been taken by some
workers as proof of relationship with the Terebrat-
ellidae. It was early held that the Devonian genus
Tropidoleptus was the forerunner of the Terebrat-
ellidje, neglecting the fact that the latter division did
not appear till Mesozoic time, an enormous time
interval that in itself is strong evidence against any
relationship between the genus under discussion and
the Terebratellidse.
In the 1913 edition of Zittel-Eastman, Tropidolep-
tus was placed in association with the Strophomenacea,
GENERA OF THE SUBORDER ORTHOIDEA
153
where its position is equally anomalous with the one
described above. The presence of endopunctas at once
rules the genus out of the Strophomenacea (Kozlowski
having shown that the shell substance of the stropho-
menoids is impunctate), and there are therefore only
two possible places to put it, either in the Dalmanellacea
or in the Terebratulacea. It appears to us now, after
a long study of the orthoid genera, that the best — at
any rate, the least anomalous — position is in the Dal-
manellacea. We would place it here because of the
punctate shell, the open delthyrium, and the general
orthoid nature of the brachial processes, which was
suggested by Hall long ago. The endopunct.-c of
Trop'uioUptus are very similar to those of Dalmanella
and allies, but are not so close to those of the Tere-
bratulacea in pattern, the latter being much more
dense.
The structure of Tropidoleftus accords well with
that of the dalmaneUoids in having an open delthyrium,
a wide hinge-line, and an interarea on both valves.
In the dorsal valve there is a small chilidium such as
one finds in Heterorthis and other punctate genera.
The ventral musculature is suggestive of the orthids,
as Hall pointed out. In the dorsal valve the cardinal
process is bilobed but is not of the type common in
Strofhomena and allies, in which the lobes are usually
isolated. The teeth and sockets are grooved much as
in Parmorthis among the dalmaneUoids. The so called
loop is of course the most difficult structure to account
for. This in itself, however, does not have the appear-
ance of the true terebratelloid loop that grows out from
the septum and unites with the descending lamellae
of the crura; rather these processes are nothing other
than very long crura as in some Rhynchonellas, but
instead of remaining free they appear to unite with the
median septum. We hold that this type of arm sup-
port could have developed many times, instead of but
once. In conclusion, then, we believe that Tropi-
doleptus is a highly specialized and terminal dalman-
elloid of short geological life."
At present it is difficult to say definitely out of what
dalmaneUoids Tropidoleptus may have come, but we
suggest that it may have been out of the Parmorthis
stock.
PART V. THE GENERA OF THE SUBORDER PENTAMEROIDEA
Derived out of the Orthacea, the Pentameroidea
retain their impunctate tests, but most of them tend
with time to lose more and more of their transverse
shells with wide interareas and to become elongate and
subrostrate, smooth or costate, with well developed
spondylia and characteristic cardinalia. The delthy-
rium is usually open but may be modified by deltidia
or marginal thickenings.
The Pentameroidea begin in the Middle Cambrian
and die out with the Devonian. They include the
superfamilies Syntrophiacea Schuchert and Cooper and
Pentameracea Schuchert.
Superfamily SYNTROPHIACEA Schuchert and Cooper 1931
Specializing Protremata derived out of the Orthacea
(probably the ancestral stock of the Billingsellidas ) ,
developing a more or less lobate exterior, interiors with
either pseudospondylia or spondylia of the simplex type,
and occasionally cruralia. Cardinal process absent or
rudimentary. Delthyrium and notothyrium open.
Test fibrous, impunctate.
Geologic range. — Middle and Upper Cambrian,
Ozarkian, and Lower Ordovician.
Embraces the Clarkellidae, Syntrophiidx, and Huen-
ellid Huenella
SVNTROPHIIDiE
Syntrophioides
^ Syntrophia
Orthacea
(probably out of an early Middle Cam-
brian ancestor of the Billingsellidae)
GENERA OF THE SUBORDER PENTAMEROIDEA
155
Family CLARKELLID/E Schuchert and
Cooper 1931
Syntrophiacea, externally like Syntroph'ta and with
a sf)ondylium simplex or a pseudospondylium. In the
dorsal valve the brachiophore supports are divergent,
discrete plates. Ventral pallial markings as in
Billingselln.
Geologic range. — Middle Cambrian to Lower
Ordovician.
Embraces the following genera:
Syntrophioides Schuchert and Cooper
Syntrofhitut Ulrich
Clarkella Walcott
Yangtzeella Kolarova
Genus SYNTROPHIOIDES Schuchert and
Cooper 1931
PI. 15, figs. 20, 23
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 247.
Genoholotype. — Billingsella harlanensis Walcott
1905, Proc. U. S. Nat. Mus., vol. 28, p. 236; Camb.
Brach., 1912, p. 746, pi. 87, figs. 5-5d (as Wimanella
harlanensis) .
Description. Exterior. — Subelliptical to subsemi-
elliptical, hinge-line straight; cardinal extremities usu-
ally obtusely angular; lateral profile biconvex; an-
terior commissure uniplicate; dorsal fold not greatly
pronounced. Ventral interarea long, apsacline, del-
thyrium open ; surface marked only by fine, concentric
lines of growth. Test probably fibrous, impunctate.
Ventral interior. — Delthyrial cavity rather shallow,
dental plates in the type specimens not sharply marked ;
musculature clearly billingselloid, having a prominent
central adductor track which widens toward the front
and is cleft into halves by a low ridge; the front of
the adductor track elevated slightly. Diductor tracks
smaller than the adductor ones, rounded in front,
separated from the latter by low ridges. From the
anterior ends of the diductors two pairs of pallial
sinuses extend in an antero-lateral direction nearly
to the front border as in Billingsella.
Dorsal interior. — Notothyrial cavity shallow, brach-
iophore plates convergent and resting on the floor of
the valve ( ? ) ; musculature prominent, posterior ad-
ductors larger than the anterior pair, suboval in out-
line; anterior pair about half the size of the posterior
one. Two pallial sinuses have their origin at the point
of contact with the posterior adductors in the mid-line
of the shell and are separated by a slight median eleva-
tion. They extend in this closely appressed condition
as far as the front margins of the anterior adductors.
where they branch abruptly toward the antero-lateral
margins.
Geologic range. — Middle Cambrian of Tennes-
see with Billingsella (or Wimanella) harlanensis Wal-
cott and ? B. (or W. ) saffordi Walcott.
Discussion. — This genus is readily separated from
Billingsella by its concentrically marked surface, syn-
trophiid form, and dorsal musculature. B. harlanensis
was placed in Wimanella by Walcott because of its
smooth shell, but since that genus appears to have a
costellate surface, the species under consideration can
not be left there.
The dorsal musculature of Syntrophioides is well
defined and strongly suggests that seen in Syntrophina
and Clarkella, representing a divergence probably out
of some ancestor of the Billingsellidas of the early
Middle Cambrian. In these circumstances we see how
the slight generic differences in these early Cambrian
forms may have given rise to later independent families
and even superfamilies.
Genus SYNTROPHINA Ulrich 1928
PI. 15, figs. 1, 2, 15-19, 30,31
Ulrich in Weller and St. Clair, Missouri Bur. Geol. Mines,
2d ser., vol. 22, 1928, p. 74 (without description).
Genoholotype. — Syntrophia campbelli Walcott
1912, Camb. Brach., pp. 801-802, t. figs. 73A-F.
Description. Exterior. — Subelliptical, hinge-line
narrower than the greatest width of the shell ; cardinal
extremities rounded. Lateral profile strongly bicon-
vex; ventral valve deeply sulcata, dorsal valve with a
prominent fold; anterior commissure uniplicate. Ven-
tral palintrope short, apsacline; delthyrium open.
Dorsal interarea shorter than the ventral, apsacline to
anacline; notothyrium open. Surface marked only
by fine concentric lines of growth. Test fibrous,
impunctate.
Ventral interior. — Delthyrial cavity deep, teeth
strong, dental plates convergent, forming a true spon-
dylium simplex. Muscle impressions borne on the
upper surface of the spondylium; diductor marks on
the sides and floor of the spondylium at the back;
adductor impressions (?) in front of the diductor scars
at the narrow end of the spondylium. Pedicle callist
at the posterior. Pallial marks two broad trunks ex-
tending antero-laterally from beneath the spondylium.
Umbonal cavities and umbo-lateral spaces marked by
low radial ridges. Complete or incomplete accessory
septa occur in the vicinity of the spondylium in some
specimens and show a convergence toward Clarkella.
Dorsal interior. — Notothyrial cavity deep, brachio-
phores long, brachiophore supports divergent, extend-
ing to the floor of the valve. Cardinal process rudi-
mentary, elevated on a narrow shelf at the posterior
of the notothyrial cavity. Posterior adductor scars the
156
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
larger, situated a little outside the anterior pair. A
prominent pallia! sinus extends antero-laterally from
the anterior end of each adductor muscle impression.
Geologic range. — Upper Cambrian to Lower
Ordovician of North America.
American Species
Syntrofhina 3 n. spp. (Ulrich Coll.)
Syntrofhia cam f belli Walcott 1908
S.isis Walcott 1924
S. nuniina Walcott 1905
S. fdmata Cleland 1900
S.ferilla Walcott 1924
S. rotundata Walcott 1905
? Triflesia ■primordialis Whitfield 1877
Distinguishing characters. — Syntrophina may
be recognized by its external resemblance to Syntro-
fhia and by the presence of a ventral spondylium, but
differs in having two dorsal divergent brachiophore
supports and consequently no cruralium simplex.
Discussion. — Interesting features of this genus are
the well defined muscle marks on the dorsal side of the
spondylium, the peculiar shelf at the posterior of the
notothyrial cavity, and the dorsal muscle and pallial
marks. Internal molds from Phillipsburg, Quebec,
preserving the spondylia, show on them a median ridge
toward the anterior, which widens and becomes some-
what more elevated, terminating at the back end of
the median septum. This anterior ridge or elevation
may represent the impression of a deeply sunk adductor
track. Behind the "adductor track," and surrounding
it partially, are the probable impressions of the diductor
muscles on the floor and sides of the spondylium (see
pi. 15, fig. 15). The correct identification of these
muscle marks is attended with some difficulty, but the
suggested arrangement would be in accord with the
mechanics of opening or closing a brachiopod shell and
would homologize with the same marks seen in valves
not provided with a spondylium.
In the dorsal valve the brachiophores project for
some distance into the valve and are supported by stout
plates which show as subparallel or slightly divergent
slots on internal molds (see pi. 15, figs. 2, 17, 19, 30).
These plates form the lateral walls of a deep notothy-
rial cavity, which has at the back end a low shelf built
on the sides of the brachiophore supports and the pos-
terior slope of the notothyrial depression. In the mid-
line of the valve and the shelf at its back end there is
in some specimens a low median elevation, interpreted
as the cardinal process (pi. 15, figs. 30, 31). This
shelf and the cardinal process probably mark the seat
of attachment of the diductor muscles.
The adductor muscle scars are thickened at their
front ends and give off broad pallial sinuses that ex-
tend toward the antero-lateral extremities of the valve.
The musculature of Syntrophina strongly resembles
that of Syntrophioides and Finkelnburgia.
The genus Syntrophina has a long series of species
(mostly undescribed) continuous from the Upper
Cambrian into the Lower Ordovician. So far as
known there are no Syntrophia s. s. in the Cambrian
or Ozarkian. It is true that Walcott considered
S. rotundata as the Cambrian representative of Syn-
trophia, but this appears not to be correct, since the
type specimens in the United States National Museum
have the characters of Syntrophina. The reference of
the species to Syntrophia is due to Walcott's mistaking
a ventral valve for a dorsal, thereby giving the essential
structure of Syntrophia. Other specimens in the same
lot (Cat. No. 52493), however, have the features of
Syntrophina.
Ulrich's new genus Syntrophinella, as yet unde-
scribed, is internally like Syntrophina but is multi-
costellate externally. Its genotype is S. typica, n. sp.,
illustrated on our plate 15, figures 4, 5, 13.
Genus CLARKELLA Walcott 1908
Pi. 15, figs. 6-11
Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 110;
Camb. Brach., 1912, p. 809, pi. 104, figs. 2-2d.
Genoholotype. — Polytaechia ? montanensis Wal-
cott 1905, Proc. U. S. Nat. Mus., vol. 28, p. 295.
Description. Exterior. — Like Syntrophia, with
a prominent fold and sulcus. Test fibrous, impunctate.
Ventral interior. — There is a spondylium simplex
but in some species it is supported by two or more
lateral accessory septa. Two strong divergent pallial
sinuses extend antero-laterally from the umbonal
cavities.
Dorsal interior. — Essentially like that of Syntro-
phina, but there are accessory lateral septa, at most
two in number, which are united with the descending
brachiophore supports. There are six pallial sinuses
radiating from the umbonal cavities and in front of
the muscle area.
Geologic range. — Upper Cambrian (Ozarkian).
American Species
Polytaechia montanensis Walcott 1905
Syntrofhia nanus Walcott 1924
Distinguishing characters. — The character
which gives Clarkella generic standing is the structure
of the cardinalia with its prominent accessory plates.
Discussion. — In the original definition of the genus,
Walcott described spondylia in both valves, supported
by accessory septa. This structure can not be ques-
tioned in the ventral valve, since there is here a spon-
dylium simplex supported by a stout median septum
and two or more accessory septa. The latter are, how-
ever, not universally present, being lacking in S. nonus
GENERA OF THE SUBORDER PENTAMEROIDEA
157
(Walcott). In the dorsal valve there is no cruralium
as Walcott has described and illustrated. Instead of
there being a continuous spoon-shaped plate supported
by lateral septa, there are two plates beneath the
brachiophores which converge medially but never unite.
Each plate is supported by two or more septa, the usual
number being two, one inner and one outer (see pi. 15,
figs. 7, 10).
CLirkella is evidently very closely related to Syntro-
fhina and is characteristic of the Ozarkian. It is
widely distributed geographically, being known from
Montana, British Columbia, and Phillipsburg, Quebec.
plex which is supported for nearly its entire length by
a septum which is short and thick; septum extending
for half the length of the valve. There are accessory
lateral septa up to four in number aiding in the
support of the spondylium. Between these are other
low radial ridges.
Dorsal interior. — Notothyrial cavity deep; sockets
deep, at the posterior the brachiophore plates form a
small, deep, spoon-shaped muscle platform supported
at the back by one or two pairs of lateral septa. After
a short distance the platform, which is evidently for the
attachment of the diductors, ends, but the two lateral
«>
I
Fig. 22. — Yangtzedla foloi (Martelli). Serial sections through the beak of a mature shell. The internal structure
allies this genus with Clarkella Walcott and proves conclusively that it has no relationships with Triflesia. The stippled areas
indicate adventitious shell substance which fills the umbonal chambers of both beaks. Such a filling is common in many
genera of spondylium-bearing shells. The shell sectioned was 19.3 mm. in length. All structures disappeared 8.5 mm.
from the beak. Distances from beak:
1 — 1.4 mm.
2—2.5
3—3.2
4 — 4.5
5 — 5.8 mm.
6 — 6.8
7—7.3
Genus YANGTZEELLA Kolarova 1925
PI. 15, figs. 24-26; t. figs. 22, 23
Kolarova, Bull. Geol. Soc. China, vol. 4, 1925, p. 219,
pi. l,t. fig. 1.
Genoholotype. — Triflecia foloi Martelli 1901,
Bull. Soc. Geol. Ital., vol. 20, fasc. 1, pp. 302-304,
pi. 4, figs. 13-22.
Description. Exterior. — Outline subquadrate,
hinge-line straight, narrower than the total width of
the shell ; cardinal extremities rounded ; lateral profile
biconvex, the dorsal valve having the greater con-
vexity. Anterior commissure uniplicate ; ventral sul-
cus very deep, defined only on the front half of the
shell; dorsal fold pronounced only in the anterior
area. Ventral interarea longer than the dorsal, apsa-
cline; beak curved slightly and may or may not be
resorbed by pedicle pressure; delthyrium open. Dorsal
interarea curved, apsacline, beak strongly curved, umbo
inflated, notothyrium open. Surface nearly smooth,
marked by concentric growth-lines and distant lam-
ellae, and by faint radiating ridges. Test fibrous,
impunctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong ; dental plates thick, forming a spondylium sim-
septa persist, each bearing a laterally directed shelf and
a rather long brachial process.
Geologic range. — The only known species is
y. foloi (Martelli) of the ? Lower Ordovician of
China.
Distinguishing characters. — The chief diag-
nostic characters of Yangtzeella are its nearly smooth
exterior, Triflesia-hke or syntrophioid outline and pro-
file, ventral spondylium simplex which may be sup-
ported by two or four accessory lateral septa, and in
the dorsal valve a spoon-shaped plate supported by two
primary lateral and two accessory lateral septa. It is
impossible to say whether or not this plate bore muscles.
Discussion. — Yangtzeella shows several interesting
features. One of these is the great amount of adven-
titious shell substance deposited in the umbonal cavities
of the valves, chiefly in the ventral one. In Kolarova's
sections (his pi. 1, figs. 2-6) the ventral shell for about
3 mm. from the beak is wholly test, and the same is
true of the Yale specimens for 2.8 mm. from the
beak. However, the septa show clearly in the .idventi-
tious substance so that none of the shell anatomy is
obscured in the sections.
The supporting plate beneath the ventral spondylium
is commonly split or fractured so that it appears to be
a duplex septum, and yet it is not precisely like the
158
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
duplex septum of Pentamerus, but is single as in Ck-
tambonites or Vellamo, which occasionally also have
the septum fractured medially. The spondylium is
supported for practically its whole length and there are
generally two lateral septa as in some species of Clark-
ella. At its front end the spondylium hangs free of the
septum, which is prolonged forward as a ridge on the
floor of the valve. Between the main septa on the
floor of the valve are numerous accessory radiating
ridges, such as are common in Syntrofhina and Clark-
ella. These radiate from each of the umbonal cavi-
ties, the larger ones forming the septa. They are
interpreted by Kolarova as ridges or septa between the
diductor muscles. According to our view, they are
Fig. 23. — Yangtzeella foloi (Martelli). Section cut
through an adult specimen, showing septa of both valves
and notothyrial chamber of the dorsal valve, x about 4.
for attachment of the ovarian bodies, and so far as our
knowledge goes, the ventral muscle marks in spon-
dylium-bearing shells are always located on the upper
or dorsal surface of the spondylium, and such shells
never have additional muscle-scars on the valve floor.
Low ridges upon the spondylium of Yangtxeella sug-
gest that the muscles here were also attached to the
upper surface of the spondylium.
The dorsal valve is especially interesting and quite
unlike any other brachiopod except Clarkella. There
is a narrow, spoonlike platform supported by two
lateral septa, and two or more accessory ones. After
about 3.5 mm. in a specimen 20 mm. long, the spoon
terminates, but the lateral septa persist and are overlain
by horizontal plates or shelves that may or may not be
supported by septa. The brachiophores consist of
rather long processes extending into the valve from
the extremity of the brachiophore plates, as in
Syntrofhina.
This shell was originally referred to Triflesia and in
the 1929 classification of Schuchert was placed in asso-
ciation with this and allied genera. Yangtxeella, how-
ever, has no forked cardinal process, and besides, the
presence of a spondylium and cardinalia like those of
Clarkella shows that it belongs with the Syntrophiidae,
where Miss Muir-Wood placed it.^ It is closest to
Clarkella in a broad sense, having many septa in each
valve. However, Clarkella does not have a spoon-
shaped dorsal plate or lateral processes such as occur in
Yangtzeella.
Family SYNTROPHIID^ Schuchert 1896
Smooth biconvex Syntrophiacea having well devel-
oped interareas, a spondylium simplex, and a cruralium
simplex.
Geologic range. — Lower Ordovician.
Embraces but one genus, Syntrofhia Hall and
Clarke. Walcott has referred to this family his
Swantonia, a genus whose taxonomic position is wholly
unknown, but we leave it here as we are not able to
place it.
Genus SYNTROPHIA Hall and Clarke 1891
PI. 15, figs. 3, 27-29, 32
Hall and Clarke, Pal. N. Y., vol. 8, pt. I, 1891, p. 270;
pt. 2, 1893, p. 216, pi. 62, figs. 1-10.
Genoholotype. — Triflesia lateralis Whitfield
1886, Bull. Amer. Mus. Nat. Hist., vol. 1, no. 8, p.
303, pi. 24, figs. 9-11.
Description. Exterior. — Transversely oval, hinge-
line narrower than the greatest width, cardinal ex-
tremities obtuse; lateral profile biconvex; anterior
commissure unipHcate; fold and sulcus usually shal-
low; areas on both valves; ventral interarea apsa-
cline, delthyrium open; dorsal interarea anacline,
notothyrium open. Surface marked only by fine con-
centric lines of growth. Test fibrous, impunctate.
Ventral interior. — "Teeth small" ; dental plates
uniting with a median septum to form a spondylium
simplex that is free at its anterior end. Muscle con-
fined to the spondylium.
Dorsal interior. — Much like the ventral, the brach-
iophore supports converging and uniting with a
median septum to form a cruralium. Pallial trunks
radiating from the muscle area as in Syntrofhina.
Geologic range. — The only known species is the
genotype, which comes from the Lower Ordovician
(upper Beekmantown) of Vermont.
Distinguishing characters. — The presence of a
spondylium and a cruralium is the chief distinguishing
feature.
Discussion. — When Hall and Clarke based Syn-
trofhia on Triflesia lateralis, they were struck most by
the external form and the presence of a spondylium.
>Zool. Record, 1926.
GENERA OF THE SUBORDER PENTAMEROIDEA
159
For these reasons they included in the genus many
similar species, making, as we now see, a rather hetef-
ogeneous lot of shells. Since Triplesui lateralis is the
genotype, the name must be based upon it, and as so
restricted, all of the other species formerly placed here
must be taken out of the genus.
Specimens of Syntrophui are exceedingly rare and
none were available to us for sectioning. It is therefore
not known with certainty whether the genus possessed
a spondylium simplex or one of the duplex type.
Polished specimens in the National Museum at Wash-
ington do not show a suture line in the septum of the
spondylium, hence the presumption is that the latter
was of the simplex type,
? Genus SWANTONIA Walcott 1905
Walcott, Proc. U.
Camb. Brach.
S. Nat. Mus., vol. 28, 1905, p. 296;
1912, p. 796, pi. 104, figs. 5-5b.
Genoholotype. — Camerella antiquata Billings
1861, Pal. Foss., vol. 1, pp. 10-11, fig. 13.
Description. Exterior. — The species and genus
are based on a single ventral valve. Shell ovate, mod-
erately convex, subrostrate, with a shallow sulcus
toward the front; multicostate (8-12 costs). Inter-
area narrow and long; delthyrium open; teeth rudi-
mentary, muscle-scars not preserved.
Geologic range. — Lower Cambrian of Swanton,
Vermont (S. antiquata (Billings) 1861) and Nevada
{S. weeksi Wz\coK 1905).
Discussion. — There is some superficial resemblance
here to Camerella, but the internal structure is very
different. According to Walcott, S. antiquata has a
"narrow, strong, concave shelf or area; the area or
shelf is free from contact with the bottom of the
valve, a recess or chamber existing beneath it." This
feature he has taken to indicate a free spondylium, but
the presence of such a structure may be questioned.
The specimen is preserved as a mold of the interior.
In the vicinity of the beak the specimen is indented
on each side, the indentation representing the position
of the lateral interareas. Immediately under the beak,
however, there is no excavation such as would be ex-
pected if there were a free spondylium, and the internal
mold is united to the matrix rock just as if there were
an open delthyrium now filled up. Were it not for
the strong costje on the outside of the shell, the posi-
tion of Swantonia among articulate brachiopods might
be questioned.
Swantonia therefore appears to be a narrow-hinged
form without a spondylium, but its family position can
not at present be determined, especially in the absence
of any knowledge of the dorsal valve. S. weeksi is
also based on a single ventral valve, and shows external
characters only. However, as Walcott referred the
genus to the Syntrophiida:, we will leave it here
provisionally.
Family HUENELLID^ Schuchert and
Cooper 1931
Syntrophiacea externally like Syntrofhia but costate
or costcllatc. Ventral valve with a pseudospondylium ;
dorsal brachiophore plates discrete, subparallel.
Geologic range. — Upper Cambrian and Ozar-
kian.
Embraces but two genera, Huenella Walcott and
Huenellina Schuchert and Cooper.
Genus HUENELLA Walcott 1908
T. fig. 24
Walcott, Smiths. Misc. Coll., vol. 53, 1908, p. 109;
Camb. Brach., 1912, p. 804, pi. 103, figs. 1-li.
Genoholotype. — Syntrofhia iexana Walcott
1905, Proc. U. S. Nat. Mus., vol. 28, p. 294.
Description. Exterior. — Subelliptical in outline;
hinge-line straight, always narrower than the total
width of the valves; cardinal extremities rounded.
Lateral profile biconvex. Anterior commissure unipli-
cate; dorsal fold broad in front, prominent; sulcus
deep. Ventral interarea longer than the dorsal, apsa-
cline, delthyrium open ; dorsal interarea anacline, noto-
thyrium open. Surface costate or costellate, especially
toward the front. Test fibrous (?), impunctate.
Ventral interior. — Delthyrial cavity deep ; teeth
strong and somewhat elongate; dental plates well
developed, converging to the floor of the valve to form
a pseudospondylium which bears the muscle-scars.
Two broad paUial trunks diverge antero-laterally from
either side of the pseudospondylium and follow the
shell sulci nearly to the front margin.
Dorsal interior. — Notothyrial cavity deep; brachio-
phore supports short, convergent, but cemented directly
to the floor of the valve. At the anterior they are
extended forward and laterally as low ridges which
separate the anterior from the posterior adductor scars.
Cardinal process simple, very faintly visible or absent.
Adductor impressions elongate, tear-shaped or oval,
directed antero-laterally. A pallial sinus is given off
from the anterior extremity of each adductor impres-
sion. The inner trunks extend along the margins of
the sulcus, while the outside trunks pass .ilong the
anterior portion of the lateral lobes.
Geologic range. — Upper Cambrian and Ozar-
kian of North America.
Species
Costate section
Huenella ainormis {W ikon) 1905
H.iillingii (Walcott) 1905
//. A^rj Walcott 1924
H. Iexana (Wilcon) 1905
H.texanalttviusculus iyizXcoxx) 1905
160
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Costellate section
H.ic etas 'Wilcott 1924
H.juba Wilcott 192+
H. lesleyi Wilcoti 1908
? H.simonW Aeon 1924
? H. vermontana Walcott 1912
f H.weedi^i\co\X 1924
? Hebertella battis (Billings) 1 865
Distinguishing characters. — Huenella is recog-
nized most readily by its syntrophinoid outline and
profile, costate or costellate exterior, pseudospon-
dylium, convergent brachiophore supports, and dorsal
musculature.
Fig. 24. — a-c, Huenella abnormis (Walcott). a, ventral
internal mold, showing muscular impressions on the imprint
of the spondylium. b, c, dorsal internal mold and interior,
showing musculature and brachiophore plates {brf). ov,
ovarian impressions (mistaken by Walcott for muscle
marks); di, diductor impressions; ad, adductor impres-
sions; Ps, pallial sinus.
d, e, H. texana (Walcott), ventral and dorsal exteriors,
showing coarse ribbing and strong fold and sulcus.
After Walcott 1912, pi. 103.
Discussion. — Huenella differs from Syntropkia and
Syntrofkina not only in the external costation but also
in internal characters. Internally there is a pseudo-
spondylium bearing the muscle impressions; at the
front it is elevated slightly on a prominent thickening
of secondary shell. From the musculature of H. ab-
normis the myology of this genus would appear to be
essentially the same as that of Syntrofhina. However,
the diductor and adductor scars are not flabellate im-
pressions outside the pallial trunks as Walcott describes
and figures in that species (1912, p. 806, pi. 103,
fig. 2b). As he figures these impressions, the adductor
scars are posterior to the diductors; their position and
arrangement are accordingly unlike the ventral mus-
culature of any other known brachiopod. Walcott has
evidently mistaken impressions that are in the position
of, and are usually considered to be, ovarian impres-
sions. Furthermore, in the same figure the muscula-
ture is shown clearly on the floor of the pseudospon-
dylium and is essentially the same as that which is seen
commonly in Syntrofhina.
This genus as now constituted may be divided into
two groups on the basis of the external ornamentation,
as shown above.
H. Simon and H. weedi, according to their external
form and sculpture, suggest affinities with Billingsella
rather than with Huenella.
Genus HUENELLINA Schuchert and Cooper
1931
PL 15, figs. 14, 21, 22
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 247.
Genoholotype. — Huenella triflicata Walcott
1924, Smiths. Misc. Coll., vol. 67, no. 9, p. 526,
pi. 125, figs. 1-15.
Description. Exterior. — Externally much like
Platystrofhia, being strongly sulcate and costate.
Hinge-line shorter than the greatest width of the shell,
and interareas well developed on both valves. Del-
thyrium and notothyrium open.
Ventral interior. — Delthyrial cavity deep, teeth
strong and long, with well defined crural fossettes;
dental plates strong; pseudospondylium scarcely ele-
vated in front. Adductor impression subcircular, di-
ductor scars indefinite. Umbo-lateral spaces marked by
elevated subradial ridges.
Dorsal interior. — Notothyrial cavity deep, brachio-
phores long, curved slightly; brachiophore supports
prominent, curved, and extending directly to the floor
of the valve; cardinal process rudimentary or absent.
Attached to the outside of the brachiophores and the
lower (anterior) side of the palintrope is a lateral
septum which extends obliquely toward the lateral
margins.
Geologic range. — Upper Cambrian (Ozarkian)
of Novaya Zemlya, Arctic Russia. The only known
form is H. triflicata (Walcott).
Discussion. — The main distinction between this
genus and Huenella is to be found in the lateral septa
developed under the anterior part of the dorsal palin-
trope. There is nothing among the Cambrian brach-
iopods exactly like this feature and it is diflBcult to
understand what purpose it could have served other
GENERA OF THE SUBORDER PENTAMEROIDEA
161
than additional strengthening of the palintropc. The
brachiophore supporting plates are well developed, dis-
crete, and convergent toward the floor of the valve,
defining a rather deep notothyrial cavity. The brach-
iophores, judging by internal molds, were long, slender
processes extending from the point of union of the
accessory septal plate and the palintrope.
In the ventral valve a feature of particular interest
is the shallow pit at the front end of the pseudospon-
dylium. Such a pit also occurs in Syntrophina, and is in
exactly the same position as the anterior adductor scar
in Billingsella. Behind this pit can be seen the central
adductor track and on each side of this, impressions
which are regarded as diductor scars. This antero-
central pit may represent the final place of the adductor
scar in its forward migration during growth.
Superfamily PENTAMERACEA Schuchert 1896
Specializing Protremata probably originating in the
Syntrophiacea (family Syntrophiidse ) , characterized by
spondylia that in the primitive families are nearly
always supported by single septa (^^ spondylium sim-
plex) and in the derived families by double septa
(coalesced septal plates = spondylium duplex), but in
rare instances in any of the families may hang free
TabU 17
Pentameridx
-^Stricklandidae
Camerellidae
Syntrophiidx
or posteriorly supported by a remnant of the septum.
The more important family characters occur in the
dorsal cardinalia, which may be discrete or medially
coalesced into a cruralium that bears the adductor mus-
cles. Cardinal process usually absent, or rudimentary
as a linear ridge or slight boss. Rudimentary or modi-
fied remnants of the deltidium occur rarely, and chilidia
never. Shells narrow-hinged, with small interareas,
or decidedly rostrate with plane areas; exterior smooth,
costate or multicostate. Test fibrous, and, so far as
known, without endopunctje.
Geologic range. — Middle Ordovician to close of
Devonian.
Embraces the following families:
Camerellidae Hall and Clarke
Pentamerida; McCoy
? Stricklandidjc Hall and Clarke
The genetic relationships appear to be as shown in
Table 17.
After completing their survey of the great group of
orthids, the writers turned naturally and logically to a
study of the Pentameracea. They had embarked on
this course and carried on their research for about six
weeks when it was interrupted by the removal of the
junior author to Washington. This had at once dis-
advantages and advantages. At Washington it was
possible to add observations on the strnnge genera
Brooksina and Harpidium and on the even more
aberrant Cymbidium. In the National Museum col-
lections also are some fine specimens of Orthotropia
which show the necessity for removal of this genus to
the Dalmanellacea near Linoporella.
As the presentation of the pentamerids now stands,
it represents a survey of two of the finest collections
of these shells in this country. However, the work
can not be considered as final. In any study such as
this, in which the elucidation of internal details depends
on the destruction of materials, it would have been
desirable to have still more specimens. As an example
of this need it might be stated that, in all of the speci-
mens of Pentamerus studied, we did not find a single
example which retained a deltidium, yet Hall and
Clarke reported such a structure. Furthermore,
where there was abundance of common species, the
rarer forms were represented in each collection by
one or two specimens which could not be sacrificed to
serial sectioning. Therefore much remains still to be
done. We have, however, seen, and in the majority
of cases sectioned, specimens representing the genotype
of nearly all the pentamerid genera. If nothing else,
the study strives to make clear exactly what each genus
is, and, as far as possible, to eliminate from each the
non-typical species. It has therefore been necessary to
create a few new genera. Besides Orthotropia, the
probability is that Str'icklandla will eventually have to
be removed from its honored place among the pentam-
erids. On the other hand, as we have shown on earlier
pages, the Porambonitid.'c belong with the Orthacea.
The old family Pentamerid.-c is, however, now divided
into three, the Camerellida;, Stricklandidas, and the
very varied Pentameridae, on the basis of certain in-
ternal characteristics. Recent studies by Kozlowski
have shown that the Camerophoriidae are spondylia-
bearing Rhynchonellacea.
162
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
TECHNIQUE
During the progress of this work, the junior author
has improved the old Zugmayer process of serial sec-
tioning so as to leave a remainder of the specimen,
and this is highly advantageous. Serial sectioning
has heretofore resulted in total destruction of the speci-
men, or in the destruction of so much of it that the
remainder was worthless. In our work we have fol-
lowed the course described below: Before sectioning,
the specimen is measured by micrometer. Sectioning
proceeds slowly, the structures being sketched at inter-
vals with the aid of a camera lucida, thus showing the
significant changes in spondylia, septa, and cardinalia.
This procedure is continued until that plane is reached
where the ventral teeth can be seen inserted in the
sockets of the dorsal valve. The specimen is then
cemented by balsam to a glass slide and the whole
measured. Sectioning is now resumed from the an-
terior end of the shell and continued until the internal
lamellae begin to appear. The specimen is measured,
the shell structures sketched, and this procedure fol-
lowed until the section is too thin to grind further,
when it is covered by a glass slip. In this way at least
a thin section of the specimen remains to form a record.
In sectioning from the anterior end, the distance from
the plane where internal structures first appear must
be added to the length from the beak to the plane of
articulation; addition of the thickness of the thin
slice representing the distance from the last plane of
the anterior sections to the plane of the articulation
must also be made.
In work demanding the sectioning of brachiopod
material it is desirable that a replica of the specimen
first be made, then the original should be photographed
for dorsal, ventral, lateral, anterior, and posterior
views, and these photographs should be reproduced
along with those of the other type material.
MORPHOLOGY
OF THE PENTAMERACEA
The pentamerid is a rather distinctive shell, easily
recognized by its usually strongly biconvex valves and
its spondylium duplex and elongate median septa in
both valves. It was formerly the practice of most
writers to place nearly all of the spondylium-bearing
shells among the Pentameracea, but recent advances in
brachiopod studies, and especially those of Kozlowski,
have shown that the spondylium is a rather common
structure developed independently and in different
ways in many stocks. For example, such an unmis-
takable orthid as Enteletes has been shown by
Likharev" to have developed a spondyhum in its altera-
tion to Enteletella. Among the punctate spiriferids,
- BuU. Com. Geol., vol. 45, no. 6, 1924, pp. 720-721.
Cyrt'ina has a spondylium, and among the terebratulids
Amfhigenia may be cited. No one would now consent
to the union of these genera to the Pentameracea.
Although the spondylium is of itself not a distinctive
feature of this group of shells, it is, in combination with
certain dorsal structures, a rather important additional
character. Considering the Pentameridas as a whole,
there is a distinctive tripartite division of the dorsal
septa which is characteristic of the family and appears
to be its most important taxonomic feature. The
family Camerellidas does not accord with the charac-
teristic pentameroid dorsal structure and it is for this
reason that we have given it family rank. It has
singular resemblances to the Syntrophiidas and when
material is at hand showing in detail the pallial mark-
ings of the Camerellidas, it may be necessary to make
still other family arrangements than those offered in
this book. Such material, in the form of internal
molds, is singularly lacking in both the collections
studied.
We again find among the Pentameracea, as we did
among the Orthacea and Dalmanellacea, that dorsal
structures are most diagnostic of family and mutual
relationships.
The following discussion is designed to summarize
the significant points of pentamerid anatomy.
Exterior. — There are several features of the ex-
terior of the pentamerid shell that are of some interest:
1. V entricos'tty . — Among the Camerellidas none of
the shells are flattish but all are rather globular and
the valves strongly gibbous. The Pentamerida;, on
the other hand, have a number of stocks that are
rather flattish but may have developed gibbous stocks
as offshoots. Such, for example, is the development
of the subcylindrical Pentamerus from the rather flat-
tish P. oblongus. C onchidium is evidently a strongly
gibbous stock from the start and it is difficult to ascer-
tain its ancestry; the best suggestion appears to be
that it came out of Clorinda or Barrandella. In the
Gypidulinas nearly all the genera have at least one
valve strongly arched.
2. Ornamentation. — It is at present difficult to
say whether the first of the pentamerids was smooth,
or ribbed as is known to be the case among the orthids.
In the Camerellidas the species of the primitive genus
Camerella are partially smooth and partially ribbed.
It would appear safe to say that this stock started from
a smooth one like the syntrophiids and subsequently
became anteriorly ribbed, since the culminating genus
of the family, Anastrofhia, is the most strongly costate
member.
In the Pentamerinje, on the other hand, the problem
is not so easy, since the ribbed and the smooth stocks
appear nearly simultaneously, or, as seen from present
knowledge, the ribbed stocks have a httle the better
of it from the point of view of time. Among the
Gypidulinas — Barrandella, Clorinda, Gyfidula, and
GENER.\ OF THE SUBORDER PENTAMEROIDEA
163
Siehrrella — smooth and costate stocks are essentially
contemporaneous, although in America the Harrand-
ellas and Clorindas evidently appear first, in the Brass-
field formation. With the Pcntamcrina; the first to
appear is Plotymerella (Brassfield-Alexandrian). It
may be the forerunner of Pentamerus, since the latter
nearly always shows broad radial costs, but whether
these represent secondary dying out of stronger costa-
tion or incipient development of the same is not known.
Conch'uiium was evidently always costate but may
have given rise to two secondarily smooth genera.
3. Interareas. — It has been the common belief
among paleontologists that the pentamerids have lost
their interareas. This is certainly in part true. The
reduction of the interareas, and their subsequent loss
in a few stocks, are consequent upon the narrowing of
the hinge-line and the development of rostration. It is
very possible that this rostration has gone hand-in-hand
Fig. 25. — Conchidium biloculare (Linnseus), from Klin-
tehamn, Gotland. Section showing unusual deltidial cover
of ventral valve. See pi. 29, fig. 4. The whole ventral
interior, except for the two roughly oval areas on either
side of the spondylium, is filled with adventitious shell,
represented by the stippled portions.
with the elongation and narrowing of the spondylium
in the Pentamerinae in order to produce more surface
for attachment of the diductor muscles. In the
Gypidulinae, where the spondylium has not been so
pronouncedly narrowed, there are usually preserved
well marked remnants of the interareas. This is par-
ticularly true of Sieberella.
Another feature of pentamerid shells in the vicinity
of the beaks is the production of prominent flattened
areas which greatly simulate an interarea. This fea-
ture is perhaps most strongly developed in Brooksina
which has practically no interarea but has a broad flat
region that extends from the beaks of both valves to
the point of contact of the ribbed portions. These
false cardinal areas are best developed in that genus and
in Capellinirlla, both groups having the convexity of
the valves reversed from the normal, and there may
be some mechanical connection between the two
phenomena.
Ventral interior. — Important features of the
ventral valve are the delthyrium and its accessories, the
deltidial cover and deltitidal plates, and the spondylium
and its supporting septum.
/. Delthyrium. — So far as our observations have
extended, the delthyrium of the Camerellida: is open
except for marginal thickenings along the dclthyrial
border, alluded to below. No deltidial cover such as
occurs in Conchidium has been seen.
2. Deltidial cover. — In Conchidium there is a truly
remarkable cover to the delthyrium which we hesitate
to call a deltidium, preferring the more non-committal
term deltidial cover. As commonly described, this has
been termed a "concave deltidium." Our investiga-
tions show that this structure is concave toward the
anterior portion of the delthyrium, but when followed
to the vicinity of the beak it rises above the margins
of the delthyrium and projects dorsally in the form of
a sheath with rather rectangular sides and depressed
center. A similar structure exists in one specimen of
Harpdium, but was erroneously described as convex
deltidial plates. These two occurrences are the only
ones noted by us in which there is a cover plate over
the delthyrium. A concave "deltidium," presumably
like the above, has been reported in Pentamerus but
we have not seen such. The structure in Conchidium
appears to be a pedicle sheath ; it is not known definitely
whether it had an open foramen at the apex, but it
appears to have had one. In the specimen of Harpid-
ium preserving the deltidial cover the beak is crushed
down on the cover so that its precise structure can not
be determined. Parenthetically it may be added that
among the orthids and strophomenids no such cover
as this has been observed.
3. Deltidial plates. — Hall and Clarke announced
the presence of deltidial plates in several genera studied
by them and even went so far as to use these struc-
tures as one of the generic distinctions between
Gypidula and Sieberella. The present writers have
not observed in any of the pentamerids that have come
under their observation any clearly developed, typical
deltidial plates. We have seen thickenings along the
delthyrial margins of many of the genera, and such
structures as these were termed "pscudo-deltidial
plates" by Booker."' These thickenings, in our ex-
perience, never restrict the delthyrium in any notable
degree, certainly not nearly so noticeably as do similar
thickenings in Glossorthis, Hesperorthis, and other
orthid genera. Similar structures were observed also
in specimens of Conchidium that have the deltidial
cover as well. It therefore appears to us that they are
of little taxonomic significance, certainly not sufficiently
important to warrant the removal of the Pentameracea
(restricted) to the Telotremata, as Kozlowski has
done.
' Booker, Jour. Proc. Roy. Soc. N. S. Wales, vol. 60,
1927, p. 134.
164
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
4. Sfondylium. — The spondylium is an important
feature of the pentamerids. It is always of the duplex
type as described by Kozlowski, in which the septum
is composed of two closely apposed pieces.
One tendency among the pentamerids, achieved in
only two instances, is the reduction of the septum and
the elongation of the spondyhum. In extremely ven-
tricose forms the rostral chamber is elongated and
narrowed, so much so in some species that the sides
are only a couple of millimeters apart. This elongation
and narrowing of the spondylium is evidently for
greater surficial spreading of the diductor muscles, per-
mitting a strong pull without a breaking strain on the
sides of the muscle platform.
4. Supporting plates consist of two subparallel
septa extending from the middle of the valve and unit-
ing with the inner, convex surfaces of the alar processes.
It is clear that the function of these plates is to support
and make rigid the rest of the cardinalia. In Camer-
ella the supporting plates converge inward and unite
with a septum.
Musculature. — Of great interest among the Camer-
eUidae is the position of the dorsal adductor scars in
front of the cruralium in Camerella and forward of
the parallel plates in Par astro fhinella and Anastrophia.
This is very different from the situation of the same
muscles in the Pentameridas, in which they are located
26
27
28
Figs. 26-28. — Longitudinal sections of pentamerids. 26, Pentamerus; 27, Pmtameroides; 28, ConchUium s. s. BP,
brachial process; 5fiP, base of same; /^, inner plate; Mj, median septum; O/, outer plate; O//, outer plate and septum;
Sf, spondylium.
Dorsal interior. Sefta. — The dorsal interior of
the Camerellida is fundamentally different from that
of the Pentameridas and will be treated first. Here
the dorsal septa can be divided into four more or less
distinct parts: (1) the brachial supports, (2) the alar
processes, (3) the fulcral plates, and (4) the support-
ing lamellae.
1. The brachial supports appear to be extensions
from the postero-ventral extremity of the alar processes.
They are blunt and short, and are defined by ridges
along the posterior margin of the alar plates.
2. The alar processes appear as concave plates, con-
vex inward, which define the walls of the notothyrial
cavity at the posterior. These processes in their for-
ward extension curve outward. The alar extensions
may represent the complete supports of the lophophore,
taking the place of the elongate processes in other
forms.
3. Fulcral plates are small plates, concave dorsally,
which define the sockets much as in the Orthoidea
(Plectorthidae and Schizophoriidae).
within the confines of the subparallel or divergent
septa or within the subrostral vault of the crurahum.
In the Camerellidas the situation of the adductors is
much like that of the adductors in the Syntrophiid.-e
and Huenellidas, and it is very hkely that future study
will show the origin of the Camerellida; out of these
groups. This supposition, however, must await the dis-
covery of the pallial marks in the Camerellidje and
will be decided by the course of these structures on the
inner surface of the dorsal valve.
As stated above, the muscle-scars of the Pentam-
erids are borne within the septal plates of the dorsal
valve, and in the spondylium of the opposing one.
This enclosure of the dorsal muscles by the septa is
held by us to be a markedly characteristic feature
of the Pentameridx, differentiating them from the
CamereUidae.
Cardinalia. — The cardinalia of the Pentameridx
are the most characteristic feature of the genera and
probably of the family as well. These lamellae are
GENERA OF THE SUBORDER PENTAMEROIDEA
165
divisible into four distinct units termed by Leidhold:*
(1) The inner crural plate, (2) the outer crural
plate, (3) the crural band or border, (4) the septal
plate. We prefer to term the first two of these parts
simply the outer and inner plates, since we do not feel
that it is at present certain that they are the homologues
of the crura such as occur in the Rhynchonellacea and
Terebratulacea.
1. The inner plates are curved, convex ventrally,
and unite with the outer plates and the wall of the
valve to form a prominent umbonal chamber. The
sockets into which the ventral teeth fit are notches
in the inner plates where they unite with the wall
of the valve. The designation "inner plates" is not
entirely apt, since, when the valves are seen in ventral
view, the plates are actually the outermost part of the
cardinalia. Leidhold evidently coined his expressions
from a specimen that had been split longitudinally
(this at least is the way he figures the structures).
Thus seen from the side, the plates are innermost, being
next to the spondylium.
2. The outer plates are rather thin and low, and
unite with the dorsal edge of the inner plates and are
separated from the septal or supporting plates by (3) a
band or longitudinal thickening, the "Cruralleiste" of
Leidhold.
4. The septal or supporting plates unite with the
floor of the valve or with each other if a cruralium is
present, and they support the other structures. They
are commonly rather long and may be the best devel-
of)ed of the tripartite cardinalia.
Further discussion is necessary regarding the Crural-
leiste or base of the brachial support as we prefer to
term it. This band is prolonged into a free process
that commonly extends to the front end of the ventral
spondylium. It is this elongate, free process that
undoubtedly was the support of the lophophore. The
Cruralleiste represents the growth path of this brachial
support or rather the remnant of the brachial support
which has been enclosed and encroached upon during
the forward growth of the inner and outer plates.
These brachial processes are rather stout in the Gypidu-
linx but in some members of the Pentamerina are long
and slender. In Brooksina, with its strongly arched
valve, the processes are exceedingly long.
The cardinalia of the Pentamerida; as herein de-
scribed are absolutely distinctive, nothing like them
being known elsewhere. There is a slight difference
between the septa of the Gypidulina: and the Pentam-
erinje. That of the former is commonly bowed or
convex outward, especially where the inner and outer
plates unite with the base of the brachial support. This
is notably true of Gypidula, Sieberella, and Pentamer-
ella. In the Pentamerinae, on the other hand, the
plates are generally higher and consequently not
notably bowed.
* Abhandl. preuss. geol. Landesanst., n. ser., Heft 109,
1928, pp. 51-53.
GENERIC AND EVOLUTIONARY
TRENDS
The following discussion points out the more im-
portant generic and evolutionary trends among the
pentamerids observed by us, and indicates as well what
characters we regard as of most import in defining the
genera.
Loss OF INTERAREAS AND DEVELOPMENT OF A
PLANAREA. — In all of the pentamerids the inherited
interareas are reduced to mere remnants and in many
of the genera they have totally disappeared. But along
with their vanishing comes the development in a few
stocks of planareas or so-called false areas, plane (or
nearly so) surfaces developed on either side of the
delthyrium and largest in Brooksina. This develop-
ment of planareas is of little taxonomic significance
so far as present knowledge goes. The great reduc-
tion of the interareas is of course characteristic of the
whole superfamily.
RosTRATiON. — Elongation of the beaks is best
developed in Conchtdium, Harfidium, and Lissoccelina,
and along with this extreme rostration has come a
great arching of the ventral beaks over the dorsal ones.
Reversion of normal convexity. — This is a
common tendency among many brachiopod stocks and
the cause of it is not fully understood. In Strofhomena
of the Strophomenacea it has been correlated by Sarde-
son" with a pendant growth habit, but this gravity
causation does not appear to be responsible for the
reversion in Brooksina and Cafelliniella.
Reversion of fold and sulcus is another common
feature, and one that is not uncommonly attended by
rather profound alterations of the interior, and yet
Pentamerella and Sieberella are structurally alike in-
ternally though the fold and sulcus are reversed. In
Virgiana, Twenhofel' says that the reversion of fold
and sulcus takes place during growth, hence he regards
it as a generic character, but to us this is certainly not
so important as the internal features.
Trilobation. — The flattened pentamerids such as
Pentamerus and Rhifidium developed pronounced tri-
lobation, which may be tied up with their incurrent
and excurrent canals as explained in the Orthidx.
This trilobation is also exhibited in the galeate pentam-
erids and the Camerellida by the development of a
fold and sulcus.
Ornamentation. — It appears clear that the first
of the known Camercllid<-c were practically smooth
during early growth and that later the stock became
more and more costate. Among the Gypidulina; the
first members to appear, Clorinda and Barrandella,
were smooth, and were followed by costate genera.
Pan-Amer. Geol., vol. 51, 1929, pp. 37-38.
'Geol. Surv. Canada, Mus. Bull. 3, 1914, pp. 27-28.
166
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Gyfiduln becomes secondarily smooth or nearly so in
the late Devonian. On the other hand, smooth
Gyfidula fseudogaleata may represent a totally differ-
ent stock generically from any of the others.
The first of the known American Pentamerinae
are the costate Platymerella and Virgiana. They were
followed by smooth forms (Pentamerus, Pentamer-
oides, etc.), and these were later succeeded by Con-
chidium and allies. The strongly costate forms are
certainly characteristic of the high Middle and Upper
Silurian, especially of central United States and Alaska.
Loss OF THE VENTRAL SEPTUM. — Many pentam-
erids eliminate more or less of the ventral septum.
Complete loss was nearly achieved by Pentamerella
and some species of Gyfidula, and total loss of the
septum is the case in Cymbidium and Holorhynchus.
On the other hand, Platymerella and Virgiana, earliest
of the Pentamerinas, had exceedingly short dorsal septa,
and some later stocks had longer ones.
Development of a cruralium. — Among the
galeate Pentamerinae Sieberella and Barrandella alone
have cruralia. In the Pentameridas the genus Pentam-
eroides is the only one known to have this structure.
Conchidium with a cruralium is theoretically possible,
but so far none is known.
PARALLEL TRENDS
The subfamily, on the basis of external characters, is at
once separable into two divisions, Laeves and Costatae,
with the following arrangement in equivalent states of
development:
Smooth
Pentamerus
Pentameroides
Lissocaelina
C apelliniella
Holorhynchus
Har-pidium,
Costate
Platymerella, Rhifidium
None as yet known
Conchidium,
Brooksina
Cymbidium
None known, but to be
looked for in Conchid-
ium with abbreviated
septum
We do not mean to say that these two groups repre-
sent two genetic lines. This is possible, but as yet we
do not know pentamerids well enough to state it as a
fact. There are too many possibilities in the way of
smooth stocks becoming costate and costate stocks
going back into the smooth state. However, our
scheme is interesting, even if not established. It will be
noticed that out of the six possibilities, four of the
smooth stocks have a costate genus in a corresponding
stage of development.
A number of interesting parallel developments were
seen during this study in various groups of the pentam-
erids. One of these is in the development of a
cruralium. Camerella has a cruralium in the dorsal
valve but its homoeomorph, Parastrophinella, has the
dorsal septa separate. In Barrandella there is a cru-
ralium but in Clorinda, its homceomorph, the dorsal
plates are widely separate. The same is true of Pen-
tamerus and Pentameroides, and of Sieberella and
Gypidula. Hall and Clarke^ regarded this develop-
ment of a cruralium as of not more than specific
value and placed more reliance on the external form
of the shell. The trend of more recent times is, how-
ever, to take the opposite view, regarding the internal
variations as of greater importance than the exterior.
Accordingly we recognize the presence of a cruralium
as of generic value.
SUMMARY
In summarizing the above remarks, we can not sur-
vey the evolution of the pentamerids in any clearer
way than by showing our conceptions of the interrela-
tions of the various members of the Pentamerinae.
' Pal. N. Y., vol. 8, pt. 2, p. 246.
Family CAMERELLID^ Hall and Clarke
1894
(Syn. Parastrophinina; Schuchert 1929)
Primitive, small, usually multicostate Pentameracea
with the dorsal shell the deeper and with small, nar-
row ventral interareas; probably derived out of the
Syntrophiidse. All have a spondylium duplex. Dorsal
cardinalia tripartite, with the septal plates either dis-
crete or united into a cruralium supported by a median
septum; arm supports short. Adductor muscles at-
tached to the floor of the dorsal valve in front of the
septal plates. Delthyrium open and but rarely modi-
fied by narrow delthyrial marginal growths.
Embraces the following genera:
Camerella Billings
? Branconia Gagel
Parastrophinella Schuchert and Cooper
Anastrophia Hall
Metacamerella Reed
The genetic relations appear to be as shown in
Table 18.
GENERA OF THE SUBORDER PENTAMEROIDEA
167
Discussion. — Hall and Clarke say:"
Whatever may be the oscillation in form and the varia-
tion in secondary characters presented by Camarella, Para-
strofhu and their allies, present evidence indicates that
they must be regarded as the genetic precursors, as they
are the secular precedents of the great group of true
pentameroids.
And on page 355 they erect the family Camerellidre
for CamereUa, Parastrophui, Anastrophia, and ? Bran-
coma; all the other genera referred here by them are
now excluded from this family.
Table 18
Camerellid^
Anastrophia
Parastrophinella
Metacamerella
CamereUa 2,
^ Branconia
Syntrophiid^
Beecher and Clarke' have shown
that in early age the shells of Anastrophia are normally
biconvex, and the brachial valve scarcely deeper than the
opposite. ... In this condition the form of the shell
resembles that of normal individuals of Camarella volborthi,
and in this series of forms, beginning in Camarella where
senile shells evince a gibbosity of the brachial valve and a
tendency toward reversion of convexity, and ending with
the Lower Helderberg Anastrophia verneuili, we have a
consecutive and gradational development in internal struc-
ture, which is accompanied by more abrupt variations in
exterior.*"
As conceived by the present writers, the Camcrellidx
consist of shells in which the dorsal valve is usually
more convex than the ventral. The shells are com-
monly multicostate. The ventral interior has a promi-
nent spondylium duplex, but the most important family
*Pal. N. Y., vol. 8, pt. 2, p. 341.
» N. Y. State Mus., Mem. I, 1889, p. 32.
" Hall and Clarke, op. cit., p. 225.
characters arc in the dorsal valve in connection with
the cardinalia. The brachial processes are supported by
alate plates, concave outward, and these arc, in turn,
supported by septal plates which are cither discrete and
fastened directly to the floor of the valve as in Para-
strophinella and Anastrophia, or converge and unite
with a median septum to form a cruralium as in
CamereUa. Another feature of significance is the
attachment of the adductor muscles to the floor of the
dorsal valve entirely outside the septal plates. This is
a more primitive feature than in the derived Pentam-
eridas, in which the adductor muscles are confined
either within or on the dorsal septal plates or cruralium
when such a structure is present.
The family as now constituted contains one genus,
Branconia, which is of doubtful value, and another,
Metacamerella, which has not been adequately de-
scribed. The former, which occurs in the Middle
Ordovician of Europe, is probably identical with Cam-
ereUa. Metacamerella, on the other hand, suggests an
Anastrophia, having a ventral fold, but the alate proc-
esses of the dorsal valve were not reported by the
nomenclator of the genus.
In the Camerellidas the delthyrium appears to be
open or partially encroached upon by marginal growths
which have been called dcltidial plates, but they are
not like those in the Telotremata and it appears proba-
ble that true deltidial plates do not occur in this family.
Genus CAMERELLA Billings 1859
PI. 25, figs. 3-6, 8-13, 16, 20-22, 24, 27-30, 43
Billings, Canadian Nat., vol. 4, 1859, p. 301.
HaU and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 219,
pi. 62, figs. 11-18 (Camarella).
Horn. Parastrofhia Hall and Clarke, Ibid., p. 221, pi. 63,
figs. 1-3.
Syn. Parastrophina Schuchert and LeVcne 1929.
Genolectotype (Hall and Clarke). — C. volhor-
thi Billings 1859.
Description. Exterior. — Subglobular to subpen-
tagonal in outline; hinge-line narrow, cardinal ex-
tremities broadly rounded; profile unequally biconvex,
the dorsal valve having the greater convexity in mature
individuals; anterior commissure uniplicate. Ventral
interarea narrow, nearly obsolete; delthyrium open,
so far as known. Dorsal interarea obsolete. Surface
costate on the anterior half, smooth posteriorly. Shell
substance fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep; teeth
strong; dental and septal plates convergent to form
a spondylium duplex. Septal plates in conjunction
and prolonged in front of the spondylium for some
distance.
Dorsal interior. — Notothyrial cavity deep and elon-
gate; brachial supports rather short and blunt; septa!
plates, which buttress the brachial support, elongate
168
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
and convergent, forming a cruralium duplex; short
alx present just anterior to the brachial supports.
Geologic range. — Middle Ordovician (Chazy)
to Middle Silurian of North America.
Species
Camerella n. sp.
C. volborthi Billings 1859
Parastrofhia greenei (Hall and Clarke) 1 895 (placed here
after a study of Hall and Clarke's figure)
P . hemiflicata {HnW) 1847
P. hemifUcata rotunda (Winchell and Schuchert) 1893
P. rotundijormis WiUard 1928
P. ? scojieldi (Winchell and Schuchert) 1893
Distinguishing characters. — Camerella as here
restricted is characterized by the presence of a spon-
dylium duplex, a cruralium duplex, and dorsal septa
having short alate extensions on the outside.
Discussion. — ^The genotype selected by Hall and
Clarke is C. volborthi Billings, which proves to be
structurally identical with Parastrofhia hemiflicata
Hall, the type species of that genus. Both forms have
the same kind of spondylium and cruralium and possess
the ala which are so much better developed in Anastro-
fhia. It is evident, then, that Parastrofhia Hall and
Clarke 1893 (a homonym replaced by Parastrofhina
Schuchert and LeVene 1929) and Camerella Billings
1859 are synonyms, and the latter name has priority.
Regarding Cafnerella, Hall and Clarke say that
these shells have "in effect, a rhynchonelloid exterior,"
with a well defined spondylium supported by a short
median septum, and an open delthyrium without del-
tidial plates. The cardinalia consist of "crural plates
converging and forming a short, very small median
cavity, which is supported by a long septum," and
this hinge structure "is similar to that of Camarotoe-
chia . . . The crura are short, and the lateral divi-
sions of the hinge-plate small. No cardinal process
exists. The internal structure of Camerella is, thus,
not unlike that of Syntrofhia, notwithstanding the wide
difference of exterior."
It is evident that there is needed a revision of the
species commonly referred to Camerella under the
current conception of the genus." The present writers
exclude from this genus C. hella Fenton, C. ambigua
(Hall), C. tnornata Weller, and the following species
of Billings: C. varians, C. longirostris, C. fanderi,
C. costata, C. folita, and C. farva. Some of these
" For the early Middle Ordovician (Chazy) shells which
have usually been called Camerella, but which have a differ-
ent internal structure, we proposed the name Rhyncho-
camara in our "Synopsis" of 193 1, and left the genus under
the family Camerellids. We are now convinced that it is
in reality a rhynchonellid. For the convenience of workers
on that group its description is amplified in the Appendix
to this work.
species must be removed to entirely different groups.
C. tnornata Weller does not have the external form
of either Camerella or Rhynchocamara and should
probably be assigned to ? Cyclosfira. "Camerella"
fanderi appears from etched specimens to possess spiralia
and is without a spondylium, as is also C. longirostris.
"Camerella" ottawaensis from Paquette Rapids (pi. 16,
figs. 6, 9, 13) apparently belongs to Orthorhynchula.
In Camerella the ventral muscles are confined to
the spondylium as is normal for spondylium-bearing
shells, but in the dorsal valve internal molds show
clearly four adductor impressions bisected by the septum
of the cruralium. This must be regarded as a primi-
tive character and is in contrast to the Pentameridas
in which the muscles are enclosed by the septal plates
or are confined to the cruralium. In the Camerellidae
the cruralium is the base of attachment of the diductor
muscles.
Genus BRANCONIA Gagel 1890
(Compare with C amerella)
Gagel, Beitr. z. Naturkunde Preuss. hrgb. von d. Physik.-
Oekonom. Gesell. z. Konigsberg, vol. 6, 1890, p. 62,
pi. 4, fig. 12.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 223.
GENOHOLOTyPE. — B. borussica Gagel 1890.
Description (translation from Gagel). — Outline
transversely lengthened, ventral valve (? dorsal)
strongly arched, provided with a thick, keel-like ele-
vated fold, which is divided in the middle by a low, but
definite groove. On the anterior margin the ventral
(dorsal ?) valve is provided with a deep indentation;
the beak is small but so strongly incurved that it touches
the dorsal valve and no foramen can be perceived.
Hinge margin somewhat narrower than the greatest
shell width, slightly curved. Dorsal valve (? ventral)
flattened, with a small beak, from each side of which
there runs a small flat surface that joins with the shell
proper at an angle. Close under the beak begins a
very deep, steep sinus; at the anterior margin the dor-
sal valve is drawn out into a rather noticeable tongue
which is bent gradually toward the remaining valve at
a right angle ; the tongue fills up the indentation of the
anterior margin of the ventral (? dorsal) valve. Un-
fortunately this part of the anterior margin is quite
damaged, so that the exact outline can no longer be
ascertained. The outer shell layer is preserved in a
few places only, and shows a very fine, concentric
ornamentation. Both valves are distinguished by the
possession of a very large, strong, median septum which
extends from the beak to half the length of the shell.
Aside from these septa, which are clearly visible on the
outer surface of the shell, nothing is known of the
interior.
Discussion. — Gagel thought Branconia was a rhyn-
chonellid but found that it agreed with no known
GENEILA OF THE SUBORDER PENTAMEROIDEA
169
genus. It does not belong to Rhynchonella or Cam-
erophoria, since the sinus is situated on the dorsal
(? ventral) valve; moreover, from Rhynchonella as
well as from Enton'ut and Pentamerus it is clearly dif-
ferentiated in having a very large strong septum in
each valve. The only existing example was found in
a "Lower Silurian" (Ordovician) erratic boulder
thought to belong to the Jewe horizon of the Estonian
Ordovician.
Hall and Clarke remark on the fact that the author
may have reversed the position of the ventral and dorsal
valves. The presence of a septum in each valve and
the occurrence of the shell in rocks of probable Trenton
age suggests a relationship of Branconia to Camerella.
However, in the absence of definite information re-
garding the nature of the interior and in the absence of
comparative material, the genus will stand for the
present.
Genus PARASTROPHINELLA Schuchert
and Cooper 1931
PI. 25, figs. 23, 25, 26; pi. 29, fig. 7
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 248.
Genoholotype. — Pentamerus reversus Billings
1857, Geol. Surv. Canada, Rept. Prog, for 1856,
p. 295 ; Hall and Clarke, Pal. N. Y., vol. 8, pt. 2,
pi. 63, fig. 11.
Description. Exterior. — Shell subglobular in out-
line, hinge-line narrow, lateral profile biconvex, the
dorsal valve always the more convex and usually
arched somewhat over the ventral interarea. Anterior
commissure broadly uniplicate. Ventral interarea nar-
row, apsacline, beak curved slightly, delthyrium open,
so far as known. Dorsal interarea obsolete, beak in-
curved, umbo strongly arched. Surface costate, the
costje being faint or obsolete at the umbones as in
Camerella. Shell structure fibrous, impunctate.
Ventral interior. — Like that of Camerella, with a
prominent spondylium duplex, the septal plates of
which are prolonged for some distance in front of the
spondylium. In one species and in some individuals of
other species the spondylium is sessile at the posterior of
the shell.
Dorsal interior. — Like that of Anastrophta, with the
septal plates discrete or convergent only at their front
ends. Alse somewhat better developed than in Camer-
ella. Adductor scars anterior to the cruralium.
Geologic range. — Upper Ordovician to Middle
Silurian of North America.
Species
Parastrophia divergens Hall and Clarke 1895
P. latiflicala Hall and Clarke 1895
P. multiflicala Hall and Clarke 1895
P. ops (Billings) 1862
/». rw/ff/d (Billings) 1857
Distinguishing characters. — This new genus
differs from Camerella srnsu stricto chiefly in the
divergence of the septa of the dorsal valve, which do
not form a cruralium duplex. It thus forms, with
the other Camerellidx, a parallel scries with the
Gypidulina:.
Discussion. — Hall and Clarke proposed the name
Parastrophia and typified the genus by Atrypa hemi-
plicata Hall. Little did they realize that they had
selected a genotype whose internal structure is identical
with that of Camerella volbortht Billings. However,
several of the later species usually placed under the old
name of Parastrophia prove to have features in the dor-
sal valve differing from those of Camerella and are
here placed under the new name Parastrophinella,
chosen to preserve a semblance of the old term.
It is known from internal molds that the adductor
muscles of the dorsal valve of Parastrophinella were
situated entirely outside of the cruralium as in Camer-
ella. In this respect, Parastrophinella agrees with the
other members of the family.
Genus ANASTROPHIA Hall 1867
PL 25, figs. 14, 15, 19, 33-36, 38-42
HaU, N. Y. State Cab., 20th Rept., 1867, p. 163.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 224,
pi. 63, figs. 31-38.
Horn. Brachymerus Shaler 1865
Genolectotype (Hall and Clarke). — Pentamerus
verneuili Hall 1857, N. Y. State Cab., 10th Rept.,
p. 104, figs. 1, 2.
Description. Exterior. — Globular to subellipti-
cal; hinge-line straight, narrow; cardinal extremities
broadly rounded; lateral profile unequally biconvex,
anterior commissure uniplicate, the dorsal fold usually
being defined only in the anterior half of the valve.
Ventral interarea small and narrow, cleft by an open
delthyrium; dorsal interarea obsolete; beak curved,
commonly resorbed. Surface multicostate ; shell sub-
stance fibrous, impunctate.
Ventral interior. — Teeth narrow, sharp, with deep
crural fossettes, the teeth forming a strengthening
ridge along the delthyrial margin; dental plates con-
vergent, making with the septal plates a spondylium
duplex which is sessile or nearly so at the posterior of
the shell and is supported in front by the median
septum. Scar of pedicle attachment located just be-
neath the dental ridges.
Dorsal interior. — Notothyrial cavity deep; brachial
supports stout curved processes, carinate on their pos-
terior face, sloping laterally into a concave fulcral plate
which is attached to the inner shell wall. Sockets deep.
Septal plates nearly vertical lamell.-c, subparallel or con-
verging slightly toward the anterior. On the outside
of these plates and beneath the brachial supports are
winglike plates which are concave outward. In the
170
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
middle of the space between the septal plates is a low
ridge with diductor scars on each side which probably
served as a cardinal process. The adductor impres-
sions are four in number, a posterior pair located on
the outside of the anterior ends of the septal plates,
and a larger anterior pair that is elongate or sub-
trigonal in outline.
Geologic range. — Middle Silurian to Lower
Devonian.
American Species
Anastrofhia brevirostris (Hall) 1852
A. internascens Hall 1879
A.interflicata CHiW) 1852
A.verneuili (Hall) 1857
European Species
Anastrofhia deflexa {Siov/erhy) 1839
A.magnifica Kozlowski 1927
Distinguishing characters. — Anastrofhia is dis-
tinguished from Parastrophinella chiefly by the more
completely costate exterior.
Discussion. — ^There is some variation in the spon-
dylium of Anastrofhia. In some specimens it is sup-
ported for its whole length by the ventral septal plates,
but in others the posterior end rests on the floor of the
valve. In one unique individual (pi. 25, fig. 42) the
walls of the spondylium have bent inward and united,
forming a tubular chamber open at the front and back.
Such a structure must have impaired the activity of the
muscles and is regarded as a pathologic case. In many
of the specimens the scar of the pedicle attachment is
to be seen in a depression on each side of the spon-
dylium just beneath the tooth ridges. The ventral
beak and the dorsal umbo as well are commonly more
or less abraded by the pedicle.
The cardinalia of the dorsal valve are typical of the
family. There are long brachial supports and outside
of these are broad, alate expansions. The posterior
ends of the septal plates unite with the inner surfaces
of the alae, which are carinate, thickened in the back,
and slope off on the outside to unite with a thick,
concave plate that serves as a socket. Adductor scars
are visible at the front ends of the septal plates, not
having become enclosed as in the Pentamerinae.
several longitudinal plications chiefly developed towards
front end; beak high, incurved, with open delthyrium;
small false area on each side; interior with small subum-
bonal spondylium and short median septum. Brachial valve
with lower beak than opposite valve; low median fold near
anterior end, composed of several longitudinal plications;
interior with pair of long recurved crura, pair of long
parallel median septa, and muscle-scars as in Parmtrofhia.
Shell thick, fibrous, punctate externally.
Discussion. — In the absence of material. Reed's
genus is difficult to place in our taxonomic scheme.
From the morphology as described by him, it is evident
that Metacamerella is very close to Parastrophinella
and to Anastrofhia. It differs from the former extern-
ally in possessing a fold on both valves. Unfortunately
Reed's illustrations do not adequately bear out this
statement, as figure 18, of the dorsal valve, shows a
decided sulcus and appears to be a totally different shell
from the one under consideration. Figures 15 and 17,
however, clearly have a fold. According to Reed, the
muscle marks of the dorsal valve are like those of
Camerella (Parastrofhia), but the figures again, except
for figure 18, do not show them. Should figures 14
and 18 represent opposite valves, the genus would not
be difficult to place and we could say at once that it is
structurally a Parastrophinella with fold and sulcus
reversed, and clearly belongs in association with Ana-
strofhia and Camerella.
The question of punctation among pentamerids is a
very important one. Reed states that the punctation
is external, and we have shown in our discussion of
orthids that exopunctse have no taxonomic significance
beyond genera. This is best seen in Porambonites and
Linoforella, genera that have developed the same kind
of exterior, but the former has an impunctate shell
and the latter is endopunctate as in the Dalmanellacea.
From the internal characters of Metacamerella it
would appear to be impunctate as are all other
pentamerids.
From the above discussion it seems best to place
Metacamerella close to Anastrofhia, the chief known
generic difference of the former being a fold on the
ventral valve. Were it not for Reed's assertion that
Metacamerella possessed a dorsal fold, which seems
unlikely, to judge by the ventral valve he figures, we
would exclude from his genus his figures 15 and 17.
Genus METACAMERELLA Reed 1917
Reed, Trans. Roy. Soc. Edinburgh, vol. 51, art. 4, 191 7,
p. 934, pi. 23, figs. 14-18.
Genoholotype. — Stricklandia ? balcletchiensis
{balclatchiensis) Davidson 1883, Brit. Foss. Brach.,
vol. 5, Sil. Suppl., p. 166, pi. 9, figs. 27-29.
Original description. — Shell oval, biconvex. Pedicle-
valve with low median fold near anterior end composed of
Family PENTAMERIDS McCoy 1844,
emend.
Terminal, usually rostrate Pentameracea, probably
derived out of the Camerellids. Shells smooth, costate
or multicostate. Ventral interareas short and narrow,
but often obsolete, or plane areas are developed. In
nearly all there is a more or less large spondylium
GENERA OF THE SUBORDER PENTAMEROIDEA
171
duplex, supported by cither very long or short double
septa; but in two genera the spondylium hangs free.
Dorsal cardinalia — the most characteristic feature of
the family — tripartite; consisting of discrete plates, or
united into a cruralium that bears the adductor muscles.
When the plates are discrete, the adductors are on the
floor of the shell between them. Brachial processes
very long, and in some forms terminally divergent.
A cardinal process is usually absent or, when present,
is a rudimentary septum or a low callosity. A concave
deltidium and incipient deltidial plates are sporadically
developed, but in general the delthyrium is open.
Shell substance fibrous, impunctate.
Geologic range. — Silurian and Devonian.
Embraces two subfamilies: Gypidulins Schuchert
and Pentamerinae Waagen.
Discussion. — The Camerophoriina; of the Devo-
nian and Carboniferous, long included in the Penta-
meracea, are now considered to be spondylia-bearers of
the Rhynchonellacea, and the Porambonitidas are in the
present work shown to be much modified Orthacea.
Subfamily GYPIDULIN^ Schuchert 1929
Pentamerids more or less galeatiform, with small
ventral interareas. Ventral valve always the more con-
vex and deeper. Cardinal process simple, but usually
absent. Shells smooth, or with some low or many
rounded costae.
Geologic range. — Silurian and Devonian.
Includes the following genera:'^
Clorinda Barrande (syn. Barrandina Booker
1926)
Barrandella Hall and Clarke
Gyfidula Hall
Sieberella Oehlert
Pentamerella Hall
? Zdimir Barrande
The genetic relations are about as shown in Table
19.
Discussion. — We include in the subfamily Gypidu-
linae all of the galeatiform Pentameridae having the
internal structure of the family. This subfamily was
rather prominent in the Silurian and Devonian but
evidently did not survive the latter period. As pre-
viously constituted, it included Virgiana, but the struc-
ture of the dorsal septal plates in the latter genus is so
close to that in Pentamerus that it must be referred
to the Pentamerinae. Its previous constant association
with the Gypidulinje is undoubtedly due to the errone-
ous figure of the interior published by Hall and Clarke.
" Our genus Lioccetia, which was included in this sub-
family in 1931, is now seen to be a rhynchonellid; it is
further described in the Appendix to this work.
Clor'ttida and Barrandella show some internal varia-
tions from the rest of the subfamily. At the junction
of the inner and outer septal plates of the dorsal valve
there is a small process extending in a ventral direction
and into the notothyrial chamber. This feature has
not been observed in Gyp'tdtda, Sirherella, or Penta-
?nerclla, but was noticed in one specimen of Clorinda.
In the Gypidulinae occur some interesting paral-
lelisms. Barrandella and Clorinda are externally alike
but in the former the plates of the dorsal valve form a
Table 19
Gypidulin^
Pentamerella
Pentamerin*
Barrandella
CAMERELLIDiC
cruralium whereas in the latter they are discrete. The
same relations also hold for Sieberella and Gypidula.
These striking features are not only of great interest
but are of considerable importance to students of strati-
graphy and paleogeography.
Genus CLORINDA Barrande 1879
PI. 26, figs. 8-12, 21; t. fig. 29
Barrande, Syst. Sil. Boheme, vol. 5, 1879, p. 109, pi. 1 19,
figs. 1-4.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 244.
Syn. Barrandina Booker 1926 (genotype, B. wilkinsoni
Booker 1926 ^ Pentamerus linguifera var. wilkinsoni
Etheridge 1892 (pars)), Jour. Proc. Roy. Soc. N. S.
Wales, vol. 60, p. 131.
Genoholotype. — C. armata Barrande 1879.
Description. Exterior. — Subgaleatiform ; hinge-
line straight, cardinal extremities broadly rounded;
lateral profile biconvex, the ventral valve having the
greater convexity. Anterior commissure uniplicate;
ventral sulcus usually ill defined; anterior of ventral
172
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
valve produced into a long tongue; dorsal fold low,
best defined at the front. Ventral interarea narrow
and short, curved apsacline to orthocline, beak strongly
curved, umbo inflated; dorsal interarea obsolete, beak
curved, umbo swollen. Valves unornamented except
by concentric lines of growth. Shell structure fibrous,
impunctate.
Ventral interior. — Delthyrial cavity shallow; teeth
small, dental and septal plates forming a small spon-
dylium duplex, which is free at its anterior end.
Dorsal interior. — The septa of the dorsal valve are
subparallel or divergent as in Gyfidula. At the junc-
tion of the inner plates with the base of the brachial
process there is a carina pointing ventrally. The
brachial process is wide, moderately long.
Geologic range. — Silurian of North America,
Europe, and Australia.
and accordingly we feel that this carina has no signifi-
cance in generic taxonomy. A plate of this kind was
seen also in one specimen of C onchidium, and Booker
shows them as well in Gyfidula galeata from Gotland.
We therefore hold that Clorinda is the smooth equiva-
lent of Gyfidula, having its fold on the dorsal valve.
In this latter respect it differs from certain smooth
Gypidulas (G. fseudo galeata^ which may ultimately
be referred to a new subdivision.
Booker has recently proposed a new genus Bar-
randina for shells having the external form of Clorinda,
but thought to differ from the latter in the dorsal
interior. He defines his genus in part as follows:
At the junction of the crural plates and septa a pair of
curved, outwardly convex plates are developed. These are
attached throughout their entire length to the cruralium,
at the junction of the crural plates [inner plates] and septa
1^. ^'^
Fig. 29. — Serial sections of Clorinda fseudoUnguijera Kozlowski. After Kozlowski. ca, carina at the limit of crural
plates and crural septa; cr, crural plates (inner plates); dt, teeth; scr, crural septa (outer plates); sm, spondylium;
s, septum.
American Species
Athyris {?) tumidula Billings 1866
European Species
Clorinda ancillans Barrande 1879
C. armata Barrande 1879
C. bubo Barrande
C. fseudoUnguijera Kozlowski 1 929
Distinguishing characters. — Clorinda is a
smooth shell, internally resembling Gyfidula, and hav-
ing the fold on the dorsal valve.
Discussion. — Inside the ventral valve the septum
is very short and the spondylium hangs free for most
of its length. The dorsal cardinalia are like those of
Gyfidula and have rather long brachial processes as is
typical of the family. The most notable distinction
to be seen from Gyfidula is the carina which runs
along the base of the brachial process at its junction
with the inner plate. In pentamerids of this type from
Australia a carina may be seen also at the junction of
the base of the brachial process with the outer plate.
[outer plates], either along the median line of the convex
side of the plate, or at the edges, being then intercalated
between the septa and crural plates. These plates extend
beyond the anterior termination of the crural plates and
septa for fuUy one-third of their length and terminate at
a point slightly anterior to the end of the spondylium.
The sub-genus Barrandina has been erected for the recep-
tion of certain Australian Pentamerids, with the fold on
the brachial valve and sinus on the pedicle valve, in which
the cruralium is modified by the development of an extra
plate at the junction of the septa and crural plates. The
two species comprising the sub-genus were first described
by Etheridge as Pentamerus linguifera var. zvilkinsoni.
Subsequent work on the pentameroids of the Yass district
has revealed a series of forms paralleling in their structures
the Barrandella and Sieberella series of Europe and America,
but all characterized by the development of an extra plate in
the cruralium.
It is our belief that the "extra plate" of Booker is
actually the same as the brachial process of all other
pentamerids but has more pronounced ridges than is
usual along the junction of the inner and outer plates
with the base of the brachial process. In our opinion
the internal structure of Barrandina does not differ
GENERA OF THE SUBORDER PENTAMEROIDEA
173
generically from that of Clorinda. In B. minor
Booker the septal plates are more widely divergent
than in B. wilkinsont, in which they are subparallel.
The latter species is approaching Barrandella, but the
former is quite a typical Clorinda. We therefore
regard Barranditia as a synonym of Clorinda.
Genus BARRANDELLA Hall and Clarke 1893
PI. 26, figs. 1-3, 5-7; t. fig. 30
Hall and Clarke. Pal. N. Y., vol. 8, pt. 2, 189.% pp. 241,
245, pi. 71, figs. 1-3, t. fig. 173; H.indbook, pt. 2,
1895, p. 844, figs. 457-458.
Genoholotype. — Atrypa linguifera Sowerby
1839, in Murchison, Sil. Syst., p. 629, pi. 13, fig. 8.
Distinguishing characters. — Barrandella is to
the genotype. Later Schuchert (1897) regarded it
as a synonym of the older Clorinda. Recently the
name has been revived by Booker (1926) and Koz-
lowski (1929), the latter recognizing Barrandella as
a genus and Clorinda as a subgenus, but we prefer to
regard both groups as of generic rank.
Geologic range. — Silurian of North America and
Europe.
American Species
Clorinda ventricosa (Hall) 1860
? C.jornicata (Hall) 1852
European Species
Barrandella linguifera (Sowerby) 1839
^ .. Oh
c\^n\^T 185 3
P. felagica Barrande 1879 (in part)
Distinguishing characters. — Gyfidula is most
readily recognized externally by its galeate form and
the position of the fold on the ventral valve. Intern-
ally the differential characters are in the dorsal valve,
in the discreteness of the brachial supports, which form
a double track on the dorsal surface when the shell is
eroded or seen in section.
Discussion. — ^The ventral morphology of Gyfidula
presents no departures from that in Clorinda, Pentam-
erella, and other genera of this subfamily. The septum
is exceedingly variable in its length and this is true like-
wise of the spondylium. The latter in some species
(G. romingeri and G. coeymanensis) is free for more
than three-fourths its length. The internal surface is
marked with elongate pustules and low ridges which
are interpreted usually as evidences of ovarian struc-
tures. The teeth are sharp and slender.
The dorsal interiors of G. coeymanensis and G.
romingeri, of which excellent examples are at hand,
are especially instructive in illustrating the characters
of the genus. In these the dorsal septal plates are
divisible clearly into three parts, termed by Leidhold'*
(1) inner crural plates, (2) outer crural plates, and
(3) septal plates (see pp. 164-165).
A linear cardinal process was observed by Hall and
Clarke in the genotype, but the occurrence of such a
structure is not general throughout the various mem-
bers of the genus. The usual condition is for the
diductors to attach to the floor of a deep pit under
the beak. It has been noted in some instances that
the pit is divided by a low ridge which may be inter-
preted as a cardinal process, although it was appar-
ently never functional as such in the sense of bearing
the muscles.
Hall founded the genus Gyfidula on Petitamerus
occidentalis and G. Iwvtusculus and stated distinctly
that the lamella of the dorsal valve were separate and
diverging. This therefore excludes from Gyfidula
shells like Sieberella sieberi in which the septal lamellae
unite with a median septum. Hall and Clarke, reason-
ing with no knowledge of homceomorphy and the
confusion it may cause by obscuring the true relation-
ships of genera, maintained that the union or diver-
gence of the crural lamellas was of little import, being
only of specific value. In so holding, they could find
no distinction between the two genera except that
Sieberella was lacking in "deltidial plates" and a "car-
dinal area." This distinction between the genera has
been perpetuated by most recent authors. Schuchert in
1897 placed Sieberella in the synonymy of Gyfidula
>' Abh. preuss. geol. Landesanst., N. F., Heft 109, 1928,
pp. 49-53.
GENERA OF THE SUBORDER PENTAMEROIDEA
175
and this was also Leidhold's solution (1928).''' In
1913,'^ however, the former author indicated S'leber-
ella as a subgenus of Gyfidula and in the Zittel-
Eastman Text-book of Paleontology both were given
independent rank. Recently Belanski (1928), in a
study of the Iowa Upper Devonian pentamerids, notes
the internal differences mentioned by Hall and Clarke
and also the fact that Sicherella sieberi actually has a
cardinal area. The latter fact has been corroborated
by the present writers. This heretofore superficial dis-
tinction therefore fails, with the result that the chief
difference between the genera lies in the dorsal interior.
It is just as correct to assume a line of reasoning
diametrically opposed to that of Hall and Clarke:
commissure sulcate; ventral fold usually defined only
on the front half of the shell. Ventral interarea rather
wide for the subfamily, curved, apsacline, delthyrium
open, beak incurved strongly, umbo inflated. Dorsal
interarea obsolete, beak incurved, umbo swollen. Sur-
face multicostate ; shell substance fibrous, impunctate.
Ventral interior. — Like Gyp'ulula.
Dorsal interior. — The tripartite character of the car-
dinalia is essentially the same as that of Gypidula, but
the septal plates, instead of uniting directly with the
floor of the valve, unite with a low median septum.
Geologic range. — Silurian and Devonian of
North America and Europe.
(D (t^
QX)
\J
\j
Fig. 31. — Sieberella sieberi Barr. Sections showing internal structure,
dorsal septa to form a single plate. Distance of sections from beak:
1 — 1.6 mm.
2—2.8
3—3.5
4 — +.0
Of greatest significance is the union of the
5 — 4.8 mm.
6—7.9
7—9.2
the internal structures can be seized upon as diagnostic,
the cruralium of Sieberella distinguishing that genus
from Gypidula, which has divergent lamellae. The
striking external resemblance in form we therefore
attribute to homoeomorphy.
Genus SIEBERELLA Oehlert 1887
PI. 26, figs. 25, 30, 33; t. fig. 31
Oehlert in Fischer, Man. Conch., 1887, p. 1311.
HaU and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, pp. 241,
246, pi. 72, figs. 4, 5, t. fig. 176.
Genoholotype. — Pentamerus sieberi Von Buch in
Barrande 1847, Brach. Sil. Schichten Boehmen, p.
103, pi. 21, figs. 1, 2.
Description. Exterior. — Outline galeatiform as
in Gypidula, hinge-line faintly arcuate; cardinal ex-
tremities rounded. Lateral profile biconvex, the ven-
tral valve usually with the greater convexity. Anterior
"Op. cit., p. 50.
*' Marj'land Geol. Surv., Lower Devonian, p. 342.
American Species
Sieberella emarginata Belanski 1928
S.insolita Belanski 1928
S. roemeri Hall and Clarke 1893 (in part)
European Species
Sieberella multistriata Roemer
S. sieberi (V. Buch) 1847
S. sieberi rectifrons (Barrande) 1879
Discussion. — Hall and Clarke restricted the name
Sieberella to shells not having a cardinal area on the
ventral valve, this being their sole distinction. A re-
study of the genotype, however, shows that it possesses
a well defined area. Nevertheless, there is a funda-
mental internal difference, the convergence of the
septal plates to meet a median septum. This type of
structure is not common and is restricted seemingly
to rather transverse shells which are costate over nearly
the whole surface. Sieberella has the fold restricted to
the ventral valve and is thus a homoeomorph of
Gypidula. The two genera form a striking example
of internal variation combined with a stable external
expression.
176
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Genus PENTAMERELLA Hall 1867
PI. 26, figs. 4, 13-17, 19,20; t. fig. 32
Hall, 20th Rept., N. Y. State Cab., 1867, p. 163.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, pp. 242,
245, pi. 71, figs. 21-29.
Genolectotype (Hall and Clarke). — Atrypa
arata Conrad 1841, 5th Rept. N. Y. Geol. Surv.,
p. 55.
Description. Exterior. — Outline subtriangular to
subpentagonal ; hinge-line narrow; cardinal extremi-
ties rounded ; lateral profile biconvex, the ventral valve
having the greater convexity. Anterior commissure
uniplicate; dorsal fold usually low, in some species
nearly obsolete. Ventral interarea narrow, curved,
apsacline, beak incurved strongly, umbo swollen; del-
P. intrdineata (Winchell) 1 866
P. missouriensis Branson 1922
P. favilionensis (HaW) 1860
Distinguishing characters. — Externally Pen-
tamerella most closely resembles Gypidula, but differs
in having the fold on the dorsal valve. Internally, it
is similar to SieberelLa in having the septal plates unite
with a low septum to form a cruralium.
Discussion. — Of interest in Pentamerella is the ex-
tremely short septum of some of the species. In shells
referred to P. favilionensis , from Moreland, Kentucky,
the septum may be confined to the very posterior of
the shell as a short rib. In the brevity of its sep-
tum Pentamerella represents an advanced generic
development.
o o 6 6 <5 O
I
8
Fig. 32. — Pentamerella aff. P. ■favilionensis (Hall), Alpena, Michigan. Of prime interest in these serial sections is
the extreme brevity of the median septum in the ventral valve. It was apparently a ridge on the posterior wall of the
shell. X 1 . Distance from beak:
1 — 1.9 mm.
2—3.9
3—4.2
4—4.9
5 — 5.5 mm.
6— 6.9
7— 7.6
8—11.25
thyrium with incipient deltidial flates. Dorsal inter-
area obsolete, beak curved under that of the ven-
tral valve. Surface usually multicostate, occasionally
smooth. Shell substance fibrous, impunctate.
Ventral interior. — Teeth narrow and sharp; spon-
dylium duplex shallow; floor of spondylium longi-
tudinally striated, supporting septum short; intern.il
umbo-lateral ovarian spaces pustulose.
Dorsal interior. — Notothyrial cavity deep; plates
supporting brachial processes broad and flat, supported
by thin curved plates which unite in the mid-line of
the shell to form a cruralium that in some specimens is
supported by a low duplex septum. In the apex is a
shallow pit divided by a low ridge ; the two pits are the
areas of the diductor scars.
Geologic range. — Devonian (Middle and Up-
per) of North America.
Species
Pentamerella arata (Conrad) 1841
P.dubia (Hall) 1860
P. juhoneiisis Branson 1922
Booker^* has recently published figures of "Pentam-
erella" molongensis Mitchell, which are obviously not
of this genus. In this form the septal plates are widely
divergent as in Clorinda or Gyfidula. The same
is true also of "Pentamerella" sublinguifer Maurer,
figured by Leidhold.'^ In this shell the dorsal septa
are wide-spread and the form is certainly not a Pen-
tamerella. The figures suggest Clorinda, as the shell
is quite smooth.
Hall and Clarke say that in Pentamerella "there
are occasionally evidences of lateral, erect or convex
growths upon the margins of the delthyrium, which
may be interpreted either as remnants of a resorbed
convex deltidium, or as highly accelerated secondary
deltaria" (pp. 341, 342). We have also seen these
plates, and interpret them as incipient deltidial plates.
"Jour. Proc. Roy. Soc. N. S. Wales, vol. 60, 1926, pp.
140-142.
" Abh. preuss. geol. Landcsanst., N. F., Heft 109, 1928,
p. 57, pi. 4, fig. 14, t. fig. 25.
GENERA OF THE SUBORDER PENTAMEROIDEA
177
Genus ZDIMIR Barrande 1881
B.irrande, Syst. Sil. Centre Bohcmc, vol. 6, 1881, p. 171,
pi. 292, figs. 1 7-20.
Genoholotype. — Z. solus Barrande.
Discussion. — A single isolated valve from the De-
vonian of Bohemia, of "unusual and enigmatic" ap-
pearance, was named Z/iimir and provisionally referred
by Barrande to the Pelecypoda. The specimen, ac-
cording to the author, resembles the arched valve of
certain elongate pentamerids, but is slightly inequi-
lateral. He states further that the specimen has a
moderately developed, curved beak, almost as in the
pentamerids, without trace of an area, and the surface
of the beak is broadly open. The exterior is orna-
mented by cost.T diverging from the beak. No muscle
or pallial marks were observed. Aside from the allu-
sions to its possible affinities with the pentamerids,
Barrande compares the specimen with Isocardia and
places it in the Pelecypoda.
It was later referred to as scarcely separable from
Uncites gryfhus by Freeh.** Novak,'* however,
studied and prepared a specimen of Z. solus in the
Bohemian museum at Prague, showing that fragments
of the shell substance adhering to it had the structure
of brachiopod shells and that it had a spondylium sup-
ported by a septum. Ztlimir is therefore quite clearly
a pentamerid. In 1913 Schuchert"" considered the
genus as a synonym of C onchidium . The latter genus
is, however, not certainly known in the Devonian.
Barrande has described many species of Gyp'tdula
from Bohemia but Novak claims that Zdimir is not
referable to any of them. Two courses can be taken
with this doubtfully valid genus: (1) the name can be
restricted to the existing specimens; or (2) it can be
placed provisionally as a synonym of Conchidium
which is known doubtfully from the Devonian.
C apeUinirllit Strand
Holorliyncluts Kiaer
Harpidium Kirk
Costa tse
Rhifid'tunt Schuchcrt and Cooper
Conchidium Linna;us
Brooksina Kirk
Platymerella Foerste
Cymbidiuni Kirk
Virgiana Twenhofel
The genetic relationships are thought to be as shown
in Table 20.
Discussion. — The Pentamerinx are a large and
interesting group of shells intimately tied together by
their rather elongate and non-galeate form as com-
pared with the Gypidulina. Internally their spon-
dylium is like that of the other subfamily. In the
dorsal interior the only difference of note lies in the
septa, which are less bowed than in the Gypidulinas.
The subfamily is provisionally divided into two
groups on the basis of its external sculpture. The
significance of this division is discussed in the pre-
liminary remarks. Suffice it to say here, that nearly
every smooth stock is represented by an equivalent
costate one. For example, Pentamerus represents a
flattish smooth stage, and has its costate equivalent in
Rhifidium.
The writers found that Orthotropia, which has
long been classified with the Pentamerina;, is actually
an orthid. In the ventral valve it has a pseudospon-
dylium and in the dorsal there is a short cruralium
occupied by a prominent, simple cardinal process. The
structure of Orthotropia allies the genus with Lino-
porella, but its exterior is at present unknown.
Subfamily PENTAMERINX Waagen 1883
Large, rostrate, elongate, non-galeate Pentam-
eridas, usually without distinct interareas. It is in this
subfamily that the internal characters of the family
are t)'pically developed. Shells smooth, costate or
multicostate.
Geologic range. — Silurian and early Devonian.
Has the following genera:
Laeves
Pentamerus Sowerby
Pentameroides Schuchert and Cooper
Lissocceitna Schuchert and Cooper
" Zeits. deut. geol. Gesell., vol. 38, 1886, p. 920.
'» Ibid., vol. 40, pp. 588-590, 1888.
^^ Zittel-Eastman Text-book of Paleontology, 2d ed., vol.
l,p. 394.
Laves or Smooth Pentamerinse
Genus PENTAMERUS Sowerby 1812
PL 27, figs. 4, 8, 9, 10, 12, 15, 17-19; pi. 29, fig. 11;
t. fig. 26
Sowerby, J., Min. Conch., vol. 1, 1812, p. 73, pi. 28.
Davidson, Brit. Foss. Brach., vol. 1, Introd., 1851-1855,
p. 97; vol. 3, pt. 7, 1866-1871, pi. 18, figs. 1-12,
pi. 19, figs. 1, 2 {oblongus).
HaU and Clarke, Pal. N. Y., vol. 8, pt. 2, 1895, p. 236,
pi. 67, figs. 11-13, 20, pi. 68, figs. 1-8, pi. 69,
figs. 1-14, pi. 70, figs. 1-5, t. figs. 169-171 (all of
oblongus) .
Syn. Pentaiicre Blainville 1824, Diet. Nat. Sci., vol. 32,
p. 301.
Genolectotvpe (Hall and Clarke). — P. Itpvis
Sowerby 1812.
Description. Exterior. — Shell large, pentagonal-
hexagonal in outline, commonly trilobate in front;
178
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
hinge-line gently arcuate; cardinal extremities round-
ed; lateral profile subequally biconvex. Anterior com-
missure usually rectimarginate. Fold present or ab-
sent on both valves. Interareas obsolete; ventral beak
curved over the dorsal; umbo prominent. Surface
P. cylindrktis Hall and Whitfield 1872
P. diver gens Foerste 1909
P. oblongus Sowerby 1812
P.ovalis HaU 1852
P. farvulus Savage 1913
/>. ^ffwrw Whitfield 1882
Table 20
Lissoccelina
Pentameroides
CapeUiniella
Pentamerus
Holorhynchus
Platymerella «■
Rhipidium
(costate)
Brooksina
Cymbidium
/
Conchidium
Harpidium
(smooth)
.Virgiana
Clorinda (GvPiDULiNiE)
smooth or with faint undulations at the front. Shell
substance fibrous, impunctate.
Ventral interior. — The dental plates are convergent
and with their septal plates unite to form a spondylium
duplex.
Dorsal interior. — A tripartite division of the crural
plates is recognizable. Thin inner plates unite with
the walls of the valve to form lateral chambers. The
sockets are notches in the partitions of these chambers
next to the wall of the valve. The brachial processes
are long. The septal plates are discrete, divergent or
parallel, continued to the internal surface of the valve.
Between the septal plates a low median septum divides
the septal chamber into two parts. The cardinal
process is a callosity under the beak.
Geologic range. — Throughout the Silurian of
Europe and North America and probably widely
elsewhere.
American Species
Pentamerus bisinuatus McChesney 1861
P. comfressui Kindle and Breger 190+
P. corrugatus Waller and Davidson 1 896
European Species
Pentamerus borealis Eichwald 1842
P. esthonus Eichwald 1860?
P. gothlandicus Lebedeif 1 892
P. Iwvis Sowerby 1812
P. oblongus Sowerby 1812
P. samojedicus Keyserling 1 846
P. schmidti Lebedeff 1 892
Distinguishing characters. — The genus Pen-
tamerus is characterized by its comparatively smooth
exterior, long spondylium duplex, discrete septal plates,
and tripartite cardinalia.
Discussion. — Hall and Clarke state that Pentam-
erus "is an exceedingly plastic type," and limit the
name to smooth shells typified by P. Icevis Sowerby.
The latter is considered by European paleontologists
as the young of P. oblongus.
The specific name P. oblongus has in America been
applied to a wide variety of forms, among them P.
oblongus subrectus Hall and Clarke. In this form
the septal plates of the cardinalia are united to form
a duplex septum which supports a shallow cruralium.
GENERA OF THE SUBORDER PENTAMEROIDEA
179
This development is so different from Pfntainerus
that we are distinguishing it as a new genus under the
name Pe'titamerouifs.
The most interesting internal feature of Pintam-
erus is the long brachial process which reaches to the
anterior end of the spondylium. The two processes
appear to remain separate, judging by serial sections
prepared by us.
Genus PENTAMEROIDES Schuchert and
Cooper 1931
PI. 27, figs. 13, 14; pi. 28, figs. 19, 22; t. fig. 27
Schuchert and Gx)per, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 248.
Genoholotype. — Pentamerus suhrectus Hall and
Clarke, 1893, Pal. N. Y., vol. 8, pt. 2, p. 238, pi. 69,
figs. 2, 3, 8-10.
Distinguishing characters. — Externally the
members of this genus are precisely like Pentamerus,
but internally there is a cruralium in the dorsal valve
that in some specimens is sessile for a short distance
at the posterior but is elevated at the front. In some
species, however, the cruralium is supported by a promi-
nent median septum for its whole length. In all of
the species the dorsal septum is rather long and is not
uncommonly longer than the ventral one. A careful
study of internal molds, a common mode of occurrence
of the genus, shows that the adductor muscles were
attached to the upper surface of the cruralium, for no
trace of muscle scars has been observed on the floor
of the valves.
We have selected Pentamerus suhrectus as the type
of the genus. This is a well defined species charac-
terized by its shouldered dorso-lateral extremities.
There are a number of unnamed species occurring in
the Wisconsin dolomites, especially at Bailey's Harbor.
Here occurs a flat form much like the Clinton P. ob-
longus, but another type externally nearly identical
with Pentamerus cylindricus is also known.
Discussion. — Pcntameroides has a wide distribution
in Silurian strata, being fairly common in Iowa and
Wisconsin. It was also found associated with a small
Stricklandia in the Silurian beds on the shore of the
Bay of Chaleur at Black Point postoffice. New Bruns-
wick. Some of the shells called Pentamerus borealis
by European writers are of this type. It is thus clear
that there must be a drastic revision of the species of
Pentamerus s»nsu lata.
Geologic range. — Widely distributed in the Silu-
rian of North America and Europe, but the species
are not at all worked out, being referred to other
genera and mainly to Pentamerus.
American Species
P.tubrectus Hall and Clarke 1893
Genus LISSOCOELINA Schuchert and Cooper
1931
(Gr. lissosy smooth ; ko'ilia, belly)
PI. 28, figs. 7, 14, ? 13, ? 15, .? 16, ? 21
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 248.
Genoholotype. — Pentamerus fergibbosus Hall
and Whitfield 1875, Pal. Ohio, vol. 2, p. 139, pi. 7,
figs. 10, 11.
Distinguishing characters. — This name is pro-
posed for smooth shells having the external form of
Conc/iuiium in profile and outline and the internal
structure of Pentamerus. It represents an offshoot
from the Pentamerus line in the Middle Silurian. The
genotype is perhaps the best known example. The
ventral valve is elongated and the ventral beak is arched
over that of the dorsal valve as in C onchid'tum. In
Pentamerus sensu stricto there is not the great develop-
ment of the beak and the strong arching of the valves.
Even in the young of "fergibbosus" the same shape
of the adult is faithfully preserved and forbids any
relationship with Pentamerus s. s. In the ventral inte-
rior the median septum is extremely long and in the
dorsal valve the septa are rather close together and
subparallel as in Pentamerus. Externally the shell
preserves no trace of radii.
We are placing in this association, but somewhat
doubtfully, P. maquoketa Hall and Clarke. In this
species the ventral septum is short and in this respect
suggests Harfidium but otherwise agrees fairly well
with that of Lissocoelitia.
Subgenus CAPELLINIELLA Strand 1928
Strand, Arch. Naturgeschicht., Berlin, vol. 92, A8, 1928,
p. 38.
H.ill and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 248,
pi. 70, figs. 6-14.
Horn. CafelliHia Hall and Clarke 1893.
Genoholotype. — C. mh-a (Hall and Clarke)
1893.
Description. Exterior. — Subpentagonal in out-
line; hinge-line exceedingly narrow; cardinal ex-
tremities obsolete. Anterior commissure rectimargin-
ate. Lateral profile unequally biconvex, the dorsal
valve always with the greater convexity. Ventral
interarea exceedingly narrow, almost obsolete. Del-
thyrium open. Dorsal interarea obsolete, beak strongly
curved, umbo swollen. Surface marked by obscure
radiating costa; and a broad low fold on each valve as
in Pentamerus. Shell substance fibrous, impunctate.
Interior. — Essentially as in Pentamerus.
Geologic range. — Silurian of Wisconsin.
Discussion. — Specimens of this subgenus appear to
be rather rare and restricted geographically to Wis-
180
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
consin. It forms a remarkable example of reversion
of relative convexity of the valves and from its com-
paratively smooth shell is clearly an offshoot from
Pentamerus. The ventral median septum is rather
long, reaching about to the middle of the valve. It
extends practically to the beak, showing the spondylium
to have been supported for its whole length. The
spondyhum as shown on interiors is, however, rather
short, shorter than usual in Pentamerus. In the dorsal
valve the septal plates are rather closely placed and
nearly parallel. The portion bounded by them is
divided by a low median ridge as is usual in the
pentamerids.
Genus HOLORHYNCHUS Kiaer 1902
PI. 27, fig. 20
Kiaer, Norg. geol. unders. aarbog for 1902, 1902, p. 68,
figs. 1-7, pp. 103-110.
Genoholotype. — H. giganteus Kiaer 1902.
This name was proposed by Kiaer for shells ex-
ternally like Pentamerus ohlongus Sowerby except that
they are transverse and have a free spondylium in
the ventral valve. The structure of the dorsal valve
is like that of Pentam,erus.
Geologic range. — The only known form, the
genotype, is from the Silurian of Norway.
Genus HARPIDIUM Kirk 1925
Kirk, Proc. U. S. Nat. Mus., vol. 66, 1925, pp. 1-5, pi. 1,
figs. 1-6, pi. 2, fig. 7.
Genoholotype. — K. insignis Kirk 1925.
Description. Exterior. — Shells large, longitudi-
nally subtriangular ; hinge-line narrow; cardinal ex-
tremities obsolete. Lateral profile unequally biconvex,
the ventral valve usually having the greater convexity.
Anterior commissure emarginate, sulci of both valves
rather shallow. Interareas obsolete or exceedingly
narrow. Beaks of both valves strongly arched, the
ventral one bent over that of the dorsal. Beaks acutely
pointed; umbo swollen; delthyrium covered by a
prominent deltidium. Shell thick, fibrous, impunctate.
Ventral interior. — Spondylium duplex long and nar-
row, septum short.
Dorsal interior. — As in C onchidium and Pentam,-
erus, there are three sets of plates. The inner ones
form chambers at the back of the valve ; the outer ones
bear long brachial processes and are supported by low
septa. The septal plates are subparallel and always
discrete.
Species
H arfidium insignis Kirk 1 92 5
H.latus Kirk 1925
H. rotunius Kirk 1925
Distinguishing characters. — Harpidium may
be recognized easily by its smooth exterior, strongly
incurved beaks, unusually long spondylium and very
abbreviated septum.
Discussion. — This very interesting genus has ob-
vious similarities to Conchidium. These are seen in
the elongate beaks, the disproportionate size of the
valves, and the whole physiognomy of the shell. Fur-
ther, Harfidium and Conchidium have the peculiar
concave type of deltidium, the only instances of its
occurrence in the Pentameridas.
Despite these obvious relationships there are two
points of difference of considerable significance. One
of these is the smooth surface which, together with the
external configuration, makes this shell unique. The
other difference is found in the abbreviated septum.
In typical Conchidiufn the septum extends for nearly
the full length of the valve and supports the spondylium
for nearly its entire length. In Harpidium, on the
other hand, the septum is unusually short and the
spondylium hangs free for nearly its whole length.
In one specimen the length of the septum is 17 mm.,
that of the spondylium about 54 mm., with a greatest
width of 1.5 mm., while the length of the shell meas-
ures 75 mm. One wonders how the spondylium,
hanging free as it does, can be strong enough to serve
as the seat of attachment of the opening and closing
muscles of the shell. Strength is evidently obtained
by the narrowness of the spondyhum and the broad
surface of muscle attachment.
Of most interest in H arfidium is the deltidium,
which Kirk described as "convex, elevated, deltidial
plates." These are, however, not deltidial plates, but
are the protruding sides of the deltidium, which is a
continuous plate convex postero-dorsally. This struc-
ture is like that of Conchidium (see pi. 29, fig. 4;
t. fig. 25).
Harpidium is evidently restricted to the Silurian of
the Pacific province in Alaska. At Louisville, Ken-
tucky, occurs a species, usually called Pentamerus per-
gibbosus Hall and Whitfield, which is externally like
Harpidium in being smooth, but is like Conchidium
internally, and for this shell, which represents a stage
of pentameroid evolution, we have proposed the new
name Lissocaelina.
Costatje or Costate Pentamerina:
Genus RHIPIDIUM Schuchert and Cooper
1931
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 249.
Genoholotype. — Pentamerus knappi Hall and
Whitfield 1872, 24th Rept. N. Y. State Cab. Nat.
Hist., p. 184.
This name is proposed for rather flattish shells that
have commonly but erroneously been classed with
GENERA OF THE SUBORDER PENTAMEROIDEA
181
Conchid'tum. They are the costatc equivalent of Pen-
tamcrus and agree in many other external details with
that genus. For example, they are distinctly trilobate,
the trilohation being produced by an elongate tongue
extending forward from both valves. This trilobation
is carried to its extreme in this genus in the species
R. trilohata (Kindle and Breger).
Rhip'uiiurn is a contemporary of Pentamerus, and
probably lived before Conch'uiium arrived in American
seas.
Internally the genus is like Pentamerus in the ar-
rangement of its septa. Externally the ribs are as a
rule implanted or split at the front. Other species
besides the genotype assigned to this genus are:
ConchiJium multicostatum (Hall) 1860
C. riysius (Hall and Whitfield) 1872 (see Hall and Clarke,
Pal. N. Y., vol. 8, pt. 2, p. 235)
C. tenukoita (Hall and Whitfield) 1 872
C. triloiala Kindle and Breger 1904
Genus CONCHIDIUM Linnaeus (1753) 1760
PI. 28, figs. 1-6, 8-12, 17, 18, 20, 23, 26; pi. 29,
fig. 4; t. figs. 25, 28, 33
Linnxus, Syst. Nat., ed. 12, vol. 2, 1760, p. 163.
Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 231,
pi. 66, figs. 11-14.
Syn. Gyfidia Dalman 1828, K. Vet. Akad. Handl. for
1827, pp. 93, 100, pi. 4, figs. la-g.
Syn. Antirhynchonella Quenstedt 1868-1870, Petref.
Deutsch., vol. 2, pp. 231, 727.
Genotype. — C. b'doculare Linnasus 1753, Mus.
Tess., pi. 5, fig. 8.
Description. Exterior. — Subtriangular to sub-
trapezoidal in outline, hinge-line very narrow; lateral
profile biconvex, the ventral valve usually having the
greater convexity. Anterior commissure rectimargin-
ate, sulcate or uniplicate, fold and sulcus usually nar-
rowly pointed and uncurved; delthyrium covered by
a specialized "deltidium" ; dorsal beak obtusely pointed,
umbo more or less swollen. Shell thick in the posterior
region, costate or multicostate ; shell substance fibrous,
impunctate.
Ventral interior. — Spondylium duplex elongate, sup-
ported by a duplex septum usually for more than one-
half its length. Septum exceedingly long.
Dorsal interior. — Septal plates divergent, consisting
of three parts: (1) The inner plates which form two
chambers on each side of the interior, uniting laterally
with the walls of the valve. The sockets are excavated
in the antero-lateral extremities of these plates adjacent
to their junction with the wall of the valve. (2)
Outer plates. The structures noted above are sup-
ported by two diverging lamella; which unite with the
valve directly. The line of union is marked by a
thickening. (3) Brachial supports. Two small plates.
expanded at the free ends and united to the thickening
at the juncture of the outer plates and the inner plates.
The brachial processes extend into the cavity of the
valve, in some specimens, for a distance greater than
the length of the septal plates. At their distal extremi-
ties they curve laterally. Between the septal plates is a
low median septum, dividing the adductor impressions.
Geologic range. — Late Silurian.
American Species
Conchidium arcticum Holtedahl (Rept. 2d Norw. Arctic
Exped., "Fram," 1898-1902, No. 32, 1914, p. 5)
C.colletti (Miller) 1891
C. crassoradius (McChesney) 1861
C.cumberlandicum Prouty 1923
C. exfonens Hall and Clarke 1895
C. greenii Hall and Clarke 1893
C. lajueatum (Coniid) 185 5
C. lindenense Foerste 1903
C.littoni (Hall) 18 59
C. nettelrothi Hall and Clarke 1 893
C. obsoletum Hall and Clarke 1895
C.occidentde {WiSS) 1852
C. scofarium Hall and Clarke 1895
C . unguiforme (Ulrkh) 1886
? C. georgits Hall and Clarke 1895 (may be Gyfidula)
European Species
Conchidium biloculare Linnaeus 1 760
C. miinsteri Kiaer 1901 ?
C. tenuistriatum Walmstedt
Distinguishing characters. — The features of
Conchidium that distinguish it from the other Pentam-
erinas are the strongly multicostate exterior, usually
strongly biconvex valves, and extended beak, below
which there is a narrow interarea, a wide delthyrium,
and in some species a modified deltidium. Internally
Conchidium is like Pentamerus.
Discussion. — It will be profitable to discuss several
morphologic features of Conchidium, i. e., the del-
tidium, the spondylium duplex, and the cardinalia.
Deltidial plates have been reported in many of the
pentamerids, such as Gyfidula. These plates have also
been termed pseudodeltidial plates by Booker.^' In
Conchidium, many specimens show these thickenings
along the margins of the delthyrium, but in addition
they have a concave or, in some instances, an elevated
plate covering the delthyrium. The two types — plates
and "deltidium" — may be observed on the same speci-
men. Obviously, then, the thickenings along the del-
thyrial margin are not true deltidial plates. This
statement will become more certain after a detailed
=' lourn. Proc. Roy. Soc. N. S. Wales, vol. 60, 1927,
p. 134.
182
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
account is given of the occurrence and structure of the
"concave deltidium" of C onch'tdtum . This plate in
most specimens is truly concave and bears a median
groove giving it the appearance of having been formed
by the symphysis of two plates. One specimen of
C. biloculare, however, shows toward the end of the
beak that the plate is elevated above the margins of the
delthyrium, forming a cover with nearly rectangular
sides. In another specimen of the same species the
plate is elevated fully 3 mm. dorsally from the del-
specimens is more than half the length of the ventral
shell and in some it extends for nearly the full length.
The cardinalia, are, as is usual in the Pentameridae,
the most interesting and significant structures of the
genus. Here, as in Gyfidula, Pentamerella, etc., three
distinct "plates" can be determined. The inner crural
plates are convex and unite with a narrow flat shelf
forming the inner postero-lateral margins of the valve.
The union is marked by a low ridge and groove which
forms the suture line between the valve and plate.
^ CD ci) (2)
^^
Fig. 33. — Conchidium biloculare Linn. Sections 1-3 show the delthyrial plate in place at a considerable distance
(4.2-6.1 mm.) from the beak. It is here rather concave, having been depressed from an elevated structure like that in
fig. 25. In section 4 lateral plates are visible in the dorsal valve. Similar plates were seen in Strkklandia (see pi. 29, fig. 6)
but their function and meaning are unknown. Distance from beak:
1 — 4.2 mm.
2—5.0
3—6.1
4 — 7.4
5—8.1
6—8.7
7 — 9.9 mm.
8—11.0
9—12.1
10—14.4
11—15.0
thyrial margin, having nearly rectangular sides, and
bears a shallow median groove. There is no visible
evidence that it has developed by the symphysis of two
plates. Further, the "deltidial plates" are visible along
the delthyrial border in specimens carrying the cover
plate. This modified deltidium must therefore have
been a sort of pedicle sheath housing the proximal
portion of the pedicle.
Conchidium is usually defined as lacking a "cardinal
area" (interarea), but in all of the specimens exam-
ined a narrow but very definite interarea could be seen.
The spondylium duplex in Conchidium is remark-
able for the great depth of the delthyrial cavity and
the great length of the septum. The latter in most
The inner plates thus form narrow lateral chambers.
Posteriorly the terminations of the chambers are thick-
ened, and together with a boss or callus beneath the
beak form the "cardinal process" or seat of diductor
attachment. The outer plates appear to be represented
by narrow longitudinal ridges, the base of the brachial
process. On the inner sides of some specimens, each
of these ridges bears a plate directed dorso-medially.
These are probably posterior extensions of the brachial
process which extend anteriorly with a slight curve for
a considerable distance ; they are curved very slightly
laterally but none were observed to unite into a "loop."
The two inner plates and bases of the brachial processes
are supported by thin divergent septal plates.
GENERA OF THE SUBORDER PENTAMEROIDEA
183
Of the species heretofore referred to Conchidium.
several must be removed to other genera. C. ktuippi,
for example, does not have the elongated and ex-
tremely incurved beak of this genus; it is essentially a
rather strongly costatc Pcntamrrus and belongs to our
Rhip'uiium. Likewise C. Icgoensis Foerste and C. cras-
iipititi Hall and Clarke do not belong in Con-
chidium, the non-bifurcation of the ribs being of little
significance. Savage" has correctly removed C. de-
cussatum to the genus Virgiana.
Genus BROOKSINA Kirk 1922
PI. 28, fig. 24
Kirk, Proc. U. S. Nat. Mus., vol. 60, 1922, pp. 2-5.
Genoholotype. — B. alaskensis Kirk 1922.
Description. Exterior. — Transversely subellipti-
cal in outline; hinge-line narrow; cardinal extremi-
ties obsolete. Lateral profile unequally biconvex to
convexo-concave, the dorsal valve strongly convex,
the ventral gently so, flat or strongly concave. Ventral
interarea narrow, almost obsolete. Ventral cardinal
slopes flat and defined by prominent ridges extending
from the beak to the point of juncture of the costellate
portion of both valves. Delthyrium probably always
open. Dorsal interarea obsolete ; umbo swollen. Sur-
face of the valves multicostellate ; shell substance
fibrous, impunctate.
Ventral interior. — Spondylium duplex supported by
a long duplex septum. Spondylium narrow but
exceedingly deep.
Dorsal interior. — Septa and lamellae as in Con-
chidium and other genera of the Pentamerina:.
Geologic range. — Upper Silurian of Alaska.
Possibly Lower Devonian of the Urals.
American Species
Brooksina alaskensis Kirk 1922
Asiatic Species
Pentamerus of talus Tschernyschcw 1885? (wow Barrande)
Distinguishing characters. — Brooksina may be
differentiated from all other pentamerids by its con-
vexo-concave profile and costellate exterior.
Discussion. — As would be expected, the interior
of this genus differs somewhat from other members of
the family because of the reversed convexity of its
valve. The ventral septum is long and extends to the
anterior margin of the spondylium. Toward the front
"Jour. Geol., vol. 26, 1918, p. 335.
it is strongly corrugated. The spondylium is exceed-
ingly narrow and deep and the anterior margin is
rather straight. Postero-latcrally its sides flare outward
noticeably where they meet the delthyrial margins.
In the dorsal valve all parts of the cardinalia can be
distinguished as in Conchidiutn and there is a long
brachial process which terminates near the anterior
end of the spondylium. In a specimen 30 mm. long
this process is 9 mm. in length.
The young of Brooksina are almost equally biconvex
and this gives a clue to its ancestry. It certainly must
have come out of some Conchidium stock, perhaps out
of the " biloculare" line or some form resembling C.
nysius (Hall and Whitfield). It certainly did not
come out of the "knighti" stock, with which it is
contemporaneous.
Brooksina is in the same stage of development as
Cafelliniella and is thus to Conchidium what Cafel-
liniella is to Pentamerus. These two forms and
Anastrophia are the only representatives of this stage
of evolution so far observed in the pentamerids, but
other "reversed" forms as aberrant developments are
to be expected.
Genus CYMBIDIUM Kirk 1926
T. fig. 34
Kirk, Proc. U. S. Nat. Mus., vol. 69, art. 23, 1926, p. 2,
pi. 1, figs. 5-13; t. fig. 34.
Genoholotype. — C. acutum Kirk 1926.
Description. Exterior. — Subelliptical in outline;
lateral profile subequally convex, the dorsal valve with
the greater convexity. Interareas obsolete; delthyrium
open so far as known. Each side of the delthyrium
bounded by a broad flattened area. Dorsal beak
strongly arched, umbo swollen. Surface multicostate,
shell substance fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep; bounded
by a free spondylium which extends for a long distance
forward.
Dorsal interior. — Septal plates widely spaced, rather
short. Inner plates exceedingly short. A low short
median ridge exists in the middle of the notothyrial
cavity.
Discussion. — Cymbidium is a most unusual brach-
iopod and its careful description by Kirk leaves little to
be added. Of special interest is the free spondylium,
which is a very rare structure in this class of organisms.
Careful sectioning by Kirk failed to reveal any trace
of a septum or any evidence that the spondylium had
previously been sessile. Among the pentamerids Hol-
orhynchus is the only other genus having a free
spondylium.
In the dorsal valve the septa are clearly pentameroid
although not absolutely typical. Division into three
184
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
sets of plates is not entirely clear. The inner plates
appear to be exceedingly short, making small chambers
at the rear as in Conchtd'tum. In front of the inner
plates the septal ones are low and bear elongate
processes as is usual in pentamerids.
It is difficult to trace the lineage of Cymhidium.
From its external form it would appear to be related
to Conchidium {"biloculare") but the spondylium is
much wider than is usual in that genus. The loss of
the ventral septum appears to be rare among pentam-
erids, and in the orthids with spondylia is seen only in
the Middle Cambrian Protorthis and Loferia.
Genus PLATYMERELLA Foerste 1909
PI. 27, figs. 2,3,5, 11
Foerste, Bull. Sci. Lab. Denison Univ., vol. 14, 1909,
p. 70, pi. 1, figs. lA-D; vol. 19, 1920, p. 223,
pi. 23, fig. 5.
American Species
Platymerella man?:ie?!sis Foerste 1909
Conchidium crassiflica Hall and Clarke 1 895
Distinguishing characters. — Platymerella was
distinguished by its nomenclator as unique for the fol-
lowing reasons: (1) absence of a straight hinge mar-
gin, (2) non-galeatiform exterior, (3) ventral and
dorsal beaks approximate, (4) median septum short.
Discussion. — Some time after the appearance of
the original description of Platymerella, Dr. Foerste
redescribed the genus on the basis of new material
showing perfectly the character of the internal struc-
ture, which had hitherto been unknown. As shown
by these specimens, the genus has essentially the same
structure as Pcntamerus, but the plates in both valves
are unusually short, actually making it difficult to
distinguish the ventral from the dorsal, as stated by
12 5 4. ^
F,c. Z\.—Cymbidium acutum Kirk. Sections cut through the beak of a dorsal valve, showing pentameroid character
of the septal plates. Distance from beak:
1 — 1 mm. + — 5 mm.
2—3 5—6
3—4
Genoholotype. — p. manniensis Foerste 1909.
Description. Exterior. — Longitudinally suboval,
hinge-line narrow; cardinal extremities rounded.
Lateral profile subequally biconvex; anterior commis-
sure rectimarginate. Fold and sulcus indistinct, or
ventral sulcus shallow and dorsal fold low. Beaks
subequal, incurved. Surface multicostate ; shell sub-
stance fibrous, impunctate.
Ventral interior. — Spondylium duplex short, septum
short. Spondylium directed antero-dorsally. Ovarian
areas marked by elongated pustules.
Dorsal interior. — Cardinalia confined to the poste-
rior, exceedingly short. Septal plates short, discrete or
united by extra shell deposit to form a small chamber
which is U-shaped in cross-section, making a pseudo-
cruralium. Brachial processes as in Pentamerus. In
front of the pseudocruralium is a long, slender, but
low median ridge. The adductors are elongate impres-
sions on each side of the median ridge.
Geologic range.— Early (and ? Middle) Silurian.
Foerste. The published description of the genus leaves
little to be added now that the interiors are known.
However, Foerste figures and describes two types of
shells in Platymerella. In one of these, the septal
plates of the cardinalia are united at their junction
with the valve by extra testaceous substance which
forms a pseudocruralium, as may be seen in Foerste's
figures 5E and 5F. The other type appears in figures
5G and 5H; it shows two elongate septal plates ex-
tended for a considerable distance along the inner
surface of the valve, and strongly resembles Pentam-
erus. In the type which forms a pseudocruralium
there is no trace of the extensions of the septal plates
forward, and, on the other hand, in the type with the
elongate, parallel plates there is no evidence of a median
septum. There are two possible explanations: (1)
we are here dealing with homceomorphs, one type
representing Platytnerella and the other being refer-
able to Pentamerus; (2) we may look at the problem
from another angle and maintain that both types belong
to the genus Platymerella, the form with the pseudo-
GENERA OF THE SUBORDER PENTAMEROIDEA
185
cruralium being developed from the type with the
parallel plates by deposition of adventitious shell mat-
ter between the plates. Specimens from Mannie,
Tennessee, examined by us appear to conform to the
first type, that with the pseudocruralium, and it is
to this form that the name must be restricted unless
further acquisition of material shows that Platymerella
s. s. develops from a type with parallel plates and no
adventitious material. One specimen from Illinois sec-
tioned by us is of the Pentamerus type, and probably
the Alexandrian species from Illinois now referred to
P. mantuensis are actually not the same species and
may not be of the same genus.
Foerste has suggested that Platymerella is closely
related to Pentamerella. The cardinalia are sugges-
tive of this relationship but the shape of the valves, the
nature of the beaks, and the structure of the spon-
dylium are quite different. Furthermore, there is
an enormous time discrepancy between the two genera
which makes the relationship rather remote. Platy-
merella is of great interest because it is the earliest
known pentamerid (together with the Pentam.erus-\\\it
form referred to above). Here again a plicated form
introduces a large group of shells.
Genus VIRGIANA Twenhofel 1914
PI. 27, figs. 1,6, 7, 16; t. fig. 35
Twenhofel, Geol. Surv. Canada, Mus. Bull. 3, 1914, p. 27.
Genoholotype. — Pentamerus barrandei Billings
1857, Geol. Surv. Canada, Rept. Prog, for 1856,
p. 296.
Description. Exterior. — Elongate-oval, hinge-
line short, lateral profile biconvex, the ventral valve
having the greater convexity. Anterior commissure
sulcate, uniplicate, or nearly rectimarginate. Ventral
valve usually with a low fold, which in young stages
forms a median plica in a low sulcus; the dorsal valve
in young shells usually has a noticeable fold, which
may reverse at maturity into a sulcus or may remain
as a low fold. Interareas obsolete, ventral beak in-
curved strongly, umbo swollen; dorsal beak curved
under the ventral. Surface unevenly multicostate ;
shell substance fibrous, impunctate.
Ventral interior. — Delthyrial cavity deep ; spon-
dylium duplex long, free anteriorly; duplex septum
short.
Dorsal interior. — Dorsal valve provided with two
short, stout septal plates which extend nearly vertically
and attach directly to the internal surface of the
valve.
Geologic range. — Early Silurian of North
America.
Species
ClorinJa barrandei Billings 18 57
Pentamerus decussatus Whiteaves 1891
Virgiana anticostiensis Twenhofel 1928
V. major Savage 1916
V. mayvillensis Savage 1916
Distinguishing characters. — Virgiana is most
readily identified by its strongly convex ventral valve
and relatively gently convex dorsal valve, elongate
spondylium, and short, discrete septal plates.
Discussion. — In the ventral valve of young indi-
viduals of V. barrandei, for 2 or 3 millimeters there
is a shallow sulcus, but after this distance a low
median plica develops in the depression. As growth
continues, the sulcus becomes shallower and finally
disappears, but the median plica enlarges and continues
to the front margin as a low fold. In some varieties
the median plica consists of a bundle of low costs.
The fold at the front margin is very gentle and is
usually narrow.
On the dorsal valve of young individuals of V . bar-
randei the young are provided with a low plica, in-
dented medially by a shallow stria. With continued
growth and bifurcation of the median plica, the fold is
lost in the ornamentation of the valve. In some speci-
mens the antero-median portion of the valve is de-
pressed into a very shallow sulcus. It is this phenom-
enon of the "reversion" of the fold and sulcus that
Twenhofel considered the most important generic
character of his genus. However, in the specimens
from Anticosti in the Peabody Museum there are many
in which the dorsal fold maintains its identity through-
out the length of the valve. This is especially true
of the small V. anticostiensis. Furthermore, some
specimens of V. mayvillensis preserve the fold from
near the beak to the front margin.
More important in the diagnosis of the genus than
reversion of the fold and sulcus is the internal struc-
ture of the valves. The ventral shell has an exceed-
ingly long spondylium which is free for most of its
length. In the dorsal valve the cardinalia are remark-
able for their simplicity and shortness; in one indi-
vidual having a length of 36.5 mm. the septal plates
extend for only 5 mm. These plates arc pentameroid,
uniting directly with the valve. This structure differs
from that of Clorinda in having the plates nearly
parallel in horizontal section and in not possessing the
inner carin.t which project into the cavity bounded by
the plates. The structure therefore is not greatly
different from that of Conchidium and we are remov-
ing the genus to the subfamily Pentamerina: where it
properly belongs.
Hall and Clarke""^ figure an interior of Pentamerus
barrandei showing a spondylium in both valves, that
"Pal. N. Y., vol. 8, pt. 2, 1893, p. 243, t. fig. 174.
186
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
of the dorsal one being shallow and supported by a very
low median septum. This figure is utterly incorrect
and gives an entirely wrong impression of the interior
of Virg'iana. The dorsal structure of this genus is
precisely like that of Pentamerus in composition and
most nearly resembles that of Platymerella in the
brevity of its septa.
discrete, with more or less long brachial supports.
The only genus is Strlcklandia Billings of the Silurian.
The origin of this family is not yet known, but it
may have come out of camerellids. Instead of retain-
ing the shell form of the camerelHds, however, the
Stricklandida; developed into wide-hinged types. It is
possible also that the stricklandids came out of a much
O (D O O C)
s
o
6
10
II
Fig. 35. — Serial sections of Virgiana barrandei (Billings), from Anticosti. Notice the general similarity of the structure
to that of Pentamerus s. s., pi. 29, fig. 11. The difference between the two genera internally is the brevity of the dorsal
septa in Virgiana, in this specimen a little more than 2 mm. Distance from beak:
1 — 1.0 mm. 7 — 6.4 mm.
2—2.2 8— 7.7
3 — 2.9 9 — 8.9
4 — 4.4 10—10.5
5—5.2 11—11.5
6—5.9
The shell sectioned was 41.8 mm. in length. All trace of the spondylium disappeared at 24 mm. from the beak; the
ventral septum disappeared at about 5 mm. These facts indicate an exceedingly long spondylium and very abbreviated
septum.
? Family STRICKLANDIDA Hall and
Clarke 1894
Divergent large Pentameracea, probably developed
out of the Camerellidas. Spondylium short, supporting
a short septum. Cardinalia simple but specialized and
older stock, the Syntrophiids. In neither supposition are
the annectant genera known, but it is more natural
to look for them in the later Ordovician, in which
event the origin would be out of the camerellids.
The Stricklandias are first met with in the early
Silurian of North America in faunas of northwestern
GENER/\ OF THE SUBORDER PENTAMEROIDEA
187
European origin, and the ancestral stock is to be looked
for in the later Ordovician of Europe.
Interareas are characteristic of the Orthacea and
Strophomcnacea of the Protremata, and in the Tclo-
tremata are of common occurrence only among the
Spirifcracea. They manifest themselves in some of
the Pcntameracea only and their appearance here, say
Hall and Clarke,"^ "may be regarded as the resumption
of a primitive or original character which was normal"
for the Protremata.
Regarding interareas among the rostrate pentam-
erids, Hall and Clarke say:"^
Every now .ind then specimens will show a clearly devel-
oped cardinal area; always in Stricklandinia, frequently and
normally in Gyfidula, rarely and of exceptional occurrence
in Pentimterdla. Stricklandinia possesses so straight and long
a hinge, so sharply defined an area and so short a spon-
dylium, that it is more natural to regard this genus as the
accompaniment, rather than the close organic kin of the
other pentameroids, deriving its differentials directly from
those long-hinged and straight-hinged shells of the early
Silurian [=: Ordovician], which constitute the genus
Syntrofhia.
Genus STRICKLANDIA Billings 1859
PI. 28, figs. 25, 27, 28; pi. 29, fig. 6
Billings, Canadian Nat. and Geol., vol. 4, 1859, p. 132,
figs. 8-9 {lens).
HalJ and Clarke, Pal. N. Y., vol. 8, pt. 2, 1893, p. 249,
pi. 73, fig. II.
Syn. Stricklandinui Billings 1863.=^
Genolectotype (Hall and Clarke). — 5. gasfeen-
w Billings 1859.
Description. Exterior. — Shells variable in size but
tending to be large, elongate-oval, transversely oval, or
subcircular in outline ; hinge-line straight, cardinal ex-
tremities rounded. Lateral profile biconvex, the dorsal
valve usually having the greater convexity. Anterior
commissure rectimarginate or gently uniplicate; ven-
tral sulcus shallow or obsolete or raised into a low
fold. Dorsal fold usually present, low. Ventral inter-
area wide, curved, apsacline; delthyrium open. Dor-
sal interarea reduced, apsacline. Surface smooth or
multicostate. Shell substance fibrous, impunctate.
Ventral interior. — ^Teeth small, dental plates short
and stout, uniting to form a small spondylium duplex.
Supporting septa short.
Dorsal interior. — Internally there are two slightly
divergent plates which slope toward each other but do
■* Pal. N. Y., vol. 8, pt. 2, 1894, p. 3 36.
" Op. cit., p. 342.
^^ Stricklandia, a plant, does not invalidate Stricklandia
Billings 1859, as that author supposed.
not unite. The inner margins of the plates are thick-
ened and give off long processes which form the arm
attachments. Adductor impressions are elongate pits
on the floor of the valve, the anterior pair slightly
divergent distally, the posterior pair narrower and
subparallel.
Geologic range. — Lower and Middle Silurian.
American Species
Stricklandia aniicostiensis Billings 1863
S. billingsiana {Dzwion) 1880
S.brevis Billings 1859
S. breviuscula (Savage) 1916
S. canadensis Billings 1859
S.castellana (White) 1876
S. chafmani (Hall and Clarke) 1895
5. circularis (Savage) 1916
S.davidsoni {'&\\\\ng%) 1868
S. dejormis (Meek and Worthen) 1870
S. gasfeensis Billings 1859
S. manitouensis (M. Y. Williams) 1919
S.melissa (Billings) 1874
S.multilirata {'WKxtfidd) 1877
S.norzcoodi (Yoersii) 1906
S . fyriformis (Sivigc) 1916
S. fyrijormis elongata (Savage) 1916
S. fyrijormis varicosa (Savage) 1916
S.salteri (Billings) 1868
5. j/ria/j (Twenhofel) 1928
S. triplesiana (Foersle) 188 5
Clorinda becsciensis (Twenhofel) 1928
European Species
A try fa lens Sowerby 1839
Sfirifer liratus Sowerhy 1839
Pentamerus microcamerus McCoy 1859
Distinguishing characters. — Stricklandia is best
identified externally by its lenticular outline, wide
hinge-line, and well developed interarea. The spon-
dylium and its supporting septum are very short. The
cardinalia consist of two concave plates giving off long
brachial processes from their posterior inner margins.
Discussion. — Billings' genus differs widely from
all members of the Pentameracea in several features,
both internal and external. The most striking external
variation is the width of the hinge-line, which is
narrow in all other known members of the super-
family. Along with the wide hinge-line goes a short
but wide interarea, seen best in the genotype. All of
the pentamerids retain remnants of the interarea but
they are confined to the margins of the delthyrium and
in some species are nearly obsolete.
The spondylium is a typical duplex one, and is re-
markable for the abbreviation of both the septum and
the spoon. These features in themselves are of no
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
great taxonomic importance, but in combination with
the peculiarities of the dorsal valve form a unique
ensemble. The structure of the cardinalia is compar-
able to that of Orthorhynchula among the early Rhyn-
chonellacea, is much simpler than in the Pentameridae,
but not more so than in the Camerellidas. In Ortho-
rhynchula the crural bases are concave plates hanging
free in the valve and bear long, curved crural processes.
Regarding Stricklandia, Hall and Clarke have this
to say:
These pentameroids are principally remarkable for the
unusual development of the cardinal areas of both valves
in the larger and more typical species, and the straight
orthoid hinge in the earlier and smaller members of the
group. The combination of such features with an internal
chambered structure is not of frequent occurrence among
these genera. [The interareas] are sharply defined on both
valves, and so persistent are they that we look for the origin
of this combination, not among the various pentameroids. . .
but to the small, transverse shells of the early faunas to
which the term Syntrofhia has been applied,
as Syntrofhia ? arachne and S. ? arethusa of the Lower
Ordovician; these species, however, are not of the
genus Syntrofhia but may belong to Huenella. This
origin may not be the correct one, but in that event
why do we not find any Ordovician stricklandid ? We
are therefore inclined to look for the origin of the
family in the Camerellidae, with the idea that the
small inherited interareas are redeveloped into the
much larger ones of Stricklandia.
In the dorsal valve of Stricklandia, according to
Hall and Clarke, "the short dental plates, at their
inner angles, bear long crural processes," and are
analogous with those of Amfhigenia, but do not unite
to form a hinge-plate or cruralium as in that genus.
On page 355 these authors erect the family Strick-
landidas for the genera Syntrofhia and Stricklandia.
The present authors agree that Stricklandia can not be
incorporated in the family Pentameridae, and we there-
fore accept the family Stricklandids but exclude from
it Syntrofhia.^^
^' The junior author would exclude the Stricklandid^
from the Pentameroidea entirely. The cardinalia are
totally unlike anything known in that order (Syntrophiacea
and Pentameracea). In his opinion the best place for
Stricklandia, so far as present knowledge goes, is among the
early RhynchoneUacea.
APPENDIX
?
Superfamily RHYNCHONELLACEA Schuchert 1896
Genus RHYNCHOCAMARA Schuchert and
Cooper 1931
(Gr. rhynchos, beak; knmnra, chamber)
PI. 25, figs. 1,2, 7, 17, 18
Schuchert and Cooper, Anier. Jour. Sci. (5), vol. 22, 1931,
p. 248.
Genoholotype. — R. flicata Schuchert and Cooper
1931.
(D
Cb
internal structure of Rhynchocamara is essentially
rhynchonelloid, not pentameroid, since the notothyrial
or subrostral chamber has much the same shape as that
seen in later rhynchonellids.
Geologic range. — Ordovician (Chazy), so far as
known.
American Species
Camerella bella Fenton 1928
C. variam Billings 1859
Rhynchocamara flicata Schuchert .ind Cooper 1931
CD
5
e
Fig. 36. — Liocoelia froxima (Barrande). The beak and spondylium of Liocoelia are rather strongly curved, which
accounts for the peculiar oval seen in section 1. Sections 4 and 5 show the rhynchonelloid chamber in the dorsal valve.
Distance of each section from the beak:
1 — 1.4 mm.
2—2.6
3—3.3
4 — 3.5
.5 mm.
6-5.2
7—6.2
In a shell 18.6 mm. in length the dorsal septum persisted for 8.5 mm. and the ventral septum was present 9 mr
anterior to the beak.
The chief distinguishing features of Rhynchocamara
are the camereUoid exterior, short hinge-line, ventral
spondylium duplex, and rhynchonelloid cruralium.
From Camerella it differs in outline, the former being
more globular, and in the structure of the dorsal valve.
The cruralium duplex of Camerella is long and nar-
row, extending for perhaps one-fourth the length of
the valve, whereas in Rhynchocamara it is confined
to a small region beneath the beak. The dorsal
Genus LIOCCELIA Schuchert and Cooper 1931
(Gr. leios, smooth; koilia, belly)
PI. 25, figs. 31,32, 37; pi. 29, fig. 9; t. fig. 36
Schuchert and Cooper, Amer. Jour. Sci. (5), vol. 22, 1931,
p. 248.
Genohoi.OTVPE. — Pentamerus froxima Barrande,
see Syst. Sil. BohSme, 1879, vol. 5, pi. 9, fig. 5, pi. 81,
fig. 5.
190
GENERA OF THE SUBORDERS ORTHOIDEA AND PENTAMEROIDEA
Description. Exterior. — Subpentameral in out-
line; hinge-line narrow; lateral profile subequallv
biconvex; anterior commissure uniplicate, the fold and
sulcus being defined at the front half. Ventral beak
curved over the dorsal. Surface smooth ; test fibrous,
impunctate.
Ventral interior. — In the ventral valve there is a
long spondylium supported for nearly its full length
by a high median duplex septum which extends for
nearly half the length of the valve.
Dorsal interior. — There is a small and short cru-
ralium supported by a high septum. This cruralium is
partially covered by lateral plates which overhang the
notothyrial margins much as deltidial plates, repre-
senting a divided hinge-plate. In a valve about
20 mm. long the subrostral chamber is only 2 mm.
in length.
Geologic range. — Silurian of Bohemia.
Discussion. — At first it appears difficult to assign
Lioccelia to its proper place among either the pentam-
erids or the rhynchonellids. The external form is
essentially pentameroid, and the ventral valve with its
spondylium duplex is a normal pentameroid feature.
But in the dorsal valve the cardinalia are rather those
of the rhynchonellids, such as Camerofhoria, especially
in the small subrostral vault. It would thus appear
that Liocaelia is essentially a smooth Camerofhoria
having an external form like that of Clorinda, Merista,
or Meristella.
PLATES
PLATE A
Brachiopod Morphology
A CP, accessory cardinal process
AcS, accessory dental socket
Adti, adductor scars
AtiJt, adductor track
Adj, adjustor scars
Adt, adventitious testaceous substance
Br, brachiophore
Brf, brachiophore plate
BrP, brachiophore process
CF, crural fossette
CA, chilidlum
CP, cardinal process
CPF, crural pit filling
D, deltidium
DA, duplex adductor scar
DC, delthyrial cavity
DeP, dental plate
Di, diductor scar
F, foramen
FP, fulcral plate
las, impression of adductor scar
LP, lateral plate
Mbrf, mold of brachiophore plate
Mcf, mold of cardinal process
Mms, mold of median septum
MR, median ridge
MS, median septum and euseptum
Ov, ovarian impression
PC, pedicle callist
PFF, pedicle foramen filling
PPS, primary pallial sinus
PS, pallial sinus
PsS-p, pseudospondylium
SF, filling of socket
Sf, spondylium
SPS, secondary pallial sinus
T, tooth
TPS, tertiary pallial sinus
194
PLATE A
SF
CPF
Z^J
CP-^ x\
DA-^
DeP
CP /Ch
Adt Ch
M
ms
?^^
Xi.
MS
W'/'J44n
10
Addt
PPS 5P5 TP5
Ov
MR-
Adj
p 5 ■'"*'/'?-f ^'"TifflnwA^"''' ■
11
12
14
15
195
PLATE 1
YiGs. Bohemiella romingeri (Barrande)
1^ 18. — Wax replicas of dorsal interior, showing cardinalia
which are orthoid in aspect. Cf. pi. 4, fig. 17. Note
differences from cardinalia of BllUngsella and Eoor-
ihis, figs. 13 and 28.
3. — Internal mold of small ventral valve, showing diver-
gent pallia! trunks.
22. — Wax replica of dorsal exterior. Cf. fig. 6.
Mid.Cambrian,Skrej, Bohemia. Cat.No. S12. x 2.
5. — Dorsal exterior, showing also ventral valve in place.
Deltidium lacking and profile piano- or concavo-
convex.
1 1 . — Dorsal interior, showing remarkable growth of adven-
titious shell over brachiophores. Cf. pi. 5, figs. 1 7, 24.
Wax impressions of molds. Mid. Cambrian, Skrej,
Bohemia. Originals U. S. Nat. Mus. Cat. No.
52267. x2.
Orusia atava (Matthew)
2. — Internal mold, showing slotlike molds of brachiophore
plates. Erroneously referred to Eoorthis by Walcott.
After Walcott, Camb. Brach., pi. 95, fig. 7b. x 0.5.
Orusia lenticularis (Wahlenberg)
7. — Ventral internal mold, showing dental plates.
9. — Dorsal internal mold, showing slotlike molds of brach-
iophore supporting plates, probably very similar to
those of Finkelnburgia.
After Walcott, Camb. Brach., pi. 98, figs. 2d, 2f'.
Reduced.
Oligomys exporrectus (Linnarsson)
4, 15. — Ventral internal mold, showing impression of small
delthyrial cavity and muscle tracks.
Mid. Cambrian (Paradoxides zone), Westrogothia,
Lovened, Sweden. Cat. No. S 16. Fig. 4 x 2.65 ;
fig. 15x6.
8. — Dorsal interior, showing cardinalia. Cf. Billingsella,
fig. 13. The brachiophores of Oligomys, when com-
plete, are similar to those of OrtAis s. s. Replica of
specimen figured by Walcott, Camb. Brach., pi. 88,
fig. 1 1.
17. — Dorsal internal mold, showing pallial marks. After
Walcott, Camb. Brach., pi. 88, fig. Ik. Reduced.
Mid. Cambrian (Agnoi/us Itevigatus zone), Gud-
heim, 12.5 miles SSE of Skara, Sweden. Cat. No.
52249 U. S. Nat. Mus.
Billingsella cf. pepina (Hall)
6^ 19_ — Dors.il and ventr.il exteriors, showing ornamenta-
tion.
1 3. — Dorsal interior, showing cardinalia. Note short brach-
iophores. Cf. Eoorthis, fig. 28.
21^25. — Ventral interiors, showing perforate deltidium.
Fig. 25 shows thickening of median portion of mus-
cular area. Note the large teeth. The deltidium is
an arch as in other orthoids. Cf. pi. 7, fig. 16.
Up. Cambrian, Grand Teton, S. of Muskrat Lake,
Teton Creek, Idaho-Wyoming state line. Cat. No.
S2220. x2.
Figs. Billingsella lindstroemi (Linnarsson)
10. — Ventral internal mold, showing divergent pallial trunks
and reniform ovarian impressions. Cf. Orthis, pi. 2,
fig. 18. After Walcott, Camb. Brach., pi. 87, fig. 6e.
Reduced.
Mid. Cambrian {Paradoxides jorchhammeri zone),
Alunbruk, Oeland I., Sweden.
27. — Ventral internal mold, showing pallial markings and
adherent fragments of shell. A thin section of the
shell substance (see pi. 29, fig. 12) shows it to be
fibrous, and fibres are visible with a hand lens also.
Mid. Cambrian (Paradoxides zone), Westrogothia,
Lovened, Sweden. Cat. No. S 20. x 2.
Protorthis billingsi (Hartt)
12. — Ventral internal mold, showing free spondylium.
Cambrian (Acadian), Seeley St., St. John, N. B.
Cat. No. S94. x2.65.
14. — Ventral valve, showing free spondylium.
After Hall and Clarke, Pal. N. Y., vol. 8, pt. 1,
1892, pi. 7A, fig. 16. Reduced.
Nisusia festinata (Billings)
16. — Wax replica of exterior of a small ventral valve.
Low. Cambrian, near Emigsville, York Co., Penn.
Cat. No. S 9. X 2.
20. — Dorsal internal mold, showing musculature. Cardi-
nalia similar to those of Billingsella but more primi-
tive. After Walcott, Camb. Brach., pi. 100, fig. Ig.
Reduced.
Low. Cambrian, near Emigsville, Penn.
Eoorthis remnicha (Winchell)
23. — Dorsal interior, showing cardinalia. A low cardinal
process or ridge has risen between the seats of muscle
attachment on the notothyrial platform.
Up. Cambrian, S. side Gallatin Valley, Mont.
U. S. Nat. Mus. X 2.
Eoorthis cf. remnicha (Winchell)
26. — Ventral interior, showing thickening on floor of del-
thyrial cavity. This type of structure is called a
pseudospondylium, but the resemblance to a spon-
dylium is very remote in Billingsella and Eoorthis.
28. — Dorsal interior, showing flat, oblique brachiophores.
This specimen is deprived of a cardinal process, hence
the muscles were attached on the floor of the notothy-
rial cavity.
Up. Cambrian, Flat River, Mo. U. S. Nat. Mus. x 2.
Jamesella cf. perpasta (Pompeckj)
24. — Ventral internal mold of a large specimen, showing
muscular marks.
Up. Cambrian, Skrej, Bohemia. Cat. No. S 1944.
x2.
196
PLATE 1
197
PLATE 2
Pigs. Nicolella cf. actoniae (Sowerby)
1, 3. — Dorsal and ventral views of a well preserved indi-
vidual. Cleft chilidium, or chilidial plates, visible in
fig. 1. Compare angular costs and predominantly
concentric finer ornamentation with those of Orthis
(figs. 9, 11, 12, 15).
Ordovician (Lyckholm, Fj), Piersal, Estonia. Cat.
No. S151. x2.
Nicolella actoniae (Sowerby)
4, 6. — Dorsal and ventral views of a large specimen, show-
ing anterior bifurcation of costs.
5. — Ventral internal mold, showing muscle impressions.
Ordovician (Chasmops Is.), Ostragothia, Sodra Fre-
berga, Sweden. Cat. No. S 1 52. x 2.
Nicolella, n. sp.
2. — Dorsal view of a specimen related to A^. moneta
(Eichw.), showing coarse angular costs.
Ordovician (Wierland group, Echinosphsrites Is.),
Popovka near Leningrad, Russia. Cat. No. S 147.
x2.65.
Orthis cf. calligramma Dalman
7, 9, 1 1, 1 3. — Posterior, dorsal, ventral, and lateral views of
the same specimen. Note biconvexity of shells,
rounded costs, and parvicostells in the stris.
Middle Ordovician, Pulkova, near Leningrad, Russia.
Cat. No. 8 167. x 2.
Orthis rotunda Pander
10. — Dorsal interior, showing simple brachiophores, septum-
like cardinal process, small adductor impressions, and
pallial sinuses radiating from them. The sockets for
the teeth are the space between the brachiophores and
the wall of the valve.
Ordovician ( Walchow) , opposite Iswos, Russia. Mus,
Comp. Zool., Harvard Coll. x 2.
Figs. Orthis rotunda Pander — Cont.
16. — Dorsal interior, showing median ridge and pallial
markings.
18. — Ventral interior, showing two prominent pallial trunks,
closely apposed and separated by a small, low ridge.
These trunks bound, on the inside, subreniform
ovarian markings. It is this type of interior that char-
acterizes the ventral valve of the Orthids as here
conceived.
Ordovician (Walchow) , opposite Iswos, Russia. Mus.
Comp. Zool., Harvard Coll. x 2.
Orthis callactis Dalman
8, 12, 15. — Posterior, ventral, and dorsal views of the same
individual. Coarse, simple, rounded ribs covered by
fine radii and finer concentric growth markings clearly
visible. O. callactis is the type of the genus Orthis,
and the kind of shell to which this generic name
should be restricted. Compare the outline and con-
tour with those of O. calligramma (figs. 7, 9, 11, 13).
A critical study of large collections of European Orthis
may prove the advisability of separating the O. calli-
gramma type as a subgenus.
Ordovician (Walchow, Glauconite Is.), Iswos, Wal-
chow River, Russia. Cat. No. S 144. x 2.
1 7. — Dorsal interior, showing small, simple brachiophores.
Ordovician, opposite Iswos, Russia. Shaler Mem.
Exped. Colls., Mus. Comp. Zool., Harvard Coll. x2.
Cyrtonotella aflf. C. frechi (Wysogorsky)
14. — A kind of biconvex Orthis with prominent concentric
lines covering the costs.
Ordovician (Echinosphsrites Is., C), Popovka, near
Leningrad, Russia. Cat. No. S 2099. x 2.
198
PLATE 2
199
PLATE 3
p,Q5 Panderina abscissa (Pander)
1 , 4. — Dorsal and ventral views of a specimen belonging to
the genotype, showing characteristic ornamentation,
especially concentration of growth toward the front.
Note reduced (shortened) ventral interarea well shown
in fig. 1.
Ordovician (Glauconite ss.), Popovka, near Lenin-
grad, Russia. Cat. No. S 157. x2.25.
Panderina tetragonum (Pander)
2, 3. — Dorsal and ventral interiors. After Lamansky, Mem.
Com. Geol., 1905, pi. 2, figs. 11,12.
Ordovician (Walchow, Bi^), Popovka, near Lenin-
grad, Russia. Slightly enlarged.
Paurorthis parva (Pander)
5. — Ventral interior, showing teeth, crural fossettes, median
ridge, and lateral ovarian areas. The muscle area
shows a broad adductor-diductor impression. Cf.
Dalmanella rogata, pi. 17, fig. +.
7. — Dorsal interior, showing subradial pallial sinuses, indis-
tinct muscle field, and prominent elevated median
ridge. Brachiophores oblique, divergent plates sup-
ported by a swelling of adventitious tissue, to be seen
at posterior portion of median ridge. Cardinal process
a faintly discernible ridge just behind the swelling of
adventitious substance. Cf. Ddmanella rogata, pi. 17,
fig- 31.
8, 10. — Ventral and dorsal exteriors of a large mdividual.
Note reduced (shortened) ventral interarea and sub-
fasciculate costellx. The general external resemblance
of P. farva to Dalmanella is a striking instance of
homoeomorphy. Paurorthis, however, differs intern-
ally as illustrated above (figs. 5,7). It differs also in
being impunctate (no endopunctas) but possesses nu-
merous exopunctae which have led to its misidentifica-
tion as Dalmanella.
Ordovician (Glauconite Is.), Gornaja Scheldicha,
Lake Ladoga, Russia. Cat. No. S 1 36. x 3.
6. — Ventral interior, showing broad pallial trunks sepa-
rated by a low median ridge. Subreniform ovarian
areas occupy lateral portions of valve. Wide adductor-
diductor track clearly visible and adjuster (?) im-
pressions outside these may be seen. The interior of
Figs. Paurorthis parva (Pander) — Cant.
Paurorthis is thus close to that of Orthis s. s., and the
genus forms a remarkable homoeomorph of Dalman-
ella s. s.
Ordovician, opposite Iswos, Russia. Shaler Mem.
Exped. Colls., Mus. Comp. Zool., Harvard Coll. x 3.
Productorthis parallela (Pander)
9. — Ventral interior, showing reduced (shortened) inter-
area, prominent dental plates, and peculiar muscle
field. The small, elliptical impressions at the base of
the dental plates have usually been interpreted as
diductor scars; they are, however, smaller than is
common for the scars of the diductors and probably
represent adjustor muscle impressions. The diductor-
adductor impressions occupy the large central elevated
area.
13, 16. — Ventral and dorsal exteriors, showing imbricating
lamellx or "ruffles," remarkable "productoid" form,
and nearly obsolete interareas.
Ordovician (Chazy, Glauconite Is.), Gornaja Schel-
dicha, Lake Ladoga, Russia. Cat. No. S 126. x 3.
1 1 . — Dorsal interior, showing elongated cardinal process
with its compressed myophore. The brachiophores
have developed into cuplike structures which receive
large teeth. Circular chilidium visible on dorsal sur-
face of free or posterior end of cardinal process.
Bipartite character of anterior adductor impressions
clearly visible. The ribbed elevated border around
the periphery of the shell is an aid in articulation.
12. — Reverse, or dorsal, surface of fig. 11, showing imbri-
cated exterior and small, umbrella-like chilidium cov-
ering free end of cardinal process.
Ordovician (Chazy, Glauconite Is., BJ, Popovka,
near Leningrad, Russia. Cat. No. S 127. x 3.
Productorthis cf. eminens (Pander)
14, 15. — Ventral and dorsal exteriors of a species having
finer ribbing. The "ruffled" exterior, however, is
well exhibited. In fig. 15, ventral interarea nearly
obsolete, and a rounded foramen formed by resorp-
tion of the beak by the pedicle.
Ordovician (Glauconite Is., BJ, Popovka, near Len-
ingrad, Russia. Cat. No. S 122. x 3.
200
PLATE 3
201
PLATE 4
Figs. Cyrtonotella semicircularis (Eichwald)
1,4,5,11. — Ventral, dorsal, posterior, and lateral views,
showing multicostate exterior, short interarea, and
concave dorsal valve.
Ordovician (Echinosphaerites Is.), Popovka, near
Leningrad, Russia. Cat. No. S 169. x 5.
Glossorthis tacens Opik
2^ 8. — External and internal views of the same dorsal valve.
The latter illustrates the cardinal process and the
thickening or swelling just in front of it that supports
the brachiophores. The latter structures are broken
off near the sockets so that their full length is not
revealed. Anterior adductor scars bipartite as in
Productorthis and many other orthoid genera.
7, 9. — External and internal views of an exceptionally well
preserved ventral valve. Fig. 9 illustrates vvell the
pseudospondylium and also the various muscle impres-
sions. This pseudospondylium is entirely a secondary
feature, being best developed in mature shells, and is
formed as a deposit under the muscle attachments. In
G. extensa, the pseudospondylium is not developed to
such a marked degree. For details of the ventral
interarea, see fig. 28.
12. — ^Ventral valve, tilted upward to afford a better view
of the pseudospondylium. The short septum visible
in front, and the thick rim, are adventitious deposits
simulating a spondylium.
28. — Enlarged view of interarea of ventral valve of the
same specimen illustrated in fig. 9, x 3, showing pon-
derous teeth and heavy later-il (deltidial? ) plates
along delthyrial margin. On the right side of the
delthyrium, one of these is well shown, the suture
being emphasized by slight fracturing.
Mid. Ordovician (Cj), Kohtla, Estonia. Cat. No.
S2100. All except fig. 28 x 1.5.
Glossorthis extensa (Verneuil non Pander)
3^5^ 10. — Dors.-il, posterior, and lateral views of the same
individual.
Ordovician (Glauconite Is., B,), Popovka, near Len-
ingrad, Russia. Cat. No. S 161. x 1.5.
Productorthis parallela (Pander)
15^ 16. — Internal and external views of posterior of the
same individu.il as in pi. 3, figs. 1 1, 12._ Note unusual
cardinal process and cuplike adventitious shell sup-
porting brachiophore in fig. 15, and umbrella-like
chilidium in fig. 16.
Ordovician (Glauconite Is., B,), Popovka, near Len-
ingrad, Russia. Cat. No. S 127. x 3.
Figs. Hesperorthis tricenaria (Conrad)
13, 14, 25. — Ventral, dorsal, and posterior views of a com-
plete individual. Contrast broad interareas of figs. 14
and 25 with shortened ones of Orthis, figs. 7 and 8
of pi. 2.
26. — Smaller specimen preserving remnantal chilidium and
deltidium.
Ordovician (Black River), Cannon Falls, Minn.
Cat. No. S199. x 1.5.
17. — Internal view of dorsal valve, showing chilidium,
brachiophores, strong median elevation, and internal
marginal ribbing. This type of marginal ribbing,
with a cleft internal rib corresponding to the stria
(groove) of the exterior, is common to many genera
of the Orthida;. x 2.
18. — Same shell, tipped forward to give a better view of
the convex chilidium. x 2.
29. — Enlargement (x 4) of cardinalia of fig. 1 8, to show
chilidium and brachiophores in greater detail. These
brachiophores are typical of the ''Orthis" type, long
and pointed, grooved on the inside, triangular in sec-
tion, the outer sloping face forming resting places for
the teeth of the ventral valve, the crural fossette of the
ventral tooth resting on the carinate, postero-ventral
ridge of the brachiophores.
Ordovician (Trenton), St. Paul, Minn. Cat. No.
S210.
19, 27. — Ventral interiors, showing long interarea and short
deltidium. Notice distinct suture-lines between mar-
gins of delthyrium and deltidium. In fig. 27 the
slender ridge dividing the main pallial trunks of the
ventral valve is visible, and a few of the elevated lines
of the ovarian areas can be seen near the hinge
margins.
2 1 . — Dorsal interior, showing cardinal process and brachio-
phores. Anterior portion of the cardinal process bear-
ing a shallow groove.
Ordovician (Trenton), ScuUsburg, Wis. Cat. No.
S176. Fig. 19 X 1.5; figs. 21 and 27 X 2.
20. — Ventral valve, showing details of interarea. This
specimen illustrates a feature of unusual interest: the
delthyrium is extremely narrow, having been dimin-
ished by the growth of margin.il plates inside the
teeth. (See fig. 28.) Deltidial plate an arch under
delthyrial margins.
Ordovician (Black River), Minneapolis, Minn.
Cat. No. S 2101. X 1.5.
Hesperorthis davidsoni (Verneuil)
22, 23. — Dorsal and ventral exteriors of a well preserved
individual. In fig. 22 perforations are visible on the
surface of the costa:, but these extern.il apertures are
not to be confused with puncts (endopunctae).
24. — Dorsal interior, showing muscle-scars and cardinalia.
Silurian (Gotlandian), Gotland, Sweden. Cat.
Nos. S203, S204 (fig. 24). x 1.5.
202
PLATE 4
203
PLATE 5
Figs. Eridorthis rogersensis Foerste
1, 5. — Dorsal exteriors, showing fold. In early stages the
dorsal valve bears a sulcus which later reverses and
becomes a fold.
Ordovician (Trenton, Cynthiana), Rogers Gap, Ky.
Cat. No. 78712, U. S. Nat. Mus. x 1.5.
Eridorthis aff. E. nicklesi Foerste
2. — Ventral internal mold, showing Orthis-Wke muscula-
ture, pallial trunks, and low median rib.
Ordovician (Eden, Fulton), New Richmond, Ohio.
Cat. No. S 2102. x 2.
Eridorthis nicklesi Foerste
9. — Ventral valve, showing depression of fold to form a
sulcus at front of valve.
Ordovician (Trenton, Cynthiana), Rogers Gap,
Ky. Cat. No. 7871 1 U. S. Nat. Mus. x 1.5.
Glyptorthis fausta (Foerste)
4. — Dorsal interior, showing H esferorthis-\\k& cardinalia.
7. — Ventral interior, illustrating musculature of the genus.
Silurian (Brassfield), near Dayton, Ohio. Cat. No.
S236. xl.5.
8. — Dorsal exterior, showing incipient sulcus at posterior.
Silurian (Brassfield), Centerville, Ohio. Cat. No.
S238. xl.5.
Figs. Schizoramma fasciata (Hall) — Cont.
This genus has been described as a subgenus of
Orthostrofhia, but from its internal structure is dis-
tinct enough to merit generic ranic. Schizoramma
does not have the small, confined ventral muscle area
and the elevated adductor impressions of the other
genus.
Dolerorthis rustica osiliensis (Schrenk)
10, 12, 19,21. — Lateral, posterior, dorsal, and ventral views
of exterior, fig. 1 0 showing faint concavity of ventral
valve toward the front.
15. — Dorsal interior, showing orthoid brachiophores and
cardinal process, and notothyrial platform.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
S282. xl.5.
20. — Ventral interior, showing closely apposed pallial trunks
separated by a low septum that forks at the front.
Subreniform ovarian impressions bounded by these
sinuses. Compare with Orthis s. s., Hesferorthis, and
Glyftorthis (pi. 2, fig. 18; pi. 4, fig. 27; pi. 6,
fig. 26).
23. — Dorsal interior, showing median ridge, orthoid cardi-
nalia, large posterior adductor scars, and smaller bipar-
tite anterior adductor impressions. Cf. fig. 24.
Silurian (Wenlock), England. Mus. Comp. Zool.,
Harvard Coll. x 1.5.
Schizoramma ? gotlandica Schuchert and Cooper, n. sp.
3, 6. — Dorsal and ventral exteriors.
Silurian (Gotlandian), Gotland, Sweden. Cotypes.
Cat. No. S 228. xl.5.
Schizoramma rjisis (Hall and Whitfield)
11, 16. — Ventral and dorsal exteriors of a silicified speci-
men, showing ornamentation.
Silurian (Niagaran, Meniscus) , W. Tennessee. Cat.
No. S221. Fig. 11 X 1.5; fig. 16 x2.
Schizoramma fasciata (Hall)
13. — Ventral interior, somewhat crushed, showing orthoid
musculature, and, more indistinctly, the two closely
apposed palli-il trunks.
14. — Dorsal interior, to show orthoid brachiophores; low,
broad, median ridge; simple cardinal process; and
accessory ridges on each side of it. Small adductor
impressions more indistinctly visible.
Silurian (Clinton), Osgood, Ind. Cat. No. S 222.
X 1.5.
Dolerorthis jnterplicata (Foerste)
18. — Dorsal interior, showing characteristic cardinalia.
Silurian (Niagaran, Osgood), Osgood, Ind.
No. 8 279. X 1.5.
Cat.
Dolerorthis flabellites (Foerste)
1 7, 24. — Obese dorsal interiors, illustrating interesting old-
age modifications of cardinalia and notothyrial plat-
form, and brachiophores heavily overgrown with ad-
ventitious shell substance, which hides them almost
completely. Note "orthoid" ribbing of internal mar-
gin. In fig. 24, note especially adductor impressions
and compare with fig. 23. Compare fig. 24 with
fig. 8 of pi. 1.
22. — Ventral interior, showing orthoid musculature, and
pallial sinuses bounding subreniform ovarian impres-
sions. Cf. fig. 20, and ventral interiors of Orthis,
Hesferorthis, and Ghftorthis.
Silurian (Niagaran, Osgood), Osgood, Ind. Cat.
No. S272. xl.5.
204
PLATE 5
205
PLATE 6
Figs. Ptychopleurella bouchardi (Davidson)
1, 33. — Ventral interiors, showing musculature, pedicle cal-
list, and median ridge.
3, 4. — Ventral and dorsal exteriors, showing prominent
costje and lamellose exterior.
6, 32. — Dorsal interiors, showing cardinal process, brachio-
phores, and adductor impressions.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
S285. Figs. 1, 3, 4, 6 x2; figs. 32, 33 x 3.
Ptychopleurella matapedia Schuchert and Cooper, n. sp.
2, 5. — Dorsal and ventral exteriors of a silicified specimen,
showing strongly lamellose surface.
High Silurian or basal Devonian, Upsalquitch road,
Matapedia, Quebec. Holotype. Cat. No. S287. x 2.
Ptychopleurella lamellosa (Twenhofel)
9. — Posterior view of holotype, showing slitlike delthyrium
produced by growth of lateral plates.
Ordovician (Ellis Bay), Ellis Bay, Anticosti. Cat.
No. 10411 Y. P. M.' X 5.
Archseorthis electra (Billings)
7. — Ventral exterior, x 2.
8. — Ventral interior, showing callus extending forward
from muscular area.
16. — Dorsal interior, showing low median ridge, nearly ob-
solete cardinal process, and brachiophores. x 4.
Ordovician (Canadian), Levis, Quebec. Cat. No.
740, Nat. Mus. Canada. All silicified.
Deltatreta typica Ulrich MS.
10, 19. — Dorsal and ventral exteriors, x 1.5, showing costel-
late exterior and hollow costellas.
14. — Portion of a silicified ventral valve, x 3, showing del-
tidium and large, subapical foramen. Faint radial
lines also visible on interarea.
30. — Silicified dorsal interior, x 2.25, with a ventral valve
lying in it. Primitive nature of brachiophores and
their lateral supports like those of Vellamo plainly
shown, also simple cardinal process and chilidial plates
projecting posteriorly from notothyrial margin. The
ventral interior shows well the pedicle callist.
Ordovician (up. Canadian, ca. 1000 feet beneath
top of Arbuckle Is. (formation name not yet given) ) ,
near Berwyn, Okla. (U. S. G. S. loc. 191K). U. S.
G. S. colls., U. S. Nat. Mus.
Deltatreta sp.
15. — Ventral interior, showing prominent dental plates and
pseudospondylium, the latter produced by a deposit of
adventitious shell beneath the muscles. Cf. ventral
interior in fig. 30; cf. also fig. 13.
Ordovician (2d Ceratopea zone), "inlier," sect. 25,
T 6 N, R 14 W, N. E. of Wichita Mts., Okla.
U. S. Nat. Mus. X 2.
Figs. Deltatreta dice (Walcott)
II. — Dorsal interior, showing primitive cardinalia.
13. — Ventral interior, showing pseudospondylium. Cf. fig.
15.
Drift (probably Ordovician (Canadian)), St. Albans,
Vt. Impressions from type specimens, U. S. Nat.
Mus. Cat. No. 52248. x 1.5.
Glyptorthis cf. bellarugosa (Conrad)
1 2. — Dorsal exterior, showing lamellose surface.
Ordovician ("Simpson"), Criner Hills, Okla. Cat.
No. S 251. x2.
Glyptorthis insculpta (Hall)
17, 20, 21. — Ventral, dorsal, and lateral views of exterior.
Lateral profile biconvex. Cf. same view of Hebert-
ella, pi. 11, fig. 19.
1 8, 26. — Ventral interiors, showing "Orihis" pattern to
perfection. Note muscle area; central adductor track
straight, diductor tracks elongate tear-shaped; and
adjustor scars visible at base of dental plates. Ex-
tending forward from the adductor track is a low sep-
tum which divides the closely apposed pallial sinuses
originating at the front ends of the diductor impres-
sions. Lateral spaces occupied by subreniform ovarian
impressions. Elevated lines in these impressions con-
sidered to be muscle attachments for ovarian bodies.
29. — Dorsal interior, showing an old shell heavily ridged
by pallial markings. Note adductor scars. The car-
dinalia of Glyftorthis are of the "Orthii" type, dif-
fering markedly from those of Hebertella. See pi. 11,
figs. 24, 26.
Glyftorthis has been usually considered to be a sub-
genus of Hebertella, but its lenticular profile and inter-
nal structure relate it rather XoHesferorthis and Orthis.
Ordovician (Richmond), Oxford, Ohio. Cat. No.
S242. X 1.5.
Orthostrophia strophomenoides (Hall)
22. — Dorsal internal mold, showing muscle area and pallial
markings.
25. — Impression from the above, showing elevated muscle
area.
Devonian (New Scotland), near Clarksville, N. Y.
Cat. No. S 320. X 2.
27, 28. — Ventral and dorsal exteriors, showing characteris-
tic ornamentation.
Devonian (Birdsong), Henry Co., Tenn. Cat. No.
9702 Y. P. M. xl.
Orthostrophia aff. O. strophomenoides (Hall)
24. — Ventral internal mold, showing small muscle area and
pallial markings.
Devonian (Hunton), near Crusher, Okla. Cat. No.
S322. xl.5.
Orthostrophia dartae Schuchert and Cooper, n. sp.
23. — Ventral internal mold of paratype, showing small mus-
cle area.
3 1 . — Dorsal exterior of holotype, showing ornamentation.
Silurian (Bouleaux), Port Daniel, Quebec. Cat.
No. S 1985. X 1.5.
206
PLATE 6
207
PLATE 7
Figs. Pahlenella trigonula (Eichwald)
1, 3. — Ventral and dorsal exteriors. Dorsal valve concave.
2. — Ventral interior, showing deltidium and sessile spon-
dylium.
4. — Dorsal interior, showing short brachiophores, chi-
lidium, and elevated muscle area.
Ordovician (Canadian, Walchow, B2),Popovka, near
Leningrad, Russia. Cat. No. S 370. x 2.
Aff. Vellamo multicosta (Hudson)
5, 11. — Views of the same ventral interior, showing rem-
nant of imperforate deltidium.
8. — Ventral interior, showing septum dividing two closely
apposed pallial trunks, and, outside these, ovarian
areas as in Glyftorthis et al.
9. — Dorsal interior, showing cardinalia and musculature.
10. — Ventral interior, showing muscle impressions on spon-
dylium.
These shells are doubtfully referred to Vellamo,
differing from that genus in having what appears to
be an imperforate deltidium, and in details of the
dorsal valve.
Ordovician (Chazy), Sloop Bay, Valcour Island,
N. Y. Cat. No. S3 59. x 2.
Vellamo trentonensis (Raymond)
H. — Ventral interior, showing spondylium and its support-
ing septum, and deltidium.
28. — View of interarea and deltidium. Note position of
teeth.
Ordovician (Galena, bed 6), Kenyon, Minn. Cat.
No. S342. X 1.5.
18. — Dorsal interior, showing anchor-shaped cardin.ilia and
musculature.
Ordovician (Galena), Cannon Falls, Minn. Cat.
No. 8 348. X 1.5.
Cf. Vellamo squamata (Pahlen)
1 5. — Interarea.
31. — Interior, showing spondylium.
Ordovician (Cj) , Kohtla, Estonia. Cat. No. S 2 1 0 5 .
xl.S.
Figs. Vellamo cf. emarginata (Pahlen)
16, 29, 30, 32. — Posterior, ventral, lateral, and dorsal views
of the same individual, showing details of ornamenta-
tion and contour and outline of valve.
Ordovician (Mohawkian, Wesenberg), Wesenberg
quarries, Estonia. Cat. No. S 339. x 1.5.
Vellamo verneuili (Eichwald)
24, 27. — Dorsal and ventral exteriors of type species of
genus.
Ordovician (Cincinnatian, Lyckholm, F^), Kertel,
Estonia. Cat. No. S 347. x 1.5.
Vellamo diversa (Shaler)
25. — Dorsal interior, showing cardinalia and musculature.
Ordovician (Ellis Bay), Junction Cliff, Anticosti.
Cat. No. 10335 Y. P. M. x 1.5.
Apomatella ingrica (Pahlen)
6, 7.- — Views showing spondylium.
12. — Ventral exterior, showing also dorsal valve in con-
junction.
13. — Ventral exterior, showing procline position of inter-
area.
These shells may be somewhat remote from the true
Vellamo line.
Ordovician (Canadian, Walchow, B„), Popovka,
near Leningrad, Russia. Cat. No. S2104. x 2.
Clitambonites adscendens (Pander)
17, 19, 22, 23. — Posterior, dorsal, ventral, and lateral views
of exterior. Note particularly ornamentation and
procline interarea. Deltidium commonly imperforate
in adult shells, x 1.5.
20, 21. — Ventral and dorsal interiors, the former showing
the spondylium. Note peripheral border or frill.
x 1.5.
26. — Enlargement of exterior of specimen in fig. 19,
X ca. 4.5.
Ordovician (Canadian, Kunda), Popovka, near Len-
ingrad, Russia. Cat. No. S 372.
208
PLATE 7
209
PLATE 8
Figs. Gonambonites planus Pander emend. Pahlen
1. — Ventral interior, showing spondylium and its acces-
sory septa. Marginal thiclcening visible also.
2, 3, 20. — Dorsal, ventral, and posterior views of a small
individual, showing prominent process extending from
deltidium. Fig. 20 shows deltidium somewhat
crushed in.
4, 7. — Dorsal interiors, showing cardinalia and chilidial
plates. Brachiophores to be seen protruding from
lateral adventitious thickening just antero-laterally of
notothyrium.
5,21,26. — Posterior, ventral, and dorsal views of a large
shell, showing characteristic ornamentation.
Ordovician (Canadian, Walchow, Bj), Wassilkowo,
near Lake Ladoga, Russia. Cat. No. S 333. x 1.5.
25. — Ventral interior of a large specimen.
Same locality as above. Shaler Mem. Exped. Colls.,
Mus. Comp. Zool., Harvard Coll. x 1.5.
Estlandia marginata (Pahlen)
6. — Dorsal interior, showing cardinalia and median ridge.
Brachiophores may be seen in postero-lateral portions
of shell just outside adventitious thickenings anterior
and laterally of notothyrium.
8. — Ventral interior, showing spondylium. Foramen in
deltidium closed by a plug of shell substance.
Ordovician (Kuckers, Brandschiefer), Baron Toll's
estate, near Jewe, Estonia. Cat. No. S 327. x 1.5.
9. — A fine dorsal interior, showing cardinalia. Notice
brachiophores outside anchor-shaped adventitious
deposits.
Middle Ordovician (Cgo), Kohtla, Estonia. Cat.
No. S 2106. X 1.5. Presented by A. Opik.
Hemipronites tumidus Pander
10. — Ventral interior with deltidium missing, showing
median septum dividing two pallial trunks which in
turn surround inside margins of subreniform ovarian
impressions. Cf. Glyftorthis insculfta, pi. 6, figs. 18,
26, and Orthis, pi. 2, fig. 18. It will be noted that
the spondylium is the homologue of the dental plates
and floor of the deltidial cavity. The septum is the
homologue of the small ridge dividing the pallial
sinuses in Orthis s.s.; the sinuses are situated in
precisely the same place and bound similar ovarian
impressions.
Ordovician (Walchow, Bj), Popovka, near Lenin-
grad, Russia. Cat. No. S3 69. x 1.5.
Figs. Hemipronites tumidus Pander — Cont.
11. — Dorsal interior, showing cardinalia. Cardinal process
simple as in Orthis s. s., and brachiophores rodlike
plates supported by adventitious tissue which, in this
instance, spreads laterally to form an anchor-shaped
mass with the median ridge.
14, 15. — Posterior and ventral exteriors, showing ornamen-
tation.
Ordovician (Walchow, Bj), Popovka, near Lenin-
grad, Russia. Cat. No. S 369. x 1.5.
Hemipronites cf. maximus Pander
12,13. — Ventral and dorsal exteriors, showing fine costellae.
Ordovician (Canadian, Walchow), Popovka, near
Leningrad, Russia. Cat. No. S 365. x 1.
Marionella typa Bancroft
16. — Dorsal internal mold, showing dinorthid character of
cardinalia.
17. — Muscle-scars and pallial markings of ventral valve.
18. — Impression showing external sculpture.
Ordovician (upper Longvillian), Horderley District,
East Shropshire, England. Cat. No. S2107 (fig.
18), and S2108. x 1.5.
Multicostella platys (Billings)
19, 23. — Ventral and dorsal exteriors, showing ornamenta-
tion of this biconvex dinorthid.
Ordovician (Chazy), Speer's Ferry, Virginia. Cat.
No. S92. X 1.5.
Multicostella saffordi (Hall and Clarke)
22. — Ventral interior, showing musculature, which is simi-
lar to that of Valcourea.
27. — Dorsal interior, with crenulated dinorthid cardinal
process plainly visible. Brachiophores also similar to
those of Valcourea.
Multicostella was common in Chazy time, but evi-
dently did not survive this stage. A deltidium or
chilidium is unknown in this dinorthid stock.
Ordovician (Chazy), Washburn, Tenn. Cat. No.
S786. X 1.5.
Clinambon anomalus (Schlotheim)
24, 28. — Posterior and lateral views, showing unusual de-
velopment of chilidium, and posterior portion of
dorsal valve.
Ordovician (Mohawkian, Kegel, D,), Redder, Es-
tonia. Cat. No. S 337. x 1.5.
210
PLATE H
211
PLATE 9
FiGS. Dinorthis sweeneyi (Winchell)
1. — Ventral interior, showing form of muscle impressions
and remnantal deltidium. x 1.5.
10, 14. — Lateral and dorsal views of exterior, showing con-
vexo-concave profile and costate exterior, x 1.5.
1 1 . — Dorsal interior, showing orthoid brachiophores and
crenulated myophore of cardinal process. In its later
stages of growth, the cardinal process may become
distinctly lobate, see figs. 3 and 20. x 2.
Ordovician (Decorah), St. Paul, Minn. Cat. Nos.
S686 and S 693.
Dinorthis pectinella (Emmons)
2. — Ventral interior of a silicified specimen, showing in-
terior. X 1.
5. — Exterior, x 0.75, with its costae.
Ordovician (Trenton), Curdsville, Ky. Cat. No.
S685.
Dinorthis (Plaesiomys) subquadrata (Hall)
3. — Dorsal interior, showing cardinal process of an old
shell and lobation developed in late stages, x 2.
20. — Same, x 3, showing myophore and shaft, also orthoid
nature of brachiophores and swollen notothyrial plat-
form. Cf. pi. 10, fig. 25.
Ordovician (Richmond), Richmond, Ind. Cat.
No. S 728.
Dinorthis (Pionorthis) sola (Billings)
4^ 6^ 7^ 8. — Ventral, lateral, posterior, and dorsal views of
a large specimen, showing ornamentation and lentic-
ular outline of the species.
Ordovician (Richmond), Pt. Carleton, Anticosti.
Cat. No. S760. x 1.5.
9._Ventral internal mold, showing characteristic dinor-
thid muscle-scars.
Ordovician, cliff, W. side Vaureal Bay, Anticosti.
Cat. No. S 758. x 2.
Aff. Dinorthis (Pionorthis) carletona Twenhofel
13. — Ventral internal mold, showing muscle impressions.
Ordovician, Raven Nest, Anticosti. Cat. No. S 754.
X 1.5.
FiGs. Dinorthis (Retrorsirostra) carleyi (Hall)
21,23. — Ventral and dorsal exteriors, showing procline
ventral interarea.
Ordovician (Arnheim), Jefferson Co., Ind. Cat.
No. S 747. xl.5.
Dinorthis (Retrorsirostra) carleyi insolens Foerste
22. — Ventral interior, showing teeth, crural fossetts, curv-
ing dental plates, and muscle impressions. Note
absence of pallial marks.
Ordovician (Waynesville) ? , Hanover, Ohio. Cat.
No. S 750. xl.5.
Austinella sp.
12. — Ventral interior, showing large teeth and outline of
muscle area.
Ordovician (Maquoketa), Spring Valley, Minn.
Cat. No. S 375. xl.5.
Austinella whitfieldi (N. H. Winchell)
15. — Ventral internal mold, showing muscle-scars. These
and the pallial trunks diverging from the anterior
ends of the diductor impressions appear to relate the
genus most closely to Dinorthis.
16, 19. — Ventral and dorsal exteriors.
18. — Reverse side of fig. 15, dorsal internal mold, showing
adductor impressions.
This genus has been referred to as a subgenus of
Plectorthis, but structurally it has nothing to do with
PUctorthis or the Plectorthidse.
Ordovician (Maquoketa), Spring Valley, Minn. Cat.
Nos. S 374 and S 376 (figs. 16, 19). x 1.5.
Austinella scovillei (Miller)
22. — Ventral interior, showing teeth, crural fossettes, curv-
tinctly dinorthid in structure.
Ordovician (Richmond), near Lebanon, Ohio. Cat.
No. S 377. xl.5.
212
PLATE 9
213
PLATE 10
Pigs. Cyclocoelia sordida (Hall)
1, 5. — Ventral and dorsal exteriors.
2, 4.- — Ventral and dorsal internal molds, the former show-
ing short dental plates and the latter the mold of the
median septum.
Ordovician (Maysville, Fairmount), Cincinnati,
Ohio. Cat. No. S 383. x 2.
Cycloccelia sectistriata (Ulrich)
3, 7, 9. — Lateral, dorsal, and ventral views of exterior.
Ordovician (Maysville, Fairmount), Cincinnati,
Ohio. Cat. No. S 387 (one of Ulrich's type lot).
x2.
Skenidioides billingsi Schuchert and Cooper
6, 11, 13, 14. — Lateral, ventral, posterior, and dorsal views
of holotype.
8, 10, 12. — Dorsal interiors of paratypes, illustrating well
high dorsal septum, cardinal process, and cruralium.
Fulcral plates visible forming sockets. Brachiophores
broken off, but when preserved, very long.
Ordovician (Black River), Paquette Rapids, Ottawa
River, Quebec. Cat. No. S 20 13 (holotype, 2013a).
x4.
Dinorthis (Plaesiomys) subquadrata (Hall)
15. — Ventral internal mold, showing characteristic muscle-
scars. The adjustor scars are prominent in the whole
dinorthid stock.
Ordovician (Richmond), Spring Valley, Minn. Cat.
No. S 732. X 1.5.
17, 18. — Dorsal and ventral exteriors, x 1.
24. — Ventral interior, showing musculature and course of
pallial markings, x 1.5.
Ordovician (Richmond), Richmond, Ind. Cat.
No. S728.
Figs. Dinorthis (Plaesiomys) subquadrata (Hall) — Cont.
25. — Dorsal interior, showing cardinalia. x 1.5.
26. — Interior of a gerontic ventral valve, showing extreme
thickening of shell, x 1.5.
Ordovician (Richmond), Richmond, Ind. Cat.
No. S728.
Valcourea magna Schuchert and Cooper, n. sp.
16, 20, 27, 29. — Posterior, lateral, dorsal, and ventral views
of exterior.
28. — Ventral interior, showing musculature and pallial
markings. This specimen is not provided with a del-
tidium but the pedicle callist is visible.
Ordovician (Simpson). Criner Hills, Okla., sect.
35, 6 S, 1 E. Cotypes. Cat. No. S 779. x 1.5.
Valcourea deflecta (Conrad)
19. — ^Ventral interior, showing muscle-scars and deltidium
in place.
21. — Dorsal interior, showing cardinalia. Notothyrial
platform greatly thickened.
23. — Interarea of specimen shown in fig. 19, showing del-
tidium, and teeth with accessory sockets.
Ordovician (Black River), Allen Hunter quarry.
Fountain, Minn. Cat. No. S 771. x 1.5.
Valcourea loricula (Hall and Clarke)
22. — Ventral interior, showing musculature and lateral
ovarian impressions. This specimen is not provided
with a deltidium but in its place is a decided callist.
This suggests that the deltidium, when present in
Valcourea at least, is the seat of pedicle attachment.
Ordovician (Black River), Allen Hunter quarry,
Fountain, Minn. Cat. No. S 771a. x 1.5.
214
PLATE 10
215
PLATE 11
Plectorthis fissicosta (Hall)
1, 3, 5, 15.- — Dorsal, lateral, ventral, and posterior views of
exterior.
Ordovician (Maysville), Cincinnati, Ohio. Cat.
No. S306. X 1.5.
Plectorthis jamesi (Hall)
2. — Ventral interior, showing dental plates and muscula-
ture. Cf. fig. 14.
Ordovician (Corryville), Cincinnati, Ohio. Cat.
No. S 316. xl.5.
Plectorthis plicatella (Hall)
4. — Dorsal interior. The incurving brachiophore plates
which unite with the valve under the cardinal process
are clearly visible. Cardinal process like that of
Hebertella, see fig. 23.
9. — Ventral interior, showing a delicate dental plate.
Ordovician (Maysville), Cincinnati, Ohio. Cat.
No. S298. X 1.5.
Doleroides gibbosus (Billings)
6. — Ventral interior, to show characteristic musculature.
Cf. fig. 24.
Ordovician (Decorah sh.), Minn. Cat. No. S 537.
X 1.5.
16, 18. — Dorsal and ventral views of an old individual,
showing normal wide sulcus.
Ordovician (Black River), Fountain, Minn. Cat.
No. S 508. xl.5.
Doleroides cf. gibbosus (Billings)
7, 8, 11. — Dorsal, ventral, and posterior views of exterior
of a well preserved individual, showing pionodemoid
outline. This particular specimen has a narrower
fold and sulcus than is usual in the species.
Ordovician (Black River), Chatfield, Minn. Cat.
No. S 507. xl.5.
Doleroides pervetus (Conrad)
10, 13. — Dorsal and ventral views of exterior.
Ordovician (Black River), Lanesboro, Minn. Cat.
No. S 498. xl.5.
Figs. Doleroides pervetus (Conrad) — Cont.
12. — Dorsal interior, showing cardinalia. Brachiophores
supported by convergent plates as in Plectorthis and
Hebertella.
Ordovician (Black River), Fountain, Minn. Cat.
No. S 499. X 2.
Hebertella occidentalis sinuata (Hall)
14. — Young individual. Note resemblance to Plectorthis,
figs. 2 and 9. x 2.
17,23. — Enlarged views, x 1.75, of cardinalia of an old
shell, showing shaft and compressed myophore of car-
dinal process, brachiophores and their supporting
plates.
19,20,22,25. — Lateral, ventral, dorsal, and posterior
views of a large individual. Note convexo-concave
profile. X 1.5.
24. — Ventral interior, showing muscle area with its double-
track adductor impression and subcrescentic diductor
scars. Adjuster impressions borne, when visible, on
base of dental plates. Notice callus deposit at back
end near pedicle callist; in some specimens this
almost completely obliterates the posterior portion of
the muscular field, x 2.
26. — Adult dorsal interior, showing cardinalia. Shaft of
cardinal process simple, with compressed myophore.
Brachiophores supported by converging plates which
unite under the cardinal process; sockets defined by
fulcral plates. This is different from the usual type
in the Orthidx, in which the brachiophores are simple
rods or blades supported only by a swelling of adventi-
tious shell. X 2.
Ordovician (Maysville), Cincinnati, Ohio. Cat.
Nos. S388 (figs. 19, 20, 22, 25), S 397 (figs. 14,
24), and S451 (figs. 17, 23, 26).
Hebertella frankfortensis Foerste
21. — -Ventral interior, showing bipartite adductor track.
Cf. fig. 24.
Ordovician (Trenton), Frankfort, Ky. Cat. No.
S440. x2.
216
PLATE II
26
217
PLATE 12
Pics. Schizophorella fallax (Salter)
1 , 9. — Ventral interiors, the former an internal mold, x 2,
and the latter an impression taken from it, x 1.5.
Cat. No. B 52133, Brit. Mus. Nat. Hist.
2. — Dorsal exterior, x 1.5, the external mold correspond-
ing to fig. 4. Cat. No. B 52123, Brit. Mus. Nat.
Hist.
3. —Ventral exterior, x 1.5. Cat. No. B 52121, Brit.
Mus. Nat. Hist.
4. — Dorsal internal mold, x 2. Cat. No. B 44610, Brit.
Mus. Nat. Hist.
7. — Impression from the above, x 1.5, showing support-
ing plates of brachiophores.
Ordovician (upper Bala, Drummock group. Starfish
bed), Thraive Glen, Girvan, Ayrshire, Scotland.
Cat. Nos. S 486 and S 487. Impressions of British
specimens.
Mimella globosa (Willard)
5, 10, 14, 15. — Posterior, dorsal, lateral, and ventral views
of exterior. This species was previously referred to
Pionodema, with which it forms a heterochronous
homoeomorph.
Ordovician (Chazy), Luttrell, Tenn. Cat. No.
S483. X 1.5.
6. — ^Dorsal interior, showing septum, cardinal process, and
sessile cruralium.
8. — Ventral interior, showing trilobed muscle area.
Ordovician (Chazy), Washburn, Tenn. Cat. No.
S482. xl.5.
Mimella melonica (Willard)
20. — Ventral interior, showing trilobed muscle field and
pallial markings.
Ordovician (Chazy), Luttrell, Tenn. Cat. No.
S474. xl.5.
Mcewanella lineolata (Savage)
11, 12. — Ventral valve, the latter showing the interarea.
1 8, 22. — Dorsal exterior and interior. Brachiophores of
dorsal interior like those of Platystrofhia, and the
plates supporting them unite beneath the cardinal
process.
2 1 . — Ventral interior. Muscle-scars not defined and mus-
cle field with thickened peripheral rim.
Ordovician (Fernvale), old quarry S. of Regen-
hardt's quarry, N. W. edge of Cape Girardeau,
Missouri. Cat. No. 65872, U. S. Nat. Mus. x 1.
Figs. Mcewanella raymondi Foerste
17. — Ventral exterior, to show characteristic ornamentation.
Ordovician (top of Kimmswick), Cape Girardeau,
Missouri. U. S. Nat. Mus. x 1.5.
Platystrophia crassa (James)
13. — Dorsal interior, showing gerontic condition of car-
dinalia.
Ordovician (Maysville), Spring Valley, Minn. Cat.
No. S583. x 1.5.
Platystrophia laticosta (Meek)
1 6. — Dorsal interior, showing incurving brachiophore plates
which are clearly visible only in young Platystrofhia.
Cf. Plectorthis, pi. 11, fig. 4.
23. — Ventral interior of young shell, showing dental plates
and muscle area. Dental plates not visible in gerontic
shells, see fig. 26.
27. — Dorsal interior, showing muscle impressions and car-
dinalia. The cardinal process of Platystrofhia is
usually much aborted. This figure shows the brachio-
phores and their supporting plates much thickened by
callus deposit.
Ordovician (Maysville), Cincinnati, Ohio. Cat.
No. S 575. xl.5.
Platystrophia cf. laticosta (Meek)
19. — Very young dorsal valve, showing strongly incurving
brachiophore plates and fulcral plates. Cf. similar
views of Plectorthis and Hebertella.
Ordovician (Maysville), Roh's Hill, Cincinnati,
Ohio. Cat. No. S 566. x 3.
Platystrophia acutilirata (Conrad)
24. — Ventral interior of gerontic individual. Dental plates
obsolete and interior pitted by ovarian? impressions.
Ordovician (Whitewater), Oxford, Ohio. Cat. No.
S545. xl.5.
Platystrophia ponderosa Foerste
25. — Dorsal interior, showing a gerontic individual. Car-
dinalia so thickened as to obliterate fulcral plates and
exaggerate brachiophore supports, x 1.5.
26. — Gerontic ventral valve. Dental plates obsolete, owing
to filling in of umbonal cavities, x 1.
Ordovician (Maysville), Cincinnati, Ohio. Cat.
No. S5 56.
218
PLATE 12
219
PLATE 13
PiGs. Skenidium insigne (Hall)
1,2,5,8. — Posterior, anterior, dorsal, and postero-dorsal
views of three individuals, showing characteristic ex-
ternal form. Figs. 1 and 8 show uncovered del-
thyrium, and spondylium.
3. — Dorsal interior, showing wide hinge-plate.
4. — Ventral interior, showing spondylium.
Devonian (New Scotland), Indian Ladder, Albany
Co., N. Y. C.it. No. S2025. x 6.
Finkelnburgia sp.
6, 1 1 . — ^Ventral exterior, and interior showing pseudospon-
dylium.
Ozarkian (Eminence, near top), S. slope of hill
4% to 5 miles S. of Potosi, Missouri. Wax impres-
sions from originals in U. S. Nat. Mus. Cat. No.
S60. x3.
Finkelnburgia sp.
7^ Ig. — Dorsal interiors, showing incurving brachiophore
plates and subradial muscle impressions and strongly
elevated ridges about each impression.
Ozarkian (Huzzah Creek section, bed 7), 10 miles
E. of Slideville, Missouri. Wax impressions from
originals in U. S. Nat. Mus. Cat. No. S 58. x 3.
Finkelnburgia armanda (Billings)
9, 10. — Dorsal internal mold, and wax impression taken
from it.
12. — ^Wax impression of ventral exterior, showing sculpture.
15. — ^Wax impression of dorsal interior. This and fig. 10
show the simple cardinal process and the incurving
brachiophore plates, and the fulcral plates. Structure
much like that of Hebertella or Plectorthis.
Ozarkian (near base of Logan's B3) near Phillips-
burg, Quebec. Cat. No. S 2109. x 2.20.
Fics. Finkelnburgia sp.
13,1 7. — Dorsal and ventral exteriors of a silicified specimen.
16. — Dorsal interior, reverse of fig. 13, showing converg-
ing brachiophore plates and elevated seats of muscle
attachment.
19. — Ventral interior, reverse of fig. 17, showing pseudo-
spondylium.
Ordovician (Canadian), 3 miles S. E. of Rainy Mt.,
Kiowa Co., Okla. Ulrich Coll., U. S. Nat. Mus.
x3.
Finkelnburgia aflf. osceola (Walcott)
14. — Ventral internal mold, showing filling of delthyrial
cavity.
Finkelnburgia appears to be the earliest genus in the
plectorthid line.
Ozarkian, Crawford Co., Missouri. Cat. No. S 62.
x3.
Angusticardinia recta (Pander)
20, 22. — Ventral and dorsal views of this rhynchonelloid
orthid.
2 1 . — Dorsal interior, showing brachiophores and their sup-
porting plates which unite at the floor of the valve
with the median ridge, forming a narrow notothyrial
orthid.
Ordovician ( Walchow, Glauconite ss., Bip) , Popovka,
near Leningrad, Russia. Cat. No. S 171. x 3.
Angusticardinia striata (Pander)
23. — View showing profile.
Ordovician (Walchow, Glauconite ss.,B,3), Popovka,
near Leningrad, Russia. Cat. No. SI 70. x 3.
220
PLATE 13
PLATE 14
Figs. Porambonites teretior (Eichwald)
I, 2, 4, 5, 10. — Dorsal, anterior, posterior, ventral, and lat-
eral views of a rather smooth, attenuate type.
Ordovician (Mohawkian, Kuckers), near Jewe, Es-
tonia. Cat. No. S 1520. x 1.
Porambonites deformatus (Eichwald)
6, 7, 9. — Posterior, ventral, and lateral views of a coarsely
pitted, attenuate type.
Ordovician (Mohawkian, Echinosphserites Is.).
Popovka, near Leningrad, Russia. Cat. No. S 1528.
X 1.5.
Porambonites baueri Noetling
8. — Dorsal interior, showing great internal thickening of
brachiophore (spondyloid) plates.
24. — Dorsal interior of a gerontic individual, showing
greatly thickened brachiophore plates.
Ordovician (Mohawkian, Jewe, DJ, near Jewe,
Estonia. Cat. No. S 1529. x 1.
Porambonites gigas Schmidt
14. — Posterior view, showing resorbed beaks. This condi-
tion of the beaks indicates that the pedicle persisted
throughout the life of the animal.
Ordovician (Richmond, Lyckholm, Fi), Kurkul,
Estonia. Cat. No. S 1518. xO.5.
Porambonites reticulatus Pander
3, 11-13. — Posterior, dorsal, ventral, and lateral views of
the same individual, showing suborbicular outline and
characteristic ornamentation.
15. — Anterior view of another individual, showing deep
ventral sulcus and long tongue.
Ordovician (Chazy, Walchow), Iswos on Walchow
River, Russia. Cat. No. S 1 532. x 1.
Figs. Porambonites reticulatus Pander — Cont.
29. — Enlargement of a portion of fig. 11, to show ornamen-
tation in greater detail.
Ordovician (Chazy, Walchow), Iswos on Walchow
River, Russia. Cat. No. S 1532.
Porambonites schmidti Noetling
20, 27. — Views of ventral interior, the former tipped for-
ward to show better the dental plates. These plates
are discrete but in old forms may unite by secondary
deposition on their sides and the floor of the valve.
21,28. — Two views of a dorsal valve belonging to the
ventral one above. In fig. 28, the reader is looking
directly into the shell and the short brachiophore
plates are not visible but the sockets are clearly dis-
cernible. In fig. 21, the front of the shell is tipped
forward to permit a view of the brachiophore plates,
which are also discrete. There are no structures in
either of these two shells or in the genus linking them
to the Pentameridx.
Ordovician (Mohawkian, Jewe, DJ, Spitham, Es-
tonia. Cat. No. S 1530. x 1.
Lycophoria nucella (Dalnian)
16, 18. — Ventral interiors, showing discrete dental plates.
22, 23. — Dorsal interiors, showing cardinal process.
30. — Same as fig. 22, enlarged three times to show greater
detail. Cardinal process complete and uninjured in
any way, not forked as Hall and Clarke assert. Com-
pressed brachiophore plates visible, and also short
brachiophores.
Ordovician (Chazy, Kunda). Popovka, near Len-
ingrad, Russia. Cat. No. S1515. x 1.5 (except
fig. 30).
17, 19, 25, 26. — Lateral, ventral, dorsal, and posterior views
of a complete individual, showing contour, profile,
and ornamentation.
Ordovician (Chazy, Kunda, B^), Popovka, near
Leningrad, Russia. Cat. No. S 1516. x 1.5.
222
PLATE 14
PLATE 15
Figs. Syntrophina campbelli (Walcott)
1. — Ventral internal mold, showing impression of spon-
dylium.
2, 19. — Dorsal interiors, showing subparallel or divergent
brachiophore plates. Fig. 19 also shows impression
of small callosity at back of notothyrial cavity.
Ordovician (Canadian, lower Roubidoux), hill op-
posite McCabe, Missouri. Cat. No. S 1553. x2.65.
Syntrophina breviseptata Ulrich MS.
15, 16. — Ventral interiors, 15 being an internal mold and
16 an impression taken from it. Spondylium well
shown.
17, 18. — Dorsal interiors, the latter an internal mold and
the former an impression taken from it, showing
divergent brachiophore plates.
Ozarkian? , Phillipsburg, Quebec. Cat. No. S 1 5 5 1 .
x2.
Syntrophina palmata (Cleland)
30, 31. — Dorsal internal mold and impression taken from it.
The latter shows the adductor impressions and the
posterior callosity.
Ordovician (Canadian, Tribes Hill), Fort Hunter,
N. Y. Cat. No. S 1544. x2.65.
Syntrophia cf. lateralis (Whitfield)
3. — Replica of dorsal interior, from original in Ulrich
Coll., U. S. Nat. Mus. Shows narrow, short cru-
ralium, which resembles that of some rhynchonelloids.
Ozarkian ? (Bg), Phillipsburg, Quebec. Cat. No.
S1574. x2.
Syntrophia lateralis (Whitfield)
27, 28. — Lateral and front views of ventral interior, the
latter showing musculature.
29, 32. — Posterior and dorsal views of complete individual.
From Walcott, Camb. Brach., pi. 102, figs. 6e-g,
after Hall and Clarke, Pal. N. Y., vol. 8, pt. 2,
pi. 62, fig. 9.
Syntrophinella typica Ulrich MS.
4, 5. — Ventral and dorsal exteriors, showing faint radial
sculpture.
13. — Dorsal interior.
Ozarkian ? (upper Chepultepec), ^ mile S. W. of
Elliottsville church, Bess quad., Alabama. Wax re-
plicas of originals in Ulrich Coll., U. S. Nat. Mus.
Cat. No. S 1582. X 2.65.
Figs. Syntrophioides harlanensis (Walcott)
20. — Ventral interior, with pseudospondylium and diver-
gent pallial markings.
23. — Dorsal interior, with adductor impressions and an-
terior pallial markings.
Up. Cambrian, 4 miles N. E. of Rogersville, Tenn.
Replicas of Walcott's types (Cat. No. 52252, U. S.
Nat. Mus.). Cat. No. S 1583. x 2.
Clarkella sp.
6, 11. — Ventral interiors, showing spondylium.
7, 1 0. — Dorsal interiors, showing numerous septa support-
ing brachiophore plates. These are not continuous
across the middle of the valve but separate as in
Syntrophina.
Ozarkian? , Phillipsburg, Quebec. Cat. No. S 1 567.
x3.
Clarkella afif. C. montanensis (Walcott)
8, 9. — Ventral and dorsal exteriors, showing smooth surface.
Ozarkian? (Logan's Bj), near Phillipsburg, Quebec.
Geol. Surv. Canada, x 2.
Multicostella platys (Billings)
12. — Lenticular profile.
Ordovician (Chazy), Speer's Ferry, Va. Cat. No.
S792. x2.
HuenelHna triplicata (Walcott)
14, 21. — Ventral and dorsal internal molds. Ventral inte-
rior shows an impression of the pseudospondylium and
radiating ridges diverging from it and a strong ante-
rior adductor (?) impression. Fig. 21 shows molds
of peculiar lateral plates upon which the genus is
based. Original in U. S. Nat. Mus.
22. — Replica of fig. 21, to show lateral plates.
Ozarkian?, Novaya Zemlya, Russia. Cat. No.
S1580. x2.65.
Yangtzeella poloi (Martelli)
24, 25. — Ventral and posterior views of exterior.
Up. Ordovician, Foope, China. Cat. No. S 1585.
X 1.33.
26. — Dorsal exterior.
Ordovician (Neichiashan), Neichiashan, Yangtze
gorge, Hupeh, China. Cat. No. S 1586. x 1.30.
224
PLATE 15
-7
-A
#^
^
*
225
PLATE 16
Figs. Mystrophora areola (Quenstedt)
1, 5. — Dorsal and ventral exteriors of a large specimen.
Compare the ornamentation and contour with those of
Skenidium, pi. 13.
2, 3, 4. — Dorsal, lateral, and ventral views of a smaller
specimen.
Devonian (Givetian, crinoid bed), Gerolstein, Ger-
many. Cat. No. S 2 1 1 0. x2.7.
Orthorhynchula ottawaensis (Billings)
6. — ^Ventral interior of a silicified specimen, showing long
dental plates.
9, 13. — Crural bases with ends of crural processes, which
are extremely long when present.
Certain rhynchonelliform shells from Kentucky have
been referred to this species, but they should be placed
with Camerella. The Ottawa forms (topotypes) have
commonly been referred to Camerella but belong with
Orthorhynchula. ^'■Camerella" fanderi from Paquette
Rapids, an associate of C. ottawaensis, is neither a
Camerella nor an Orthorhynchula, but allies itself
with the spire-bearing genera.
Ordovician (Black River), Paquette Rapids, Ottawa,
Canada. Cat. No. S 809. x 2.7.
Orthorhynchula linnejri (James)
12. — Silicified specimen from which the ventral valve has
been broken, revealing the crural bases.
28, 29. — Dorsal and lateral exteriors.
Ordovician (Maysville), Frankfort, Ky. Cat. No.
7539 Y. P.M. x2.
1 7. — Ventral view of exterior.
30.- — Ventral interior, showing teeth, interarea, and outline
of muscular field.
Ordovician (Maysville), Colby, Clarke Co., Ky.
Cat. Nos. S 795 and S 796 (fig. 30). x 2.
Kayserella lepida (Schnur)
7, 8, 10. — Posterior, lateral, and ventral views of exterior.
Posterior view shows deltidium indistinctly.
Devonian (Eifelian), Gerolstein, Germany. Cat.
No. S2111. x2.
p,G3. Taffia planoconvexa Butts
11. — Dorsal interior, showing orthoid character of cardi-
nal ia.
Low. Ordovician (Odenville), E. of Odenville,
Alabama. U. S. Nat. Mus.
Pomatotrema grandaeva (Billings)
1 4, 1 9. — Dorsal and ventral exteriors.
16, 23, 26, 31. — Ventral interiors, showing deltidium, den-
tal plates, internal lateral ovarian ridges, and a ridge
developed from the adductor impression.
18, 21. — Dorsal interiors, showing lateral ridges and simple
cardinal process. The specimen in fig. 21 was
actually in conjunction with that in fig. 16.
Pomatotrema shows many resemblances to the Cli-
tambonacea and, together with the members of the
Clitambonitida:, has been placed in that superfamily.
Ordovician (Beekmantown), Newfoundland. Cat.
Nos. S 81 (fig. 18) and S 82. x 2.7.
Pomatotrema muralis Ulrich and Cooper, n. sp.
15. — Ventral interior.
20. — Dorsal internal mold. Compare these figures with
those of P. grandava.
Ordovician (upper Canadian), Ardmore quad.,
Okla. Wax impressions of specimens in U. S. Nat.
Mus., Cat. Nos. S 77 (fig. 20) and S 79. x 2.7.
Planidorsa crassicostella Schuchert and Cooper, n. sp.
22, 27. — Posterior and ventral views of the holotype, the
former showing chilidial plates.
Ordovician (Chazy), Speer's Ferry, Virginia. Cat.
No. S 763. Fig. 22x1.35.
Planidorsa bella Schuchert and Cooper
24. — Dorsal exterior, x 1.35.
25. — Ventral internal mold, showing musculature, which is
essentially dinorthoid but with unusually large ad-
juster scars. X 2.
Ordovician (Chazy), Washburn, Tenn. Holotype.
Cat. No. S. 764.
226
PLATE 16
227
PLATE 17
Figs. Onniella broggeri Bancroft
I, 6. — Dorsal and ventral views, showing exterior.
Ordovician, Horderley District, E. Shropshire, Eng-
land. Cat. No. S 21 12. x2.
Onniella sp.
8, 12. — Dorsal internal mold and impression taken from it.
9, 1 1 . — Ventral internal mold and replica of it.
18. — Enlargement, x 4, of fig. 12, showing internal struc-
ture in greater detail. Cf. fig. 23.
Up. Ordovician, Horderley District, E. Shropshire,
England. Cat. No. S 2 1 1 3. All except fig. 1 8 x 2.
Dalmanella rogata (Sardeson)
2,31. — Dorsal interior, x 2.65, and enlargement of same,
X 4, showing simple, bladelike brachiophores and car-
dinal process. The myophore is lobed and from its
center there has grown forward along the shaft a
peculiar process giving the whole the appearance of
the head of a bee.
Ordovician (Black River), St. Paul, Minn. Cat.
No. S 845.
3, 5. — ^Ventral and dorsal exteriors, showing suborbicular
outline and ornamentation.
4. — ^Ventral interior, showing characteristic bilobed muscle
field.
Ordovician (Trenton), 3 miles S. E. of Cannon
Falls, Minn. Cat. No. S 811. x 2.67.
7, 13. — Dorsal and ventral views of the exterior of Sarde-
son's holotype.
Ordovician (fucoid bed), Ellsworth, Wis. Cat.
No. S 935. x2.
Dalmanella meeki (Miller)
10,20,21. — Posterior, ventral, and dorsal exterior views,
X 1.5. This transverse type of shell strongly resembles
Bancroft's Onniella.
23, 24. — Dorsal interiors, showing age variations. Fig. 23
portrays the younger shell, with its more slender car-
dinal process having a lobed myophore, indistinct ad-
ductor impressions, and bladelike brachiophores with
little adventitious thickening. The other shell shows
a prominent thickening of the cardinal process, with
some development of adventitious testaceous matter
on the inside surface of the brachiophores, and the
adductor impressions are more distinct, x 2.
33. — Ventral interior, showing well the dental plates and
deep crural fossettes. Notice that the musculature
varies from that usual in Dalmanella rogata and allies
in not being lobate in front and in having the adduc-
tor track approximately the same length as the diduc-
tor impressions. The "meeki" type of Dalmanella
may be referable to Onniella when that genus has
become better established and its lineage put on a
substantial basis, x 2.
Ordovician (Richmond), Hanover, Ohio. Cat. No.
S855.
Figs. Dalmanella ignota (Sardeson)
19. — Internal mold, showing musculature. Adjustor scars
and elongate diductor impressions visible enclosing ad-
ductor impressions. Such a muscle pattern could have
produced that of Rhifidomella by expansion of the
diductor impressions to a semiflabellate outline.
Ordovician (Wykoff), Spring Valley, Minn. Cat.
No. S 947. X 2.
Dalmanella emacerata (Hall)
22. — Ventral internal mold showing bilobate muscle area
and pallial markings. Cf. interior of Parmorthis,
pi. 21.
Ordovician (Maquoketa), Granger, Minn. Cat.
No. S 954. X 2.
Dalmanella corpulenta (Sardeson)
25. — Ventral internal mold, showing lobate muscle-scars.
X 1.5.
27, 29. — Dorsal interior and exterior, x 2.
Ordovician (Richmond), Spring Valley, Minn.
Cat. No. S 867.
Dalmanella tersa (Sardeson)
26, 30. — Dorsal interior, showing brachiophores, and dorsal
exterior. This shell is plano-convex in profile and
the ventral diductor scars wrap around the adductor
impressions. D. tersa has all the characters necessary
to produce Rhifidomella.
Ordovician (Richmond), Wilmington, 111. Cat.
No. S 871. x2.
Resserella canalis (Sowerby)
14. — Ventral internal mold, showing divergent pallial
marks.
15,1 6. — Dorsal internal mold, and impression taken from
it. Note, in the latter, structure identical with that
of D. rogata (figs. 2, 31).
Ordovician (low. Longvillian, Kjxrina zone). Long
Lane quarries S. of Horderley, E. Shropshire, Eng-
land. Cat. Nos.S 21 14 (fig. 14) and S 21 15. x 2.
Heterorthina praeculta Bancroft
17. — Ventral internal mold, x 1.5, showing p.iHial markings.
28. — Ventral internal mold, showing musculature, x 1.5.
32.- — Cardinalia of dorsal valve, x 4. Bilobed myophore
and cleft shaft clearly visible, also simple bladelike
brachiophore plates.
Ordovician (Marshbrookian, Wattsella zvattsi zone),
Horderley District, E. Shropshire, England. Cat.
No. S2116.
228
PLATE 17
' -' • "' .jfft'r,-^
23
E*-^/
'>
27
25
28
29
\
'"nr
31
32
229
26
30
PLATE 18
Figs. Heterorthina fairmountensis (Foerste)
1. — Ventral interior, showing widely divergent diductor
impressions and delicate pallial markings, x 2. Cf.
pi. 17, fig. 17.
2, 3. — Dorsal and ventral exteriors, x 1.5.
4. — Dorsal interior, to show cardinalia and musculature.
Notice lobed myophore and cleft shaft of cardinal
process, and simple divergent brachiophores. Cf.
fig. 7. x2.
Ordovician (Bellevue), Hamilton, Ohio. Cat. No.
S852.
Heterorthina praeculta Bancroft
5. — Ventral exterior, showing form of valve.
Ordovician (Marshbrookian), Horderley District, E.
Shropshire, England. Cat. No. S 21 17. x 1.5.
6, 7. — Internal mold of dorsal valve and wax replica made
from it. Compare this replica with fig. 4; the
former shows the same cleft shaft and lobate myo-
phore, similar brachiophores, muscle impressions, and
pallial marks.
8. — Replica of a dorsal external mold. Dorsal valve flat
and shell multicosteUate.
Ordovician (Marshbrookian, Wattsella uiattsi zone),
Horderley District, E. Shropshire, England. Cat.
No. S2116. X 1.5.
Cariniferella carinata (Hall)
9. — Ventral internal mold, showing muscle field and form
of muscle impressions.
15. — Dorsal internal mold, showing impressions left by
brachiophores and cardinal process.
16. — ^Wax impression taken from above.
Devonian (Chemung), Bath, N. Y. Cat. No.
S1087. X 1.5.
10, 12. — Ventral and dorsal exteriors, showing prominent
dorsal sulcus and ventral fold.
Devonian (Chemung), Arkport, N. Y. Cat. No.
8 1088. X 1.5.
Cariniferella dumonti (Verneuil)
1 1 . — ^Ventral interior, showing musculature.
Up. Devonian, ? Belgium. Mas. Comp. Zool., Har-
vard Coll. xl.5.
Linoporella punctata (Verneuil)
13, 14, 18. — Ventral interiors, showing respective stages in
development of pseudospondylium. Fig. 1 8 shows
discrete dental plates with little or no adventitious
thickening on floor of delthyrial cavity. Fig. 14
shows an advanced stage in which the deposit is ele-
vated at the front and unites the dental plates, x 2.
Silurian (Gotlandian), Visby, Gotland, Sweden.
Riks. Pal. Zool. Avd., Stockholm.
Figs. Linoporella punctata (Verneuil) — Cont.
24. — Reverse side of exterior in fig. 3 3, showing well inter-
area, teeth, dental plates, and median ridge, x 1.5.
33. — Exterior of a large ventral valve, showing characteris-
tic ornamentation, x 1.5.
Silurian (Gotlandian), Visby, Gotland, Sweden.
Riks. Pal. Zool. Avd., Stockholm.
17. — Posterior portion of large dorsal valve, showing car-
dinalia. Note extremely slender shaft of cardinal
process, with its thickened unlobed myophore. Brach-
iophore plates uniting below with median septum to
form a cruralium.
Silurian (Gotlandian), Foro, Lausa, Sweden, x 2.
Levenea subcarinata (Hall)
19,32. — Dorsal interiors, the former, x 1.5, showing ad-
ventitious growths on inside of brachiophores, and the
latter, x 2, showing well musculature and pallial marks.
31. — Ventral interior, showing characteristic musculature.
X 1.5.
Devonian (Birdsong), Birdsong Creek, west Ten-
nessee. Cat. No. S982.
20. — Enlargement of fig. 28, x 3.
28. — Dorsal interior, turned slightly to the side, showing
unmodified brachiophores in the form of flat, ob-
liquely placed blades, x 1.5.
Devonian (Helderberg). Albany Co., N. Y. Cat.
No. S 986.
21. — Dorsal interior, showing greatly modified interior.
Shaft of cardinal process modified by a process grow-
ing forward from median lobe of myophore, brachio-
phores coated on inside by adventitious material which
cements them to the valve. Lateral pallial sinuses
given off between adductor impressions clearly visible.
Devonian (Birdsong), near Holladay, Tenn. Cat.
No. S 980. xl.5.
23. — Dorsal interior of young individual, showing brachio-
phores as simple, unmodified, oblique blades, x 1.5.
25, 29. — View, x 1.5, and its enlargement, x 3.5, to show
modified brachiophores, a line of demarcation be-
tween actual plates and adventitious substance being
clearly visible.
Devonian (Birdsong) Conrad Place, near Jeanette,
Tenn. Cat. No. S 988.
30. — Ventral internal mold, showing pentagonal form of
muscle field and pallial markings.
Devonian (Helderberg), near Clarksville, N. Y.
Cat. No. S 1014. X 1.5.
Levenea cf. subcarinata (Hall)
22, 26, 27. — Posterior, ventral, and dorsal exterior views.
Devonian (Birdsong), Benton Co., Tennessee. Cat.
No. 9719 Y. P. M. X 1.5.
230
PLATE 18
•n
■ "3JJ..iH~l'
f^^
i
V
9
231
PLATE 19
Figs. Thiemella villenovia Williams
1, 5. — Dorsal and ventral exterior views, showing well the
reversion of fold and sulcus which is one of the
generic characters. The specimens figured are
squeezes of external molds in the U. S. Nat. Mus.
X 1.5.
2, 6. — Ventral internal molds, showing musculature and
long septum dividing anterior ends of diductor scars
and extending some distance in front of them. Fig.
2 X 1.5, fig. 6 X 2.
4. — Replica of dorsal internal mold, showing cardinalia.
X 1.5. Note delicacy of structures and compare with
the rather ponderous cardinalia of Aulacella, fig. 13.
9. — Dorsal internal mold, the reverse side of that in fig.
4. xl.5.
Devonian (Chemung), Dyes quarry, Villenova,
Chautauqua Co., N. Y. Originals in U. S. Nat.
Mus.
Rhipidomella vanuxemi (Hall)
3. — ^External view of ventral valve, showing swollen
costellje.
Devonian (Hamilton), Canandaigua Lake, N. Y.
Cat. No. S 1286. X 1.
Aulacella eifelensis (Verneuil)
7, 8. — Dorsal and ventral views of exterior, showing fold
and sulcus, which are not reversible, x 1.5.
11. — Ventral internal mold, showing musculature. Ad jus-
tor impressions clearer in this specimen than usual.
Cf. the same view of Thiemella, fig. 6, and note that
whereas in Aulacella the septum forks at the ends of
the diductor scars, in Thiemella there is no forking
and the septum extends a considerable distance in
front of the muscle field, x 2.
Mid. Devonian, Eifel, Germany. Cat. No. S 1096.
10. — Ventral interior, showing elongate muscle field with
diductor impressions separated by a low ridge which
forks in front, x 2.
13. — Dorsal interior, showing ponderous cardinalia which
have a strong resemblance to those of Rhifidomella.
Cf. fig. 4. xl.5.
Mid. Devonian, Eifel, Germany. Schultze Colls.,
Mus. Comp. Zool., Harvard CoU.
Perditocardinia dubia (Hall)
12,20,22. — Lateral, dorsal, and ventral views of a large
specimen, showing terebratuloid form of valves.
21. — Ventral interior, showing musculature.
Mississippian (St. Louis), Spergen Hill, Ind. Cat.
No. S 1300. x2.
16, 17. — Ventral and posterior views of exterior.
Mississippian (Carthage), Webb City, Jasper Co.,
Missouri. Cat. No. S 1293. x 2.
Figs. Perditocardinia aflf. P. dubia (Hall)
14,15. — Ventral and dorsal interiors. Ventral interior
shows clearly the lack of an interarea and consequently
of a hinge-line. Dorsal interior shows ponderous
cardinalia similar to those of Rhifidomella but with
modifications induced by the compression of the inter-
area to disappearance.
Mississippian (Salem), near Valley Park, St. Louis
Co., Missouri. Cat. No. S 1297. x 2.
Platyorthis planoconvexa (Hall)
18,19,29. — Dorsal, ventral, and lateral exterior views.
Notice particularly planoconvex profile, x 1.
23. — Ventral interior, showing flaring dental plates con-
tinued as ridges along margins of muscle field, x 1.5.
24. — Dorsal interior of silicified specimen, showing pon-
derous cardinal process and oblique, bladelike brach-
iophores. xl.5.
Devonian (Oriskany), Cumberland, Md. Cat. No.
S114S.
Platyorthis circularis (Sowerby)
27. — Dorsal internal mold. The pit marking the cardinal
process is short, showing a short cardinal process but
elevated a considerable distance in a ventral direction.
28. — Ventral internal mold, showing elongate flabellate ad-
justor-diductor fields separated by a median ridge
which carried the adductor muscles.
Devonian (Coblenzian), Siegen, Germany. Cat.
No. SI 139. xl.5.
Platyorthis opercularis (Verneuil)
31. — Dorsal view of exterior, showing flatness of dorsal
valve.
Devonian (Eifelian), Gerolstein, Germany. Cat.
No. S 1141. xl.5.
Proschizophoria personata (Zeiler) (emend. Kayser)
25. — Dorsal internal mold. Cardinal process and brachio-
phore plates ponderous. Anterior adductor impres-
sions separated from posterior impressions by hori-
zontal ridges (in the mold, depressions).
30. — Ventral internal mold, showing subtriangular muscle
field. Diductor impressions long and adductor im-
pressions imprisoned within them.
Up. Devonian, Unkel, Germany. Schultze Colls.,
Mus. Corap. Zool., Harvard Coll. x 1.
26, 32. — Ventral and dorsal internal molds.
Low. Devonian (Siegenerschichten), Seifen, Ger-
many. Cat. Nos. S 1090 and S 1089. xl.5.
232
PLATE 19
233
PLATE 20
Figs. Smeathenella hamagensis Bancroft
1, 5. — Dorsal internal mold, and a replica of it which shows
brachiophores cemented to valve to produce thornlike
structures. Cf. fig. 19, Heterorthis clytie.
2, 4. — Internal mold of crushed ventral valve, and a replica
taken from it, to show short dental plates.
3_ — Replica taken from dorsal exterior mold, showing
fascicosteUate surface.
Ordovician (basal Harnagian), Smeathen Wood,
Horderley, E. Shropshire, England. Cat. Nos.
S2119, S2120. xl.
Muscle
Harknessella vespertilio (Sowerby)
6^ 10. — ^Ventral internal mold (10), and replica.
area lobate.
7,9. — Dorsal interna! mold (9), and replica. This wax
impression shows clearly the nature of the brachio-
phores, although the lobate character of the cardinal
process is not altogether clear because of the imper-
fection of the impression. The cementing of the
brachiophores to the valve is clear, however. Cf.
fig. 19.
Ordovician (basal Caradocian, Heterorthis fatera
grits), Coston District, E. Shropshire, England.
Cat. Nos. S2122 (figs. 6, 10) and S 2123. x 1.
Harknessella sp.
8. — Dorsal internal mold.
Ordovician (basal Caradocian, Harknessella subquad-
rata zone), BuUhill, Cressage District, E. Shrop-
shire, England. Cat. No. S 2124. x 1.
11,
13,
Reuschella bilobata (Sowerby)
14. — ^Ventral internal mold (14) and wax impression
taken therefrom, showing character of muscle field. ^
15. — Dorsal internal mold, and replica. Cardinalia
close to those of Harknessella.
Ordovician (Acton Scott beds). Castle Hill, E.
Shropshire, England. Cat. Nos. S2125 (figs. 13,
15) and S2126. x 1.
Reuschella cf. R. bilobata (Sowerby)
12. — Dorsal exterior, showing coarse costells.
Ordovician (Caradocian), Cardington, Salop, Eng-
land. Cat. No. S 1065. x 1.
Heterorthis clytie (Hall)
16, 17. — ^Ventral and dorsal views of exterior.
Ordovician (Trenton), Bourbon Co., Ky. Cat. No.
S1068. X 1.5.
Figs. Heterorthis clytie (Hall) — Coni.
18. — Dorsal interior, showing cardinalia. x 1.5.
19. — Posterior view of specimen in fig. 20, showing small,
convex chilidium covering carinate median lobe of
cardinal process, x 2.
20. — Dorsal interior, showing cardinalia, small adductor
field, and pallial marks; also cementation of brachio-
phores to valve. In Heterorthis and its allies this
cementation takes place along the dorsal surface of the
brachiophores, but in Dalmanella, Levenea, etc., it is
along their flat, inner face. Shown also in this figure
is the submarginal elevation in the dorsal valve, and
the corresponding depression in the ventral valve
can be seen in fig. 21. x 1.5.
2 1 . — Ventral interior, showing semiflabeUate pattern formed
by combined diductor and adjustor scars, x 1.5.
Ordovician (Hermitage), Frankfort, Ky. Cat. Nos.
S 1067 (figs. 19-21) and S 1074.
Heterorthis cf. H. altemata (Sowerby)
25. — Ventral internal mold, showing elongate diductor and
adjustor muscles.
Ordovician (Caradocian), W. Corwan, England.
Cat. No. S 1073. x 1.5.
Rhipidomella sp.
22. — Dorsal interior turned slightly to the side showing
cardinalia. Right brachiophore shows an elongate
blade-like process extending from a median swelling.
Such a process is missing in fig. 23.
Locality unknown. Cat. No. S 1220. x 3.
Rhipidomella vanuxemi (Hall)
23. — Dorsal interior, showing swollen cardinal process and
adductor field.
27. — Ventral interior, showing postero-median position of
adductor field, and large, semiflabeUate diductor-ad-
justor area.
Devonian (Hamilton), Canandaigua, N. Y. Cat.
No. S 1286. X 1.5.
Rhipidomella musculosa (Hall)
24. — Ventral interior, showing unusually expansive devel-
opment of diductor-adjustor fields.
Devonian (Oriskany), Cumberland, Md. Cat. No.
S1193. xl.
Rhipidomella penelope (Hall)
26. — Ventral interior of an old shell, showing puckered
margins of muscle field and swollen, irregular inner
surface.
Devonian (Hamilton), Canandaigua Lake, N. Y.
Cat. No. SI 229. x 1.
234
PLATE 20
235
PLATE 21
Figs. Aff. Parmorthis visbyensis (Lindstrom)
1, 6, 12. — Dorsal, ventral, and posterior views of a medium-
sized individual.
8. — Dorsal interior, showing adductor field and trilobed
cardinal process. The concavity of the dorsal valve
has caused a bending postero-dorsally of the cardinal
process in order to maintain the necessary leverage in
opening the valves. This makes the myophore visi-
ble on the exterior of the dorsal valves (see fig. 1 ) .
1 1 . — Dorsal view of a larger shell.
15. — Ventral internal mold, showing pallial trunks swing-
ing into apposition as they extend forward. This is
the usual condition in Parmorthis and is a significant
difference between these shells and Ddmanella s. s.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
S895. x2.
Parmorthis elegantula (Dalnian)
2. — Dorsal interior seen from rear, showing (on left
brachiophore) an elongate process or crus (?).
3. — Posterior view of a dorsal interior, showing fulcral
plates and brachiophores. Parmorthis is the only dal-
manellid with corrugated dental sockets, teeth, and
fossettes.
13. — Dorsal interior, showing elongate-ovate adductor field
with its smaller anterior adductor scars. Fulcral plates
visible, and inside surface of brachiophores strength-
ened by adventitious material.
Silurian (Gotlandian), Gotland, Sweden. Cat. Nos.
S 886 (fig. 2) and S 892. x 2.
9, 14, 16. — Posterior, dorsal, and ventral views of exterior.
In fig. 14, a concentration of smaller costella; is
noticeable in the antero-median portion of the valve.
Such a concentration of ribs is a feature of these shells.
1 0, 29. — Two views of a ventral interior, showing ponder-
ous teeth and cavernous crural fossettes.
Silurian (Gotlandian), Klintehamn, Gotland,
Sweden. Cat. Nos. S 890 (figs. 9, 14, 16), and
S918. x2.
Parmorthis crassicostata Schuchert and Cooper, n. sp.
4, 5. — A rather heavily costellate species.
Silurian (Niagaran), Martin's Mills, W. Tenn.
Holotype. Cat. No. S 91 3. x 2.
Parmorthis waldronensis (Foerste)
7. — Ventral exterior of the common American shell that
has so long masqueraded under the name of Dal-
manella elegantula (Dalman).
Silurian (Niagaran), Jeflferson Co., Ind. Cat. No.
S 899. X 2.
Isorthis perelegans (Hall)
17, 18. — Dorsal and lateral views of exterior, the latter
showing biconvexity of valves.
26. — Ventral interior, showing Schizofhoria-Y\ks muscle-
scars.
28. — Dorsal interior, showing cardinalia.
Devonian (Helderberg), ClarksviUe, N. Y. Cat
No. S 1013. X 1.
Figs. Isorthis rockhousensis (Dunbar)
19. — Dorsal exterior.
Low. Devonian (Rockhouse), Rockhouse, Tenn.
Cat. No. 9750 Y. P. M. x 2.
Isorthis szajnochai Kozlowski
20. — Posterior portion of a dorsal valve, showing divergent
diductor tracks and median adductor fold. This is
very similar to the condition in Schizofhoria, see pi.
23, fig. 20. x2.
25, 30, 31, 33.— Ventral, dorsal, posterior, and lateral views
of a specimen representing the type species of the
genus. X 1.5.
27. — Dorsal interior, showing cardinalia and adductor field.
Fulcral plates visible just outside brachiophore plates.
Cf. corresponding view of Schizofhoria, pi. 23, fig.
21. X 1.5.
Up. Silurian (Borszczow), Wierzchniakowce, Po-
land. Cat. No. S2127.
Isorthis arcuaria (Hall and Clarke)
21. — Dorsal interior, showing elliptical adductor field
and prominent ridges of adventitious shell extended
around it.
23. — Ventral interior, showing prominent divergent diduc-
tor tracks and pallial sinuses extending from them.
Diductor tracks separated by a fold of shell which
bears adductor impressions.
Silurian (Niagaran), Decatur Co., W. Tenn. Cat.
No. S 1030. x2.
32. — Lateral view, showing strongly lenticular profile of
sheU.
Silurian (Niagaran), Clifton, W. Tenn. Cat. No.
S1022. x2.
Isorthis tetragonum (Roemer)
22. — Dorsal internal mold, to show pallial markings.
Devonian (Eifelian), Gerolstein, Germany. Cat.
No. S994. X 1.5.
Isorthis canalicula (Schnur)
24. — Ventral interior, with musculature and pallial mark-
ings characteristic of the genus.
Devonian, Eifel, Germany. Mus. Comp. Zool.,
Harvard Coll. x 2.
Idiorthis matura McLearn
34. — Ventral internal mold, showing musculature. Cf.
Wattsella, pi. 22. x 3.
3 5, 38. — Dorsal and ventral views of exterior, x 1.5.
36, 37. — Dorsal internal mold (37), x 1.5, and replica of it
showing strong median ridge and adductor field.
Cardinal process trilobed.
Silurian (McAdam), Arisaig, Nova Scotia. Cat.
Nos. 426 (figs. 34, 36, 37) and 426c Y. P. M.
236
PLATE 21
PLATE 22
Mendacella uberis (Billings)
1. — Dorsal interior, showing cardinalia.
2. — Ventral interior, showing musculature.
3. — Dorsal internal mold, showing elongate Dalmanella-
like muscle field.
Ordovician (Richmond, Ellis Bay), E. of Junction
Cliff, Anticosti. Cat. No. 10415 Y. P. M. x 2.
8. — ^Ventral exterior.
Silurian (Anticostian), Anticosti. Cat. No. S 1049.
x2.
Figs. Wattsella edgewoodensis (Savage) — Cont.
13. — Ventral interior, showing flaring dental plates and
heart-shaped muscle field.
22. — Dorsal interior of a silicified shell, showing remark-
ably long brachiophores (crura?).
27, 28. — Dorsal and ventral exteriors, to show ornamenta-
tion.
Silurian (Edgewood), Edgewood, Pike Co., Mis-
souri. Cat. Nos. S1075 (figs. 13, 27, 28), and
S 1083 (fig. 22). x2.
Mendacella muUochiensis (Davidson)
4, 5. — Ventral internal mold (fig. 5), x 1.5, showing mus-
culature, and wax impression taken from it, x 2.
Silurian (lower Llandovery, Mulloch Hill), Mulloch
Hill, Girvan, Ayrshire, Scotland. Brit. Mus. Nat.
Hist. (fig. 5); Cat. No. S657 (fig. 4).
Fascicostella sedgwicki (D'Archiac and Verneuil)
6. — Dorsal internal mold, showing adductor field like that
of Parmortkis, see pi. 21, fig. 13.
7. — ^Ventral exterior, showing bundled costellae.
10. — Replica of interior.
11. — Dorsal interior, showing cardinalia.
16. — Reverse side of fig. 6, showing ventral interior mold.
Of significance is the septum extending forward from
the adductor track separating two pallial trunks.
Devonian, Vise, Belgium. Mus. Comp. Zool., Har-
vard Coll. X 2.
Fascicostella gervillei (Def ranee)
12, 15. — Ventral and dorsal exteriors, showing fascicostel-
late exterior.
Devonian (Ffj), Koniepruss, Bohemia. Cat. No.
S925. xl.5.
Fascicostella sp.
3 1 .• — Large specimen, showing dorsal exterior.
Devonian, Vise, Belgium. Mus. Comp. Zool., Har-
vard Coll. X 2.
Wattsella edgewoodensis (Savage)
9, 23, 25, 29. — Several views to show dorsal interior.
Fig.
23 shows left brachiophore plate broken away to ob-
tain a clearer view of the right plate. Fig. 29 is an
enlargement of fig. 23, x 4. Fig. 2 5 shows socket and
fulcral plates.
Silurian (Edgewood), Edgewood, Pike Co., Mis-
souri. Cat. Nos. S 1078 (figs. 23, 25, 29), S 1079
(fig. 9). All except fig. 29 x 2.
Wattsella testudinaria (Dalman)
14, 19, 24. — Posterior, ventral, and dorsal exteriors, x 1.5.
21. — Dorsal interior, showing subparallel brachiophore
plates, meeting the median ridge, x 2.
Silurian, Borenshult, Sweden. Riks. Pal. Zool. Avd.
Stockholm.
17.
Wattsella wattsi Bancroft
-Ventral exterior, a replica of the internal mold.
18, 20. — Dorsal internal mold, and wax replica of it, show-
ing subparallel brachiophore plates meeting median
ridge. Cf. figs. 21, 9, and 23.
26. — Ventral internal mold, showing subcordate muscle
area.
Ordovician (Marshbrookian, W. wattsi zone),
Woolston, Horderley District, E. Shropshire, Eng-
land. Cat. Nos. S2128 (fig. 17), S2129 (figs.
18, 20), and S2130 (fig. 26). x 1.5.
Horderleyella sp.
30. — Dorsal interior, showing fulcral plates outside brach-
iophore plates.
Ordovician (Marshbrookian, Wattsella zvattsi zone),
Marshbrook, N. of Horderley, E. Shropshire, Eng-
land, x 1.5.
Horderleyella plicata Bancroft
32. — Ventral internal mold.
33. — Wax replica of dorsal external mold.
34,35. — Dorsal internal mold (fig. 35) and wax replica
of it showing cardinalia. Brachiophore plates con-
vergent and supported by low lateral septa.
Ordovician (basal Caradocian, H. flicata zone),
Horderley, E. Shropshire, England. Cat. Nos.
S 21 32-21 34. x2.
238
PLATE 22
239
PLATE 23
Figs. Pionodema subsequata (Conrad)
1, 5. — Ventral and dorsal views of the holotype.
Ordovician (Black River), Mineral Point, Wis.
Cat. No. 694/3 Amer. Mus. Nat. Hist, x 2.
3. — Posterior view of exterior, x 1.5.
7. — Dorsal interior, showing flaring brachiophore plates
and thickenings extending forward from them. Cf.
figs. 2, 4. X 3.
Ordovician (Black River), near Lanesboro, Minn.
Cat. No. S 1 364.
Pionodema redux (Barrande)
2, 4. — Dorsal internal mold (fig. 4) and wax impression of
it. Cf. fig. 7. Brachiophore plates separate, but low
ridges extend from them and converge toward the
median ridge.
Ordovician (Dd), Mt. Drabow, Bohemia. Mus.
Comp. Zool., Harvard Coll. x 1.5.
Pionodema minnesotensis Cooper
6, 10, 14. — Dorsal, ventral, and posterior views of the
holotype. Notice swollen ribs.
Ordovician (Black River), Minneapolis, Minn.
Cat. No. S 1356. x 1.5.
Pionodema cf. circularis (Winchell)
8. — Dorsal interior, showing well the flaring brachiophore
plates. Cf. fig. 21.
Ordovician (Glade Is. of Safford (?))> Lebanon,
Tenn. Cat. No. S 1360. x 2.
Pionodema cf. conradi (Winchell)
9. — Ventral interior, showing musculature and apical plate.
Ordovician (Black River), St. Paul, Minn. Cat.
No. 1359 S. X 1.5.
Pionodema uniplicata Cooper
12. — External view of ventral exterior, showing deep
sulcus.
Ordovician (Black River), Minneapolis, Minn.
Cat. No. S 1361. x 1.5.
Figs. Pionodema circularis (Winchell)
13. — Incomplete dorsal valve turned to the side in order
to show the fulcral plate which defined the socket.
Cf. fig. 18.
Ordovician (Black River), 2.5 miles S. of High
Bridge, Ky. Cat. No. S 1348. x 3.
Isorthis ? tuUiensis (Vanuxem)
15, 19. — Ventral internal mold, and reverse side showing
dorsal interior. Pallial marks distinctly spread apart,
showing pattern clearly.
Devonian (Tully), Skaneateles, N. Y. Cat. No.
S1412. X 1.5.
Schizophoria provulvaria Maurer
1 1. — Dorsal internal mold, showing pallial trunks.
Devonian, Seifen, Germany. Cat. No. S 1401.
X 1.
Schizophoria vulvaria (Schlotheim)
16.— Ventral internal mold, showing exceedingly long di-
ductor impressions separated by a long septum.
1 7. — Dorsal interior, showing pallial markings.
Low. Devonian (Cobienzian), Laubach, Germany.
Mus. Comp. Zool., Harvard Coll. x 1.
Schizophoria iowensis (Hall)
18. — Same specimen as in fig. 21, turned to side to show
brachiophore supports and fulcral plates.
20. — Ventral interior, showing musculature and median
fold which carries adductor impressions.
21. — Dorsal interior, showing flaring brachiophore plates,
fulcral plates, and musculature.
Up. Devonian, Rockford, Iowa. Cat. No. S 1441.
x2.
Schizophoria aff. striatula (Schlotheim)
22-25. — Posterior, dorsal, lateral, and ventral views of ex-
terior. Compare fig. 24 with fig. 19 of pi. 11.
Devonian (Craghead Creek), E. of Toledo, Calla-
way Co., Missouri. Cat. No. S 1447. x 1.
240
PLATE 23
PLATE 24
FiQS. Enteletes lamarcki Fischer
1, 5, 8, 9. — Dorsal, ventral, posterior, and lateral views of
exterior, showing fine Schizofhoria ornamentation
superimposed over plications.
Up. Carboniferous, Mjatschkowa, Russia. Cat. No.
S1495. xl.
Enteletes dumblei Girty
2, 6, 10. — Ventral interior, showing three prominent septa,
X 1.5. Figs. 2 and 6 seen from the side.
3. — Dorsal interior, showing flaring brachiophore supports
and curved brachiophores, x 2.
7. — Small interarea of ventral valve, x 1.5.
Pennsylvanian (Word) , Glass Mts., W. Texas. Fig.
2 is Cat. No. S 2224, the others are specimens in
the Univ. of Texas collections.
Enteletes cf. dumblei Girty
25. — Dorsal valve seen from the side, showing tusklike
brachiophores and a fulcral plate in place.
Permian (Wolfcamp), N. E. of Wolfcamp, Glass
Mts., W. Texas. Cat. No. S 1 501. x 3.
Parenteletes cooperi King
11, 13, 18. — Anterior, lateral, and posterior views of exte-
rior, showing strong ventral fold and ornamentation
of an adult.
14, 16. — Ventral and dorsal views of exterior of a young
specimen.
Pennsylvanian (Gaptank), near Gaptank, Glass Mts.,
W. Texas. Univ. Texas colls.
Figs. Parenteletes cooperi King — Cont.
2 1 , 26. — Ventral interior of cotypes, showing septa and
camera under anterior end of median septum.
Permian (Uddenites zone), Hill 4752, Glass Mts.,
W. Texas. Cat. No. S 1494. x 2.
Enteletella nikschitschi Likharev
4. — Lateral view of a complete individual, after Likharev.
Low. Permian, northern Caucasia.
Orthotichia afJ. morganiana (Derby)
12. — Extreme posterior portion of dorsal valve, showing
cardinal process and a complete brachiophore. x 1.5.
15. — Posterior portion of a ventral valve, showing elevated
median septum, x 2.
22. — Ventral view, with shell worn off, showing three
septa, X 1.
23,24,27. — Posterior, ventral, and dorsal exterior views.
X 1.
Pennsylvanian, near Saddle Mt., S. E. of Winkel-
man, Ariz., near Gila River. Cat. No. S 1493.
Enteletina latesinuata (Waagen)
17. — Ventral interior, showing subparallel dental plates and
simple median septum. Cf. fig. 10.
19. — Ventral exterior, showing prominent fold.
20. — Dorsal interior. Shape of brachiophore process
normal, but lateral curvature undoubtedly incorrect.
Middle Productus Is., Musakheyl, India. All after
Waagen 1887.
242
PLATE 24
PLATE 25
Figs. Rhynchocamara plicata Schuchert and Cooper
1,2,7. — Ventral, posterior, and dorsal views of exterior,
showing subrhynchonelloid form.
17. — Posterior portion of ventral interior, showing spon-
dylium.
18. — Dorsal interior, showing small chamber beneath beak
of dorsal valve, formed by union of crural plates with
strong median septum. This is a rhynchonelloid fea-
ture and places this form and its congeners with the
Rhynchonellacea.
Ordovician (Stones River, Central Is.), near Mur-
freesboro, Tenn. Cotypes. Cat. No. S 2035. x 1.5.
Camerella hemiplicata (Hall)
3, 4, 6, 10. — Posterior, ventral, lateral, and dorsal views of
a somewhat crushed specimen, showing strongly con-
vex dorsal valve and relatively smaller ventral valve.
X 1.
43. — ^Thin slice of interior, showing spondylium, cruralium,
and crural als. x ca. 4.
Ordovician (Trenton), Lowville, N. Y. Cat. Nos.
S1593 and SI 597 (fig. 43).
9, 1 1 . — Ventral and anterior views, showing sulcus, x 1 .
16. — Ventral view of a young shell, showing median sep-
tum. X 1.
24. — Section of interior of a rather young form, showing
spondylium and cruralium. A faint crural alar exten-
sion can be seen, x 4.
Ordovician (Trenton), Watertown, N. Y. Cat.
Nos. S1588 (figs. 9, 16), S 1600 (fig. 11), and
S1603 (fig. 24).
Camerella volborthi Billings
5. — Ventral interior, with prominent spondylium.
Ordovician (Black River), Paquette Rapids, Ottawa
River, Quebec. Cat. No. 1594S, x 1.5.
20, 21. — ^Ventral and dorsal views of a young specimen.
27, 30. — Lateral and dorsal views of a larger individual.
These specimens were among Billings' types.
Same horizon and locality as above. Cat. Nos.
1 148b, 1 148a, Nat. Mus. Canada, x 2.
22, 28, 29. — Lateral, dorsal, and posterior views of the
same individual, showing exterior. Cf. C. hemifli-
cata, especially fig. 9.
Same horizon and locality as above. Nat. Mus.
Canada, x 2.
Figs. Camerella scofieldi (Winchell and Schuchert)
8, 12, 13. — Ventral, posterior, and dorsal views of exterior.
Ordovician (Galena), near Cannon Falls, Minn.
Cat. No. 8 1 592. x 1.
Anastrophia vernemli (Hall)
14, 15, 19. — Lateral, posterior, and dorsal views of exterior,
showing implantation of ribs in fold, x 1.
Devonian (Helderberg), near Clarksville, N. Y.
Cat. No. S 1619.
33, 36. — Dorsal interior, showing partial side and dorsad
views. Fig. 36 shows musculature well, x 1.5.
34, 35. — Spondylium in partial side and direct or dorsad
view. Septum supports spondylium for nearly its
whole length, x 1.5.
38, 39. — Different views of the same specimen, showing to
perfection crural ala:, supporting plates, and muscula-
ture. X 1.5.
Devonian (Helderberg), Clarksville, N. Y. Cat.
No. S 1640.
41. — Interior of both valves in conjunction, x 1.5.
42. — Same view of another specimen, in which the sides
of the spondylium have grown over, restricting the
area of muscular attachment to a narrow opening.
xl.5.
Devonian (Helderberg), near Clarksville, N. Y.
Cat. Nos. S 1632 (fig. 41) and S 1631.
Anastrophia deflexa (Sowerby)
40. — Thin section, showing arrangement of internal plates.
There are lateral alas on the spondylium as well as
in the dorsal valve.
Silurian (Wenlock), Dudley, England. Cat. No.
S1623. xca. 4.
Parastrophinella ops (Billings)
23,25,26. — Ventral, posterior, and dorsal views of ex-
terior.
Silurian (Chicotte),Anticosti. Cat. No. S 1608. x 1.
Liocoelia proxima (Barrande)
31, 32, 37. — Ventral, dorsal, and lateral views of exterior
of this smooth rhynchonellid. See t. fig. 36.
Silurian (Etage Eej), Kolednik, Bohemia. Cat.
No. S 1696. X 1.
244
PLATE 25
245
PLATE 26
Figs. Barrandella linguifera (Sowerby)
1,3,5,6. — Dorsal, ventral, posterior, and lateral views of
a complete individual.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
8 1680. xl.
Figs. Gypidula multicostata Dunbar
18. — Ventral interior, showing spondylium greatly thick-
ened by growth of adventitious shell.
Devonian (Birdsong), Birdsong Creek, Camden
Road, Tenn. Cat. No. S 1 764. x 1.
Barrandella sp.
2, 7. — Dorsal and posterior views of an internal mold,
showing septa.
Silurian (Brassfield), Eaton, Ohio. Cat. No.
S1674. xl.
Gypidula acutilobata procerula (Barrande)
22, 23, 27. — Lateral, ventral, and dorsal views, showing
exterior.
Devonian (Ff,), Koniepruss, Bohemia. Cat. No.
S1803. xl."
Pentamerella cf. arata (Conrad)
4. — Dorsal interior, showing long plates of dorsal valve
which carry brachial processes.
17. — Ventral interior, showing spondylium. Septum very
short.
Devonian (Onondaga), Falls of the Ohio, Louis-
ville, Ky. Cat. No. S 1731. x 1.5.
13. — Ventral interior, showing short spondylium and two
pallial trunks.
Devonian, Moreland, Ky. Cat. No. S 1726. x 1.
Pentamerella arata (Conrad)
20. — Dorsal view of internal mold, showing septa.
Devonian (Schoharie grit), Schoharie, N. Y. Cat.
No. S 1735. xl.
Pentamerella fultonensis Branson
14-16. — Ventral, dorsal, and lateral views of exterior.
Devonian (Callaway Is.), Auxvasse church, Calla-
way Co., Missouri. Cat. No. S 1724. x 1.
Gypidula dudleyensis Schuchert
24, 28, 34, 37. — Dorsal, ventral, lateral, and posterior
views, showing external form and ornamentation.
Silurian (Wenlock), Dudley, England. Cat. No.
S1789. xl.
Gypidula coeymanensis Schuchert
26, 29. — Posterior and dorsal views of exterior, x 1 .
31,35. — Interior, showing spondylium, median septum,
and brachial processes in place, x 1.5.
32. — Dorsal interior, showing plates, x 1.5.
40. — Both valves in conjunction. The spondylium and
its relation to the dorsal plates are clear, and the nature
of the septum is visible, x 1.5.
Devonian (Helderberg, Coeymans), Clarksville,
Albany Co., N. Y. Cat. Nos. S 1697 (figs. 31,35),
S 1792 (figs. 26, 29), and S 1797 (figs. 32, 40).
38. — Posterior portion of ventral valve, showing spondylium
and median septum.
Devonian (Coeymans), Indian Ladder, N. Y. Cat.
No. S 1782. X 1.
Pentamerella cf. pavilionensis (Hall)
19. — Dorsal interior, showing important lamella:.
Devonian, Alpine, Mich. Cat. No. S 1736. x 1.
Clorinda tumidula (Billings)
8, 1 2. — Dorsal and posterior views, showing characteristic
exterior.
9, 10, 11,21 . — Ventral, anterior, dorsal, and lateral views
of exterior.
Silurian (Gun River), Anticosti. Cat. Nos. S 1685,
S 1693 (figs. 8, 12). X 1.
Gypidula romingeri Hall and Clarke
36, 39. — ^Ventral and dorsal interiors, showing internal
plates. Brachial processes broken from dorsal valve.
Devonian, Grand Lake, Presque Isle Co., Mich.
Cat. No. S 1698. x 1.5.
Sieberella sieberi (V. Buch)
25, 30, 33. — Dorsal, lateral, and ventral views of two speci-
mens, showing contour and profile of valves.
Devonian (Ffj), Koniepruss, Bohemia. Cat. No.
S1721. X 1.
246
PLATE 26
^ ^^ A ^^
9 1
_ >5 16 17
PLATE 27
Figs. Virgiana barrandei (Billings)
1,6,7, 1 6. — Lateral, ventral, dorsal, and posterior views
of a large specimen.
Silurian (Becscie River), Becscie River, Anticosti.
Cat. No. S 1668. x 1.
Platymerella aff. manniensis Foerste
2, 3, S, 11. — Ventral, dorsal, posterior, and lateral views of
exterior.
Silurian (Alexandrian, Sexton Creek), Belleview,
Calhoun Co., m. Cat. No. SI 84 5. i 1.
Pentamerus cf. oblongus Sowerby
4. — Internal septa in a specimen broken through the
middle.
8, 12, 18. — Lateral, dorsal, and ventral views of exterior.
10. — Dorsal exterior of a young specimen.
Silurian (Clinton), Rochester, N. Y. Cat. Nos.
S1805,S 1833 (fig. 10), and 8 1851 (fig. 4). x 1.
Figs. Pentamerus aff. oblongus Sowerby
17, 19. — Posterior and dorsal views of an internal mold,
showing septa.
Silurian (Niagaran), near Richmond, Ind. Cat.
No. S 1808. xO.5.
Pentamerus cf. cylindricus Hall and Whitfield
9, 1 5. — Ventral and dorsal views of an internal mold, show-
ing impressions of septa.
Silurian (Niagaran), Yellow Springs, Ohio. Cat.
No. SI 826. xO.5.
Pentameroides subrectus (Hall and Clarke)
13, 14. — Internal molds of dorsal and ventral interiors of
the same specimen. Note single septum in dorsal
valve,
Silurian (Maquoketa), Jones Co., Iowa. Cat. No.
S1848. x 1.
Holorhynchus giganteus Kiaer
20. — Dorsal view of exterior. This genus is interesting
for its possession of a free spondylium.
Silurian (zone 5b), Sandviken, Boerum, Norway.
Cat. No. S 2135. x 2.
248
PLATE 27
249
PLATE 28
Figs. Conchidium biloculare Linnaeus
1,5, 6. — Dorsal, ventral, and lateral exteriors of a small
individual.
3. — Posterior view.
8, 11, 12, 18. — Dorsal, ventral, lateral, and posterior views
of a large specimen. Posterior view shows a remnant
of the deltidium in place. Ventral view shows a
long crack, marking position of median septum.
9. — Dorsal tiew, showing nearly complete deltidium in
place.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
51859. X 1.
2. — Internal mold seen from dorsal side.
23. — Specimen broken in plane of median septum. Long
brachial process visible on the right.
Silurian (Gotlandian), Hejde, Gotland, Sweden.
Cat. No. S 1867. x 1.
4. — Small individual in dorsal view, to show uncovered
delthyrium.
26. — ^Apical portion of dorsal valve with internal plates.
Silurian, Klintehamn, Gotland, Sweden. Cat. No.
S1872. xl.
1 0. — Interior of apical portion of dorsal valve.
20. — Spondylium of ventral valve.
Silurian, Gotland, Sweden. Cat. No. 7839 Y. P. M.
xl.5.
Conchidium tenuistriatum Walmstedt
17. — Exterior of large specimen, in dorsal view.
Silurian (Gotlandian), Gotland, Sweden. Cat. No.
51860. xO.S.
Lissocoelina pergibbosa (Hall and Whitfield)
7, 14. — Dorsal and lateral views of an internal mold, the
former showing dorsal plates and the latter the unusual
gibbosity.
Silurian (Niagaran), Cedarville, Ohio. Cat. No.
S1834. X 1.
Lissocoelina ? maquoketa (Hall and Clarke)
13, IS, 16. — Ventral, dorsal, and posterior views of this
gibbous pentamerid, showing internal septa. This
form must be excluded from Harfidium because of
the short median septum.
Silurian (Niagaran), Maquoketa, Iowa. Cat. No.
S1840.
Figs. Lissocoelina ? maquoketa (Hall and Clarke) — Cont.
2 1 . — Lateral view of an unusually gibbous form.
Silurian (Niagaran), Maquoketa, Iowa. Cat. No.
S 1836.
Pentameroides subrectus (Hall and Clarke)
19. — Posterior view of an internal mold, showing septa.
Note single septum in dorsal valve.
Silurian (Clinton), Stony Creek, Ontario. Cat.
No. S 1842. X 1.
Pentameroides, n. sp.
22. — View of dorsal exterior, showing single median
septum.
Silurian ("Stricklandia-Pentamerus" zone of the
Clemville), Black Point, New Brunswick. Cat. No.
S1841. X 1.
Brooksina alaskensis Kirk
24. — Internal septa of a specimen broken through the
middle.
Silurian, S. E. shore Kosciusko Island, Davidson
Inlet, S. E. Alaska. Cat. No. S 2223. x 1.
Stricklandia gaspeensis Billings
25. — Posterior of dorsal valve, showing brachial processes.
This structure is more nearly rhynchonelloid than
pentameroid. Davidson figured the brachial process
affixed to the extremities of the lateral plates bound-
ing the notothyrium.
Silurian (La Vieille), La Vieille Cove, E. of Gascons,
Quebec. Cat. No. S 1899. x 2.
27. — Posterior of ventral valve, showing cardinal area and
fractured spondylium.
Silurian (Clinton), S. W. corner of Barachois at
Port Daniel, Quebec. Cat. No. S 1887. x 1.
Stricklandia lirata (Sowerby)
28. — Dorsal exterior.
Silurian, Gotland, Sweden. Cat. No. S 1883. x 1.
250
PLATE 28
251
PLATE 29
Figs. Pionodema cf. conradi (N. H. Winchell)
1 . — ^Thin section, showing endopunctas. It is to this type
of internal shell perforation that we restrict the term
endopunctje. The section figured is a portion of the
shell shown on pi. 23, fig. 9.
Ordovician (Black River), St. Paul, Minn. Cat.
No. S 1367. xca. 12.
Aulacophoria keyserlingiana (De Koninck)
2,5,10. — Ventral, dorsal, and lateral views of complete
individual. Anterior like that of Schizofhoria, but
prominent fold and sulcus a divergence toward
Enteletes.
Carboniferous, Welton, England. Cat. No. S 1924.
xl.
Hesperorthis laurentina (Billings)
3. — ^Thin section, showing deltidium in place. Cf.
Silurian, Anticosti. Cat. No. S 2221. x 4.
fig. 8.
Conchidium biloculare Linnaeus
4.-
-Cross section of shell, showing deltidium in place.
In an anterior direction from the position of this sec-
tion (which is near the beaks) the deltidium becomes
a flatly concave plate. In this figure the sides of the
deltidium have been broken from the walls of the del-
thyrial cavity. In Conchidium the deltidium was
evidently a pedicle sheath open at the posterior. A
similar structure appears in H arfidium. See t. fig. 25.
Silurian (Gotlandian), KJintehamn, Gotland,
Sweden. Cat. No. S 1872. x 3.
Stricklandia davidsoni Billings
—Section showing duplex spondylium and cardinalia.
Notice also lateral elevated plates on cardinal region
of dorsal valve.
Silurian (Jupiter River), East Jupiter Cliff, Anti-
costi. Cat. No. S 1898. x5.
Parastrophinella reversa (Billings)
—Section showing spondylium and cardinalia. Note
prominent dorsal plates and folded or duplex charac-
ter of alae in dorsal valve.
Silurian, base of White Cliff, Cape Eagle, Anti-
costi. Cat. No. S 1607. x4.5.
Fics. Vellamo diversa (Shaler)
8. — Section showing spondylium. Note thickening in
umbo-lateral chambers (cf. fig. 14). Note deltidium
built against delthyrial edge and strengthened by
shell deposit on sides of delthyrial cavity (T = trace
of tooth showing as an irregularly oval spot). x4.5.
14. — Section showing umbonal chambers completely filled
by adventitious shell. Note thickened deltidium and
callus spread on inside of delthyrial cavity, x 3.
Ordovician (Ellis Bay), W. side Ellis Bay, Anticosti.
Cat. Nos. S 2222a (fig. 8) and S 2222b.
Liocoelia proxima (Barrande)
-Section showing spondylium and cardinalia which
strongly suggest Camerofhoria and the rhynchonellids.
See t. fig. 36.
Silurian (Etage Eej), Kolednik, Bohemia. Cat.
No. SI 696a. x4.5.
Pentamerus aflf. oblongus Sowerby
1 1. — Section showing duplex spondylium and characteristic
dorsal lamella.
Silurian (Jupiter River), Belle River, Anticosti.
Cat. No. S 1819. x ca. 4.
Billingsella lindstromi (Linnarsson)
12. — ^Tangential section showing fibrous structure. Frag-
ment of shell taken from specimen figured on pi. 1,
fig. 27.
Mid. Cambrian (Paradoxides zone), Westrogothia,
Lovened, Sweden. Cat. No. S 16a.
Billingsella coloradoensis (Shumard)
1 3. — ^This tangential section was figured by Walcott (Camb.
Brach., p. 299, fig. 5) but the greater magnification
used by him did not reveal the true structure. There
are no punctse in Billingsella and the section shows
the fibers. See fig. 12.
Up. Cambrian, Morgan Creek, Burnet Co., Texas.
U. S. Nat. Mus.
252
PLATE 29
253
INDEX
The majority of the species listed in this index are not discussed in the memoir, but merely cited in the species
lists to which the page number refers. Pages on which species or genera are discussed are in bold-face type. All
species are listed under the specific name ; in addition, species whose generic reference has been changed are listed
under the genus to which they were formerly referred. Synonyms are in italics. Asterisks signify illustrations.
abnorinis (Hucnella), 159, 160*
abscissa (Panderina), 81
actonia: (Nicolella), 77, 78
aculeatus (Productorthis), 82
acuminata (Platystrophia), 65
acutilirata (Platystrophia), 65, 66
prolongata (Platjstrophia), 65
acutilobus (Bilobites), 130
acutiplicata Reed (Porambonites), 102
acutiplicata Waagcn (Enteletina), 148
acutolobatus (Gypidula), 174
procerula (Gypidula), 174
acutum (Cymbidium), 183, 184*
Adductor muscles, 6, 30, 31, 33,* 39, 40*
Adjuster muscles, 6, 30, 31, 33*
adscendens Davidson (V'ellamo), 114
adscendens Pander (Clitambonites), 26, 113
iqualis (Hemipronites), 116
xqualis (Orthis), 76
«equirostris (Porambonites), 102, 104
aKjuivalvis Hall (Plectorthis), 58
latior (Plectorthis), 58
pcrvagata (Plectorthis), 58
aquivdvis Shaler, see Mendacella uberis
agilera (Nicolella), 77
alaskensis (Brooksina), 183
alberta (Nisusia), 45
alsa (Rhipidomella), 133
altaica (Rhipidomella), 134
alternata (Heterorthis), 137
altirostris (Rhipidomella), 133
altissimus (Clitambonites), 114
altus (Clitambonites), 113
altus (Hemipronites), 116
altus (Porambonites), 102
alveata (Hebertella), 60
richmondensis (Hebertella), 60
ambigua ("Camerella"), 168
americana (Vcllamo), 114
amii {'. Nisusia), 45
amocna (Plat}strophia), 65
longicardinalis (Platj'strophia), 65
Anastrophia, 162, 164, 167, 169
ancillans (Clorinda), 172
andii (Enteletes), 146
angulata (Gypidula), 174
Ancusticardima, 69, 84
Angusticardiniina:, 74, 84
annamitica (Dinorlhis), 94
annieana (Platystrophia), 65
anomala Schlotheim (Clinambon), 115
anomala Walcott (Wimanella), 50
anthonensis (Skcnidioides), 72, 73
anticosticnsis Billings (Stricklandia), 187
anticosticnsis Shaler (Plaesiomys), 94
anticosticnsis Twenhofel (Virgiana), 185
antiquata (Swantonia), 159
aperturata (Platystrophia), 66
Apical plates, 6, 22
apicalis Billings (Hesperorthis), 86
apicalis Whitfield (Pohtoechia), 110
Apomatella, 24, 107, 117
appalachia (Billingsella), 49
arachne (? Syntrophia), 188
arata (Pentamerella), 176
Arch.€;orthis, 21, 26, 74, 80
arcticum (Conchidium), 181
arcuaria (Isorthis), 150
areola (Mystrophora), 22, 131, 132*
arethusa (? Syntrophia), 188
arisaigensis (Mendacella), 127
arkansana (Rhipidomella), 133
armanda (Finkelnburgia), 5 5
armata (Clorinda), 171
Articulation, 6, 24
assimilis (Rhipidomella), 133
asteroidca (Nicolella), 77
atava (Orusia), 54
atavoides (Dinorthis), 94
Athyris (?) tumidula, see Clorinda
Atr}-pa dorsata, see Platystrophia
galeata, see Gypidula
lens, see Stricklandia
nucella, see Lycophoria
attenuata (Platystrophia), 65
AULACELLA, 19, 119, 122, 136
AULACOPHORIA, 141, 145, 147
aurora (Eostrophoniena), 8 5
AUSTINELLA, 94, 99
avelinei (Dalmanella), 120
avita (Idiorthis), 128
Baker, F. C, 1 1
balclatchiensis (Glyptorthis), 90
balclatchiensis (Mctacamerella), 170
Bancroft, B. B., 96, 138
Barrande, J., 177
barrandei Billings (Virgiana), 185, 186*
barrandei Schuchcrt and Cooper (Heterorthis), 138
Barrandei-la, 162, 163, 165, 166, 171, 173
Barrandina, see Clorinda, 172
basalis (Parmorthis), 129
258
INDEX
bassleri (D.ilmanella), 120
Bather, F. A., 1 3
Bathycoelia, see Pionodema
battis (? Huenella), 160
baueri (Porambonites), 102, 103
bavarica (? Archasorthis) , 81
beaumonti (Schizophoria), 143
becsciensis (Stricklandia), 187
Beecher, C. E., 16, 130, 131, 167
Belanski, C. H., 175
bella Fenton (Rhynchocamara), 189
bella Schuchert and Cooper (Planidorsa), 101
bellarugosa (Glyptorthis), 90
bellula (Pionodema), 14-1
biforata (Platystrophia), 64
fissicostata (Platystrophia), 66
lynx reversata (Platystrophia), 65
sardoa (? Platystrophia), 66
BiLLiNGSELLA, 22, 27, 28, 32, 37, 40, 41, 48, 76
alberta, see Nisusia
billingsi, see Protorthis
bivia, see Nisusia
dice, see Deltatreta
exporrecta, see Oligomys
festinata, see Nisusia
harlanensis, see Syntrophioides
hlcksi, see Oligomys
latourensis, see Protorthis
orientalis, see Nisusia
quacoensis, see Protorthis
romingeri, see Bohemiella
rugicostata, see Oligomys
saffordi, see Syntrophioides
transversa, see Nisusia
Billingsellids, 22, 27, 32, 34, 35, 37, 39, 41, 44, 48, 107
billingsi Hartt (Protorthis), 46
billingsi Schuchert and Cooper (Skenidioides), 72
billingsi Walcott (Huenella), 159
billingsiana (Stricklandia), 187
bilobata (ReuscheUa), 139
BiLOBlTES, 119, 130
Bilobitids, 119, 130
bilobus (Bilobites), 130
biloculare (Conchidium), 163,* 181, 182
bivia (? Nisusia), 45
Bohemiella, 50, 52
Booker, F. W., 163, 172, 173, 176, 181
borealis Eichwald (Pentamerus), 178
borealis Walcott (Wimanella), 50, 51
borussica (Branconia), 168
bouchardi (Ptychopleurella), 92
Brachidia, 6
Brachiophore processes, 6, 37
supports, 6, 37
Brachiophores, 6, 37
brachynota (Platystrophia), 65
Branconia, 167, 168
brevirostris (Anastrophia), 170
brevis Billings (Stricklandia), 187
brevis Pander (Hemipronites), 116
brevis Pander (Productorthis), 82
brevis Willard (Multicostella), 98
breviuscula (Stricklandia), 187
broggeri Bancroft (Dalmanella), 120
broggeri Lamansky (Porambonites), 102
Brooksina, 163, 165, 166, 178, 183
bubo (Clorinda), 172
Buckman, S. S., 14, 16, 17,20
burgessensis (Nisusia), 45
burlingtonensis (Rhipidomella), 133
Butts, C, 109
buttsi (Orthis), 75,86
caducus (Gypidula), 174
callactis (Orthis), 7, 37, 75, 76
calligramma (Orthis), 37, 76
subplicata (Schizoramma), 88
Caiman, W.T., 12
Camarium, 6
camerata (Platystrophia), 65
Camerella, 162, 164, 166, 167
bella, see Rhynchocamara
ottawaensis, see Orthorhynchula
varians, see Rhynchocamara
Camerellids, 161, 162, 163, 164, 165, 166, 167, 171
campbelli (Syntrophina), 155
canadensis Billings (Stricklandia), 187
canadensis Clarke (Orthostrophia), 71
canalicula (Isorthis), 150
canaliculata (Levenea), 124
canalis (Resserella), 126
Cafellinia, see Capelliniella
Capelliniella, 163, 165, 166, 178, 179
carbonaria (Rhipidomella), 133
Cardinal angles, 6
area, 6
process, 6, 34
Cardinalia, 34, 164
carinata (Cariniferella), 122
epsilon (Cariniferella), 122
carinatus (Tropidoleptus), 152
Cariniferella, 30, 39, 119, 122
carletona (Pionorthis), 95
carleyi (Retrorsirostra), 95
insolens (Retrorsirostra), 95
carrickensis (Estlandia), 115
castellana (Stricklandia), 187
Cella, 6, 30
celsa (Schizoramma), 87
chama (Platystrophia), 66
chapmani (Stricklandia), 187
chekiangensis (Orthotichia), 144
Chilidial plates, 6, 24
Chilidium, 7, 23
choristites {Enteletes), see Enteletes lamarcki
chouteauensis (Schizophoria), 143
christianize (Archaeorthis), 81
cimex (Platyorthis), 135
circularis Pander (Hemipronites), 116
circularis Savage (Stricklandia), 187
circularis Sowerby (Platyorthis), 135
circularis Winchell (Pionodema), 141
circulus (? Mendacella), 127
Clarkella, 30, 154, 156
Clarkellidae, 154, 155
clarkensis (Rhipidomella), 133
clarksvillensis (Platystrophia), 65
Clements, F. E., 15, 16
INDEX
259
clcobis (Rhipidomella), 133
clermontensis (? Hebertella), 60
Clinambon, 107, 115
Clitambonacc.1, 22, 28, 43, 44, 48, 107
Clitambonites, 21, 22, 27, 29, 38, 107, 113
amcricanus, see V'ellamo
complectens, see \'ellamo
diversa altissima, sec \'cllamo
multistriata, sec \'ellamo
planus rctroflcxus, see Billlngsella reflexa
rogerscnsis, see Vellamo
ruedemanni, see Vellamo
semiconvexus, see Pomatotrema
trentonensis, see Vellamo
Clitambonitidae, 17, 22, 27, 33, 35, 37, 42, 48, 110
Clitambonitin.-e, 107, 113
Clorinda, 162, 163, 165, 166, 171, 178
becsciensis, see Stricklandia
fornicata, see Barrandella
ventricosa, see Barrandella
cljnie (Heterorthis), 40,* 137
coejTnanensis (Gypidula), 174
prognostica (Gypidula), 174
colbiensis (Platystrophia), 65
mutata (Platystrophia), 65
coUctti (Conchidium), 181
coloradocnsis (Billingsella), 41, 48, 49
Columbia (Pla^siomys), 94
comis (Gypidula), 17+
Commissure, 7, 19
complectens (Vellamo), 114
albida (Vellamo), 114
compressus (Pentamerus), 178
compta ("Nisusia"), 46
concava Holtedahl (Palxostrophomena), 100
concava Schmidt (Cyrtonotella), 77
concavoconvexa (Parmorthis), 129
concavus Pahlen (? Clitambonites), 113
Conchidium, 162, 163, 164,* 165, 166, 172, 178, 181
concinna (? Levenea), 123
conradi (Pionodema), 141
contractus (Entelctes), 146
Convexity, 7, 19, 165
convexus (Clitambonites), 113
cooperi (Parenteletes), 147
cora (Schizophoria), 143
cornuta (Gypidula), 174
parva (Gypidula), 174
corpulenta (Dalmanella), 120
corrugatus (Pentamerus), 178
corrjTillensis (Platj-strophia), 65
Costaa, 7
costalis (Hesperorthis), 86
costata (Platystrophia), 66
costata (Productorthis), 82
Costell^e, 7
craigensis (Skenidioides), 72
crassa (Platj-strophia), 66
crassicosta (Orthis), 76
crassicostata (Parmorthis), 129
crassicostella (Planidorsa), 101
crassiplica (Plat>-merella), 183, 184
crassiplicata (Cyclocoelia), 64
crassoradius (Conchfdium), 181
crispa (Glyptorthis) , 90
crispata (Glyptorthis), 90
Crura, 7, 37
Crural fossettes, 7, 25
plates, 7, 165
Cruralium, 7, 39, 166
cumberlandix (Rhipidomella), 133
cumberlandicum (Conchidium), 181
Cumings, E. R., 55, 67, 68, 131
cumingsi (Platystrophia), 65
Cycloccei.ia, 58, 64
Cyclococliinas, 56, 58, 64
Cyclospira, 6, 27
cylindricus (Pentamerus), 178
CvMBiDiUM, 29, 166, 178, 183
cypha (Platystrophia), 66
arcta (Platystrophia), 66
bellatula (Platystrophia), 66
tumida (Platystrophia), 66
Cyrtonotella, 74, 77
Dalmanella, 33,* 36, 58, 39, 119, 120, 133, 135
bellula, see Pionodema
carinata epsilon, see Cariniferella
cimex, see Platyorthis
circularis, see Pionodema
concavoconvexa, see Parmorthis
conradi, see Pionodema
crispata, see Glyptorthis
danbyi, see Thiemella
deshayesi, see Mystrophora
edgewoodensis, see Wattsella
electra, see Archjeorthis
Ixvis, see Archararthis
major, see Archasorthis
elmira, see Cariniferella
fairmountensis, see Heterorthina
lucia, see Platyorthis
macra, see Levenea
perelegans, see Isorthis
planoconvexa, see Platyorthis
pygmaea, see Isorthis
rockhousensis, see Isorthis
springfieldensis, see Parmorthis
sub^equata, see Pionodema
gibbosa, see Doleroides
perveta, see Doleroides
Virginia, see Cariniferella
waldronensis, see Parmorthis
wemplci, see Finkelnburgia
Dalmancllacea, 22, 43, 119
Dalmanellid.-c, 34, 42, 119, 125, 137
dalyana (Rhipidomella), 133
danbyi (? Thiemella), 136
dartae (Orthostrophia), 71
daunus (Archxorthis), 81
Davidson, T., 66, 92, 103, 104
davidsoni Billings (Stricklandia), 187
davidsoni Verneuil (Hesperorthis), 86
Davies, A. Morley, 14
Dayia, 6, 27
daytonensis (Platystrophia), 65
laurelensis (Platystrophia), 65
daytonensis (Glyptorthis), 90
260
INDEX
decipiens (Isorthis), 150
decussata (Virgiana), 185
deflecta (Valcourea), 7, 97
deflexa (Anastrophia), 170
deformatus (Porambonites), 102, 103
deformis (Stricklandia), 187
Deltarium, 7
Deltatreta, 17, 21, 22, 23, 24, 38, 107, 108
Deltatretida:, 48, 107
Delthyrial cavity, 7
Delthyrium, 7, 21, 163
Deltidial cover, 163
plates, 7, 163
Deltidium, 7, 21
demissa (Nicolella), 77
Dental plates, 7, 2 5, 42
sockets, 8, 34, 35*
dentata (Platystrophia), 66, 68
Denticles, 8, 34, 35*
Derby, O. A., 39, 145
deshayesi (Mystrophora), 131
desmopleura (? Eoorthis), 51
desmopleura nympha, see nympha
diablo (? Eoorthis), 51
dice (Deltatreta), 108, 109
DiCTYONELLA, 102
Diductor muscles, 8, 30, 31, 32, 33,* 40
dieneri (Parenteletes), 147, 148
Dietrich, W. O., 67
dimera (Bilobites), 130
diminutiva (Rhipidomella), 133
Dinorthida, 35, 37,44,93
DiNORTHis, 10, 18, 21, 31, 35, 36, 93, 94
carletona, see Pionorthis
carleyi insolens, see Retrorsirostra
Columbia, see PL-esiomys
deflecta, see Valcourea
iphigenia, see Plaesiomys
loricula, see Valcourea
meedsi, see Plaesiomys
arctica, see Plaesiomys
germana, see Plssiomys
platys, see Multicostella
recta, see Valcourea
retrorsa, see Retrorsirostra
retrostriata, see Heterorthis
rockymontana, see Plaesiomys
subquadrata, see Plaesiomys
tioga, see Cariniferella
transversa, see Plaesiomys
ulrichi, see Plaesiomys
discus (Rhipidomella), 133
disparilis (Hesperorthis), 86
divergens Foerste (Pentamerus), 178
divergens Hall and Clarke (Parastrophinella), 169
diversa (Vellamo), 114
dixoni (Orthostrophia), 71
DoLERoiDEs, 17, 36, 58, 63
DOLERORTHIS, 40, 74, 88
dolomitica (Orthotropia), 152
dorsata (Platystrophia), 66
dorsoplicata (Fascicostella), 130
dougaldensis (Loperia), 47
dubiaHall 1860 (Pentamerella), 176
dubia Hall 1858 (Perditocardina), 83, 13S
dudleyensis (Gypidula), 174
dumblei (Enteletes), 146
dumonti (Cariniferella), 122
edgelliana (Idiorthis), 128
edgewoodensis (Wattsella), 125
Eichwald, E., 103
eifelensis (Aulacella), 122
electra (Archseorthis) , 80, 81, 109
Ixvis (Archseorthis), 81
major (Archsorthis), 81
elegans (Enteletes), 146
elegantula Butts (Paurorthis), 80, 109
elegantula Dalman (Parmorthis), 128, 130
elegantula McEwan (Platystrophia), 65
amplisulcata (Platystrophia), 65
triplicata (Platystrophia), 65
elegantula Walcott (Eostrophomena), 85
elkhornensis (Platystrophia), 65
EUes, Gertrude, 1 3
ellipsoides (Heterorthina), 124
ellsworthi (Rhipidomella), 133
elmira (Cariniferella), 122
elongata Willard (Multicostella), 98
emacerata (Dalmanella), 32, 120, 121
emarginata Belanski (Sieberella), 175
emarginata Hall (Rhipidomella), 133, 134
emarginata Pahlen (Vellamo) ,114
eminens (Orthis), 76
eminens (Productorthis), 83
Encuclodema, see Cycloccelia
Endopunctse, 10, 42
Enteletella, 145, 146, 148, 162
Enteletes, 19, 30, 38, 140, 146, 149, 162
acutiplicata, see Enteletina
choristites, see lamarcki
dieneri, see Parenteletes
ferruginea, see Enteletina
globosa, see Enteletina
infracarbonica, see Aulacophoria
latesinuata, see Enteletina
pentameroides, see Enteletina
sublxvis, see Enteletina
uralica, see Aulacophoria
Enteletina, 146, 148
Enteletina, 31, 140, 141, 145
Enteletoides, 146, 147, 148
Eoorthids, 44, 50, 74
Eoorthis, 27, 37, 50, 51
bavarica, see Archxorthis
christianiae, see Archsorthis
daunus, see Archaeorthis
desmopleura nympha, see nympha
hastingsensis, see Protorthis
johannensis, see Orusia
newtonensis, see Finkelnburgia
putillus, see Archaeorthis
remnicha sulcata, see sulcata
texana, see texana
winfieldensis, see winfieldensis
tuUbergi, see Archsorthis
wimani, see Archseorthis
Eostrophomena, 85
Epidermis, 41
erecta (? Nisusia), 45
INDEX
261
Eridortius, 19, 74, 91
esthonus (Pentamcrus), 178
ESTLANDIA, 38, 38,* 107, 115
eun-one (Archiorthis), 81
Euseptum, 8
excavatus (? Gonambonites), 118
excelsus (Clitambonites), 113
exfoliata (Plectorthis), 58
Exopuncta:, 1 0, 42
expansus (Hemipronites), 116
exponens (Conchidium), 181
exporrectus (Oligomys), 53, 54
extensa McEwan (Platystrophia), 65, 68
extensa Pander (Panderina), 78, 82
extensa \*crncuil (Glossorthis), 78
fairmountensis (? Heterorthina), 124
fallax Gurich (Mystrophora), 131
fallax Salter (Schizophorella), 62
fasciata (Schizorarama), 87
Fascicostella, 125, 129
fascigera (? Eoorthis), 51
fausta (Glyptorthis), 90
jernvalensis {Platystrofhia), see Mcewanella lineolata
ferruginea (Entcletina), 148
festinata (Nisusia), 44
FUx, 8
fiUistriata (Deltatreta), 108, 109
filosa (Porambonites), 102
finkelnburgi (Finkelburgia), 55, 56
FiNKELNBURciA, 10, 17, 27, 28, 38, 40, 55, 71
Finkelnburgiidx, 44, 48, 54, 56, 58
fissicosta (Plectorthis), 58
fissiplica (Schizoramma), 87
fissistriata (Schizoramma), 87
flabellites (Dolerorthis), 89
dinorthis (Dolerorthis), 89
euorthis (Dolerorthis), 89
fissiplicata (Dolerorthis), 89
militaris (Dolerorthis), 89
flabellulum (Dinorthis), 94
carrickensis (PIxsiomys), 95
floydcnsis (Schizophoria), 143
Focrste, A. F., 88, 90, 99, 184, 185
foerstei (Platystrophia), 65
ampla (PlaR'strophia), 65
Fold, 8
fornicata (Barrandella), 173
fragilis (Schizophoria), 143
frankfurtensis (Hebertella), 60
Freeh, F., 177
frechi Fliegel (Orthotichia), 143
frechi Wysogorsky (Orthis), 76
freija (Orthis), 76
frenum (Lycophoria), 105
Fulcral plates, 8, 34, 38, 164
fultonensis (Pentamcrella), 176
futilis (Dalmanella), 120
galeata (Gypidula), 172, 174
gaspeensis (Stricklandia), 187
Genital markings, 8, 33
georgix (? Conchidium), 181
gervillei (Fascicostella), 130
gibbosa (Doleroides), 63
giganteus (Holorhynchus), 180
gigas (Porambonites), 102, 103
Girty, G. H., 147, 148
globata (Platystrophia), 65, 66
globosa Eichwald (Lycophoria), 105
globosa Girty (? Enteletina), 148
globosa McEwan (Platystrophia), 65
globosa Willard (Mimella), 61
globosus Pander (? Hemipronites), 116
globulosa (Gypidula), 174
globus (Gypidula), 174
Glossorthis, 10, 23, 28, 74, 78
Glyptorthinx, 74, 89
Glyptorthis, 37, 74, 89
sublamellosa, see Ptychopleurclla
Gonambonites, 17, 30, 38, 107, 118
inflexa, see Estlandia
marginata aspera, see Estlandia
magna, see Estlandia
panderi, see Estlandia
Gonambonitinx, 107, 118
goodwini (Rhipidomella), 133
Gorsky, I. I., 145, 147
gothlandicus Lebedeff (Pentamerus), 178
gotlandica Schuchert and Cooper (Schizoramma), 88
grandxva (Pomatotrema), 110
grandis Portlock (Valcourea), 97
grandis Tolmachew (Rhipidomella), 134
grayix (Vellamo), 114
greenei Hall and Clarke 1895 (Camerella), 168
greenei Hall and Clarke 1893 (Conchidium), 181
greenoughi (Skcnidioides), 72
Gypidula, 162, 165, 166, 171, 173
Gypidulinx, 162, 163, 165, 171, 173, 178
Hall, H. M., 1 5
Hall, J., 174
Hall and Clarke, 18, 19, 21, 26, 27, 30, 31, 34, 35, 42,
47,48, 58, 59, 60, 76, 86, 87, 95, 104, 106, 113, 114,
116, 118, 120, 121, 142, 145, 151, 161, 163, 166,
167, 168, 169, 173, 174, 176, 178, 185, 187, 188
halli (Skcnidioides), 72, 73
hamatus (Nicolella), 77
Harknessella, 39, 137, 138
Harknessellinx, 3 5, 137, 138
harlanensis (Syntrophioides), 155
harnngcnsis (Smeathenella), 139
Harpidium, 163, 165, 166, 178, 180
hartti (Rhipidomella), 134
hastingscnsis (? Protorthis), 47
haugi (Entcletcs), 146
Hebertella, 6, 10, 19, 36, 38, 58, 59, 90, 91
celsa, see Schizoramma
daytoncnsis, see Eridorthis
fausta, sec Eridorthis
impcrator, sec Mimella
insculpta, sec Glyptorthis
lineolata, sec Mcewanella
mclonica, sec Mimella
nicklesi, sec Eridorthis
rogersensis, see Eridorthis
scovillei, see Austinella
vulgaris, see Mimella
helena ("Protorthis"), 47
hemiplicata Hall 1847 (Camerella), 168
rotunda (Camerella), 168
262
INDEX
hemiplicata Hall 1852 (Enteletes), 146, 147
naias (Enteletes), 146
Hemipronites, 17, 38, 107, 115
apicalis, see Polytoechia
carrickensis, see Estlandia
thomsoni, see Estlandia
hemipronites (Hemipronites), 116
hera (HueneUa), 159
hermitagensis (Platystrophia), 6S
Hesperorthinas, 37, 85
Hesperorthis, 7, 17, 21, 22, 23, 25, 26, 37, 39, 40, 74,
76,85
hessensis (Rhipidomella), 133
Heterorthida:, 136
Heterorthina, 36, 119, 124
Heterorthins, 35, 137
Heterorthis, 24, 36, 39, 40,* 137
hicksi (Oligomys), 53
highlandensis (Wimanella), 49, 50, 51
Hinge-line, 8
hippolyte (Archasorthis) , 81
holdeni (Plectorthis), 58
Holorhynchus, 29, 166, 178, 180
holtedaUi (BiUingsella), 48
Homoeodeltidium, 22
Homoeomorphy, 16, 57, 61, 62, 63, 89, 100, 140, 175
HORDERLEYELLA, 125, 127
horderleyensis (Reuschella), 139
HuENELLA, 27, 28, 154, 159
triplicata, see Huenellina
Huenellidae, 154, 159
Huenellina, 154, 160
humilis Fuchs (Vellamo), 114
humilis Pander (Clitambonites), 113
hunnebergensis ("Protorthis"), 47
hybrida (Rhipidomella), 133
icetas (Huenella), 160
Idiorthis, 125, 128
idonea (Rhipidomella), 133
ignota (Dalmanella), 33,* 120, 121
imitatrix (Rhipidomella), 134
imperator (Mimella), 61, 62
inca (Rhipidomella), 134
inclyta (Heterorthis), 137
incurvata (? Productorthis) , 83, 84
indentus (Bilobites), 130
indianola (Eoorthis), 51
indica (Orthotichia), 144
inflata (Plasiomys), 95
inflexa (? Estlandia), 115, 118
infracarbonica (Aulacophoria), 145
infracarbonica (Schizophoria), 143
Incria, 38, 107, 112
ingrica (Apomatella) , 117
inornata (? Cyclospira), 168
inostrantzefi (Hesperorthis), 86, 87
ubjaensis (Hesperorthis), 86
viruana (Hesperorthis), 86
insculpta (Glyptorthis), 89
manitoulinensis (Glyptorthis), 90
insigne Hall (Skenidium), 73
insigne Kirk (Harpidium), 180
insolita (Sieberella), 175
Interareas, 8, 20, 163, 165, 187
intercedens (Porambonites), 102
intermedia Pander (? Porambonites), 104
intermedia Pander (Productorthis), 83
intermedia StaufFer (Rhipidomella), 133
internascens (Anastrophia), 170
interplicata Foerste (Dolerorthis), 88
interplicata Hall (Anastrophia), 170
interstriata Janischevsky (Schizophoria), 143
interstriata Willard (Dinorthis), 94, 96
intralineata (Pentamerella), 176
inyoensis ("Wimanella"), 51
iones (Taffia), 47, 85
iowensis (Schizophoria), 143, 144
magna (Schizophoria), 143
iphigenia (Plaesiomys), 94, 96
isis (Syntrophina), 156
ISORHYNCHUS, 101, 102
Isorthina:, 140, 141, 149
IsoRTHis, 36, 149
Jamesella, 34, 44, 46
jamesi (Plectorthis), 58
jerseyensis (Rhipidomella), 133
johannensis (Orusia), 54
jonesi (Harknessella), 138
juba (Huenella), 160
juvensis (Platystrophia), 65
kankakensis (Austinella), 99, 100
Kayser, E., 132
Kayserella, 24, 1 19, 132
kayseri Kozlowski (Productorthis), 83
kayseri Waagen (Enteletes), 146
keisleyensis (Ptychopleurella), 92
keyserlingianus (Aulacophoria), 145
King, R. E., 147, 149
King, W., 66, 83
Kirk, E., 183
knappi (Rhipidium), 180
knotti (Gypidula), 174
Kolarova, F. N., 158
Kozlowski, R., 10, 28, 41, 49, 80, 83, 84, 104, 106, 112,
132, 150, 161, 163, 164, 173
kozlowskii (Orthotichia), 144
kuckersensis (Porambonites), 102
kuckersiana (Orthis), 76
kuthani (Jamesella), 46
KUTORGINA, 34
laevis Sowerby (Pentamerus) , 177
Ijevis Wakott ("Protorthis"), 47
la;vissimus (Enteletes), 146
lasviusculus (Gypidula), 174
Lahusen, I., 106
Lamansky, W., 78
lamarcki (Enteletes), 146, 147
lamellosa (Ptychopleurella), 92
lapworthi (Ptychopleurella), 92
laqueatum (Conchidium), 181
Laqueus, 32
lata Lamansky (Panderina), 82
lata Pander (Productorthis), 83
latasulcata (Hebertella), 60
INDEX
263
Lateral areas, 8
plates, 9
lateralis (Syntrophia), 158
latesinuatus (Entcletina), 148
laticaudatus (Porambonitcs), 102
laticosta (Platystrophia), 66
latiplicata (Parastrophinella), 169
latissima (Paurorthis), 79
latissimus (Hcmipronitcs), 116
latourcnsis (Protorth'is), 47
latus Kirk (Harpidium), 180
latus Pander (Clitambonitcs), 1 13
latus Pander (Gonarabonites), 118
latus Pander (Hemipronites), 116
laurentina (Hesperorthis), 86, 87
legoensis ("Conchidium"), 183
lehuequetiana (Rhipidomella), 133
Leidhold, C, 165, 175, 176
lens (Stricklandia), 187
lenticularis Foerste (? Mendacella), 127
lenticularis Vanuxem (Levenea), 123
lenticularis Wahlenberg (Orusia), 54, 55, 68
atrj'poides (Orusia), 54
lyncioides (Orusia), 54
leonardensis (Enteletes), 146
leonardensis (Rhipidomella), 133
leonensis (r Thiemella), 136
lepida (Kayserella), 132
lesleyi (Huenella), 160
leucosia (Rhipidomella), 133
Levenea, 36, 39, 40, 119, 123
lewisii (Skenidioides), 72
Likharev, B., 162
lima (Porambonitcs), 102
linda (Glossorthis), 78
virgata (Glossorthis), 78
lindenense (Conchidium), 181
lindstromi (Billingsella), 41, 49
lineolata (Mcewanclla), 69
linguifera (Barrandclla), 173
wilkinsoni (Clorinda), 171, 172
linnevi (Orthorhynchula), 42
LiNo'poREi.LA, 10, 28, 38, 103, 150
Linoporellidi, 39, 150
LioccELiA, 171, 189
liratus (Stricklandia), 187
LissoccELiNA, 165, 166, 178, 179
littoni (Conchidium), 181
liumbonus (Enteletes), 146
livia (Rhipidomella), 133
logani (Rhipidomella), 133
lonensis (? Hebertella), 60
longirostris ("Camerella"), 168
LoPERiA, 44, 47
loricula (Valcourea), 97
lotis (Gypidula), 1 74
loveni (Isorthis), 1 50
lowi (? Nisusia), 45
lucia Billings (Rhipidomella), 133
lucia Clarke (Platyorthis), 135
Lycophoria, 39
Lycophoriidse, 44, 105
lynx (? Platystrophia), 66, 68
moritura (Platystrophia), 65
McEwan, Eula D., 66-69, 70
Mcewanella, 31, 69
macfarlani (Schizophoria), 144, 145
macra (Levenea), 123
magna (Valcourea), 98
magnifica (Anastrophia), 170
magnicardinalis (Rhipidomella), 133
major Savage (Virgiana), 185
major Walcott (Billingsella), 49
manitouensis (Stricklandia), 187
manniensis (Platymerella), 184, 185
maquoketa (? Lissocalina), 179
marginata (Estlandia), 22, 38,* 115
asper (Estlandia), IIS
magna (Estlandia), 115
maria (Hebertella), 60
parkensis (Hebertella), 60
Marionella, 94, 96
marmorea (Orthotichia), 144
matapedia (Ptychopleurella), 93
matura (Idiorthis), 128
maximus (Hemipronites), 116
mayvillensis (Virgiana), 185
media (? Parmorthis), 129
Median septa, 9
meedsi (Plaesiomys), 94
arctica (Plasiomys), 94
germana (Pljesiomys), 94
meeki (Dalmanella), 36, 120, 121
melissa (Stricklandia), 187
melonica (Mimella), 33,* 61
melvillei (Rhipidomella), 134
Mendacella, 39, 125, 127
meridionalis (Enteletes), 146
Merista, 6, 27
merope (?? Skenidioides), 72, 73
mesoloba (? Aulacophoria), 145
mesoplatys (Rhipidomella), 134
baylorensis (Rhipidomella), 134
Metacamerella, 167, 170
Metcalf, Z. P., 12
michelini (Rhipidomella), 133
microcamerus (Stricklandia), 187
microplocus (Enteletes), 146
Microstructure, 41
Mimella, 17, 33, 58, 61
mineolaensis (Gypidula), 174
minima Pander (Paurorthis), 79
minima Savage (Rhipidomella), 134
minnesotensis (Pionodema), 141
minor (Barrandina), 173
minuscula Barrande (Mendacella), 127
minuscula Willard (Mimella), 61
minuta Pander (Paurorthis), 79
minuta Raymond (Platystrophia), 65
mira (Capelliniella), 179
missouriensis Branson (Pentamerella), 176
missouriensis Swallow (Rhipidomella), 133
molongensis ("Pentamerella"), 176
moneta (Nicolella), 77, 78
montanensis (Clarkella), 156
monticula (Ptychopleurella), 92
morganiana (Orthotichia), 40, 144
chihsiaensis (Orthotichia), 144
264
INDEX
morrowensis (Platystrophia), 65
munsteri (Conchidium), 181
Muir-Wood, H. M., 158
mullochiensis (Mendacella), 127
multicosta (Vellamo), 114
multicostata Dunbar (Gypidula), 174
multicostatum Hall (Rhipidium), 181
MULTICOSTELLA, 94, 98
multilirata (Stricklandia), 187
multiplicata Bancroft (? Wattsella), 125
multiplicata Hall and Clarke (Parastrophinella), 169
multisecta Meek (Dalraanella), 120
multistriata Hall (Schizophoria), 143
multistriata Roemer (Sieberella), 175
muralis (Pomatotrema), 109
Muscle impressions, 9, 30, 39
musculosa (Rhipidomella), 134
Myophore, 9, 35
Mystrophora, 17, 22, 39, 119, 131
Mystrophorids, 39, 119, 131
nautes (? Nisusia), 45
navis (Dalmanella), 120
neglecta Barrande (Isorthis), 150
neglecta James (Plectorthis), 58
nettelrothi Foerste (Dolerorthis), 89
nettelrothi Hall and Clarke (Conchidium), 181
nevadensis (Rhipidomella), 134
newsomensis (Orthostrophia), 71
newsomensis (Rhipidomella), 134
newtonensis (Finkelnburgia), 55
nicklesi (Eridorthis), 91
NiCOLELLA, 24, 74, 77
nikschitschi (Enteletella), 148
nisis (Schizoramma), 87
Nisusia, 26, 27, 34, 44
Nisusiida:, 37, 43, 44, 50
nitida (Platystrophia), 65
nodocostata (Ptychopleurella), 92
Noetling, F., 103
NoETLINGIA, 101, 105
nonus (Clarkella), 156
norwoodi (Stricklandia), 187
Notothyrial platform, 9, 34, 39
Notothyrium, 9, 23
Novak, O., 177
nucella (Lycophoria), 105, 106
nucleolata (Gypidula), 174
nucleus (Gypidula), 174
nundina (Syntrophina), 156
nympha (? Eoorthis), 51
nysius (Rhipidium), 181
oakensis (Polytoechia), 110
oblata (Rhipidomella), 134
oblongus Pander (Clitambonites), 1 13
oblongus Sowerby (Pentamerus), 162, 178
subrectus, see subrectus
obsoletum (Conchidium), 181
obtusa (Productorthis), 82
obtusus (Hemipronites), 116
occasus (Rhipidomella), 134
occidentale Hall 18 52 (Conchidium), 181
occidentalis Hall 1858 (Gypidula), 173, 174
occidentalis Hall 1847 (Hebertella), 60
sinuata (Hebertella), 60
occlusa (Isorthis), 150
ochus (? Eoorthis), 51
oehlerti (Enteletes), 146
Old-age characters, 42
Oligomys, 50, 53
Onniella, see Dalmanella
opercularis (Platyorthis), 135
Opik, A., 69, 79, 100, 112, 114, 117, 118
ops (Parastrophinella), 169
optatus (Brooksina), 183
orbicularis (Hemipronites), 116
oriens ("Nisusia"), 46
orientalis (? Nisusia), 45
Orientation, 18
oriskania (Schizophoria), 143
Ornamentation, 162, 165
Orthacea, 43, 154
orthambonites (Orthis), 76
Orthambonites crassicosta, see Orthis
parvus, see Paurorthis
rotundata, see Orthis
trigona, see Paurorthis
Orthidje, 33, 34, 35, 37, 39, 42, 44, 48, 73, 94, 101, 119
Orthinx, 37, 74, 75
Orthis, 18, 21, 26, 32,* 35, 37, 40,* 74, 75, 86
acton iae, see Nicolella
{squivalvis, see Mendacella uberis
annamitica, see Dinorthis
anticostiensis, see Plasiomys
apicalis, see Hesperorthis
areola, see Mystrophora
attenuata, see Heterorthis
balclatchiensis, see Glyptorthis
basalis, see Parmorthis
bellarugosa, see Glyptorthis
biforata, see Platystrophia
lynx, see Platystrophia
bouchardi, see Ptychopleurella
calligramma subplicata, see Schizoramma
canalicula, see Isorthis
canaliculata, see Levenea
canalis, see Dalmanella
carinata, see Cariniferella
carleyi, see Retrorsirostra
circularis, see Platyorthis
concava, see Cyrtonotella
concinna, see Levenea
corpulenta, see Dalmanella
costalis, see Hesperorthis
crispa, see Glyptorthis
davidsoni, see Hesperorthis
decipiens, see Isorthis
dimera, see Bilobites
disparilis, see Hesperorthis
dorsoplicata, see Fascicostella
edgelliana, see Idiorthis
eifelensis, see Aulacella
elegantula, see Parmorthis
ellipsoides, see Heterorthina
emacerata, see Dalmanella
euryone, see Archxorthis -
INDEX
265
Orthis — Cont.
cxtcnsa, sec Glossurthis
f.isci.ita, see Schizoramma
tissiplica, see Schizoramma
flabellitcs, see Dolcrorthis
dinorthis, see Dolcrorthis
cuorthis, sec Dolcrorthis
fissiplicata, see Dolcrorthis
militaris, sec Dolcrorthis
flabcllulum, sec Dinorthis
carrickensis, see Plxsiomys
frcchi, see Cyrtonotella
frcija, see Cyrtonotella
futilis, see Dalmanclla
gervillei, sec Fascicostella
grand is, see Valcourea
hcmipronitcs, sec Hcmipronites
highlandensis, see VVimanella
hippolyte, see Arch.*orthis
ignota, see Dalmanclla
inclyta, see Heterorthis
incurvata, see Productorthis
inflata, see Pl.-esiomys
inostrantzefi, see Hcspcrorthis
ubjaensis, see Hcspcrorthis
viruana, sec Hcspcrorthis
interplicata, sec Dolcrorthis
kankakensis, see AustincUa
keisleyensis, see Ptychopleurclla
keyserlingiana, see Aulacophoria
kuckersiana, see Cyrtonotella
lamellosa, see Ptychopleurclla
lapworthi, see Ptychopleurclla
lenticularis Vanuxem, see Levenea
lenticularis Wahlenberg, see Orusia
atrypoides, see Orusia
lyncioides, see Orusia
leonensis, see Thiemella
lepida, see Kayscrella
lewisii, see Skenidioides
loveni, see Isorthis
media, see Parmorthis
meeki, see Dalmanclla
minuscula, see Mendacella
moneta, see Nicolella
monticula, see Ptychopleurclla
morrowensis, see Platystrophia
mullochiensis, see Mendacella
multisecta, see DalmancUa
neglccta, see Isorthis
nettelrothi, see Dolcrorthis
nisis, see Schizoramma
occlusa, sec Isorthis
opercularis, sec Platyorthis
parvula, see Paurorthis
pectincUa sweencyi, sec Dinorthis sweeneyi
pepina, sec Billingsclla
personata, see Proschizophoria
plicata, see Hcspcrorthis
porcata, sec Plxsiomys
porrecta, see Dalmanclla
punctata, see Linoporclla
punctostriata, see Linoporella
pyramidalis, sec Hcspcrorthis
Orthis — Cont.
quadrans, sec Levenea
radians, see Hcmipronitcs
rcdux, sec Pionodcnia
rigida, see Schizoramma
rogata, see Dalmanclla
rugiplicata, sec Ptychopleurclla
rustica, sec Dolcrorthis
saffordi, see Multicostclla
sedgwicki, see Fascicostella
scmicircularis, see Cyrtonotella
scmiovalis, see Dinorthis
stracheyi, sec AustincUa
striata, see Nicolella
striatocostatus, see Plassiomys
subcarinata Dunbar, see Levenea
subcarinata Hall, see Levenea
subdivisus, see Plssiomys
subfissicosta, see Schizoramma
sweencyi, see Dinorthis
tersa, see Dalmanclla
tcstudinaria (Dalman), sec WattscUa
testuditiaria (Hall and Clarke), see Orthis rogata
tetragonum Roemer, see Isorthis
lata, see Isorthis
thakil, see Dinorthis
convexa, see Dinorthis
trifida, see Dinorthis
tricenaria, see Hcspcrorthis
trigeri, see Isorthis
trigonula, see Pahlenella
turgida, see Linoporella
uberis, see Mendacella
unguis, see Nicolella
vespertilio, see Harknessella
wisbyensis, see Parmorthis
Orthisina, see Clitambonites
adscendens, see Vellamo
complectens, see Vellamo
concavus, see Clitambonites
diversa, see Vellamo
emarginata, see Vellamo
grandseva, see Pomatotrema
ingrica, see Apomatella
marginata, see Estlandia
planus altus, see Gonambonites
pyron, see Estlandia
schmidti, sec Clitambonites
squamata, see Vellamo
verneuili, see Vellamo
wescnbergensis, see Vellamo
volborthi, see Estlandia
Orthoidea, 43
Orthorhynchula, 26, 42
Orthostrophia, 33, 70
fissistriata, see Schizoramma
Orthostrophiina:, 56, 58, 70
Orthotichia, 30, 31, 40, 140, 141, 144
Orthotropia, 152
Orusia, 38, 54, 56, 58
Osborn, H. F., 1 3
osceola (Finkelnburgia), 5 5,* 56
corrugata (Finkelnburgia), 5 5
ottawaensis (Orthorhynchula), 42
266
INDEX
Otusia, 50, 52
ovalis (Pentamerus), 178
Ovarian markings, 33
ovata (Orthis), 76
ovata (Productorthis), 83
oweni (Rhipidomella), 134
Pahlenella, 10, 107, 117
Pal^ostrophomena, 94, 100
Paleoecology, 16
Palintrope, 9
Pallial markings and sinuses, 9, 32, 40
palmata (Syntrophina), 156
Pander, C. H., 113, 117
panderi Billings ("Camerella"), 168
panderi Opik (Estlandia), 1 15
panderiana (Orthis), 75, 86
Panderina, 74, 81
papyracea (Gypidula), 174
parallela (Productorthis), 83
parallelus (Porambonites), 102
Parastro-phia, see Camerella
divergens, see Parastrophinella
greenei, see Camerella
hemiplicata, see Camerella
rotunda, see Camerella
latiplicata, see Parastrophinella
multiplicata, see Parastrophinella
ops, see Parastrophinella
reversa, see Parastrophinella
rotundiformis, see Camerella
scofieldi, see Camerella
Parastrofhina, see Camerella
Parastrophinella, 164, 166, 167, 169
Parenteletes, 6, 19, 30, 145, 146, 147
Parmorthis, 22, 25, 36, 39, 125, 126, 128
parva Billings ("CamereUa"), 168
parva Opik (Vellamo), 114
parva Pander (Paurorthis), 79, 80
Parvicostells, 7
parvula Lamansky (Paurorthis), 79
parvulus Savage (Pentamerus), 178
patera ("Heterorthis"), 138
pauciplicata (Platystrophia), 65
Paurorthis, 10, 74, 79, 81
pavilionensis (Pentamerella), 176*
pecosi (Rhipidomella), 134
pectinella (Dinorthis), 93, 95, 96
sweeneyi (Dinorthis), see sweeneyi
Pedicle callist, 9, 33*
foramen, 9
muscles, 9, 30, 31
pelagica (Gypidula), 174
peloris (Rhipidomella), 134
penelope (Rhipidomella), 134
penniana (Rhipidomella), 134
pennsylvanica (Rhipidomella), 134
pentamera (? Enteletes), 146
Pentameracea, 28, 43, 161
Pentamerella, 165, 166, 171, 176
Pentameridae, 27, 161, 162, 164, 165, 170
Pentamerinx, 162, 163, 165, 166, 171, 177
Pentameroidea, 43, 154
Pentameroides, 164,* 166, 178, 179
pentameroides (Enteletina), 148
Pentamerus, 10, 27, 162, 163, 164,* 165, 166, 177, 178
acutolobata, see Gypidula
procerula, see Gypidula
caducus, see Gypidula
globus, see Gypidula
knappi, see Rhipidium
linguifera, see BarrandeDa
microcamerus, see Stricklandia
optata, see Brooksina
pelagica, see Gypidula
proxima, see Liocoelia
subrectus, see Pentameroides
ventricosus, see Porambonites
pepina (Billingsella), 49
peraltus (Hemipronites), 116
Perditocardinia, 133, 135
perelegans (Isorthis), 36, 150
pergibbosa (Lissocoelina), 179
perilla (Syntrophina), 156
perlatus (Hemipronites), 116
perminuta (Rhipidomella), 134
perpasta (Jamesella), 46
macra (Jamesella), 46
subquadrata (Jamesella), 46
pcrsonata (Proschizophoria), 123
pesovis (Pentamerus), 178
Pionodema, 22, 23, 30, 37, 38, 139, 140, 141, 144
globosa, see Mimella
minuscula, see Mimella
PlONORTHIS, 94, 95
Pl.esiomys, 10, 31, 33, 35, 94, 95, 96
brevis, see Multicostella
elongata, see Multicostella
plana (Productorthis), 83
planareas, 165
Planidorsa, 24, 94, 100
planissimus (Productorthis), 83
planoconvexa Butts (Taffia), 85
planoconvexa Hall (Platyorthis), 36, 135
planus (Clitambonites), 113
planus (Gonambonites), 118
planus (Porambonites), 102
retroflexus (Billingsella), 49
Platymerella, 163, 166, 178, 184
Platyorthis, 36, 133, 135
platys (Multicostella), 98
Platystrophia, 19, 31, 36, 55, 64
fernvalensis, see Mcewanella lineolata
Platystrophiinx, 56, 58, 64
playfairi (Orthis), 76
Plectambonites, 38
Plectambonitins, 112
Plectella, 38, 107, 112
Plectellinx, 107, 112
Plectorthids, 34, 36, 38, 39, 44, 48, 56
Plectorthinx, 57, 58
Plectorthts, 26, 36, 38, 54, 57, 58, 68
crassiplicata, see Cyclocoelia
sectistriata, see Cyclocoelia
sordida multiplicata, see Cyclocoelia
whitfieldi, see Austinella
Plica, 10
plicata Bancroft (Horderleyella), 127
INDEX
267
plicata Schuchcrt and Cooper (Rhvnchocamara), 189
plicata Sowcrbv (Hesperorthis), 86
plicatclla Hall^Plcctorthis), 57, 58
trcntonensis (Plcctorthis), 58
plicatclla Walcott (BillingscUa), 49
plummcri (Entelctes), 146
polita ("Camcrella"), 168
poloi (Yangtzeella), 157, 158*
polonicum (Mystrophora), 131
polygramma (Rhipidomclla), 134
pentlandica (Rhipidomclla), 134, 152
PoLYTtECHIA, 21, 107, 110
montanensis, sec ClarkcUa
POMATOTREMA, 24, 38, 107, 109
ponderosa (Platystrophia), 66
arnheimensis (Platystrophia), 66
auburnensis (Platystrophia), 66
PoRAMBONiTES, 7, 11,' 28, 29, 39, 101, 102
costata, see Platystrophia
dentata, see Plat)strophia
recta, see Angusticardinia
striata, see Angusticardinia
Porambonitida:, 44, 101, 103
porcata (Plcesiomys), 95
porcias (Taffia), 47, 85
porrecta (Dalmanella), 120
poststriatula (Schizophoria), 143
priceps (Clitambonites), 113
prsculta (Heterorthina), 124
praK:ursor (Platystrophia), 65
angustata (Platystrophia), 65
latiformis (Platystrophia), 65
praerupta (Clitambonites), 113
precedens (Platystrophia), 65
preoblata (Rhipidomclla), 134
preponderosa (Platystrophia), 66
prima (Schizophoria), 143
primordialis (? Syntrophina), 156
proavita (Dinorthis), 94
Productorthinse, 74, 81
Productorthis, 17, 24, 31, 35, 38, 39, 74, 82
Productus abscissus, see Panderina
aculeatus, see Productorthis
brevis, sec Productorthis
costatus, sec Productorthis
eminens, sec Productorthis
cxtensus, see Panderina
intermedius, see Productorthis
latissimus, see Paurorthis
latus, see Productorthis
minimus, see Paurorthis
minutus, see Paurorthis
obtusus, sec Productorthis
ovatus, see Productorthis
parallelus, sec Productorthis
cf. plana, sec Productorthis
planissimus, see Productorthis
pterygoideus, see Nicolella
quinqueradiatus, sec Productorthis
tenuis, sec Productorthis
tetragona, see Panderina
profundosulcata (Platystrophia), 66
hopensis (Platystrophia), 66
promincns (Hcmlpronites), 116
Pronites, sec Clitambonites
adsccndcns, sec Clitambonites
altus, see Clitambonites
convexa, see Clitambonites
cxcclsa, sec Clitambonites
humilis, sec Clitambonites
latus, sec Clitambonites
propinqua (Isorthis), 150
Proschizophoria, 119, 123
Protegulum, 10
Protorthidas, 37, 44, 46
Protorthis, 28, 29, 44, 46
dougaldensis, see Loperia
provulvaria (Schizophoria), 143
proxima (Liocoelia), 189
Pseudocruralium, 10, 37, 39
pseudogaleata (? Gypidula), 166, 172, 174
rccurrens (Gypidula), 174
Pseudointerarca, 20
pseudolinguifera (Clorinda), 172*
Pseudoresupination, 10, 19
Pseudospondylium, 10, 27, 42
pterygoideus (Nicolella), 77
Ptychopleurella, 23, 74, 92
Punctx, 10, 41, 42, 170
punctata (Linoporella), 150, 151
punctostriata (Linoporella), 151
putilla (ArchaMrthis), 81
pygmaea (Isorthis), 150
pyramidalis Hall (Skenidioides), 72, 73
pyramidalis Opik (Vellamo), 114
arcuata (Vellamo), 114
pahleni (Vellamo), 114
simplex (Vellamo), 114
pyramidalis Twenhofel (Hesperorthis), 86
pyriformis (Stricklandia), 187
elongata (Stricklandia), 187
varicosa (Stricklandia), 187
pyron (Estlandia), 115
quacoensis (Protorthis), 47
quadrans (Levcnea), 123
quadriplicata (Dinorthis), 94, 96
Qucnstedt, F. A., 103
quinqucradiata (Productorthis), 83
radians (Hemipronites), 116
Rafincsquina (?) atava, see Orusia
Raymond, P. E., 80, 96, 121
raymondi (Mcewanella), 69
recta Conrad (Valcourea), 97
recta Pander (Angusticardinia), 69, 84
redux (Pionodema), 141, 142
Reed, F. R. C, 152, 170
regularis (Platystrophia), 65
remnicha (Eoorthis), 51, 52
sulcata, see sulcata
texana, sec texana
winfieldensis, see winfieldensis
Resserella, 125, 126
resseri (BillingscUa), 49
resupinata (Dalmanella), 120
268
INDEX
resupinata (Schizophoria), 143, 144
lata (Schizophoria), 143
rotundata (Schizophoria), 143
Resupination, 10, 19
resupinoides (Schizophoria), 143
reticulatus (Porambonites), 102
retrorsa (Retrorsirostra), 95
Retrorsirostra, 2 1 , 94, 95
retrostriata (Heterorthis), 137
Reuschella, 39, 137, 139
reuschi (Dalmanella), 120
reversa Billings (Parastrophinella), 169
reversa McCoy (Rhipidomella), 134
Rhipidium, 165, 166, 178, 180
Rhipidomella, 25, 30, 31, 32, 35, 36, 39, 133
circulus, see Mendacella
rhynchonelliformis, see Mendacella
tenuilineata Foerste, see Mendacella
tenuilineata Hall, see Thiemella
Rhipidomellidas, 133
Rhynchocamara, 189
Rhynchonella frenum, see Lycophoria
globosa, see Lycophoria
sordida, see Cyclocoelia
? Rhynchonellacea, 189
rhynchonelliformis McEwan (Platystrophia), 65
rhynchonelliformis Shaler (Mendacella), 127
Rhynchotrema, 84
ribeiro (Porambonites), 102
rigida (Schizoramma), 88
rockhousensis (Isorthis), 150
rockymontana (Plisiomys), 94
roemeri Hall and Clarke 1893 (Gypidula), 174
roemeri Hall and Clarke 1893 (Sieberella) (in part), 175
rogata (Dalmanella), 120, 121
rogersensis Foerste 1909 (Eridorthis), 91
rogersensis Foerste 1910 (Vellamo), 114
romingeri Barrande (Bohemiella), 52, 53
romingeri Hall and Clarke (Gypidula), 174
rossicus (Enteletoides), 148
Rostration, 165
rotunda (Orthis), 40,* 76
rotundata Pander (Orthis), 76
rotundata Walcott (Syntrophina), 156
rotundiformis (Camerella), 168
rotundus Kirk (Harpidium), 180
rotundus Pander (Clitambonites), 113
rotundus Pander (Hemipronites), 116
rudis (Nicolella), 77
ruedemanni (Vellamo), 114
rugiplicata (Ptychopleurella), 92
rugosicostatus (Oligomys), 53
rustica (Dolerorthis), 89
osiliensis (Dolerorthis), 89
sadewitzensis (Orthis), 76
saflFordi Foerste (Rhipidomella), 134
safFordi Hall and Clarke (Multicostella), 98
saffordi Walcott (Syntrophioides), 155
Sahni, M. R., 14
salme (Nicolella), 77
salteri (Stricklandia), 187
samojedicus (Pentamerus), 178
sandbergi (Otusia), 52
Sardeson, F. W., 32, 41, 121, 165
Savage, T. E., 183
Schellwien, E., 148, 149
Schizophorella, 17, 58, 62
arisaigensis, see Mendacella
Schizophoria, 6, 17, 26, 30, 31, 35, 37, 38, 40, 40,* 41,
88, 141, 143, 146,
mesoloba, see Aulacophoria
Schizophoriidje, 22, 34, 38, 139
Schizophoriinse, 140
Schizoramma, 26, 32,* 35, 74, 87
schmidti LebedefF (Pentamerus), 178
schmidti Noetling (Porambonites), 102, 103
schmidti Pahlen (Clitambonites), 113
schmidti Wysogorsky (Orthis), 76
schuchertensis (Orthotichia), 144
scofieldi (Camerella), 168
scoparium (Conchidium), 181
scotica (? Plectorthis), 58, 59
scovillei (Austinella), 99, 100
sectistriata (Cyclocoelia), 64
sedaliensis (Schizophoria), 143
sedgwicki (Fascicostella), 130
semele (Rhipidomella), 134
semicircularis Eichwald (Cyrtonotella), 77
semicircularis Pander (Orthis), 76
semiconvexum (Pomatotrema), 110
semiglobata (Reuschella), 139
semiovalis (Dinorthis), 94
senecta (Schizophoria), 143, 144, 150
senex (Platystrophia), 65
Septa, 10, 29, 39, 164, 166
Serial sectioning, 162
Shaft, 10, 35
shallochiensis (Vellamo), 114
shelbyensis (Wimanella), 50
Sieberella, 163, 165, 171, 174, 175
sieberi (Sieberella), 175
rectifrons (Sieberella), 175
simon (? Huenella), 160
simplex Foerste (Gypidula), 174
simplex Walcott (Wimanella), 49, 50, 51
sinuata (Hebertella), 59, 60
sinuatis (Plectorthis), 58
sinuatus (Porambonites), 102
Skenidiidse, 39, 44, 56, 71
Skenidioides, 17, 38, 71, 73, 112
Skenidium, 71, 73, 112
anthonense, see Skenidioides
craigensis, see Skenidioides
fallax, see Mystrophora
grayiae, see Vellamo
greenoughi, see Skenidioides
merope, see Skenidioides
nodocostata, see Ptychopleurella
polonicum, see Mystrophora
pyramidalis, see Skenidioides
shallochiensis, see Vellamo
Solaris, see Pionorthis
solitaria, see Levenea
Smeathenella, 39, 137, 139
INDEX
269
Socket plates, 37
Sockets, 10, 25, 34, 35*
sob (Pionorthis), 95
Solaris (Plxsiomys), 95
solitaria (r Lcvenea), 123
solus (Zdimir), 177
sordida (Cyclococlia), 64
multiplicata (Cyclococlia), 6+
SowerbvcUin.'c, 112
spcncci (? Nisusia), 45
spherica (Hemipronites), I 16 •
Spirifer, 22, 87
aperturata, see Platystrophia
chama, see Platystrophia
liratus, see Stricklandia
tridens, see Platystrophia
tscheffkini, see Noetlingia
Spirifera biforata fissicostata, see Platystrophia
Spondylium, 10, 26, 162, 164
Spondyloid, 1 1
springfieldensis (Parmorthis), 129
squamata (V'ellamo), 114
stracheyi (Austinella), 99
Stris, 1 1
striata Pander (Angusticardinia), 84
striata Pander (Nicolella), 77
striata Twenhofel (Stricklandia), 187
striata Walcott (Billingsella), 49
striato-costatus (PL-Esiomys), 95
striatula (Schizophoria), 143, 144
marjlandica (Schizophoria), 143
Stricklandia, 161, 187
balclatchiensis, see Metacamerella
Stricklandidx, 161, 186
strigosa (Platystrophia), 65
Stropheodonta, 22
Strophomena, 19, 97, 165
aurora, see Eostrophomena
ventrocarinata, see Valcourea
Strophomenacea, 21, 22, 48
strophomenoidcs Hall (Orthostrophia), 33,* 70
strophomenoides Raymond (Valcourea), 97
subaequata (Pionodema), 141, 142
gibbosa (Dolcroides), 63
perveta (Doleroides), 63
subsequivalvis (Enteletes), 146
subcarinata Dunbar (Levenea), 123
subcarinata Hall (Levenea), 36, 123
subcordiformis (Rhipidomella), 134
subdivisus (PK-esiomys), 95
subelliptica (Schizophoria), 143
subfissicosta (Schizoramma), 88
subglobosa (Gypidula), 174
subjugata (Hebertella), 60
sublsevis (Enteletina), 148
sublamellosa (Ptychopleurella), 92
sublaticosta (Plat)-strophia), 65
sublimis (Platystrophia), 66
sublinguifer ("Penfamerella"), 176
suborbicularis (Rhipidomella), 134
subplicata Bancroft (Harknessella), 138
subplicata Reed (Orthis), 76
subquadrata Bancroft (Harknessella), 138
subquadratus Hall (Plxsiomys), 32, 32,* 94, 95, 96
subrcctus (Pcntamcroides), 178, 179
subrossicus (Enteletoidcs), 149
Suess, E., 103
sucssi (Parentclctes), 147, 148
acuticosta (Parentclctes), 147, 148
sulcata (Eoorthis), 51
Sulcus, 1 1
swallow! (Schizophoria), 143
Swantonia, 44, 159
sweeneyi (Dinorthis), 23, 94
symmetrica (Polytoechia), 110
Syntrophia, 40, 154, 158
campbelli, see Syntrophina
isis, see Syntrophina
nona, see Clarkella
nundina, see Syntrophina
palmata, see Syntrophina
perilla, see Syntrophina
rotundata, see Syntrophina
Syntrophiacea, 43, 48, 154
Syntrophiids, 154, 158, 161, 167
Syntrophina, 154, 155
Syntrophinella, 156
Syntrophioides, 40, 154, 155
szajnochai (Isorthis), 149
tacens (Glossorthis), 78
Taffia, 85
Taffiinx, 74, 85
Teeth, 1 1 , 24
Teichert, C, 104
tenuicosta (Rhipidium), 181
tenuicostata Eichwald (Platystrophia), 66
tenuicostata Weller (Rhipidomella), 134
tenuilineata Foerste (Mendacella), 127
tenuilineata Hall (Thiemella), 136
tenuilineata Savage (Rhipidomella), 134
tenuis (Productorthis), 83
tenuistriatum (Conchidium), 181
tenuistriatus (? Hemipronites), 116
Terebratula lynx, see Platystrophia
tenuicostata, see Platystrophia
Terebratulitcs xquirostris, see Porambonites
biforatus, see Platystrophia
teretior (Porambonites), 102, 103
tersa (? Dalmanella), 120, 121, 133, 135
tesluJinaria Hall and Clarke, see Orthis rogata
testudinaria Dalman (Wattsella), 120, 121, 125, 126
tetragonum Pander (Clitambonites), 113
tetragonum Pander (Orthis), 76
tetragonum Pander (Panderina), 82
lata (Panderina), 82
tetragonum Roemcr (Isorthis), 150
texana Girty (? Orthotichia), 144
texana Walcott (Eoorthis), 51
texana Walcott (Huenella), 159, 160*
Ixviuscula (Huenella), 159
thakil (Dinorthis), 94
convexa (Dinorthis), 94
trifida (Dinorthis), 94
Thiemei.i-a, 19, 133, 136
thiemi (Rhipidomella), 134
Thomas, I., 25, 26
Thomson, J. Allan, 14, 30, 32, 33
270
INDEX
thomsoni (Estlandia) ,115
tioga (Cariniferella), 122
transversa King (Rhipidomella), 134
transversa Pander (Orthis), 76, 84
latestriata (Orthis), 84
transversa Walcott (Nisusia), 45
transversus Pander (Clitambonites), 113
transversus Pander (Hemipronites), 116
transversus Willard (Plassiomys), 94, 96
trempealeauensis (Billingsella), 49
trentonensis McEwan (Platystrophia), 65, 68
champlainensis (Platystrophia), 65
perplana (Platystrophia), 65
trentonensis Raymond (Vellamo), 114
tricenaria (Hesperorthis), 23, 86, 87
tridens (Platystrophia), 66
trigeri (Isorthis), 150
trigona (Paurorthis), 79
trigonula (Pahlenella), 117
Trilobation, 165
trilobatum (Rhipidium), 181
Triplesia lateralis, see Syntrophia
poloi, see Yangtzeella
primordialis, see Syntrophina
triplesiana (Stricklandia), 187
triplicata (Huenellina), 160
triplicatella (Plectorthis), 58
Tropidoleptidx, 152
Tropidoleptus, 152
truncatus (Porambonites), 102
tscheffkini (Noetlingia), 105
tschernyscheffi (Enteletes), 146
tullbergi (Archa^orthis), 81
tulliensis (Schizophoria), 143, 150
tumidula (Clorinda), 172
tumidus (Hemipronites), 115
turgida (? Linoporclla), 151, 152
Twenhofel, W. H., 92, 95, 165
typa (Marionella), 96
typica (Syntrophinella), 156
uberis (Mendacella), 127
Ulrich, E. O., 27, 43, 68, 109
ulrichi (Plassiomys), 94, 96
ultima (Vellamo), 114
umbo (Orthis), 76
unicostata (Platystrophia), 66
crassiformis (Platystrophia), 66
unguiforme (Conchidium), 181
unguis Bancroft (Wattsella), 125
unguis Sowerby (Nicolella), 77
uniplicata Cooper (Pionodema), 141
uniplicata McEwan (Platystrophia), 65, 68
uticana (Platystrophia), 65
uniplicata Nettelroth (Gypidula), 174
uralica Gorsky (Aulacophoria), 145
uralicum Tschernyschew (? Skenidium), 73
utahensis Walcott 1905 (? Nisusia), 45
utahensis Walcott 1912 (Otusia), 52
Valcourea, 10, 19, 22, 23, 25,* 94, 97, 98
vanuxemi (Rhipidomella), 134
pulchella (Rhipidomella), 134
variabilis (Rhipidomella), 134
varians (Rhynchocamara), 189
varicus (Bilobites), 130
Vellamo, 17, 23, 38, 107, 114
ventricosa Hall (Barrandella), 173
Ventricosity, 162
ventricosus Kutorga (Porambonites), 102
ventrocarinata (Valcourea), 97
vermontana (? Huenella), 160
Verneuil, E. de, 1 1 3, 1 17, 1 18
verneuili Eichwald (Vellamo), 1 14
wesenbergensis (Vellamo), 114
verneuili Hall (Anastrophia), 169
verneuilianus (Bilobites), 130
vespertilio (HarknesseUa), 138
villenovia (ThiemeUa), 136
ViRGiANA, 165, 166, 171, 178, 185
Virginia (Cariniferella), 122
beta (Cariniferella), 122
visbyensis (Parmorthis), 36, 129
volborthi Billings (Camerella), 167, 168
volborthi Pahlen (Estlandia), 115
vulgaris (? MimeUa), 61, 62
vulvaria (Schizophoria), 143
Waagen, W., 147, 148
waageni (Enteletes), 146
Walcott, C. D., 22, 27, 41, 44, 45, 46, 47, 48, 49, 50, 51,
52, 53, 54, 80
waldronensis (Parmorthis), 129
wallowayi (Platystrophia), 66
Wattsella, 39, 125
Wattsellidse, 34, 124
wattsi (Wattsella), 121, 125
weedi (? Huenella), 160
weeksi (Swantonia), 159
wemplei (Finkelnburgia), 55
wesenbergensis (Porambonites), 102
whitfieldi (Austinella), 99
whittakeri (Dalmanella), 120
wichitaensis (Eoorthis), 51
wilkinsoni (Clorinda), 171, 172
Williams, H. S., 122, 132, 136
Wimanella, 50
wimani (Archiorthis), 81
Winchell, N. H., 99
Winchell and Schuchert, 23, 95, 96, 142
winfieldensis (Eoorthis), 51
wingi ("Protorthis"), 47
wolfcampensis (Enteletes), 146
wordensis (Enteletes), 146
Wysogorsky, J., 69, 78, 80
Yangtzeella, 30, 154, 157
Zdimir, 177