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. D. Walcott — Position of the OleneUvs Fauna. 33

The slender Hyolithellus is much like H. micans of the
Olenellus fauna, but, in the absence of the characteristic oper-
culum, it does not seem best to identify it as the same species.

As known at present six species only pass from the Olenel-
lus* zone to the superjacent strata, in the Rocky Mountain
province. They are : Kutorgina pannnla^ AcrotJide suhaid/ua,
Acrotreta gemma^ SceneUa connvla^ HyoUthes BiUvngsi and
Olenoidea quadricepa. Of these Acrotreta gemma extends up
to the Upper Cambrian zone, in Montana.

Newfawadland. — The fauna of the Olenellus zone contains
but one species that ranges up into the Paradoxides zone —
Hyolithes princes, AgrauloB strenuus is closely allied to
Agraulos sodalis of the Paradoxides fauna, and Platyceras
mnmwvum is very like P, minutiesim/i of the Upper Cam-
brian.

The review of the sections shows but little specific relation-
ship between the two faunas, as only nine 4>®ci^ 2U*e now
known to range from zone to zone. A review of the genera
shows a large percentage common to the two zones. Of the
68 genera of the Olenellus zone 47 pass up into the Middle
Cambrian.

The genera confined to the Lower Cambrian, in America,
are:

Coleoloides.



Leptomitus.

Protopbaretra.

Spirocyatbus.

Coscinocyathus.

Etbmopbyllum.

Modioloides.

Fordilla.

Helenia.



Hyolitbellus?

Protocaris.

Olenellus.

Batbynotus.

Avalonia.

Oryctocephalus.

Protypus.



Of the European genera, the following five ;



Mickwitzia.

Volborthella.

Platysonites.



Medusites ?
Freena.



are referred only to the Lower Cambrian.

II. Rdationa of the Genera and Species of the Lower and
Middle Camhrian. — The comparison between the two sub-
faunas will be made by considering the genera and species of
each class of the Lower Cambrian and comparing it with the
same class of the Middle Cambrian fauna.

AlgcB. — As far as known to me, there are no true Al^ in
the rocks of the Lower Cambrian. That such forms existed,
there can scarcely be any doubt, but after a study of all of the
reported species, I think that they can be referred to trails of

Am. Joutt. Sol— Thied Seeies, Vol. XXXVni, No. 223.— July, 1889.
3



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34 C. D, Walcott — Position of the OleneUus Fauna.

worms or inollusks with much more proprie^ than to the
AlffSB. Specimens of Cruziana, collected in S'ewfoundland,
lead me to think that it is a trail or burrow and not an Alga.

No traces of land vegetation have been discovered in the
rocks of the Cambrian Period.

SpongioB, — The sponges of the Lower Cambrian are limited
to two genera, of which one, Protospongia, is found in the
upper beds of the OleneUus zone of the Atlantic Province,
and also in the Middle Cambrian in Nevada, New Brunswick,
Newfoundland, Wales and Sweden. Leptomitus is confined to
the Lower Cambrian.

Hydrozoa. — It is to the researches of Dr. A. G. Nathorst
that we owe a knowledge of the occurrence of Medusae in the
Lower Cambrian rocks of Sweden. By a series of compari-
sons between the casts found in the rocks at Lugnas and the
casts made by the impressions of recent Medusse, more espe-
cially of Aurelia aurita and Cyrena ca^iUata^ he has shown
that it is extremely probable, if not certam, that the delicatelv
constructed Medusae lived during the Lower Cambrian epocn
and left traces of their existence in the clays and sands of the
seashore. Dr. Nathorst figures and describes* Medusites Lind-
stromi Linnrs., M.favoans Nathorst and M, radiata Linnrs.,
and states that he thinks the so-caUed species of Eophyton are
the casts of trails made by the Medusae in moving along the
sea bed.

There are, in the collections of the United States Geological
Survey, a group of forms from the middle part of the Cambrian
in Alabama, that appear to be generically related to Medusitea
Lindatromi, They will be described with the description of
the Middle and Upper Cambrian fauna. In ascendmg the
geological series, it is not until the lithographic slate of the
Upper Jura, at Solenhofen, etc., is reached, tnat traces of the
Medusae are again met with.

The GraptoTitidae are represented by two species that are pro-
visionally referred to the genera Phyllograptus and Olimaco-
graptus. These generic types are not met with again until the
base of the Ordovician is reached, where they are largely devel-
oped. Mr. Matthew has described two species of graptolites
from the Middle Cambrian of New Brunswick, which he refers
to Dendrograptus and Protograptus.

A ctinozoa,— It has been an open question for some years
whether the forms referred to the genus Archaeocyathus were
corals or sponges. Dr. G. J. Hinde has recently reviewed the
genera and species, and concluded that they form a special family
of the Zoantharia sclerodermata^ in some features allied to the

* Kongl. Svenska Yetenskaps-Akademiens Handlingar, Bandet 19, N. 1, 1881.
Om Aflryck af Medusor i Sveriges Eambriska Lager.



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C, D. Walcott — Position of the Olenellus Fauna, 35

group of perforated corals. A re-study of all the species and
a personal examination of Dr. Hinde's specimens leads me to
agree with him that they should be referred to the Actinozoa.

With the exception of the single doubtful species of Archse-
ocyathus, described by Mr. Matthew, from the Paradoxides
zone of St. John, N. K, A, f pavonoidea^ there are no repre-
sentatives of this family (ArchseocyathinsB) in the later Cam-
brian. The first true corals met with in the 'ascending series
occur near the base of the Ordovician.

Echinodermata. — The Echinodermata are represented by a
few scattered plates of a species of Cystid, which is referred
provisionally to the genus Eocystites. It is impossible to make
any comparison between it and the Cystids of the Middle
Cambrian.

Anndida^ etc, — The trails, burrows and tracks of animals,
that occur in the Lower Cambrian, are nearly all duplicated in
the Upper Cambrian. This is true of the genera rianolites,
Helminthoidichnites, Scolithus and Cruziana, of the American
rocks. As far as determined by traces left by their passage
the same type of animals existed throughout the Cambrian.

Brachiopoda. — The Brachiopoda, with 10^ genera and 29
species, afford a much broader opportunity for comparison, but
even here the specific connection is very slight between the
two zones. Of the genera, Linffulella is represented in the
Paradoxides zone by a group of forms that have received the
names Z. Linguloides and Z. Dawaoni^ in New Brunswick ;
LinguleUa sp., in Linnarsson's Brachiopoda of the Paradoxides
beds of Sweden (Plate III, fi^. 24-28), and Z. GranvUleiisis^
in the Olenellus zone of New York. The species of the genus
Acrotreta, of the Paradoxides zone of Sweden and New Bruns-
wick and the Middle Cambrian zone of the Rocky Mountain
Province, are so closely allied to the species from the Olenellus
zone in Nevada that we consider that one species, A. gemma,
ranges from the base of the Cambrian through to the Upper
Cambrian. Acrothele subaidua also ranges from the Lower
Cambrian to the Middle Cambrian, in the Rocky Mountains ;
and A, Matthewi, of the Paradoxides zone of New Brunswick,
is a closely allied if not indentical species.

The genus Iphidea has a vertical range from the Olenellus
zone in Labrador, to the Middle Cambrian in Sweden, where it
ifi found in the Panadoxides beds. A very closely allied species
also occurs in the lower portion of the Cambrian section, in the
Grand Canon of Arizona, an horizon that will probably be
referred to the Middle Cambrian.

The ^enus Kutor^na has one &pecies, K, Lahradorica, that
has a wide geographic range, and a closely allied representative
species, K. Stissingensis, occurs in the Middle Cambrian zone



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36 C. D. Walcott — Position of the Olenellus Fav/na,

of New York. K, pannvla ranges from the Olenellus zone to
tlie Middle Cambrian, in Nevada, and is found in the upper
portion of the Olenellus zone in New York.

Ltnnarsaonia sagiUalis var. Taconica is scarcely to be con
sidered a typical Olenellus zone species, as it occurs so high in
the Lower Cambrian section. Still, as it is associated with
Olenellus we may consider it as forming a part of the fauna,
and compare it directly with the same species as found in the
Paradoxides zone of New Brunswick and Sweden. Of the six
species of the genus Obolella none are known to occur in the
Middle Cambrian, and it is not until we reach the Upper Cam-
brian that we find representatives of the genus. Tne genus
Orthis, as represented by O. Salemensis and O. Righlanaensia
(the broad and narrow hinge types), is not known to occur in
the Middle Cambrian zone, although both forms of the genus
are represented in the Ordovician. Among the species re-
ferred to Orthisina, we find that O. orientcuis is very closely
related to O.pepina of the Upper Cambrian, also that Cfesti-
nata is of the type of O. exporecta of the Paradoxides zone of
Sweden and Orthts BiUin^si of the New Brunswick Middle
Cambrian. Camerella antiquata and C, minor have no repre-
sentatives in the Middle or Upper Cambrian.

As a whole, the Brachiopoda are strongly represented in the
Lower Cambrian and do not exhibit any special evidence of
embryonic character when compared with the fauna of the
Middle and Upper Cambrian.

LameUibranchiata, — The genus Fordilla and the form de-
scribed as Modioloidea prisca appear to be the representatives
of the Lamellibranchiata in the Olenellus zone. The presence
of these two shells is of unusual interest, as none of the same
class are met with in the geologic succession before the abrupt
appearance of the group of species in the Arenig (Lower Ordo-
vician) strata of South Wales.

Oaateropoda. — Among the Gasteropoda, the genus Scenella
is represented in the Upper Cambrian by simple patelloid
shelte. It has not been found in the Paradoxides fauna of the
Atlantic basin, but in the Middle Cambrian strata of the Mt
Stephen section in the Rocky Mountains a representative
species was found by Dr. Kominger. The forms referred to
tne genus Stenotheca are very closely allied if not identical in
the Lower and Middle Cambrian zones. '8. ruaosa^ of the
Lower Cambrian, and S, Acadica of the Paradoxides zone are
examples of this intimate specific relationship. The little Pla-
tyceras of the Lower Cambrian has a representative in the form
described by Dr. C. Eominger from tne Mt Stephen Middle
Cambrian of British Columbia. A single species m the Upper
Cambrian connects this genus with the Ordovician fauna. Pleu-



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C. D. WalcoU — Position of the OleneUus Fauna. 37

Totomaria Attleborensis does not appear to have a representa-
tive before reaching the species of tne Lower Ordovician fauna,
and StraparoUina remota has no connection through the known
Middle Cambrian fauna with the fauna of the Ordovician.

Pteropoda. — The four genera and fifteen species of this
-dose are very strongly related to those of the Middle Cam-
brian fauna. HyoUthes princeps is a large form that is very
abundant in the Olenellus zone, and it has a great geographical
range. It is found in Western Nevada, Eastern Massachusetts
and Eastern Newfoundland. A closely allied if not identical
species occurs in the Paradoxides zone in Newfoundland. H,
TfiaxirmjLB of the Paradoxides zone of Bohemia is of this same
specific type, although differing considerably in detail of form.
H. Americanus is very closely allied in form to JI, Aoadioa
of the Paradoxides zone in New Brunswick, and the same
type is abundant in the Upper Cambrian of the Mississippi
V alley, under the name of Ji. primordiulis. H. BiUingsi is
known to range from the Lower to the Middle Cambrian, and
has been found in Labrador, New York and Nevada. H. com-
munis, II. impar, II. quadricostatus and H. Terranovicus are
species which do not appear to have representatives in the
Middle Cambrian fauna. II, siinUis is very much like H.
primtcs of the Paradoxides zone of Bohemia. The genera
Hyolithellus and Coleoloides do not appear to be represented
by well authenticated species in the Middle Cambrian. Sal-
terella is not met with again until the Ordovician fauna is
reached and there very doubtfully.

Orustaeea. — Of the true Crustaceans, Leperditia dermor
toides has a close specific relationship with an undescribed
spnecies from the Middle Cambrian of the Grand Canon section
of Arizona; and a representative species, Z. StissingensiSy
occurs in the New York Middle Cambrian.

The genus Aristozoa, although abundantly represented in
the Silurian fauna of Europe, is not known from the Middle
Cambrian fauna. Protoca/ns Ma/rshi still remains the oldest
known Phyllopod crustacean. The Upper Cambrian Phyllo-
pod, Symenoca/ria venmcan/day is the next met with, unless
some 01 the forms referred to Stenotheca, in the Paradoxides
zone, are portions of the carapace of some species whose gen-
eric relations are undetermined.

TrUobita. — The sixteen genera and fifty-three species of tri-
lobites constitute less than one-third of the entire fauna. The
range of variation among the genera and species includes forms
with and without eyes, and with and without facial sutures.
One of the surprising facts is that the genus Agnostus, which
has been theoretically considered the ancestral form of the
trilobite, does not appear to exist in the lower portion of the



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38 C. D. Walcott — Position of the OleneUus Fwwna.

Olenellus faana, but, as shown by Brogger, in Sweden it is
more typical of the Middle Cambrian than of the Olenellus zone.
The undoubted species of the genus, known from the Olenellus
zone, are found in the upper portion, in association with types
of the Middle Cambrian fauna. The reference of Agnoatus
nohUis Ford, from the lower part, to Agnostus is very doubt-
ful, as the form is probably a Microdiscus. The type which,
b^ a priori reasoning, should succeed Agnostus is Microdiscus^
with its three and four segments and eyeless cephalic shield*
As known, however, it occurs at the base of the Olenellus
zone, and its specific variations indicate prolonged existence in
a period of which the record has not yet been discovered.
Reaching its known maximum development, in species and
size, in the Olenellus zone, the genus diminishes in the Para-
doxides zone in about the same ratio that Agnostus increases
in importance. In the Upf)er Cambrian Microdiscus is repre-
sented only by Pemphigdspia bullata Hall. Agnostus continues
on into the Middle Ordovician. Microdiscus connexuSj of the
upper portion of the Olenellus zone, in New York, is the Para-
doxides zone tvpe of the genus, M.minctatus^ while M. scvlptuSy
of the lower raradoxides zone of South Wales, is the Olenellus
zone type, M. speciosus.

The genus Olenellus has been found wherever the Lower
Cambrian fauna is known. It presents great variation in specific
characters, and I have included several of the species m the
sub-genus Mesonacis. The marked difference between this
genus and Paradoxides is the absence of true facial sutures and
m the general configuration of the central portion of the head,
more notably in the form of the eye. Among the species of
Paradoxides the eyes of P. ruguLosus Corda and the group of
species from the St. John terrane, of New Brunswick, approach
most nearly to those of Olenellus. In the type O, Thompsoni^
the distinction between it and Paradoxides is very striking.
The absence of facial sutures and the long spine-like telson
finds no counterpart in the latter.

0, {Mesonivcii) Yerraontana has the typical Paradoxides form
of pygidium, also a peculiar posterior series of thoracic segments
that are related to those of Paradoxides. This species appears
as a link between the type O. Thompsoni and the remaining
species referred to the genus, all of which have a pygidium
like that of Paradoxides, and none of the pleurse of tfie tho-
racic segments are prolonged, as in the type of the genus and
in the young of some species of Paradoxides.

I would nere call attention to the fact that while no true
facial sutures may exist in Olenellus there is, on the underside
of the test of the head, a line like depression that corresponds
in position to the suture in Paradoxides. It may be well to



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C. D. Walcott — Position of the OleneUus Fauna. 39

note that Olenellas resembles the living Limulus in having
well developed eyes, without the presence of facial sutures.
The external resemblance to Limulus is further enhanced by
the telson-like pygidium of O. TJiompsoni, The structure of
the cephalic appendages of the trilobite also relate it to Limu-
lus.*

If we consider the head of Limulus to belong to a more
highly organized form than the head of Paradoxides, the fact
that the head of OleneUus is without facial sutures does not
make it rank below Paradoxides. In fact, OleneUus Broggeri^
of Newfoundland, impresses me as being as highly organized
as any of the species of Paradoxides, if not more highly.
Olermlus Thommoni and O. GiWerti might be considered the

Srogenitors of Paradoxides, inasmuch as they have a strong
evelopment of the pleura of one of the thoracic segments, a
feature that is present in the young of P. BoJiemicm^ but does
not continue in the adult.

American paleontologists have considered the genus Olenel-
lus as the descendant of Paradoxides, but the fact of occurrence
proves such a theory to be incorrect. The argument advanced
by Mr. Ford,t that the young of OleneUus asaphoides passed
through the Paradoxides stage, in its embryonic development,
may be explained in another way, by assuming that the species
of OleneUus, having the pleurae of the third segment prolonged
(macropleural), originated earUer than those with the pleurae of
uniform length (brachypleural), and hence the prolonged
pleurae are shown only in the embryonic phases of growth in
the brachypleural species. As pointed out by Mr. Ford, the
genus Paradoxides, like OleneUus, has brachypleural and ma-
cropleural species, but it is significant that it is in the young
of Paradoxides that the macropleural feature of O, Thomp-
8oni is developed, while in the adult it is reduced to a very
insignificant character. That an intimate if not a genetic rela-
tionship exists between OleneUus and Paradoxides there is
little doubt. OleneUus exhibits greater specific variation and
is more diversified by spines on the head and thorax, but in
the essential elements of structure it is very closelv related to
Paradoxides. With the exception of 0, {Mesona<yis) Vermon-
tcma there are no known connecting species between the typi-
cal forms of the two genera.

The genus Olenoides is largely developed in the Middle
Cambrian of the interior of the continent. One species only,
O. Marcouiy is found in the lower portion of the OleneUus
zone. Two other species, O. Fordi and O, quadriceps^ are in
the upper portion, near the passage between the Lower and

•Bull Mua. Comp Zool. Harvard College, vol. viii, No. 10, 1881, pp. 208-211.
t This Journal, III, vol. xxii, 1881, pp. 250-259.



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40 (7. D. Walcott — Position of the OleneUua Fauna.

Middle Cambrian. As far as the Specimens of O, Ma/rcoui of
the Lower Cambrian will permit of comparison, it and O.
Ifevadensia of the Upper Cambrian are closelj^ related.

The two species of Zacanthoides, Z. Eatom and Z. levis^ are
representative species of the genus, and serve to unite the
fauna with that of the Middle Cambrian, as Z, iA/picalis and
several species occur in the Middle Cambrian of the interior of
the continent. The genera Bathynotus, Avalonia, Orycto-
cephalns and Protypus are peculiar to the fauna and do not
appear to be represented in the Middle or Upper Cambrian..

Conocoryjphe triiineata is one of the best marked forms in
the New York Lower Cambrian, and is closely related to C.
dega/nB and (7. coronata^ of the Paradoxides zone, in having
the same general form and in the absence of eyes. The ffenus
Ptychoparia is represented by nine species, all of which are
more or less closely related to forms in the Middle and Upper
Cambrian.

AgroAiloB BtrenvAis is represented in the Upper Cambrian bjjr
A. bocIoUb. ElUpBOcephaluB NordenBkioldi^ of Sweden, is
represented by E. Hqjfi of the Paradoxides zone of Bohemia.
Cr&picej>haluB Augusta and C, IMiana are types that are more
or less abundant in the Upper Cambrian fauna of the interior
of the continent. They are not represented, to my knowledge,
in the Middle Cambrian fauna. The small head that I have
referred to Anomoca/re pa/rvum in2ij be compared to A, Bvlcor
i/hbm of the Paradoxides beds of Sweden. The ^enus Soleno-
pleura, with its five species, is also well developed m the Middle
Cambrian fauna. 8, Howley% from the base of the Olenellus
zone of Newfoundland, is very closely related to the type of
the ffenus, 8, holometopa^ of the Paradoxides zone of Sweden.

VompariBon of the Faunas as a whole. — The first thing
that strikes one in comparing the fauna of the Olenellus zone
with that of the Middle Cambrian is that the latter is not
wholly known, or in other words, there existed somewhere a
Middle Cambrian fauna which has not yet been found. We
are now obtaining evidence of a considerable fauna that lived
during Middle Cambrian time, on the west or Pacific coast of
what then existed as the North American continent, and of
which there is scarcely any representation in the Middle Cam-
brian or Paradoxides fauna of the Atlantic Province. This
will add to the fauna, but there is still a notable absence of
certain forms in the Middle Cambrian fauna which are present
in the Lower Cambrian. The first noticeable exception is the
absence of representatives of the peculiar group of corals that
occur in the Olenellus zone. With a single possible exception
the Archseocyathinee are not represented in the Middle Cam-
brian.



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(7. D. WalcoU — Position of the Olenellics Fauna. 41

Among the Brachiopoda the genus Obolella has a large
development in the Lower Cambrian and is present in the
Upper Cambrian, but is scarcely represented m the Middle
Cambrian ; and the Brachiopoda, as a whole, are more largely
developed in species and number of individuals than in the
Middle Cambrian. Lamellibranchs are represented in the •
Lower Cambrian, but not in the Middle Cambrian.

Among the Gasteropods, Pleurotomaria and Straparollina are
jet to be discovered in the Middle Cambrian. The same is
true of the Phyllopod crustacean Protocaina Ma/rshi,

Viewing the Olenellus fauna as a whole and comparing
it with the known Middle Cambrian fauna of the Atlantic
Basin, or the Paradoxides fauna, the impression made is that
the former is more highly differentiated, and, zoologically con-
sidered, the successor of the Paradoxides fauna. If, m our
comparison, we include the Middle Cambrian fauna of the inte-
rior of the continent, this conclusion will be changed, owing
to the presence of a group of trilobites, from the Middle Cam-
brian of Nevada, Utah and British Columbia, that includes
the genera Olenoides, Asaphiscus, Bathyuriscus, Karlia and
Ogygojwis. These genera suggest the trilobites of the second
or Ordovician fauna, and serve to connect the Middle Cambrian
fauna so closely with the second fauna that the idea of its
preceding the Olenellus fauna cannot be entertained.

It was owing to the comparison made between the two
faunas in the Atlantic Basin that led me to so long retain the
view that the Olenellus fauna succeeded the Paradoxides fauna
in time, and to think that the Paradoxides fauna would be
found, if at all, beneath the Olenellus zone, in the interior of
the continent. Now that we know that the Olenellus fauna
occurs beneath the Paradoxides zone in America, and that
there is a representative Middle Cambrian fauna, in the valley
of the Hudson, that serves in a measure to connect the Para-
doxides fauna of the Atlantic Basin and the Middle Cambrian
fauna of the interior of the continent, there is no hesitation in
referring the group of species, forming the fauna between the
Olenellus and the Upper Cambrian zone, in the Eocky
Mountain province, to tne Middle Cambrian, and in correlating
its stratigraphic position with that of the Paradoxides fauna oi
the Atlantic Province.

Com/pa/rison a/nd Correlation. — If a comparison is made be-
tween the fauna of the Olenellus Zone and that of the Ordo-
vician, the superiority of the latter in number of species,



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