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THE CHICAGO ACADEMY OF SCIENCES

The

Paleontology of the Niagaran Limestone
in the Chicago Area

THE TRILOBITA

BY

STUART WELLER

OF THE UNIVERSITY OF CHICAGO

BULLETIN No. IV.
PART II.

OF

s

THE NATURAL HISTORY SURVEY

ISSUED MAY 20, 1907

LETTER OF TRANSMITTAL

CHICAGO, ILL., October i, 1906.
DEAR SIR:

By direction of the Board of Managers of The Natural
History Survey of The Chicago Academy of Sciences, I herewith
submit to you for publication a report on The Trilobita, to be
issued, under the rules of the Academy governing such matters,
.as Part II of Bulletin No. IV, on The Paleontology of the Nia-
:garan Limestone in the Chicago Area, prepared by^Stuart Weller
of the University of Chicago.

Respectfully,

WILLIAM K. HIGLEY,

Chairman
To THOMAS C. CHAMBERLIN,

President of The Chicago Academy of Sciences.

The Board of Managers of The Natural History^Survey of
The Chicago Academy of Sciences: .

WILLIAM K. HIGLEY, Chairman.
CHARLES S. RADDIN, Secretary.
THOMAS C. CHAMBERLIN.
GAYTON A. DOUGLASS ,,
STUART WELLER.

THE NATURAL HISTORY SURVEY

The report on the paleontology of the area covered by the
Natural History Survey will be issued in parts, prepared by
Dr. Stuart Weller, of the University of Chicago, and will con-
stitute Bulletin No. IV.

The present report constitutes the second part of this bul-
letin and includes descriptions and figures of the Trilobita of the
Niagaran limestone of Chicago and vicinity. Nineteen new
-species and one new genus are described and figured.. It is
noteworthy that about forty per cent, of the species of North
American Silurian trilobites have been recognized in the
'Chicago area. The description of these, together with the
•excellent illustrations prepared by Dr. Weller, will furnish a
valuable manual on the subject for the use of students in local
investigations.

The territory covered by the Survey includes Cook and Du
Page counties and the nine north townships of Will County, in
Illinois, with a portion of Lake County, Indiana. This gives
.an area of about forty -eight or fifty miles square, or a land sur-
face of nearly 1,800 square miles.

The Board of Managers desires to acknowledge its obligations
to the University of Chicago, the Field Museum of Natural
History, the Northwestern University, as well as to the indi-
viduals whose courtesy to Dr. Weller greatly facilitated the work
•of preparing this report. Especial mention should be made of
the generosity of our patrons, whose continued interest in the
work of the Academy has made it possible to issue the present

CONTENTS

PAGE

Preface. ........ 163

Introduction 166

Classification of the Trilobita 176

Bibliography of North American Silurian Trilobita 181

A Bibliographic List of Species of North American Silurian

Trilobita 185

Glossary 211

Description of Genera<and Species 213

PREFACE

The present report upon the trilobites of the Niagaran
limestone of the Chicago area is issued as Part II of Bulletin IV
•of the Natural History Survey of the Chicago Academy of
Sciences, Part I of the same Bulletin being a description of the
crinoids, published in 1900. In the preparation of the different
parts of this Bulletin, no attempt is being made to follow the
zoological order of sequence of the different groups of fossils,
and the next class to be studied will probably.be the Brachi-
opoda.

In the preparation of the present paper, the collections
preserved in the Walker Museum of the University of Chicago
have furnished most of the material, although the Egan collection
in the museum of the Academy of Sciences has been freely
•drawn upon, as well as the collections of the Field Museum of
Natural History.

The writer is under especial obligation to Mr. L. H. Hyde,
formerly of Joliet, Illinois, but now of Pipestone, Minnesota,
-and to Messrs J. H. Handwerk and J. H. Ferris, of Joliet, for
many important specimens. These gentlemen have collected
extensively in the rock excavated from the Chicago drainage
-canal, and have secured much valuable material from near
Lemont. Without the material furnished by them the paper
would have been far from complete. The specimens used for
illustration from their collections have been generously parted
with and are now preserved in the collections of Walker Museum.
Besides these gentlemen, Mr. G. H. Harris, of Chicago, has
presented several important specimens to Walker Museum
which have been made use of in the preparation of this paper.
Another rich source of valuable material has been the Van Horne
collection, recently presented to the Walker Museum by Sir
William Van Horne. This collection contains many choice
specimens from the Niagaran limestone of northeastern Illinois
and southeastern Wisconsin, which have lent great assistance
in the study of the trilobites of this region.

Most of the species which are here described are known to
actually occur in the limestones of the Chicago area, but a few
have been seen only from Wisconsin. These species, Harpes
telleri, Dicranopeltis nasuta and D. telleri, were all collected by
Mr. E. E. Teller, of Milwaukee, and are now in his collection.

164 THE CHICAGO ACADEMY OF SCIENCES.

The writer is under very great obligation to Mr. Teller, not only
for the use of these specimens but also for the privilege, on
several occasions, of examining his collection, a privilege which
has rendered great assistance in the understanding of many of
the species from the localities in the Chicago area.

The species described in this report are from several dis-
tinct horizons in. the Niagaran limestone, and do not constitute
a part of one compact fauna. The lowest horizon represented is
a brown limestone from near Channahon, Will County, Illinois,
near the Des Plaines river. The material from Joliet is higher,
that from Lemont still higher, and that from • Hawthorn and
Bridgeport highest of all. The higher horizons are probably
nearly as young as the Guelph formation of Canada and New
York, while the lowermost may be as old as the Clinton in the
New York section. Accurate correlation of these beds can be
attempted, however, only when much additional detailed
stratigraphic work has been done throughout the area.

A number of the species which have been recognized are
closely related to European forms. Among these may be men-
tioned Deiphon americanus, Staurocephalus obsoletus, Cerato-
cephala goniata, etc., and the presence of such forms in the
interior of North America, adds strength to the hypothesis of
communication between this region and northern Europe by
way of the north polar region, which was set forth in the "Geo-
logic Introduction" to part I. of this Bulletin. \

Since the publication of the "Geologic Introduction," how-
ever, it has been established that there were two quite distinct
faunal provinces in North America during Silurian time. One
of these was the great Mississippian province in which the
Chicago area lies, and it was this province that was in communi-
cation with north Europe during middle and later Niagaran
time. During the time preceding this northern communication,
while the Clinton beds were being deposited, it seems probable
this Mississippian province was not so extensive and that its
connection was with the Altantic basin, perhaps in some south-
easterly direction.

During later Silurian time a quite distinct faunal province
occupied the northern Appalachian region. The sea in which
this Appalachian fauna flourished, occupied an. embayment from
the Atlantic which stretched northward from Maryland across
Pennsylvania and New Jersey into New York, which has been
called the Cumberland basin by Ulrich and Schuchert.* The

*Rep. N. Y. State Paleontologist, for 1901, p. 647 (1902).

THE NATURAL HISTORY SURVEY. 165

Cumberland basin was probably initiated in early Silurian time,
and continued to extend its boundaries while the waters were
being withdrawn from the Mississippian basin, perhaps to the
north, so that in age it is at its culmination younger than the
Silurian Mississippian sea.

The age of the great mass of Silurian sediments of the
Cumberland basin is probably about equivalent to that of the
Salina beds of the interior, and is therefore younger than any of
the Silurian beds of the Chicago area. However, .these Cumber-
land basin faunas are the direct outgrowth from older Silurian
faunas, without doubt contemporaneous with the Niagaran of
the Chicago area and other portions of the interior, which flour-
ished along the eastern shores of the Atlantic basin, and at its
southern extremity in Maryland there are sediments which were
deposited contemporaneously with the Niagaran formations of
the interior.

In the appended bibliographic list of North American Silur-
ian trilobites (pp. 185 to 210 of this Bulletin), one hundred and
five species are recorded, and of this number forty-one, or nearly
40%, are recognized in the Chicago area, this being the largest
number'of Silurian trilobites. recognized from any area of similar
size in America.

With the exception of two or three figures, the accom-
panying illustrations have been made by Miss Mildred L. Marvin*

INTRODUCTION*

The branch or phylum of the animal kingdom known as
Arthropoda or joint-footed animals, includes those segmented
organisms furnished with a jointed, chitinous exoskeleton, each
segment or somite of which is typically provided with a pair of
jointed appendages which are also covered with the exoskeleton
in like manner with the body proper. The segments of the
arthropod body are more or less unequally developed and in
many cases groups of them are united. Usually a greater or
less number of the pairs of appendages which were primitively
for the function of locomotion, have been specialized for the
performance of other functions.

The major classification of the Arthropoda into two sub-
phyla is based upon the nature of the respiratory organs, the
BRANCHIATA being those which breathe by means of gills, or by
lungs or tracheae which are metamorphosed from gills, and the
TRACHEATA, those which breathe by tracheae or air tubes. Each
of these sub -phyla is divided into classes based upon the seg-
mentation of the body and the modification of the appendages.

Under the BRANCHIATA two classes are recognized, the
CRUSTACEA and the ACERATA. The crustaceans are, with few
exceptions, aquatic animals breathing with gills, although a few
carry on respiration through the general surface of the body;
they possess one or two pairs of appendages, the antennae, in
front of the mouth, which are mainly sensory in function; back
of the mouth there are several pairs of appendages which are
more or less completely modified for serving the mouth, and
back of these others whose function is for locomotion, either for
walking^ or for swimming. Each appendage typically consists
of a basal joint, the protopodite, which is continued distally in
two jointed branches, the exopodite and the endopodite, each of
which may be variously modified.

The. ACERATA are arthropods which are primitively branch-
iate, but in which the branchiae may function as gills or lungs,
or they may be metamorphosed into air tubes or tracheae which
penetrate the body. The body is divided into a cephalothorax
anteriorly and an abdomen posteriorly, the line between the

*In the preparation of the following pages of the "Introduction" and "Classifica-
tion of the Trilobita," the chapter upon this group of organisms in Eastman's translation
of Zittel's Text Book of Paleontology, by Prof. C. E. Beecher. has been largely drawn upon.
The matter has been somewhat rearranged and changed but in some cases nearly the same
words have been used. The indebtedness of the writer to this work is here acknowledged.

THE NATURAL HISTORY SURVEY. i6/

two regions passing between the sixth and seventh pairs of
appendages. The segments of the cephalothorax are usually
coalescent, those of the abdomen being either free or not. The
antennae are absent. Two sub-classes are recognized under
this class, the MEROSTOMATA being aquatic forms which are for
the most part extinct, but are represented by the living Limulus;
and the ARACHNIDA or spiders, scorpions and their allies, in
which the primitive branchias have been modified for aerial
respiration. Because of their terrestrial habits the arachnids
are rarely preserved as fossils.

The TRACHEATA are divided into two classes, the MYRIOPODA
or thousand -legged worms and centipedes, and the HEXAPODA
or insects. The body of the myriopods is worm-like, and con-
sists of a distinct head, followed posteriorly by numerous similar
segments, each of which bears one or two pairs of appendages.
The body of the mature insect, HEXAPODA, has the three regions,
head, thorax and abdomen, fully differentiated. The append-
ages of the head are specialized sensory organs, the antennae,
and the mouth parts; the thorax bears the organs of locomotion,
three pairs of legs and usually two pairs of wings.

In the process of growth all arthropods undergo a series of
moults. The exoskeleton with which all are furnished, is
capable of but limited expansion, so that if these creatures are
to increase in size it is necessary for them to shed this covering
periodically. With each successive moult the new exoskeleton
which is secreted is somewhat larger than the preceding one.
During the stages of immaturity the creatures assume after each
moult, new characters which successively approach more and
more nearly those of the mature individual, but after the adult
characteristics of body and appendages have been acquired, the
succeeding changes at the moulting periods are only an increase
in size until the maximum dimensions have been attained.
Among those aquatic arthropods, the crustaceans and some
Acerata, whose habitat is most favorably situated for preserva-
tion in a fossil condition, the abandoned exoskeleton is frequently
firm and hard and fully capable of being buried in the sand or
mud to become fossilized at some later period. On account of
their habit of moulting, each one of these creatures has an
opportunity to leave a fossil record of itself as many times as the
number of its moulting periods. This may account for the great
abundance of fossil trilobites in some formations. The large
number of fossil remains, in some cases, may not really mean that

168 THE CHICAGO ACADEMY OF SCIENCES.

the creatures were more numerous, when alive, than the associated
molluscs or other forms which had but one chance to leave a
record of their lives because they secreted but a single shell
during their lifetime.

The trilobites, with which the present Bulletin has to deal,
are a group of Arthropods which constitute the most primitive
one of the three sub-classes of the Crustacea. They have been
extinct since the close of Paleozoic time, and had their maximum
development in the earlier periods of that era. During Silurian
time when the trilobites here discussed were living, they had
already passed the period of their greatest expansion and were
just starting on their decline as an important element in the
marine faunas of the earth. The beginning of the history of
the trilobites is unknown, as they were already fully differentiated
in Cambrian time when we have the first really definite evidence
of life upon the earth. In all there have probably been over
two thousand species of trilobites described, belonging to nearly
two hundred genera.

The only portion of the trilobite commonly preserved in the
fossil condition is the hard exoskeletal covering of the dorsal
surface of the body. This test or carapace is rarely more than a
millimeter in thickness, and is usually much thinner; it consists
of thin laminae of carbonaceous matter and calcium phosphate,
and in its original condition was more or less chitinous in char-
acter. In some forms the test is pierced with pores of greater
or less size which give to the surface a punctate appearance. In
many forms the surface is perfectly smooth and in others it is
covered with rounded tubercles of variable size or with other
sorts of surface ornamentation. Some forms, as will be seen
by the specific descriptions later, are furnished with great hollow
spines. In general form the carapace is usually sub-oval,
rounded at both ends, and almost always longer than wide, and
it is usually convex transversely. It is divided longitudinally
by two dorsal or axial furrows into three regions or lobes, a
character which first gave to these organisms the name trilobites.
The central region is called the axis and in the living organism
contained the principal organs, the viscera, the heart and the
central ganglia of the nervous system. The two lateral regions
are called pleura or pleural lobes. The body is also divided
transversely into three regions, i) the cephalon or head; 2) the
thorax ; and 3,) the pygidium or abdomen. Along its margin the
carapace does not terminate as a simple lamellae, but is turned

THE NATURAL HISTORY SURVEY. 169

under to form a reflexed margin or doublure. This doublure
is separated from the dorsal test by a narrow space, and pro-
duces the hollow spines at the ends of the thoracic segments as
well as the genal spines when they are present, also the infolded
margin of the cephalon and the pygidium. Among some
species of trilobites two forms have been observed, one broader
and larger which has been considered to be the male, and a
smaller and narrower form believed to be the female. Still
another supposed sexual difference has been observed in at
least one species of Dalmanites^ where the female form has a
more ancestral type of glabella and rounded genal angles, the
male exhibiting more progressive characters in the glabella
and well developed genal spines.

The cephalon or head of the trilobite comprises the anterior
one of the three transverse regions of the carapace, and is sup-
posed to have originated through the coalescence of several
segments in some unknown ancestral form. It is crescentiform,
semicircular, semielliptical, or sub -triangular in form, ' and is
sometimes greatly produced in front. Its postero-lateral angles
are known as the genal angles and are often produced into spines
of greater or less length, the genal spines. The axial portion of
the head, bounded by the axial or dorsal furrows, is more or less
sharply differentiated from the general surface and is called the
glabella. The glabella is exceedingly variable in size and form;
in its primitive condition it is divided by transverse furrows
into five lobes which are supposed to represent the original five
segments which have been consolidated. In many genera the
primitive pentamerous lobation of the glabella has been nearly
or wholly obscured by the modification or elimination of the
transverse furrows. The five primitive lobes of the glabella
are designated, beginning with the anterior one, the frontal
lobe, -the first, second and third pairs of lateral lobes, and the
occipital segment or lobe. With the exception of the posterior
one, the four transverse furrows of the primitive glabella are
usually not continuous across the median portion of the glabella,
they are designated, beginning anteriorly, the first, second and
third lateral glabellar furrows, and the occipital furrow. The
occipital furrow is always retained whatever may be the modi-
fication of the lateral furrows.

The pleural regions of the head or cephalon are called cheeks.
In the great majority of trilobites each cheek is divided into

*G. van Ingen, School of Mines Quart., Vol. 23, p. 69 (1901).

170

THE CHICAGO ACADEMY OF SCIENCES.

FIGURE i.— The cephalon of a trilobite: r,
glabella; a/, axial or dorsal furrows; fxc, fixed
cheeks; fc. free cheeks; s, facial suture; ft,
frontal lobe of glabella; 1, 2, 3, first, second
and third lateral glabellar furrows; /*, /2, /', first,
second and third lateral glabellar lobes; of, occi-
pital furrow; ost occipital segment; p, palpebral
or ey e lobes; ,, visual surf ace of eye;m/ margin-
al furrow; mbt marginal border; gs, genal spines.

two portions by the*
facial sutures, and
among the different
orders, families and
genera, these sut-
ures are exceedingly
variable in position
and direction and are
of great taxonomic
value. The portion
of the cheeks lying
between the facial
sutures and the dorsal
or axial furrows are
known as the fixed

cheeks, and ,the out-

er portions as the free cheeks. The compound eyes, when
present, are always situated upon the free cheeks adjacent
to the facial sutures; the lobe-like extension of the fixed
cheek adjacent to the inner margin of the eye is known
as the palpebral lobe or eye lobe. The portions of the facial
sutures lying in front of the eyes are known as their anterior
limbs, while the portions back of the eyes are their posterior
limbs. The anterior limbs of the facial sutures may unite and
pass around the anterior end of the glabella, or they may remain
separate, in which case they terminate at the anterior margin
of the head ; their posterior limbs may terminate at the posterior
margin of the head, near the genal angles or upon the lateral
margins of the head. That portion of the cephalon lying be-
tween the facial sutures, comprising the glabella and the fixed
cheeks, is known as the cranidium. It frequently happens
that^the free cheeks have become separated before fossilization
takes place, in which case the specimen consists of the cranidium
alone. In many cases the marginal portion of the head, some-
times only laterally and again laterally and anteriorly, is dif-
ferentiated from the general surface as a marginal border;
this may be flattened, convex or concave, and may vary greatly
or may be entirely absent. The furrow or groove limiting
the marginal border internally is the marginal furrow-. Fre-
quently the cheeks are traversed near their posterior margins
by .furrows which originate at or near the lateral terminations
of the occipital furrow of the glabella, and continue in a di

THE NATURAL HISTORY SURVEY. 17!

rection more or less parallel with the posterior margin, towards
the lateral margins of the head, sometimes becoming coalescent
with the marginal furrows in front of the genal angles; these
furrows are known as the posterior cheek furrows.

Most trilobites possess compound eyes, but a few genera
are furnished with simple eyes or occelli, while in a few others
organs of sight seem to be absent altogether. The compound
eyes vary greatly in size, sometimes being very small, while
in a few forms they occupy nearly the entire area of the free
cheek. In some genera, especially the earlier and more primi-
tive forms, the eyes are situated at the distal extremities of
elevated ridges or eye lines which extend outward from near
the anterior extremity of the glabella. According to their
structure, two kinds of compound eyes are recognized. In
the great majority of genera the outer or visual surface of the
eyes is covered with a smooth or granular integument which
entirely obscures, externally, their compound nature. Such
eyes are termed holochroal. Only a few genera, in fact only the
members of a single family, possess the second or schizochroal
type of eyes. In these the visual surface is made up of small,
polygonal or rounded openings for the individual facets which
are separated by an interstitial test. In the schizochroal eyes
the facets are much larger than in the holochroal and can always
be seen with the naked eye when they are well-preserved;
in number they vary from fourteen to six hundred, while in
the eyes of the holochroal type of structure the number of
facets sometimes reaches fifteen thousand. The shape of the
eyes is usually more or less crescentiform, with the visual sur-
face on the convex side and -directed laterally. In those tri-
lobites in which the surface of the eyes describe a complete
half circle, the facets are directed in such a manner as to receive
the light from all directions, from the front, from the rear and
from the sides.

Upon the ventral side of the cephalon, the hypostome,
which is homologous with the upper lip or labrum of other
crustaceans, is a separate plate attached by an articulating
edge to the reflexed anterior border of the cephalic shield.
In different genera the hypostome is more or less variable in
shape, but it is frequently more or less deeply notched along
its posterior border. Its position upon the under side of the
animal is nearly horizontal. In some genera, especially among
those in which the anterior limbs of the facial sutures are con-

172

THE CHICAGO ACADEMY OF SCIENCES.

tinuous around the anterior extremity of the glabella, the area
in front of the hypostome is partly occupied by a separate
plate which is sometimes visible dorsally. The remaining
characters of the 'ventral side of the head, so far as they are
known, will be described later in connection with the discussion
of the ventral appendages.

The thorax of the trilobites consists of a series of short,
transversely elongate, articulating segments, which vary in
number among different genera from two to twenty -nine. Each
thoracic segment consists of the central or axial portion lying
between the dorsal or axial furrows, and the lateral or pleural
portions. The axial portion is usually more or less strongly
convex transversely ; the pleura are usually depressed below the
axis and have a proximal or inner more or less flattened portion,
and a distal or outer portion which is bent more or less abruptly
downward and backward, terminating in a backwardly pointing
angular extremity. The articulation between the thoracic
segments is in the axial region where each segment bears an an-
terior extension somewhat beneath the general surface and
separated by a furrow, which passes beneath the incurved pos-
terior margin of the segment in front. The pleura of the thoracic
segments of many trilobites are grooved diagonally, the grooves
originating near the anterior margin at the dorsal furrow and

from there passing obliquely
outward and backward, often
extending to the angular dis-
tal extremities. In some gen-
era, however, the pleura are
smooth throughout.

The posterior abdominal
region of the trilobite is com-
monly known as the pygidium.
Like the cephalon and thor-
ax, it has^a central axial re-
gion or lobe, with two lateral
or pleural lobes separated
from the axis by the axial
or dorsal furrows; it is usu-
ally more or less arched'trans-
FIGURE 2.— Thorax of a trilobite: versely, especially in the axial
a, axial region; p pleural regions; af, region, though in some forms
axial or dorsal furrows; s, segments;
pfft pleural grooves. the pleura are more or les

THE NATURAL HISTORY SURVEY.

i.73

'completely flattened. In some genera the true elevated portion
•of the axis is short, being produced posteriorly into a post-axial
region which is usually limited by the continuation of the dorsal
or axial furrows, but which is not elevated above the surface
of the pleural lobes. The pygidium consists of a single piece
which has originated through the coalescence of several originally
articulating segments. The original segmentation of the pygi-
dium is usually more or less distinctly preserved, though in
*some forms it has become completely ob-
•solete. It is somewhat difficult to detect
the line of union between the thorax and
pygidium in those forms with a strongly
'segmented pygidium, except in disarticu-
lated specimens ; but in those forms with
obsolete segmentation of the pygidium,
"this line stands out strongly. The seg-
ments of the pygidium, like those of the
thorax, may be either grooved longitudin-
ally, or may be plain. There is usually a
more or less definite relationship between
the size of the pygidium and the number
•of thoracic segments, those trilobites with
.a large number of thoracic segments hav-
ing a small pygidium, and conversely,

FIGURE 3. — Pygid-
ium of a trilobite: a,
axis; p, pleural lobes;
s, segments of axis and
pleura; pa, post-axial
region; af, axial or
dorsal furrows; ct cau-
dal spine; m, marginal
border.

forms with a smaller number of thoracic segments having a
relatively larger pygidium.

The lateral and posterior margins of the trilobite pygidium
are frequently entire, the outline forming a regular sub-elliptical,
•sub-circular or parabolic curve, or it may be sub-triangular in
outline ; in other forms the distal extremity of each pleural seg-
ment is produced into a spine-like process of greater or less
length, and frequently a caudal spine, sometimes of great length,
extends posteriorly in line with the axis from the posterior
margin. The length of the elevated portion of the axis of the
pygidium varies greatly, in some forms it being less than one-
fourth the pygidium while in others it reaches to the posterior
margin and may even be produced backward in the caudal
spine. The segmentation of the pleura may reach to the lateral
margins or it may stop short of the margin and leave a more or
less flattened marginal border. The caudal spine, when present,
may be a mere posterior extension of the marginal border or it
may be a posterior extension of the axis proper.

1/4 THE CHICAGO ACADEMY OF SCIENCES.

The jointed thoracic segments of the trilobite overlap and
admit of more or less motion upon one another, so that most
trilobites possess the power of enrollment to a greater or less-
degree. In some cases the body is capable of being completely
rolled up, the posterior margin of the pygidium coming into-
close apposition with the doublure of the head, thus entirely
concealing the ventral surface. Other forms possessed this-
power to but a limited degree and in some it seems to have been
lacking altogether.

The ventral surface of the trilobites is usually so firmly
imbedded in the matrix in which the fossils are preserved, that
it is inaccessible for study, and the paired, jointed appendages,,
even when present, cannot be exposed by ordinary methods be-
cause of their great delicacy. Until within the last decade,
nearly all of our exact knowledge of the ventral surface of the-
trilobites and their appendages was derived from the section-
ing of enrolled specimens.* From a study of such material
it was discovered that the creatures were covered externally
upon the ventral side, with a thin membrane attached to the-
reflexed margins of the cephalon, thoracic segments and pygidium.
This membrane was supported by transverse processes which
became calcareous with age and to which the appendages were-
attached. More recently the structure of the ventral surface-
of Triarthrus becki Green, from the Utica slate near Rome,
New York, has been made out in great detail, and these struct-
ures may be taken, in the main, as typical of the trilobites as-
a whole.

Each segment of the cephalon,' thorax and pygidium, ex-
cepting only the anal segment, carries a pair of jointed append-
ages, all of which, save the anterior pair, are biramous. The
anterior pair of appendages are the antennae, they are attached
at the sides of the hypostome and consist of simple, many
jointed flagella. Alljthe remaining paired appendages are-
similar in structure and exhibit but a small amount of differ-
entiation. Each appendage or limb consists of a basal joint
or protopodite from which spring two branches. The inner-
branch or endopodite normally consists of six joints. The
outer branch or exopodite has one long proximal joint with a.
distal multi-articulate portion; from this branch long s'etae
extend posteriorly and on the distal portion they are so crowded
as to make a continuous fringe.

*Walcott, Bull. Mus. Comp. Zool.. Vol. 8, No. 10 (1881).

THE NATURAL HISTORY SURVEY.

175

Besides the antennae, the cephalon bears four pairs of \hese
pediform, biramous appendages, the protopodites of which are
developed into large gnathobases which function as manducatory
organs. In the higher crustaceans these cephalic appendages
have been greatly differentiated as special organs for serving
the mouth, but in the trilobites they still function in part as
organs of locomotion, and except in the strong development
of the gnathobases they do not differ materially from the thor-

FIGURE a^—Triarthus becki, Green. A, dorsal, and B, ventral aspect
(x2). After Beecher.

acic appendages and those of the pygidium, which are wholly
locomotive in function. The endopodites are jointed, ambula-
tory or crawling legs; posteriorly, especially upon the pygidium,
the joints become flattened and more or less leaf-like, carrying
tufts of setae, and are more adapted for swimming. The pro-
fusely fringed exo^odites also function as swimming organs,
although they serve in common with the entire membranous
ventral surface, as organs of respiration.

CLASSIFICATION OF THE TRILOBITA

In elaborating a natural classification of any group of or-
ganisms, a classification which will show the genetic relation-
ships of the various forms, the best results have always been
attained through the application of the law of morphogenesis
which supposes that each individual, during its development
from embryo to adult, passes through a series of stages which
more or less closely resemble the stages through which the
ancestors of this individual have passed in preceding ages.
The principles of this law can best be applied in the classifica-
tion of a group of organisms not made up of degenerate forms,
and whose geologic history is more or less complete. The
trilobites have a known life history beginning with the Cam-
brian and extending to the close of the Paleozoic, their structure
is generalized and quite uniform throughout, no degenerate
.forms are known, and they satisfy most of the conditions nec-
essary for the satisfactory application of the law of morpho-
genesis in building up a natural genetic classification.

In common with all organisms known only in the fossil
form, the trilobites . furnish almost no information in regard to
the strictly embryonic stages of growth, although minute
spherical or ovoid bodies have been found associated with trilo-
bites and have been described as the eggs of these creatures,
The smallest and most primitive fossil organisms exhibiting the
characters of the trilobite, and which have been traced through
successive stages to the adult, are small discoid or ovate bodies
named the protaspis, and do not exceed i mm. in length. The
protaspis stage has been found to be the normal larval form
characteristic of all trilobites, and it is believed that it approxi-
mates the theoretical, primitive, ancestral larval form of the
Crustacea. The characteristics possessed by the protaspis,
as now known in all the principal groups of trilobites, are given
by Beecher as follows: "Dorsal shield minute, not more than
0.4 to i mm. in length; circular or ovate in form; axis distinct,
more or less strongly annulated, limited by longitudinal grooves;
head portion predominating; axis of cranidium with five an-
nulations; abdominal portion usually less than one-third the
length of the shield ; axis with from one to several annulations ;
pleural portion smooth or grooved; eyes, when present, ante-
rior marginal or submarginal; free cheeks, when visible, nar-
row and marginal."

THE NATURAL HISTORY SURVEY.

177

The principal changes which take place in the individual
during growth are: i. The gradual elongation of the body
by the successive introduction of free thoracic segments: 2.
The change in position of the eyes: 3. The modification of the
glabella. 4. The growth of the free cheeks. 5. The final
assumption of the mature specific characters of the pygidium,
and the ornamentation.

FfG 5.

Ptychopariakingi, Meek
Cambrian. A, Protaspis
enlarged. B, Adult re-
duced. (After Beecher).

FIG 6.

Sao Mrsuta, Barran 'e.
Cambrian. A, Protaspis

FIG'. 7.
Triarthrus becki. Green.
Ordovician. A, Protaspis

enlarged. B Adult re- enlarged. B, ' Adult re-
duced (After Beecher). duced. (After Beecjher) .

B

FIG 8. FIG. 9. PIG. 10.
Proetus fiarviusculus. Acidaspts tuberculata. Dalmanites socialis. Bar-
Hall. Odrovician. A, Pro- Conrad. lyOwer Devonian, nande. Ordovician. A,
taspis enlarged. B, Adult A. ProUspis enlarged. B. Protaspis enlarged. B.
reduced. (After Beecher). Adult red uce d . (After Adult reduced. (After
Beecher). Beecher).

The simplest expression of the protaspis stage is found in
the earliest genera known, those of the Cambrian; in later
genera the process of acceleration or earlier inheritance lias
pushed forward the initiation of certain characters in the growth
of the individual until they appear in the protaspis, thus mak-
ing it far more complex than in the more primitive forms of
the Cambrian. Many of the earlier and more primitive genera
of trilobites, even in their adult form, retain certain characters
suggestive of the protaspis. Any genus of trilobites with the
cephalon large and elongate as compared with the pygidium,
with the eyes rudimentary or absent, with the free cheeks
ventral or marginal, with the glabella elongate, cylindrical,
and with five annulations, would naturally be considered as
belonging to a primitive stock.

During the protaspis stage the individual passes through
several moults previous to the complete separation of the
pygidium or the introduction of thoracic segments, which
produce the stronger annulation of the axis, the appearance
of the free cheeks upon the dorsal side and the1 increased seg-

178

THE CHICAGO ACADEMY OF SCIENCES.

mentation of the pygidium. The most important structures
introduced during these changes in the protaspis itself, are the
free cheeks, although in some forms these do not appear until
after the close of the protaspis stage. Since the visual area of

the eyes, when present, is borne

A & upon the free cheeks, these or-

gans make their appearance
upon the dorsal surface simul-
taneously with the free cheeks,
and before they appear the free
cheeks must be wholly ventral
in position. When first dis-
cernible the free cheeks are very
narrow ; in some forms they in-
clude the genal angles, while in
others they do not, the genal
angles being borne by the fixed
cheeks.

The complete ventral posi-
tion of the free cheeks in the
earliest larval stages of all but the highest trilobites, indicates
this to be a very primitive character, consequently several
genera which possess ventral free cheeks as an adult character,

FIGURE ll. — Sao hirsuta Bar-
rande. Cambrian; Skrey, Bohemia.
A, potaspis. B-F, successive stages
in the development to the adult.
(After Barrande).

2 Sao

Sao

4 Sao

1 Sao

FIGURE 12.— Ontogeny of Sao hirsuta Barrande. (Opisthofiarta.} I,
Protaspis. 2, Cephalon of a very young individual. 3, Cephalon of an im-
mature individual having eight free segments. 4, Cephalon of adult. (From
BeecheV, after Barrande.)

5 Dalmanites

6 Dalmanites

Dalmanites

8 Dalmanites

FIGURE 13.— Ontogeney of Dalmanites seczalis Barrande. (Proparia.}
5, Protaspis. 6, Cephalon of individual with three free segments. 7, Cephalon
•of one with seven free segments. 8, Cephalon of adult. (From Beecher, aftej
Barrande.)

along with other primitive features, may be assumed to occupy
a, very low rank, and are grouped together to constitute the
most primitive order of trilobites, the Hypoparia.

THE NATURAL HISTORY SURVEY.

179

As has already been mentioned, the remaining genera of
trilobites present two distinct types of head structure dependent
upon the character of the free cheeks and the direction taken

HYPOPARIA

9 Agnostus 10 Microdiscus

12 Trinucleus

IS Ampyx

FIGURE 14.— Cephala of Hypoparia. 9, Agnostus; 10, Microdiscus;
u,Harpes; 12, Trinucleus; 13, Ampyx. (After Beecher.)

by the posterior limbs of the facial sutures. In both these
types the free cheeks constitute an essential portion of the
dorsal surface of the head and are continued to the ventral
side only as a doublure or infolding of the margin. One type
of structure is characterized by having the free cheeks include
the genal angles, the distal extremity of the posterior limb
of the facial suture cutting the posterior margin of the head.
The genera possessing this type of structure constitute the
second order, the Opisthoparia.

OPISTHOPARIA

19 Illsnus

20 Proetus

21 Bronteus

22 Lichas

23 Acidaspis

FIGURE 15.— 14, Atops; 15, Conocoryphe; 16, Ptychoparia; 17, Olenus;
18, Asaphus; 19, Illacnus; 20, Proetus; 21, Bronteus; 22, Lichas; 23, Aci-
daspis. (After Beecher.)

In those forms representing the third type of structure,
the genal angles are a part of the fixed cheeks, the posterior
limb of the facial sutures being directed laterally from the
posterior extremities of the eyes, their distal extremities cutting
the lateral margins of the head. The genera having this tpye
of structure are placed in the third order, Proparia.

Among the Silurian trilobites described in this Bulletin,
-all three orders are represented. The Hypoparia, however,

i8o

THE CHICAGO ACADEMY OF SCIENCES.

are represented by a single species, and this species has as yet
been detected only at Milwaukee, although it is quite possible
that it may yet be found within the Chicago area.

PROPARIA

33 Phacops

FIGURE 16. — Cephala of Proparia. 24, Placo-paria; 25, Encrinurus;
26, Calymene; 27, Diplcura; 28, Cheirurus; 29, 30, Dalmanites; 31, Chas-
; yi.Acaste; ^Phacops. (After Beecher.)

BIBLIOGRAPHY OF NORTH AMERICAN SILU-
RIAN TRILOBITA

Barrett (S. T.) The Coralline or Niagara limestone of the Appal-
achian system as- represented at Nearpass's Cliff, Montague, N. J. (Am.
Jour. Sci., 3rd ser., vol. 15, pp. 370-372, 1878).

Bigsby (J. J.) Description of a new species of Trilobite. (Jour.
Acad. Nat. Sci., Phil., 1st ser., vol. 4, pt. 2, p. 365, pi. 23, 1825.)

Billings (E.) Fossils of the Upper Silurian rocks, Niagara and
Clinton groups. (Can. Nat. & Geol., vol. 1, pp. 57-60, pi. 1, 1856.)

— ; Descriptions of fossils occurring in the Silurian rocks of
Canada. (Can. Nat. & Geol., vol. 1, pp. 312-320, 1856.)

— , Catalogue of the Silurian fossils of the island of Anticosti,
with descriptions of some new genera and species. (Geol. Surv. Can.,
pp. 1-93, 28 figures, 1866.)

Castelnau (F. de) Essai sur le Systeme Silurien de TAmerique
Septentrionale. (Pp. 1-56, pis. 1-27, Paris, 1843.)

Conrad (T. A.) Report of T. A. Conrad on the Palaeontological
Department of the Survey. (Rep. N. Y. State Geol. Surv. 1838, pp.
107-119.)

— , Observations on the Silurian and Devonian systems of the
United States, with descriptions of new organic remains. (Jour. Acad.
Nat. Sci., Phil., 1st ser., vol. 8, pt. 2, pp. 228-280, 1842.) '

Clarke (J. M.) Notes on the genus Acidaspis. (44th Rep. N. Y.
St. Mus. Nat. Hist., pp. 91-104, pis. 1-3, 1892.)

Clarke (J. M.) and Ruedemann (R.) Guelph fauna in the state
of New York. (Mem. N. Y. St. Mus., No. 5, pp. 1-195, pis. 1-21, 1903.)

Dawson (J: W.) Acadian Geology. The geological structure,
organic remains, and mineral resources of Nova Scotia, New Brunswick,
and Prince Edward Island. Second edition. (Pp. 1-694, London, 1868.)

Foerste (A. F.) The Clinton group of Ohio. (Bull. Sci. Lab. Den.
Univ., vol. 1, pp. 63-120, pis. 13-14, 1885.)

— , The Clinton group of Ohio. Part II. (Bull. Sci. Lab. Den.
Univ., vol. 2, pt. 1, pp. 89-110, pi. 8, 1887.) The plate accompanying
this paper is published with volume III and is marked plate VIII, although
it takes the place of plate XIV in that volume.

— , Notes on Illasni. (15th Ann. Rep. Geol. & Nat. Hist. Surv.
Minn., p. 478-481, 1887.)

— , Notes on Paleozoic fossils. (Bull. Sci. Lab. Den. Univ., vol.
3, pp. 117-137, pi. 13, 1888.)

— , Notes on Clinton group fossils, with special reference to col-
lections from Indiana, Tennessee and Georgia. (Proc. Bost. Soc. Nat.
Hist., vol. 24, pp. 263-355, pis. 5-9, 1890.)

— , A description of the Trilobites, Molluscs and Brachiopods of
the Clinton group of Ohio and Indiana. (Geol. Surv. Ohio, vol. 7, pp.
522-597, pis. 25-37A, 1895.)

Grabau (A. W.) Guide to the geology and paleontology of Niagara
Falls and vicinity. (Bull. N. Y. St. Mus., No. 45, vol. 9, pp. 1-284,
1901.)

1 82 THE CHICAGO ACADEMY OF SCIENCES.

Green (J.) Synopsis of the Trilobites of North America. (Month.
Am. Jour. Geol., vol. 1, pp. 558-560, pi. 14, 1832.)

, A monograph of the Trilobites of North America. (Pp. 1-98.

I plate, 1832.)

, Description of a new Trilobite. (Am. Jour. Sci. 1st ser., vol,

'32, pp. 167-169, 1837.)

Hall (J.) Geology of New York. Part IV. Comprising the
.-survey of the fourth geological district. (Pp. 1-683, .with tables of
organic remains, 1-74, and pis. 1-19, 1843.)

, Palaeontology of New York. Volume II. Containing

descriptions of the organic remains of the lower middle division of the
.New York system. (Pp. 1-362, pis. 1-83, 1852.)

, Descriptions of new species of fossils from the Silurian rocks

.of Nova Scotia. (Can. Nat. & Geol., vol. 5, pp. 144-159, 1860.)

, Descriptions of new species of fossils; from the investigations

•of the survey. (Rep. of Prog. Geol. Surv. Wis., for 1860, pp. 9-52, 1861.)

, Catalogue of Palaeozoic fossils, from the rocks of the state of

Wisconsin. (Geol. Surv. Wis., vol. 1, pp. 428-442, 1862.)

, Notes and corrections. (16th Rep. N. Y. St. Cab. Nat. Hist.,

pp. 223-226, 1863.)

, Notice of some new species of fossils from a locality of the

Niagara group, in Indiana; with a list of identified species from the same
place. (Trans. Albany Inst., vol. 4, pp. 195-228, 1864.)

, Account of some new or little known species of fossils from

.rocks of the age of the Niagara group. (Pp. 1-48, pi. 1. Originally
published in advance, for the 18th Report of the New York State Cabinet,
January, 1865. Republished with additions in 20th Rep. N. Y. St. Cab.)

, Account of some new or little known species of fossils from

rocks of the age of the Niagara group. (20th Rep. N. Y. St. Cab. Nat.
Hist., pp. 305-401, pis. 10-23, 1867.)

, Descriptions of new or little-known species of fossils from

rocks of the age of the Niagara group. (20th Rep. N. Y. St. Cab. Nat.
Hist. (rev. ed.), pp. 347-434, pis. 10-25, 1870.)

, The] faunal of the Niagara group in central Indiana.

(28th Rep. N. Y. St. Mus. Nat. Hist. (doc. ed.), p. 99, pis. 3-34, 1877.)

— , The fauna of the Niagara group in central Indiana. (28th

Rep. N, Y. St. Mus. Nat. Hist. (mus. ed.), pp. 99-203, pis. 3-34, 1879.)

, Descriptions of the species of fossils found in the Niagara

:group at Waldron, Indiana, (llth Rep. Dep. Geol. & Nat. Hist. Indiana,
pp. 217-345, pis. 1-36, 1882.)

, Descriptions of new species of fossils from the Niagara forma-
tion at Waldron, Indiana. (Trans. Albany Inst.. vol. 10, pp. 57-76, 1883.)

Hall (J) and Clarke (J. M.) Trilobites and other Crustacea, etc.
(Pal. N. Y., vol. 7, pp. 1-236, pis. 1-36, 1888.)

Hall (J.) and Whitfield (R. P.) Description of new species of fossils
irom the vicinity of Louisville, Kentucky, and the Falls of the Ohio.
(24th Rep. N, Y. St. Mus. Nat. Hist., pp. 181-200, 1872.)

, and , Descriptions of invertebrate fossils, mainly from

the Silurian system. (Geol. Surv. Ohio, vol. 2, pt. 2, Palaeontology,
pp. 65-179, pis. 1-12, 1875.)

THE NATURAL HISTORY SURVEY. 185

r "' Harlan (R.) Critical notices of various organic remains hitherto-
discovered in North America. (Trans, Geol. Soc. Penn., vol. 1, pt. lr
pp. 46-112, 1834.)

Kindle (E. M.) The stratigraphy and paleontology of the Niagara
of northern Indiana. (28th Ann. Rep. Dep. Geo4. and Nat. Res. Indiana,,
pp. 397-486, pis. 1-25, 1904.)

Meek (F. B.) Descriptions of invertebrate fossils of the Silurian-
and Devonian systems. (Geol. Surv. Ohio, vol. 1, pt. 2, Palaeontology,,
pp. 1-243, pis. 1-23, 1873.)

Meek (F. B.) and Worthen (A. H.) Contributions to the palaeon-
tology of Illinois and other western states. (Proc. Acad. Nat. Sci..
Phil., for 1865, pp. 245-273, 1865.)

- and , Palaeontology. (Geol. Surv. 111., vol. 3, pp. 289-

572, pis. 1-20, 1868.)

and , Descriptions of new species and genera of fossils-

from the Palaeozoic rocks of the western states. (Proc. Acad. Nat.
Sci. Phil., for 1870, pp. 22-56, 1870.)

Miller (S. A.) Description of two new species from the Niagara
group, and five from the Keokuk group. (Jour. Cinn. Soc. Nat. Hist.,,
vol. 2, pp. 254-259, pi. 15, 1880.)

Miller (S. A.) and Gurley (W. F. E.) Description of some new
species of invertebrates from the Palaeozoic rocks of Illinois and adjacent
states. (Bull. No. 3, 111. St. Mus. Nat. Hist., pp. 1-81, pis. 1-8, 1893.)

Roemer (F.) Die Silurische Fauna des westlichen Tennessee.
(Pp. 1-100, pis. 1-5, Breslau, 1860.)

Ulrich (E. O.) Description of a trilobite from the Niagara group-
of Indiana. (Jour. Cinn. Soc. Nat. Hist., vol. 2, pp. 131-134, figs. 1-3,.
1879.)

van Ingen (G.) The Siluric fauna near Batesville, Arkansas.
Part II. Paleontology: Trilobita. (School of Mines Quart., vol. 23,.
No. 1, pp. 34-74, figs. 9-22, 1901.)

Vanuxem (L.) Geology of New York. Part III. Comprising the
survey of the third geological district, (pp. 1-306, 1842.)

Vodges (A. W.) A monograph of the genera Zethus, Cybele, En-
crinurus and Cryptonymus. (Pp. 1—36, pis. 1—4, 1878.)

, Short notes upon the geology of 'Catoosa county, Georgia.

(Am. Jour. Sci., 3rd ser., vol. 18, pp. 475-477, 1879.)

, Description of a new crustacean from the Upper Silurian

of Georgia, with remarks upon Calymene clintoni. (Proc. Acad. Nat.
Sci. Phil., for 1880, pp. 176-178, 1880.)

— , Description of a new crustacean from the Upper Silurian of
Georgia. (Anthrop., Cont. 1 and 2; Palaeont. Cont. 1 and 2, pp. 1-10, 1
pi., 1881.)

, Description of a new crustacean from the Clinton of Georgia,

with remarks upon others. (Pp. 1-5, 1886.)

Warder (J. A.) Ceratocephala goniata. (Am. Jour. Sci., 1st ser.,.
vol., 34, pp. 377-379, 1838.)

Weller (S.) A report on th'e Paleozoic paleontology of New Jersey..
(Pal. N. J., vol. 3, pp. 1-462, pis. 1-53, 1903.)

184 THE CHICAGO ACADEMY OF SCIENCES.

White (C. A.) Fossils of the .Indiana rocks. (2nd Ann. Rep.
Dep. Stat. and Geol. Indiana, pp. 471-522, pis. 1-11, 1880.)

Whiteaves (J. F.) On some new, imperfectly characterized or
previously unrecorded species of fossils from the Guelph formation of
Ontario. (Geol. Surv. Can., Pal. Foss., vol. 3, pt. 1, pp. 1-43, 1884.)
— , Descriptions of four new species of fossils from the Silurian
rocks of the south eastern portion of the district of Saskatchewan. (Can.
Rec. Sci., vol. 5, pp. 293-303, pi. 3, 1891.)

, Revision of the fauna of the Guelph formation of Ontario,

with descriptions of a few new species. (Geol. Surv. Can., Pal. Foss.,
vol. 3, pt. 2, pp. 45-109, pis. 9-15, 1895.)

Whitfield (R. P.) Preliminary descriptions of new species of fossils
from the lower geological formations of Wisconsin. (Ann. Rep. Wis.
Geol. Surv., for 1877, pp. 50-89, 1878.)

, Descriptions of new species of fossils from the Paleozoic for-
mations of Wisconsin. (Ann. Rep. Wis. Geol. Surv., for 1879, pp. 44-71,
1880.)

, Paleontology. (Geol. Wis., vol. 4, pp. 161-363, pis. 1-27,

1882.)

Winchell (A.) and Marcy (O.) Enumeration of fossils collected in
the Niagara limestone at Chicago, Illinois; with descriptions of several
new species. (Mem. Bost. Soc. Nat. Hist., vol. 1, pp. 81-113, pis. 2-3.
1865.)

Worthen (A. H.) and Meek (F. B.) Descriptions of invertebrates,
<Geol. Surv. 111., vol., 6, pp. 489-532, pis. 23-33, 1875.)

A BIBLIOGRAPHIC LIST OF SPECIES OF NORTH
AMERICAN SILURIAN TRILOBITA

ACIDASPIS Murchison, 1839.
Acidaspis brevispinosa Foerste.

1895. Acidaspis brevispinosa. Foerste, Geol. Surv., Ohio, vol. 7,

p. 522, pi. 37A, fig. 13.

Clinton formation: Ohio/

Acidaspis danai Hall, see Ceratocephala goniata Warder.
Acidaspis fimbriata Hall.

1882. Acidaspis fimbriata. Hall, llth Rep. Dep. Geol. and Nat.

Hist., Indiana, p. 334, pi. 33, fig. 11.
Niagara: Waldron, Ind.

1883. Acidaspis fimbriata. Hall, Trans. Albany Inst., vol. 10, p.

76.

Niagara: Waldron, Ind.

Acidaspis Ida W. <fe M., see Ceratocephala goniata Warder.
Acidaspis obsoleta van Ing.

1901. Acidaspis obsoleta. van Ing., School of Mines Quart., vol.
23, p. 51, figs. 13-14.

Silurian: St. Clair Spring, Independence Co., Ark.
Acidaspis ortoni Foerste, see Odontopleura ortoni Foerste.
Acidaspis perarmata Whiteaves.

1891. Acidaspis perarmata. Whiteaves, Can. Rec. Sci., vol. 4,
p. 300.

Up. Silurian: Long Point, Lake Winnipegosis, Sas-
katchewan.
Acidaspis quinquespinosa (Salter, M. S ) Lake.

1896. Acidaspis quinquespinosa. Lake, Quart. Jour. Geol. Soc.,

Lond., vol. 52, p. 240, pi. 7, figs. 3-4.

Wenlock Limestone.

1901. Acida$pis quinquespinosa. van Ing., School of Mines Quart,
vol. 23, p. 50, fig. 12.

Silurian: St. Clair Spring, Independence Co., Ark.
Acidaspis vanhornei Weller.

1907. Acidaspis vanhornei. Weller, This Bulletin, p. 251, pi. 23, figs.
3-4.

Niagaran: Bridgeport, 111.

AMPYX Dalman, 1826.
Ampyx niagarensis van Ing.

1901. Ampyx niagarensis. van Ing., School of Mines Quart., vol.
23, p. 53, fig. 15.

Silurian: St. Clair Spring, Independence Co., Ark.

ARCTINURUS Castelnau, 1843.
Arctinurus boltoni (Bigsby).

1825. Paradoxus boltoni. Bigsby, Jour. Acad. Nat. Sci., Phil.,
1st ser., vol. 4, pt. 2, p. 365, pi. 23.
Lockport, N. Y.

l86 THE CHICAGO ACADEMY OF SCIENCES.

1832. Paradoxides boltoni. Green, Monog. Tril. N. A., p. 60, pi. 1,.
fig. 5.

Lockport, N. Y.

1834. Paradoxides boltoni. Harlan, Trans. Geol. Soc., Penn., vol..
1, pt. 1, p. 103.

Lockport, N. Y.
1838. Platynotus boltoni. Con., Rep. N. Y. St. Geol. Surv., 1838,.

p. 118.

1843. Arctinurus boltoni. Castel., Ess. Syst. Sil. 1'Amer. Sept.,
p. 21, pi. 3, fig. 2.

Lockport, N. Y.

1843. Platynotus boltoni. Hall, Geol. N. Y., pt. 4, Tab. Org. Rem.^
19, fig. 1.

Niagara: Lockport, N. Y.

1852. Lichas boltoni. Hall, Pal. N. Y., vol. 2, p. 311, pi. 69, and
pi. 70, figs, la-g, j-l(not figs. Ih, i=Arctinurus nereus}.
Niagara: Lockport, Rochester, Sweden and Walcott,

N. Y.

1901. Lichas boltoni. Grabau, Bull. N. Y. St. Mus., No. 45, vol. 9,.
p. 225, pi. 17.

Rochester shale: Niagara, Rochester, etc., N. Y.
Arctinurus chicagoensis Weller.

1907. Arctinurus chicagoensis. Weller, This Bulletin, p. 248, pi. 23,.
figs. 7-8, pi. 22, fig. "14.

Niagaran: Hawthorn, 111.
Arctinurus nereus (Hall).

1852. Lichas boltoni. Hall, Pal. N. Y.', vol. 2, p. 311, pi. 70, figs..
1 h-i. (not figs. 1 a-g, j-1).
Niagara: Lockport, N. Y.

1863. Lichas nereus. Hall, 16th Rep. N. Y. St. Cab. Nat. Hist.,

p. 226.

1901. Lichas nereus. van Ing., School of Mines Quart., vol. 23,.
p. 64.

Silurian: St. Clair Spring, Independence Co., Ark.
Arctinurus obvius (Hall).

1870. Lichas obvius. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,.
(rev. ed.), p. 424, pi. 25, fig. 10.

'Niagara: Lyons, Iowa.
Arctinurus occidentalis (Hall).

1864. Lichas boltoni var., occidentalis. Hall, Trans. Albany Inst.,.

vol. 4, p. 223.

Niagara: Waldron, Ind.

1875. Lichas boltoni. W. & M., Geol. Surv. 111., vol. 6, p. 508,
pi. 25, fig. 5.

Niagara: Graf ton, 111.

1877. Lichas boltoni var., occidentalis. Hall, 28th Rep. N. Y. St.
Mus. Nat. Hist. (doc. ed.), pi. 34, figs. 8-11.

Niagara: Waldron, Ind.

1879. Lichas boltoni var., occidentalis. Hall, 28th Rep. N. Y. St.
Mus. Nat.-Hist. (mus. ed.), p. 198, pi. 34, figs. 8-11.
Niagara: Waldron, Ind.

THE NATURAL HISTORY SURVEY. 187

1882. Lichas boltoni var., occidentals. Hall, llth Rep. Dep.
Geol. & Nat. Hist., Indiana, p. 344, pi. 36, figs. 8-11 and 12.

Niagara: Waldron, Ind.

1890. Lichas boltoni. var., occidentalis. Foerste, Proc. Bost. Soc.,
Nat. Hist., vol. 24, p. 272.

Clinton: Cumberland Gap, Tenn.

1907. Arctinurus occidentalis. Weller, This Bulletin, p. 247, pi. 20
figs. 10-12.

Niagaran: Joliet and Bonfield, 111.

ARQES Goldfuss, 1839.

Arges arkansana van Ing., see Dicranopeltis arkansana (van Ing.).
Arges phlyctainodes (Green), see Corydocephalus phlyctainodes (Green).
Arges phlyctenoides depauperata van Ing., see Corydocephalus depau-
peratus.

ASAPHUS Brong.. 1822.

Asaphus caudatus Green, see Dalmanites iimulurus (Green).
Asaphus cordieri Castel., see Dalmanites Iimulurus (Green).
Asaphus corycaeus Conrad, see Proetus corycaeus (Conrad).
Asaphus coryphaeus Hall, see Proetus corycaeus (Conrad).
Asaphus Iimulurus Green, see Dalmanites Iimulurus (Green).
Asaphus wetherilli Green, see Dalmanites Iimulurus (Green).

BRONTEUS Goldf., 1839.
Bronteiis acamas Hall.

1865. Bronteus acamas. Hall, Adv. Sheets, IStlTHep. N. Y. St.
Cab, Nat. Hist., p. 28.

Niagara : Racine, Wis.

1867. Bronteus acamas. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 322, pi. 21, figs. 19-20.
Niagara: Racine, Wis.

1870. Bronteus acamas. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.
(rev. ed.), p. 422, pi. 21, figs. 19-20, pi. 25, fig. 21.

Niagara: Racine, Wis.
1907. Bronteus acamas. Weller, This Bulletin, p. 232, pi. 20, fig. 1.

Niagaran: Bridgeport and Romeo, 111.
Bronteus laphami Whitf.

1878. Bronteus laphami. Whitf., Ann. Rep. Wis. Geol. Surv. for
' 1877, p. 88.

Niagara: Kewaunee, Wis.

1882. Bronteus laphami. Whitf., Geol. Wis., vol. 4, p. 310, pi. 22,
figs. 1-4.

Niagara: Kewaunee, Wis.
Bronteus niagarensis Hall

1852. Bronteus ? niagarensis. Hall, Pal. N. Y., vol. 2, p. 34, pi.
70, fig. 3.

Niagara: Niagara river.

1901. Bronteus niagarensis. Grabau, Bull. N. Y. St. Mus., No. 45,
vol. 9, p. 226, fig. 158.

Niagara: Niagara river.

l88 THE CHICAGO ACADEMY OF SCIENCES.

Bronteus occasus W. & M.

1865. Bronteus occasus. W. & M., Mem. Bost. Soc. Nat. Hist.,
vol. 1, p. 104, pi. 3, fig. 12.

Niagara: Bridgeport, 111.

BRONGNIARTIA Eaton, 1832.

Brongniartia platycephala Eaton, see Homalonotus delphinocephalus
(Green).

BUMASTUS Murch., 1839.
Bumastus barriensis Hall, see Illaenus ioxus Hall.

CA'LYMENE Brong., 1822.

Calymene altirostris van Ing.

1901. Calymenne altirostris. van Ing., School of Mines Quart., vol.
23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
Calymene blumenbachii (various authors), see Calymene niagarensis

Hall, and Calymene vogdesi Foerste.
Calymene][canierata Conrad.

1842. Calymene camerata. Con., Jour. Acad. Nat. Sci. Phil., 1st
ser., vol. 8, p. 278.
Schoharie, N. Y.

1852. Calymene camerata. Hall, Pal. N. Y., vol. 2, p. 337, pi. 78,
figs, la-lf.

Coralline limestone: Schoharie, N. Y.

1903. Calymene camerata. Weller, Pal. N. J., vol. 3, p. 250, pi.
22, figs. 22-25.

Decker Ferry: Nearpass Quarry, N. J.
Calymene clintoni (Vanuxem).

1842. Hemicrypturus clintonii. Van., Geol. N. ,,Y., pt. 3, p. 79,

fig. 2.

Clinton: Vanhornsville, N. Y.

1843. Hemicrypturus tail. Hall, Geol. N. Y., pt. 4, p. 77, tab.org.

rem., 9, fig. 2.

Clinton.

1852. Calymene clintoni. Hall, Pal. N. Y., vol. 2, p. 298, pi. A66,
figs>5a-5d.

Clinton: Herkimer and Cayuga Cos., N. Y.

1852. Calymene blumenbachii. ,? var. senaria. Hall, Pal. N. Y., vol.
2, p. 299, pi. A66, figs. 6a-6e.

Clinton : New York.

Calymene]clintoni Vogdes, see Calymene vogdesi Foerste.
Calymene nasuta Ulrich.

1879. Calymene nasuta. Ulrich, Jour. Cinn. Soc. Nat. Hist., vol.
2, p. 131, figs. 1-3, p. 132.
Niagara: Osgood, Ind.
Calymene 'niagarensis Hall.

1843.' Calymene niagarensis. Hall, Geol. N. Y., pt. 4, p. 102, fig. 3,
p. 101, tab. org. rem. 10, fig. 3.

Niagara: Lockport and Rochester N. Y.

THE NATURAL HISTORY SURVEY. 189

1852. Calymene blumenbachii var. niagarensis. Hall, Pal. N. Y.,
vol. 2, p. 307, pi. 67, figs. 11-12.

Niagara: Lockport and Rochester, N. Y.
1852. Calymene sp. Hall, Pal. N. Y., vol. 2, p. 350, pi. 83, fig. 8.

Guelph: Gault, Ont.

1860. Calymene blumenbachii. Roemer, Sil. Faun. West. Tenn.,
p. 79, pi. 5, fig. 22.

Decatur Co., Tenn.

1860. Calymene blumenbachii var. Hall, Can. .Nat. and Geol., vol.
5, p. 156.

Arisaig: Nova Scotia.

1862. Calymene blumenbachii var. niagarensis. Hall Geol., Surv.
Wis., vol. 1, p. 432 (no description).

Niagara: Milwaukee and Racine, Wis.

1865. Calymene niagarensis. Hall, Adv. Sheets, 18th Rep., N. Y.
St. Cab. Nat. Hist., p. 30.
Niagara: Wisconsin.

1867. Calymene niagarensis. Hall, 20th Rep. N. Y., St. Cab. Nat.

Hist., p. 334.

Niagara: Racine, Wis.

1868. Calymene blumenbachii var. Dawson, Acad. Geol. 2nd ed.,

p. 607.

Arisaig: Nova Scotia.

1870. Calymene niagarensis. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist. (rev. ed.), p. 425.
Niagara: Wisconsin.

1875. Calymene niagarensis. H. & W., Pal. Ohio, vol. 2, p. 153,
pi. 6, figs. 14-15.

Niagara: Cedarville, Eaton and Yellow Springs, Ohio.
1877. Calymene niagarensis. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (doc. ed.), pi. 32, figs. 8-15.

Niagara: Waldron, Ind.

1879. Calymene niagarensis. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (mus. ed.), p. 187, pi. 32, figs. 8-15.

Niagara: Waldron, Ind.

1882. Calymene niagarensis. Hall, llth Rep. Dep. Geol. & Nat.
Hist., Indiana, p. 331, pi. 34, figs. 8-15.

Niagara: Waldron, Ind.

1888. Calymene niagarensis. H. & C., Pal. N. Y., vol. 7, pi. 1,
figs. 10-14.

Niagara: Waldron, Ind.

1895. Calymene blumenbachii. Whiteaves, Geol. 'Surv. Can., Pal.
Foss., vol. 3, pt. 2, p. 106.

Guelph: Gault, Ont.

1901. Calymenne niagarensis. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
1901. Calymmene blumenbachi niagarensis. Grabau, Bull. N. Y.
St. Mus., No. 45, vol. 9, p. 224, fig. 156.
Clinton: Niagara, N. Y.
Rochester shale: Niagara, Lockport, etc., N. Y.

I9O THE CHICAGO ACADEMY OF SCIENCES.

1903. Calymmcne niagarensis. C. & R., Mem. N. Y. St. Mus., N<x

5, p. 107, pi. 21, fig. 12.

Guelph: Rochester and Shelby, N. Y.

1904. Calymene cf., Vogdesi. Kindle, 28th Ann. Rep. Dep. Geol.

& Nat. Res., Indiana, p. 482, pi. 24, figs. 1-7.

Niagara: Connor's Mill, Georgetown and "Hanging

Rock," Ind.

1907. Calymene niagarensis. Weller, This Bulletin, p. 261, pi. 23,
figs. 9-10. >

Niagaran: Bridgeport, Hawthorn, Joliet, near Lemont,

etc., etc., 111.
Calymene phlyctainoides Green, see Corydocephalus phlyctainoides

(Green).
Calymene rostrata Vcgdes.

1879. Calymene rostrata. Vogdes, Am. Jour. Sci., 3rd ser., vol. 18,

p. 477.

Clinton; Catoosa Station, Georgia.

1880. Calymene rostrata. Vogdes, Proc. Acad. Nat. Sci. Phil., for

1880, p. 176, figs. 1-2.

Clinton: Taylor's Ridge near Catoosa Station and Dug
Gap, Georgia.

1881. Calymene rostrata. Vogdes, Pal. Cont., 1, p. 8, figs. 1 and 2

on accompanying plate.

Clinton: Catoosa Station and Dug Gap, Georgia.
1886. Calymene rostrata. Vogdes, Desc. New Crust. Clint, of
Georgia, etc., p. 2, figs. 1-2.

Clinton: Near Catoosa Station and at Dug Gap, Georgia-
1890. Calymene rostrata. Foerste, Proc. Bost. Soc. Nat. Hist.'
vol. 24, p. 267.

Clinton: Catoosa Station, Georgia, and New York.
Calymene trisulcata Hall, see Phacops trisulcata Hall.
Calymene vogdesi Foerste.

1880. Calymene clinicni. Vcgdes, Proc. Acad. Nat. Sci. Phil., for

1880, p. 178, figs. 3-4. (not C. clintoni Van.).

Clinton: Catoosa Station and Dug Gap, Georgia;

1881. Calymene clintcni. Vcgdes, Pal. Cont. 1, p. 9, figs. 3-7 on

accompanying plate. ^

Clinton: Catoosa Station and Dug Gap, Georgia.

1886. Calymene clintoni. Vcgdes, Desc. New Crust. Clint, of

'Georgia, etc., p. 5, fgs.*3-4.

Clinton: Catoosa Station and Dug Gap, Georgia.

1885. Calymene . Foerste, Bull. Sci. Lab. Den. Univ., vol. 1,

p. 109, pi. 13, fig. 24.

Clinton: Near Dayton, Ohio.

1885. Calymene blumenbachii ? Foerste, Bull. Sci. Lab. Den.
Univ., vol. 1, p. 110, pi. 13, fig. 25.
Clinton: Centerville, Ohio.

1887. Calymene vogdesi. Foerste, Bull. Sci. Lab. Den. Univ., voL

2, p. 95.

Clinton: Near Dayton, Ohio; Catoosa and Dug Gap-,
Georgia.

THE NATURAL HISTORY SURVEY. 19!

1890. Calymene blumenbachii var., vogdesi. Foerste, Proc. Bost
Soc. Nat. Hist., vol. 24, p. 265.

Clinton: Hanover, Ind. ; Wilmington, Ohio; Collins-
ville, Ala.; Catoosa Station and Dug Gap, Ga.; Cum-
berland Gap, Tenn.

1895. Calymene vogdesi. Foerste, Geol. Surv. Ohio, vol. 7, p. 526,
pi. 25, fig. 24-25; pi. 27, figs. 12-16.

Clinton: Ohio; Hanover, Ind.; Lockport, N. Y.

CERATOCEPHALA Warder, 1838.
Ceratocephala coalescens van Ing.

-1901. Ceratocephala coalescens. van Ing., School of Mines Quart.,
. vol. 23, p. 48, fig. 11, p. 41.

Silurian: St. Clair Spring, Independence Co., Ark.
Ceratocephala depauperata van Ing.

1901. Ceratocephala goniata (depauperata). van Ing., School of
Mines Quart., vol. 23, p. 42.

Silurian: St. Clair Spring, Independence Co., Ark.
Ceratocephala nodulata van Ingen.

1901. Ceratocephala nodulata. van Ing., School of Mines Quart.,
vol. 23, p. 44, fig. 10, p. 41.

Silurian: St. Clair Spring, Independence Co., Ark.
Ceratocephala goniata Warder.

1838. Ceratocephala goniata. Warder, Am. -Jour. Sci., 1st ser., vol.
34, p. 378, fig.

Springfield, Ohio.

1862. Acidaspis danai. Hall, Geol. Surv. Wis:, vol. 1, p. 432
. (no description).

Niagara : Wisconsin.

1865. Acidaspis danai. Hall, Adv. Sheets, 18th Rep. N. Y. St.
Cab. Nat. Hist., p. 28.

Niagara: Bridgeport, 111.

1865. Acidaspis ida. W. & M., Mem. Bost. Soc. Nat. Hist., vol. 1,
p. 106, pi. 3, fig. 13.

Niagara: Bridgeport, 111.

1867. Acidaspis danai. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 333, pi. 21, figs. 8-9.

Niagara: Bridgeport, 111.

1870. Acidaspis danai. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
(rev. ed.), p. 423, pi. 21, figs. 8-9.

Niagara: Bridgeport, 111.

1892. Ceratocephala goniata. Clarke, 44th Rep. N. Y. St. Mus.
Nat. Hist., p. 91-100, pL 1, fig. 1.

Springfield, Ohio.

1904. Ceratocephala goniata. Kindle, 28th Ann. Rep. Dep. Geol.
and Nat. Res., Indiana, p. 480, pi. 24, fig. 13.

Niagara: Pendleton, Indiana.

1907: Ceratocephala goniata. Weller, This Bulletin, p. 255, pi. 23,
figs. 1-2. .

Niagaran: Bridgeport and Hawthorn, 111.

Ceratocephala goniata (depauperata) van Ing., see Ceratocephala de=
pauperata van Ing.

192 THE CHICAGO ACADEMY OF SCIENCES.

CERAURUS Green, 1832.

Ceraurus bimucronatus Roemer, see Ceraurus niagarensis Hall.
Ceraurus clintoni Foerste.

1887. Ceraurus . Foerste, Bull. Sci. Lab. Den. Univ., vol. 2,

p. 98, pi. 8, fig. 17.

Clinton: Near Dayton, Ohio.

1895. Ceraurus (Pseudosphaerexochus} clintoni. Foerste, GeoL
Surv., Ohio, vol. 7, p. 527, pi. 27, fig. 17.

Clinton : Ohio.
Ceraurus hydei Weller.

1907. Ceraurus hydei. Weller, This Bulletin, p. 264, pi. 24, fig. 22.

Niagaran: Near Lemont, 111.

Ceraurus insignis Hall, see Ceraurus niagarensis Hall.
Ceraurus niagarensis Hall.

1852. Ceraurus insignis. Hall, Pal. N. Y., vol. 2, p. 300, pi. A66,
fig. 4; also p. 303, pi. 67, figs. 9-10. (not C. insigins Beyr.)
Clinton: New York.
Niagara: Rochester, N. Y.

1860. Ceraurus bimucronatus. Roemer, Sil. Faun. West. Tenn., p.
80, pi. 5, fig. 19. (not C. bimucronatus Murch.)

Silurian: Decatur County, Tenn.

1862. Ceraurus insignis. Hall, Geol. Surv. Wis., vol. 1, p. 433
(no description).

Niagara : Wisconsin.

1865. Ceraurus insignis. Hall, Adv. Sheets, 18th Rep. N. Y. St.
Cab. Nat. Hist., p. 31.

Niagara: Wauwatosa, etc., Wis.

1867. Ceraurus insignis. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 335.

Niagara: Wauwatosa, Wis.

1867. Ceraurus niagarensis. Hall, 20th Rep. N. Y. St. Cab. Nat,
Hist., p. 376, pi. 21, figs. 10-11.

Niagara: Wisconsin.

1870. Ceraurus niagarensis. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist. (rev. ed.), p. 427, pi. 21, figs. 10-11.

Niagara : New York and Wisconsin.

1877. Sphaerexochus romingeri ? Hall, 25th Rep. N. Y. St. Mus.
Nat. Hist. (doc. ed.), pi. 32, fig. 16. .

Niagara: Waldron, Ind.

1879. Ceraurus (Cheirurus) niagarensis. IJall, 28th Rep. N. Y.
St. Mus. Nat. Hist. (mus. ed.), p. 189, pi. 32, fig. 16.

Niagara: Waldron, Ind.

1882. Ceraurus niagarensis. Hall, llth Rep. Dep. Geol. and Nat.
Hist., Indiana, p. 335, pi. 34, fig. 16, pi. 33, fig. 10.

Niagara: Waldron, Ind.

1884. Ceraurus niagarensis. Whiteaves, Geol. Surv. Canada;
Pal. Foss., vol. 3, pt. 1, p. 42.

Guelph: Hespeler, Ont.

1895. Ceraurus niagarensis. Whiteaves, Geol. Surv. Canada;.
Pal. Foss., vol. 3, pt. 2, p. 107.
Guelph: Hespeler, Ont.

THE NATURAL HISTORY SURVEY. 193

1901. Ceraurus niagarensis. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
1904. Ceraurus ' (Crotalocephalus} niagarensis. Kindle, 28th Ann.
Rep. Dep. Geol. and Nat. Res., Indiana, p. 483, pi. 23,
figs. 1-2, pi. 24, fig. 8.

Niagara: Connor's Mill, Marion and Georgetown, Ind.
[ 1907. Ceraurus niagarensis. Weller, This Bulletin, p. 263, pi. 24,
figs. 20-21.

Niagaran: Hawthorn and near Lemont, 111.

CORYDOCEPHALUS Corda, 1847.
Corydocephalus byrnesanus (M. & G.)

1893. Lichas byrnesanus. M. & G., Bull. No. 3, 111. St. Mus. Nat.
Hist., p. 78, pi. 8, figs. 8-9.

Niagara: Near Madison, Ind.
Corydocephalus depauperatus (van Ing.).

1901. Arges phlyctenoides depauperatus. van Ing., School of Mines
Quart., vol. 23, p. 57.

Silurian: St. Clair Spring, Independence Co., Ark.
Corydocephalus phlyctainodes (Green).

1837. Calymene phlyctainodes. Green, Am. Jour. Sci., 1st ser.,
vol. 32, p. 167.

Springfield, Ohio.

1852. Arges phlyctanoides. Hall, Pal. N. Y., vol. 2, p. 314, pi. 70,
figs. 2a-2c.

Niagara: Albion, N. Y.

1893. • Lichas hanoverensis. M. & G., Bull. No. 3; 111. St.. Mus.
Nat. Hist., p. 78, pi. 8, figs. 6-7.

Niagara: Hanover, Ind.

1907. Corydocephalus phlyctainodes. Weller, This Bulletin, p. 234,
pi. 22, figs. 1-4.

Niagaran: Joliet and near Lemont, 111.
Corydocephalus ptyonurus H. & C.

1888. Lichas (Dicranogmus} ptyonurus. H. & C., Pal. N. Y., vol.
7, p. 86, pi. 19B, figs. 19-21.

Coralline limestone: Schoharie, N. Y.

CRYPTONYMUS Eichw., 1825.

Cryptonymus ornatus Vogdes, see Encrinurus ornatus H. & W.
Cryptonymus nereus Vogdes, see Encrinurus nereus Hall.

CYBELE Loven, 1845.
Cybele punctata Hall, see Encrinurus ornatus H. & W.

CYPHASPIS Burm., 1843.
Cyphaspis arkansanus van Ing.

1901. Cyphaspis arkansanus. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
Cyphaspis christyi Hall.

1864. Cyphaspis christyi. Hall, Trans. Albany Inst., v61. 4, p. 220.
Niagara: Waldron, Ind.

194 THE CHICAGO ACADEMY OF SCIENCES.

1877. Cyphaspis christyi. Hall, 28th Rep. N. Y. St. Mus. Nat-
Hist. (doc. ed.)*pl- 32, figs. 5-7.
Niagara: Waldron, Ind.

1879. Cyphaspis christyi. Hall, 28th Rep. X. Y. St. Mus. Nat.

Hist. (mus. ed.), p. 188, pi. 32, figs. 5-7.
Niagara: Waldrdh, Ind.

1880. Cyphaspis christyi. White, 2nd Ann. Rep. Dep. Stat. and

Geol., Indiana, p. 498, pi. 3, fig. 9.

Niagara: Waldron, Ind.

1882. Cyphaspis christyi. Hall, llth Rep. Dep. Gaol, and Nat.
Hist., Indiana, p. 333, pi. 34, figs. 5-7.

Niagara: Waldron, Ind.
Cyphaspis clintoni Foerste.

- 1887. Proetus . Foerste, Bull. Sci. Lab. Den. Univ., vol. 2,

p. 92, pi. 8, fig. 5.

Clinton: Dayton, Ohio.

1890. Cyphaspis clintoni. Fosrste, Proc. BDst. Soc. Nat. Hist.,
vol. 24, p. 272, pi. 6, fig. 22.

Clinton: Cumberland Gap, Tenn.

1895. Cyphaspis clintonznsis. Foerste, Geol. Surv. Ohio, vol. 7,
p. 524, pi. 27, fig. 5, pi. 31, fig. 22.

Clinton: Ohio; Cumberland Gap, Tenn; Anticosti.
Cyphaspis intermedia Weller

1907. Cyphaspis intermedia. Weller, This Bulletin, p. 231, pi. 20,
figs. 3-5.

Niagaran: Near Channahon, Will County, Illinois.
Cyphaspis spinulocervix van Ing.

1901. Cyphaspis spinulocervix. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co. Ark.

DALMANIA Emm. 1844.

Dalmania bicornis Hall, see Dalmanites bicornis Hall.
Dalmania caudata Roemer, see Dalmanites limulurus (Green).
Dalmania danae M. & W., see Dalmanites danae M. & W.
Dalmania logani Hall, see Dalmanites logani Hall.
Dalmania verrucosa Hall, see Dalmanites verrucosus Hall. ^
Dalmania vigilans Hall, see Dalmanites vigilans Hall.

DALMANITES Barr., 1872.

Dalmanites arkansanus van Ing.

1901. Dalmanites (Synphoria) arkansanus. van Ing., School of
Mines Quart., vol. 23, p. 69, figs. 20-22.

Silurian: St. Clair Spring, Independence Co., Ark.
1907. Dalmanites arkansanus. Weller, This Bulletin, p. 278, pi. 24,
fig. 5.

Niagaran: Near Lemont and near Romeo, 111.
Dalmanites aspinosa Weller.

1903. Dalmanites aspinosa. Weller, Pal. N. J., vol. 3, p. 252, pi.
22, fig. 15.

Decker Ferry: Nearpass Quarry, N. J.

THE NATURAL HISTORY SURVEY. IQ5

i
Dalmanites bicornis Hall.

1877. Dalmania bicornis. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (doc. ed.), pi. 33, fig. 18.

Niagara: Waldron, Ind.

1879. Dalmanites bicornis. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (mus. ed.), p. 198, pi. 33, fig. 18.

Niagara: Waldron, Ind.

1882. Dalmanites bicornis. Hall, llth Rep. Dep. Gaol, and Nat.
Hist., Indiana, p. 342, pi. 35, fig. 18.

Niagara: Waldron, Ind.
Dalmanites danae M. & W.

1865. Dalmania danae. M. & W., Proc. Acad. Nat. Sci. Phil., for
1865, p. 264.

Up. Silurian: Near Thebes, Alexander Co., 111.

1868. Dalmanites danae. M. & W., Geol. Surv. Ill, vol. 3, p. 263,
pi. 6, figs, la-lf.

Niagara: 2 miles above Thebes, Alexander Co., 111.
Dalmanites halli, n. sp.

1877. Dalmania vigilans. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (doc. ed.), pi. 33, figs. 1-4 (not D. vigilans. Hall,.
1862).

Niagara: Waldron, Ind.

1879. Dalmanites vigilans. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (mus. ed.), p. 193, pi. 33, figs. 1-4.

Niagara: Waldron, Ind.

1882. Dalmanites vigilans. Hall, llth Rep. Dep^Geol. and Nat.
Hist., Indiana, p. 339, pi. 35, figs. 1-4; pi. 33, fig. 9.

Niagara: Waldron, Ind.
Dalmanites illinoiensis Weller.

1907. Dalmanites illinoiensis. Weller, This Bulletin, p. 275, pi. 25,
figs. 1-2. ,

Niagaran: Joliet, Bonfield and near Lemont, 111.
Dalmanites limulurus (Green).

1832. Asaphus limulurus. Green, Monog. Tril. N. A., p. 48.

Lockport, N. Y.
1832. Asaphus caudatus. Green, Monog. Tril. N. A., p. 50.

Ripley, Ohio.
1832. Asaphus wetherilli. Green, Monog. Tril. N. A., p. 57.

Near Rochester, N. Y.

1834. Asaphus limulurus. Harlan, Trans. Geol. Soc. Penn., vol.
1, pt. 1, p. 101.

Lockport, N. Y.

1834. Asaphus wetherilli. Harlan, Trans. Geol. Soc. Penn., vol. 1,
pt. 1, p. 101.

Near Rochester, N. Y.

1843. Asaphus limulurus. Castel., Ess. Syst. Sil. 1'Amer. Sept.,
p. 18, pi. 4, fig. 1.
Lockport, N. Y.

1843. Asaphus cor.dieri. CasteJ., Ess. Syst. Sil. 1'Amer. Sept.,
p. 18, pi. 4, fig. 2.
Lockport N. Y.

196 THE CHICAGO ACADEMY OF SCIENCES.

1843. Asaphus limulurus. Hall, Geol. N. Y., pt. 4, p. 101, fig.
1-2; also tab. org. rem., 10, figs. 1-2.

-Niagara: Lockport and Rochester, N. Y.

1852. Phacops limulurus. Hall. Pal. N. Y., vol. 2, p. 303, pi. 67,
figs. 1-8.

Niagara: Lockport, N. Y.

1856. Phacops limulurus. Bill.-, Can. Nat. and Geol., vol. 1, p. 57,
pi. 1, fig- 7.

Niagara: Ontario, Canada.

1860. Dalmania caudata. Roemer, Sil. Faun. West. Tenn., p. 82,
pi. 5, fig. 21.

Silurian : Tennessee.

1901. Dalmanite's limulurus. Grabau, Bull. N. Y. St. Mus., No.
45, vol. 9, p. 224, fig. 155.

Rochester shale: Niagara and Rochester, N. Y.
Dalmanites logani Hall.

1860. Dalmania logani. Hall, Can. Nat. and Geol., vol. 5, p. 156.

Arisaig: Nova Scotia.

1868. Dalmania logani. Dawson, Acad. Geol., 2nd ed., p. 608,
fig. 215.

Arisaig.
Dalmanites platycaudatus Weller.

1907. Dalmanites platycaudatus. Weller, This Bulletin, p. 272,
pi. 25, figs. 3-5.

Niagaran: Near Lemont, 111.
Dalmanites verrucosus Hall.

1864. Dalmania verrucosa. Hall, Trans. Albany Inst., vol. 4, p.

218.

Niagara: Waldron, Ind.

1877. Dalmania verrucosa. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (doc. ed.), pi. 33, figs. 5-17; pi. 34, figs. 13-15.
. Niagara: Waldron, Ind.

1879. Dalmanites verrucosus. Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (mus. ed.), p. 195, pi. 33, figs. 5-17; pi. 34, figs:i3-15.

Niagara: Waldron, Ind.

1882. Dalmanites verrucosus. Hall, llth Rep. Dep. Geol. and Nat.
Hist., Indiana, p. 341, pi. 35, figs. 5-17; pi. 36, figs'. 13-15.

Niagara: Waldron, Ind.

1907 Dalmanites verrucosus. Weller, This Bulletin, p. 280, pi. 25,.
figs. 6-7.

Niagaran: Bonfield and Jersey County, 111.
Dalmanites vigilans Hall.

1861. Dalmanites vigilans. Hall, Rep. Prog. Geol. Surv. Wis.,

for 1860, p. 51.

Niagara: Waukesha, Wis.

1862. Dalmania vigilans. Hall, Geol. Surv. Wis., vol. 1, p. 433,

figs. 3—4, p. 69 (no description).
Niagara: Waukesha, Wis.

1865. Dalmania vigilans. Hall, Adv. Sheets, 18th Rep. N. Y. St.

Cab. Nat. Hist., p. 31.

Niagara: Waukesha, Wauwatosa, etc., Wis.

THE NATURAL HISTORY SURVEY. 197

1867. Dalmania vigilans. Hall, 20th Rep. N. Y. St. Cab. Nat*
Hist., p. 335, figs. 1-2;. p. 375, pi. 21, figs. 16-18.
Niagara: Waukesha, Wauwatosa, etc., Wis.

1870. Dalmania vigilans. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist. (rev. ed.), p. 426, figs. 13-14, pi. 21, figs. 16-18.

Niagara: Waukesha, Wis.

1901. Dalmanites (Synphoria) vigilans. van Ing., School of Mines
Quart., vol. 23, p. 67.

Silurian: St. Clair Spring, Independence Co., Ark.
1904. Dalmanites (Synphoria} vigilans. Kindle, 28th Ann. Rep.
Dep. Geol. and Nat. Res., Indiana, p. 485, pi. 23, figs. 4-7.
pi. 24, fig. 20. '

Niagara: Anderson and Pendleton, Ind.

1907. Dalmanites vigilans. Weller, This Bulletin, p. 276, pi. 24,
figs. 1-4.

Niagaran: Joliet and near Lemont, 111.
Dalmanites werthneri Foerste

1885. Dalmanites werthneri. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 1, p. 116.

Clinton: Near Dayton, Ohio.

1887. Dalmanites werthneri. Foerste, Bull. Sci. Lab. Den Univ.»
vol. 2, p. 101, pi. 8, figs. 22, 22a, 23-25.

Clinton: Near Dayton, Ohio.

1895. Dalmanites werthneri. Foerste, Geol. Surv. Ohio, vol. 7,
p. 530, pi. 27, figs. 22, 22a, 23-25.
Clinton: Ohio.

DEIPHON Barrande, 1850.
Deiphon americanus Weller.

1907. Deiphon americanus. Weller, This Bulletin, p. 268, pi. 24, fig.
14.

Niagaran: Joliet, Romeo and near Lemont, 111.
Deiphon forbesi Barr.

1850. Deiphon forbesii. Barrande, Haidinger's Berichte, p. 6.

Etage E. : Bohemia.

1865. Deiphon forbesi. Salter, Monog. British Trilobites, p. 88,
pi. 7, figs. 1-12.

Wenlock limestone and shale : England.

1895. Sphaerexochus pisum. Foerste, -Geol. Surv. Ohio, vol. 7,
p. 528, pi. 37A, figs. 14a-14b.
Niagara shale: Lockport, N. Y.
Clinton: Ohio.

1901. Deiphon forbesi. van Ingen, School of Mines Quart., vol.
23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.

DICRANOPELTIS Corda, 1847.

Dicranopeltis arkansana (van Ing.).

1901. Arges arkansana. van Ing., School of Mines Quart., vol. 23,
p. 61, fig. 19.

Silurian: St. Clair Spring, Independence Co., Ark.

198 THE CHICAGO ACADEMY OF SCIENCES.

Dicranopeltis decipiens (W. & M.).

1865. Lichas brev iceps ? Hall, Adv. Sheets, 18th Rep. N. Y. St.-
Cab. Nat. Hist., p. 30 (not L. breviceps. Hall, 1864).
Niagara: Bridgeport, 111.

1865. Lichas decipiens. W. & M., Mem. Bost. Soc. Nat. Hist.,

vol. 1, p. 104, pi. 3, fig. 11.

Niagara: Bridgeport, 111.

1867. Lichas breviceps ? Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 334; p. 377, pi. 21, figs. 12-14.

Niagara: Bridgeport, 111.; Grafton, Wis.

1870. Lichas breviceps ? Hall, 20th Rep. N. Y. St. Cab. Nat. Hist,
(rev. ed.), p. 424, pi. 21, -figs. 12-14.

Niagara: Bridgeport, 111.; Grafton, Wis.
1879. Lichas emarginatus. Hall, 28th Rep. N. Y. St. Mus. Nat.

Hist. (mus. ed.), p. 199.

1907. Dicranopeltis decipiens. Weller, This Bulletin, p. 237, pi. 22,
figs. 10-11.

Niagaran: Bridgeport, Hawthorn and near Lemont, 111.
Dicranopeltis nasuta Weller.

1907. Dicranopeltis nasuta. Weller, This Bulletin, p. 240, pi. 22,
figs. 5-7.

Niagaran: Milwaukee, Wis.
Dicranopeltis telleri Weller.

1907. Dicranopeltis telleri. Weller, This Bulletin, p. 241, pi. 22,
figs. 8-9.

Niagaran: Milwaukee, Wis.

ENCRINURUS Emm., 1844.
Encrinurus americanus Vogdes.

1866. Encrinurus americanus. Vogdes, Desc. New Crust. Clint.

of Ga., etc., p. 1.

Clinton: Near Catoosa Statipn, Georgia.

1887. Encrinurus americanus. Foerste, Bull. Sci. Lab. Den.
Univ., vol. 2, p. 102.
Clinton: Georgia.
Encrinurus egani S. A. M.

1880. Encrinurus egani. S. A. M., Jour. Cinn. Soc. Nat. Hist., vol.7'
2, p. 254, pi. 15, figs. 1-lb.

Niagara: Joliet, 111.

1907. Encrinurus egani. Weller, This Bulletin, p. 257, pi. 24, figs.
8-11.

Niagaran: Joliet and near Lemont, 111.
Encrinurus indianensis Kindle.

1904. Encrinurus indianensis. Kindle, 28th Ann. Rep. Dep. Geol.
and Nat. Res., Indiana, p. 482, pi. 24, figs. 14-15.

Niagara: Connor's Mill, Fishersburg, Huntington, Little

Deer Creek and Wabash, Ind.
Encrinurus nereus Hall.

1865. Encrinurus . sp. Hall, Adv. Sheets, 18th Rep. N. Y.

St. Cab. Nat. Hist., p. 30.
Niagara: Racine, Wis.

THE NATURAL HISTORY SURVEY.

1867 Encrinurus . sp. Hall, 20th Rep. N. Y. St. Cab. Nat.

Hist., p. 334.

Niagara: Racine, Wis.

1867. Encrinurus nereus. Hall, 20th Rep. N. Y St. Cab. Nat.
Hist., p. 375, pi. 21, fig. 15.

Niagara: Racine, Wis.

1870. Encrinurus nereus. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist. (rev. ed.), p. 425, pi. 21, fig. 15.

Niagara: Racine, Wis.

1878. Cryptonymus nereus. Vogdes, Monog. Gen. Zethus, Cybele
etc., p. 24, pi. 3, fig. 17.

Niagara: Racine, Wis.

1887. Encrinurus nereus. Foerste, Bull. Sci. Lab. Den. Univ.
vol. 2, p. 102.

Racine beds, Wisconsin.
Encrinurus ornatus H. & W.

1852. Cybele punctata. Hall, Pal. N. Y. vol. 2, p. 297, pi. A66
figs. la-Ik.

Clinton: Orleans and Niagara Cos., N. Y.

1875. Encrinurus ornatus. H. & W., Pal. Ohio, vol. 2, p. 154, pi.
6, fig. 16.

Niagara : Eaton and Yellow Springs, Ohio.

1878. Cryptonymus ornatus. Vogdes, Monog. Gen. Zethus, Cybele,.
etc., p. 23.

Niagara: Eaton and Yellow Springs, Ohio; Medina-

Reynold's Basin and Niagara, N. Y. ^_

1887. Encrinurus ornatus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 102.

Guelph limestone: Ohio.

1887. Encrinurus punctatus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 103.

Clinton : New York.

1890. Encrinurus punctatus. Foerste, Proc. Bost. Soc. Nat. Hist.,
vol. 24, p. 269.

Clinton: Collinsville, Ala., Cumberland Gap, Tenn.
1901. Encrinurus ornatus. Grabau, Bull. N. Y. St. Mus., No. 45,
vol. 9, p. 225, fig. 157.

Clinton: Niagara and Lockport, N. Y.

1901. Encrinurus punctatus. van Ingen, School of Mines Quart.,
vol. 23, p. 66.

Silurian: St. Clair Spring, Independence Co., Ark.
Encrinurus punctatus (various authors), see Encrinurus ornatus H. &

W., and Encrinurus threshed Foerste.
Encrinurus thresheri Foerste.

1887. Encrinurus thresheri. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p! 101, pi. 8, fig. 26.

Clinton: Ohio.

1895. Fncrinurus punctatus. Foerste, Geol. Surv. Ohio, vol. 7,.
p. 531, pi. 27, fig. 26.

Clinton: Ohio, Hanover, Ind.

THE CHICAGO ACADEMY OF SCIENCES.

Encrinurus tuberculifrons Weller.

1907. Encrinurus tuberculifrons. .Weller, This Bulletin, p. 259, pi. 24,
figs. 12-13.

Niagaran: Near Joliet, 111.

HARPES Goldfuss, 1839.
Harpes telleri Weller.

1907. Harpes telleri. Weller, This Bulletin, p. 213, pi. 20, fig. 2.
Niagaran: Milwaukee, Wis.

HEMICRYPTURUS.
Hemicrypturus clintoni Van., see Calymene clintoni (Vanuxem).

HOMALONOTUS Koenig, 1825.

Homalonotus atlas Castel., see Homalonotus delphinocephalus (Green).
Homalonotus dawsoni Hall.

1860. Homalonotus dawsoni. Hall, Can. Nat. and Geol., vol. 5,
p. 155, fig. 17.

Arisaig: Nova Scotia.

1868. Homalonotus dawsoni. Dawson, Acad. Geol. 2nd Ed., p.
606, fig. 214.

Arisaig.
Homalonotus delphinocephalus (Green).

1832. Trimerus delphinocephalus. Green, Monog. Tril, N. A., p.
82, fig. 1, plate.

Williamsville, Niagara Co., N. Y.

1834. Trimerus delphinocephalus. Harlan, Trans. Geol. Soc.
Penn., vol. 1, pt. 1, p. 105.

Niagara Co., N. Y.

1834. Brongniartia platycephala. Harlan, Trans. Geol. Soc. Penn.,
vol. 1, pt. 1, p. 105.

Lockport, N. Y.

1843. Homalonotus atlas. Castel., Ess. Syst. Sil. 1'Amer. Sept.,
p. 20, pi. 4, fig. 4.

Lockport, N. Y.

1843. Y H omalonotus giganteus. Castel., Ess. Syst. Sil. 1'Amer.
Sept., p. 20, pi. 3, fig. 1.

Lockport, N. Y.

1843. Homalonotus herculaneus. Castel., Ess. Syst. Sil. 1'Amer.
Sept., p. 20, pi. 4, fig. 5.

Lockport, N. Y.

1843. Homalonotus delphinocephalus. Hall, Geol. N. Y., pt. 4,
p. 103, fig. 34, tab. org. rem., 11, fig. 1.

Niagara: Lockport, Rochester, Sweden^and Wolcoot,

N. Y.

1852. Homalonotus delphinocephalus. Hall, Pal. N. Y., vol. 2,
p. 104, pi. 31, figs. 5a-5b; also p. 309, pi. 68, figs. 1-14.
Clinton: Herkimer Co., N. Y.
Niagara: Lockport, Rochester and Wolcott, N. Y.
1856. Homalonotus delphinocephalus. Bill., Can. Nat. and Geol.,
vol. 1, p. 320.

Niagara : Canada.

THE NATURAL HISTORY SURVEY. 2OI

1877. Homalonotus delphinocephalus ? Hall. 28th Rep. N. Y. St.
Mus. Nat. Hist. (doc. ed.), pi. 32, figs. 17-18.

Niagara: Waldron, Ind.

1879. Homalonotus delphinocephalus. Hall, 28th Rep. N. Y. St.
Mus. Nat. Hist. (mus. ed.), p. 187, pi. 32, figs. 17-18.

Niagara: Waldron, Ind.

1882. Homalonotus delphinocephalus. Hall, llth Rep. Dep. Geol.
and Nat?. Hist., Indiana, p. 332, pi. 34, figs. 17-18.

Niagara: Waldron, Ind.

1901. Homalonotus delphinocephalus. Grabau, Bull. N. Y. St.
Mus., No. 45, vol. 9, p. 221, fig. 153.

Rochester shale: Niagara, Lockport, etc., N. Y.
Homalonotus giganteus Castel., see Homalonotus delphinocephalus

(Green).

Homalonotus herculaneus Castel., see Homalonotus delphinocephalus
(Green).

ILLAENOIDES Weller, 1907.
Illaenoides triloba Weller.

1907. Illaenoides triloba. Weller, This Bulletin, p. 226, pi. 17, figs.
6-9, pi. 19, figs. 12-14.

Niagaran: Bridgeport, Joliet, and near 'Lemont, 111.

ILLAENUS Dalm.,' 1826.
Illaenus aboynensis Whiteaves. •

1895. Illaenus aboynensis. Whiteaves, Geol. Surv. Can., Pal.
Foss., vol. 3, pt. 2, p. 108, pi. 15, figs. 7-8.

Guelph: Aboyne, Ont.
Illaenus ambiguus Foerste.

1885. Illaenus ambiguus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 1, p. 106, pi. 14, figs. 9a-9b, lOa-lOc, 11. '

Clinton: near Dayton, Ohio.

1887. Illaenus ambiguus. Foerste, 15th Ann. Rep. Geol. and Nat.
Hist. Surv. Minn., p. 480, fig. 3, p. 478.

Niagara: Miffintown, Penn.

1887. Illaenus ambiguus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 94.

Clinton: Near Dayton, Ohio.

1890. Illaenus ambiguus. Foerste, Proc. Bost. Soc. Nat. Hist,
vol. 24, p. 267.

Clinton: Hanover, Ind.

1895. Illaenus ambiguus. Foerste, Geol. Surv. Ohio, vol. 7, p.
525, pi. 26, figs. 9a-9b, lOa-lOc, 11.

Clinton: Ohio; Hanover, Ind.
Illaenus armatus Hall.

1865. Illaenus armatus. Hall, Adv. Sheets, 18th Rep. N. Y. St.
Cab. Nat. Hist., p. 26, figs. 3-4.

Niagara: Bridgeport, 111., Grafton and Racine, Wis.
1865. Illaenus (Bumastus) worthenanus. W. & M., Mem. Bost. Soc.
Nat. Hist., vol. 1, p. 105.
Niagara: Bridgeport. 111.

2O2 THE CHICAGO ACADEMY OF SCIENCES.

1867. Illaenus armatus. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 330, figs. 3-4, pi. 22, figs. 1-3.

Niagara: Bridgeport, 111., Graf ton and Racine, Wis.
1870. Illaenus armatus. Hall, 2()th Rep. N. Y. St. Cab. Nat. Hist,
(rev. ed.), p. 41S, figs. 8-9, pi. 22, figs. 1-3, pi. 25, fig. 22;
also p. 433.

Niagara: Bridgeport, 111., Grafto/i and Racine, Wis.
1877. Illaenus armatus ? Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (doc. ed.), pi. 32, figs. 19-20.

Niagara: Waldron, Ind.

1879: Illaenus armatus ? Hall, 28th Rep. N. Y. St. Mus. Nat.
Hist. (mus. ed.), p. 189, pi. 32, figs. 19-20.

Niagara: Waldron, Ind.

1882. Illaenus urmatus. Hall, llth Rep. Dep. Geol. and Nat.
Hist., Indiana, p. 335, pi. 34, figs. 19-20, pi. 33, fig. 12.

Niagara: Waldron, Ind.

1904. Illaenus armatus. Kindle, 28th Rep. Dep. Geol. and Nat.
Res., Indiana, p. 479, pi. 22, fig. 6.

Niagara: Georgetown and Wabash, Ind.

1907. Illaenus armatus. Weller, This Bulletin, p. 222, pi. 18, figs.
4-6.

Niagaran: Bridgeport and Lockport, 111.
Illaenus barriensis Hall, see Illaenus ioxus Hall.
Illaenus chicagoensis WTeller.

1907. Illaenus chicagoensis. Weller, This Bulletin, p. 220, pi. 16,
figs. 10-12.

• Niagaran: Bridgeport, 111.
Illaenus cornigerus H.-& W.

1872. Illaenus cornigerus. H. & W., 24th Rep. N. Y. St. Mus. Nat.
Hist., p. 186.

Niagara: Falls of the Ohio.
Illaenus cuniculus Hall.

1867. Illaenus cuniculus. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist., p. 377, pi. 22, fig. 12.

Niagara: Wauwatosa, Wis.

1870. Illaenus cuniculus. Hall, 20th Rep. N. Y. St. Cab. Nat,
Hist. (rev. ed.), p. 421, pi. 22, fig. 12.

Niagara: Wauwatosa, Wis.

1907. Illaenus cuniculus. Weller, This Bulletin, p. 219, pi. 19, figs.
1-6.

Niagaran:, Hawthorn, 111.

Illaenus danielsi M. & G.

1893. Illaenus danielsi. M. & G., Bull. No. 3, 111. St. Mus. Nat,
Hist., p. 76, pi. 7, figs. 3-5.
Niagara: Bonfield, 111.
Illaenus daytonensis H. & W.

1875. Illaenus daytonensis. H. & W., Pal. Ohio, vol. 2, p. 119,
pi. 5, figs. 14-16.

Clinton: Near Dayton, Ohio.

THE NATURAL HISTORY SURVEY.

1885. Illaenus daytonensis. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 1, p. 104, pi. 14, figs. 4a-4b, 6, 7a-7c.

Clinton: Near Dayton and at Fair Haven, Ohio.
1887. Illaenus daytonensis. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 93, pi. 8, figs. 6-7.

Clinton: Ohio.

1895. Illaenus daytonensis. Foerste, Geol. Surv. Ohio, vol. 7,
p. 525, pi. 26, figs. 4a-4b, 6, 7a-7c; pi. 27, figs. 6, lOa.
- Clinton: Ohio; Lockport, X. Y.
Illaenus graftonensis M. & W.

1870. Illaenus (Bumastus} graftonensis. M. & W., Proc. Acad.
Xat. Sci.- Phil., for 1870, p. 54.
Niagara: Grafton, 111.

1875. Illaenus (Bumastus) graftonensis. W. & M., Geol. Surv. 111.,
vol. 7, p. 508, pi. 25, fig. 4.

Niagara: Grafton, 111.

1907. Illaenus graftonensis. Weller, This Bulletin, p. 223, pi. 16,
. figs. 4-6.

Xiagaran: Joh'et, and near Lemont, 111.
Illaenus harrisi Weller.

1907. Illaenus harrisi. Weller, This Bulletin, p. 218, pi. 16, figs. 1-3.

Niagaran: Bridgeport; 111:
Illaenus imperator Hall.

1861. Illaenus imperator. Hall, Rep. Prog. Geol. Surv. Wis., for

1860, p. 49.

Niagara: Racine, Wis.

1862. Illaenus imperator. Hall. Geol. Surv. Wis., vol. 1, p. 433

(no description).

Niagara: \"£isconsin.

1865. Illaenus imperator. Hall, /Vdv. Sheets, 18th Rep. N. Y. St.
Cab. Nat. Hist., p. 28.

Niagara: Racine and Waukesha, Wis.

1867. Illaenus imperator. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist., p. 332, pi. 22, figs. 15-17; pi. 23, figs. 2-3.

N iagara : Wisconsin .

1870. Illaenus imperator. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist (rev. ed.), p. 420, pi. 22, figs. 15-17; pi. 23, figs. 2-3.

Niagara: Wisconsin.

1882. Illaenus imperator. Whitf., Geol. Wis., voL 4, p. 306, pi.
21, figs. 4-5.

Niagara: Burlington, Wis.

1907. Illaenus imperator. Weller, This Bulletin, p. 225, pi. 16, figs.
13-16.

Niagaran: Joliet, 111.
Illaenus insignis Hall.

1865. Illaenus insignis. Hall, Adv. Sheets, 18th Rep. N. Y. St.
Cab. Nat. Hist., p. 27, figs. 5-6.

Niagara: Waukesha and Milwaukee, Wis.; Illinois.
. 1867. Illaenus insignis. Hall, 20th Rep. N. Y. St. Cab. Nat.
Hist., p. 331, figs. 5-6, pi. 22, figs. 13-14.
Niagara: Waukesha and Milwaukee, Wis.

2O4 THE CHICAGO ACADEMY OF SCIENCES.

1870. Illaenus insignis. Hall, 20th Rep. N. Y. St.' Cab.^Nat.
Hist. (rev. ed.), p. 419, figs. 10-11, pi. 22, figs. 13-14~

Niagara: Waukesha and Milwaukee, Wis.

1882. Illaenus insignis. Whitf., Geol. Wis., vol. 4, p. 305, pi. 21,
figs. 6-10.

Niagara: Burlington, Racine, Waukesha, near Mil-
waukee and near Wauwatosa, Wis.
1887. Illaenus insignis. Foerste, 15th Ann. Rep. Geol. and Nat.

Hist. Surv. Minn., p. 481.

1895. Illaenus insignis. Foerste, Geol. Surv. Ohio, vol. 7, p. 525,
pi. 26, fig. 11.

Clinton: Ohio.

1904. Illaenus insignis. Kindle, 28th Ann. Rep. Dep. Geol. and
Nat. Res., Indiana, p. 479, pi. 22, figs. 1-5.

Niagara: Connor's Mill, Delphi, Georgetown, Fishers -

burg and Wabash, Ind.
1907. Illaenus insignis. Weller, This Bulletin, p. 215, pi. 17, figs, 1-5.

Niagaran: Hawthorn, and Bridgeport, 111.
Illaenus insignis Meek, see Illaenus sprin&fieldensis Meek.
Illaenus ioxus Hall.

1843. Bumastus barriensis. Hall, Geol. N. Y., pt. 4, p. 102, fig.
4, p. 101: tab. org. rem., 10, fig. 4, and 19 fig. 2.

Niagara: Rochester, N. Y.

1852. Bumastus barriensis,. Hall, Pal. N. Y., vol. 2, p. 302, pi.
66, figs. 1-15.

Niagara: Lockport and Rochester, N. Y.

1860. Bumastus barriensis. Roemer, Sil. Faun. West. Tenn.,
p. 83, pi. 5, fig. 23.

Silurian :, Tennessee.

1862. Illaenus (Bumastus}' barriensis ? Hall, Geol. Surv. Wis.,
vol. 1, p. 433 (no description).

Niagara: Milwaukee, Waukesha, Racine, etc., Wis.
1865. Illaenus (Bumastus} barriensis. Hall, Adv. Sheets, 18th
Rep. N. Y. St. Cab. Nat. Hist., p. 28.

Niagara: Racine, Waukesha, Wauwatosa, etc., Wis.
1867. Illaenus (Bumastus} barriensis. Hall, 20th Rep. N. Y. St.
Cab. Nat. Hist., p. 332.

Niagara: Racine, Waukesha and Wauwatosa, Wis.
1867. Illaenus ioxus. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.,
p. 387,- fig., pi. 22, figs. 4-11, pi. 23, fig. 1.

Niagara: Wisconsin.

1S70. Illaenus (Bumastus} ioxus. Hall, 20th Rep. N. Y. St. Cab.
Nat. Hist. (rev. ed.), p. 420, fig. 12, pi. 22, figs. 4-10.

Niagara: Racine, Waukesha and Wauwatosa, Wis.
1882. Illaenus (Bumastus} ioxus. Hall, llth Rep. Dep. Geol. and
Nat. Hist., Indiana, p. 335, pi. 38, figs. 13-14.

Niagara: Waldron, Ind.

1882. Illaenus ioxus. Whitf., Geol. Wis., vol. 4, p. 304, pi. 21,
figs. 11-12.

Niagara: Hartford, Pewaukee, Genesee, Racine, Green-
field, Waukesha, Grafton, and Sturgeon Bay, Wis.
Guelph: Cedarville, Wis.

THE NATURAL HISTORY SURVEY. 2C>5

1883. Illaenus (Bumastus} ioxus. Hall, Trans. Albany Inst., vol.
10, p. 76.

Niagara: Waldron, Ind.
1890. Illaenus ioxus. Foerste, Proc. Bost. Soc. Nat. Hist., vol.

24, p. 268, pi. 5, fig: 20.

1901. Illaenus ioxus. van Ing., School of Mines Quart., vol. 23,
p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
1901. Illaenus ioxus. Grabau, Bull. N. Y. St. Mu's., No. 45, vol.
9, p. 223, fig. 154*

Rochester shale: Niagara, Lockport, etc., N. Y.
1904. Illaenus ioxus. Kindle, 28th Ann. Rep. Dep. Geol. and
Nat. Res. Indiana, p. 480, pi. 22, fig. 7; pi. 23, fig. -3.

Niagara: Pendleton, Fishersburg, Helm's Mill and

Connor's Mill, Ind.
1907. Illaenus ioxus. Weller, This Bulletin, p. 222, pi. 18, figs. 1-3.

Niagaran: Joliet, 111.

Illaenus madisonianus Whitf., see Illaenus niagarensis Whitf.
Illaenus niagarensis Whitf.

1880. Illaenus niagarensis. Whitf., Ann. Rep. Wis. Geol. Surv.,
for 1879, p. 68.

Niagara : Wisconsin.

1882. Illaenus madisonianus. Whitf., Geol. Wis., vol. 4, p. 307.
pi. 20, figs. 8-9.

Niagara : Wisconsin.

1885. Illaenus madisonianus. Foerste Bull. Sci. Lab. Den. tlniv.,
vol. 1, p. 106, pi. 14, figs, la-lb, 2a-2b.

Clinton: Dayton, Ohio.

1887. Illaenus madisonianus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 93, pi. 8, figs. 8, 9, 10, lOa.

Clinton: Near Dayton, Ohio.

1895. Illaenus madisonianus. Foerste, Geol. Surv. Ohio, vol. 7,
p. 526, pi. 26, figs. 1-2, varieties, pi. 27, figs. 7-10.

Clinton: Ohio.

1901. Illaenus madisonianus. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
1907. Illaenus niagarensis. Weller, This Bulletin, p. 219, pi. 19,
figs. 7-11.

Niagaran: Joliet and Lockport, 111.
Illaenus pterocephalus Whitf.

1878. Illaenus pterocephalus. Whitf., Ann. Rep. Wis. Geol. Surv.,
for 1877, p. 87.

Niagara: Pewaukee, Wis.

1882. Illaenus pterocephalus. Whitf., Geol. Wis., vol. 4., p. 309,
pi. 20, figs. 10-12.

Niagara: Pewaukee, Wis.
Illaenus springfieldensis Meek.

1873. Illaenus (Bumastus') -insignis ? Meek, Pal. Ohio, -vol. 1, p.
189, figs. A-B; pi. 15, figs. 5a-c.
Niagara: Springfield, Ohio.

2O6 THE CHICAGO ACADEMY OF SCIENCES.

1873. Illaenus springfieldensis. Meek, Pal. Ohio, vol. 1, p. 129'.
IHaenus transversalis Weller.

1907. Illaenus transversalis. Weller, This Bulletin, p. 224, pi. 16^'
figs. 7-9.

Niagaran: Bridgeport, 111.
Illaenus worthenanus W. & M., see Illaenus armatus Hall.

LICHAS Dalm., 1826.

Lichas boltoni Hall, see Arctinurus boltoni (Bigsby).

Lichas boltoni var. occidentalis Hall, see Arctinurus occidentalis (Hall)

Lichas breviceps Hall, see Metopolichas breviceps (Hall).

Lichas breviceps ? Hall, see Dicranopeltis decipiens (W. & M.).

Lichas byrnesanus M. & G., see Corydocephalus byrnesanus (M. & G.).

Lichas decipiens W. & M., see Dicranopeltis decipiens (W. & M.).

Lichas emarginatus Hall, see Dicranopeltis decipiens (W. & M.).

Lichas hanoverensis M. & G.. see Corydocephalus phlyctainodes (Green).

Lichas nereus Hall, see Arctinurus nereus (Hall) .

Lichas obvius Hall, see Arctinurus obvius (Hall).

Lichas ptyonurus H. & C., see Corydocephalus ptyonurus (H. & C.).

Lichas pugnax W. & M., see Metopolichas pugnax (W. & M.).

METOPOLICHAS Gurich, 1901.

Metopolichas breviceps (Hall).

1864. Lichas breviceps. Hall, Trans. Albany Inst., vol. 4, p. 222.

Niagara: Waldron, Ind.

1875. Lichas breviceps. H. & W., Pal. Ohio, vol. 2, p. 156, pi. 6,
fig. 17.

Niagara: Yellow Springs, Ohio.

1877. Lichas breviceps. Hall, 28th Rep. N. Y. St. Mus. Nat. Hist,
(doc. ed.), pi. 34, fig. 1-7.

Niagara: Waldron, Ind.

1879. Lichas breviceps. Hall, 28th Rep. N. Y. St. Mus. Nat. Hist.
(mus. ed.), p. 197, pi. 34, figs. 1-7.

Niagara: Waldron, Ind.

1882. Lichas breviceps. Hall, llth Rep. Dep. Geol. and Nat. Hist.,
Indiana, p. 343, pi. 36, figs. 1-7.
. Niagara: Waldron, Ind.
18§5. Lichas breviceps. Foerste, Bull. Sci. Lab. Den. Univ., vol.

1, p. 112, pi. 13, figs. 26a-d.

Clinton: Near Dayton and at, New Carlisle, Ohio.
1887. Lichas breviceps. Foerste, Bull. Sci. Lab. Den. Univ., vol.

2, p. 98, pi. 8, figs. 18-19.
Clinton: Near Dayton, Ohio.

1895. Lichas breviceps. Foerste, Geol. Surv. Ohio, vol. 7, p. 529,
pi. 25, figs. 26a-e; pi. 27, figs. 18-19.

Clinton: Ohio.
Metopolichas ferrisi Weller.

1907. Metopolichas ferrisi. Weller, This Bulletin, p. 244, pi. 22.,
figs. 12-13.

Niagaran: Near Channahon, Will Co., 111.

THE NATURAL HISTORY SURVEY. 2O/

Metopolichas pugnax (W. & M.)-

1865. Lichas pugnax. W. & M., Mem. Bost. Soc. Na,t. Hist., vol.

1, p. 103, pi. 3, figs.'lOa-c.
Niagara: Bridgeport, 111.

1870. Lichas pugnax. Hall, 20th Rep. N. Y. St. Cab. Nat. Hist.
(rev. ed.), p. 424, pi. 25, fig. 20; also p. 433.

Niagara: Bridgeport, 111.

1907. Metopolichas pugnax. Weller, This Bulletin, p. 242, pi. 21,
figs. 1-4.

Niagaran: Bridgeport, 111.

ODONTOPLEURA Emm., 1839.

Odontopleura illinoiensis Weller.

1907. Odontopleura illinoiensis. Weller, This Bulletin, p. 253, pi. 23,
figs. 5-6.

Niagaran: Near Joliet, 111.
Odontopleura ortoni (Foerste).

1885. Acidaspis . Foerste, Bull. Sci. Lab. Den. Univ., vol. 1,

p. 101, pi. 13, fig. 23.

Clinton: New Carlisle, Ohio.
1887. Acidaspis ortoni. Foerste, Bull. Sci. Lab. Den. Univ., vol.

2. p. 90, pi. 8, fig. 1.

Clinton: Near New Carlisle, Ohio.

1895. Acidaspis ortoni. Foerste, Geol. Surv. Ohio, vol. 7, p. 522,
1 pi. 25, fig. 23, pi. 27, fig. 1.

Clinton : Ohio.

1901. Odontopleura ortoni. van Ing., School of Mines Quart., vol.
23, p. 39.

Silurian: St. Clair Spring, Independence Co., Ark.
1904. Odontopleura ortoni. Kindle, 28th Ann. Rep. Dep. Geol.
and Nat. Res., Indiana, p. 481, pi. 24, figs. 16-19.

Niagara: Georgetown and Pendleton, Ind.
Odontopleura arkansana van Ingen.

1901. Odontopleura arkansana. van Ing., School of Mines Quart.,
vol. 23, p. 40, fig. 9.

Silurian:. St. Clair Spring, Independence Co., Ark.

PHACOPS Emm., 1839.

Phacops handwerki Weller.

1907. Phacops handwerki. Weller, This Bulletin, p. 271, pi. 24,
figs. 6-7.

Niagaran: Near Lemont, 111.

Phacops limulurus (various authors), see Dalmanites limulurus (Green).
Phacops pulchellus Foerste.

1885. Arionellus . Foerste, Bull. Sci. Lab. Den. Univ., vol.

1, p. 114, pi. 14, fig. 3.

Clinton: Near Dayton, Ohio.

1887. Phacops pulchellus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 99, pi. 8, figs. 4, 20, 21.
Clinton: Near Dayton, Ohio.

2O8 THE CHICAGO ACADEMY OF SCIENCES.

1890. Phacops pukhellus. Foerste, Proc. Bost. Soc. ,Xat. Hist.,
' vol. 24, p. 268, pi. 6, figs. 20-21.

Clinton: Cumberland Gap, Term.

1895. Phacops trisulcatus. Foerste, Geol. Surv. Ohio, vol. 7, p'.
529, pi. 26, fig. 3, pi. 27, figs. 4, 20, 21, pi. 31, figs. 20-21.

Clinton: Ohio.

1904. Phacops cf. pukhellus. Kindle, 28th Ann. Rep. Dep. Geol.
and Nat. Res., Indiana, p. 484, pi. 24, figs. 9, 12.

Niagara: Connor's Mill, Georgetown and Pendleton,

Ind.

Phacops trisulcatus Foerste, see Phacops pulchellus Foerste.
Phacops trisulcatus Hall.

1843. Calymene ? trisulcata. Hall, Geol. N. Y., pt. 4, p. 74, fig. 9,

p. 72; tab. org. rem. 8, fig. 9.

1852. Phacops trisulcatus. Hall, Pal. N. Y., vol. 2, p. 300, pi. 66y
figs. 3a-b.

Clinton : New York.

PLATYNOTUS Con., 1838.

Platynotus boltoni Con., see Arctinurus boltoni (Bigsby).
PARADOXIDES Brong., 1822.
Paradoxides boltoni Green, see Arctinurus boltoni (Bigsby).

PARADOXUS
Paradoxus boltoni Bigsby, see Arctinurus boltoni (Bigsby).

PROETUS Stein., 1831.
Proteus channahonensis Weller.

1907. Proteus channahonensis. Weller, This Bulletin p. 228, pi. 20,
figs. 6-7.

Niagaran: Near Channahon, Will Co., 111.
Proetus corrugatus van Ing.

1901. Proetus corrugatus. van Ing., School of Mines Quart., vol.
23, p. 54, figs. 16-17.

Silurian: St. Clair Spring, Independence Co., Ark.
Proetus corycaeus (Conrad).

1842. Asaphus corycaeus. Conrad, Jour. Acad. Nat. Sci. il.,

1st ser., vol. 8, pt. 2, p. 277, pi. 16, fig. 15. p^

Niagara shale: Lockport, N. Y.

1843. Asaphus coryphaeus.. Hall, Geol. N. Y., pt. 4, tab. org. rem.

19, fig. 3.'

Niagara: Lockport, N. Y.

1852. Proetus corycaeus. Hall, Pal. N. Y., vol. 2, p. 315, pi. 67,
fig. 15.

Niagara : Lockport, N. Y.
Proetus depressus Weller.

1903. Proetus ? depressus. Weller, Pal. N. J., vol. 3, p. 249, pi.
22, fig. 27.

Decker Ferry: Nearpass Quarry, N. J.
Proetus determinatus Foerste.

1885. Bathyurus . « Foerste, Bull. Sci. Lab. Den. Univ., voK

1, p. 103, pi. 14, fig. 5.

Clinton : Near Dayton, Ohio.

THE NATURAL HISTORY SURVEY. 2OQ

1887. Proetus determinalus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 2, p. 91, pi. 8, figs. 2, 3, 3a.

Clinton: Near Dayton, Ohio.

1895. Proetus determinatus. Foerste, Geol. Surv. Ohio, vol. 7,
p. 523, pi. 26, fig. 5, pi. 27, figs. 2, 3, 3a.

Clinton: Ohio.
Proetus? handwerki Weller.

1907. Proetus ? handwerki. Weller, This Bulletin, p. 229, pi. 20,
figs. 8-9.

Niagaran: Near Lemont, 111.
Proetus pachydermatus Barrett.

1878. Proetus pachydermatus. Barrett, Am. Jour. Sci., 3rd ser.,
vol. 15, p. 371.

Coralline limestone. Nearpass Cliff, N. J.

1903. Proetus pachydermatus. Weller, Pal. N. J., vol. 3, p. 248,
pi. 22. figs. 16-21. .

Decker Ferry: Nearpass Quarry, N. J.
Proetus spinosa Weller.

1903. Proetus ? spinosa. Weller, Pal. N. J., vol. 3, p. 250, pi. 22.
fig. 26.

Decker Ferry: Nearpass Quarry, N. J.
Proetus stokesii Hall.

1852. Proetus stokesii. Hall, Pal. N. Y., vol. 2, p. 316, pi. 67,
figs. 13-14.

Niagara: Lockport, N. Y.
Proetus subannulatus van Ing.

1901. Proetus subannulatus.. van Ing., School of Mines Quart.,
N vol. 23, p. 57, fig. 18, p. 54.

Silurian: St. Clair Spring, Independence Co., Ark.

SPHAEREXOCHUS Beyr., 1845.

Sphaerexochus mirus (various authors), see Sphaerexochus romingeri

Hall.

Sphaerexochus pisum Foerste, see Deiphon forbesi Barr.
Sphaerexochus romingeri f Hall.

1860. Sphaerexochus mirus. Roemer, Sil. Faun. West. Tenn,, p.
81, pi. 5, fig. 20.

Silurian: Tennessee.

1867. Sphaerexochus romingeri. Hall, Geol. Surv. Wis., vol. 1,
p. 434 (no description).

Niagara: Milwaukee and Waukesha, Wis.

1865. Sphaerexochus mirus. Hall, Adv. Sheets, 18th Rep. N. Y.
St. Cab. Nat. Hist., p. 30.

Niagara: Milwaukee, Racine, Waukesha and Green-
field, Wis.; Bridgeport, 111. ,

1867. Sphaerexochus mirus. Hall. 20th Rep. N. Y. St. Cab. Nat.
Hist., p. 334.

Niagara: Milwaukee, Racine, Waukesha and Green-
field, Wis. ; Bridgeport, 111.

2IO

THE CHICAGO ACADEMY OF SCIENCES.

1867. Sphaerexochus romingeri. Hall, 20tH Rep. N. Y. St. Cab.
Nat. Hist., p. 375,tpl. 21, figs. 4-7.

Niagara : Wisconsin and Illinois.

1870. Sphaerexochus romingeri. Hall, 20th Rep. N. Y. St. Cab.
Nat. Hist. (rev. ed.), p. 425, pi. 21, figs. 4-7.

Niagara: Wisconsin and Illinois.

1875. Sphaerexochus romingeri. W. & M., Geol. Surv. 111., vol. 7,
p. 510, pi. 24, fig. 4.

Niagara: Joliet, 111.

1882. Sphaerexochus romingeri. Whitf., Geol. Wis., vol. 4, p. 311,
pi. 21, figs. 1-3.

Niagara: Racine and Waukesha, Wis.

1888i Sphaerexochus mirus. Foerste, Bull. Sci. Lab. Den. Univ.,
vol. 3, p. 121, pi. 13, fig. 6.

Guelph: Cedarville, Ohio.

1901. Sphaerexochus romingeri. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
. 1904. Sphaerexochus romingeri. Kindle, 28th Ann. Rep. Dep.
• Geol. and Nat. Res., Indiana, p. 483, pi. 22, figs. 8-9, 12-15.

Niagara: Northern Indiana.

1907. Sphaerexochus romingeri. Weller, This Bulletin, p. 266, pi.
24, figs. 16-19.

Niagaran: Bridgeport, Lernont, Romeo, Joliet, etc., 111.

STAUROCEPHALUS Barrande, 1846.
Staurocephalus murchisoni Barr.

1891. Staurocephalus murchisoni. van Ing., School of Mines Quart.,
vol. 23, p. 35 (no description).

Silurian: St. Clair Spring, Independence Co., Ark.
Staurocephalus obsoleta Weller.

1907. Staurocephalus obsoleta. Weller, This Bulletin, p. 270, pi.
24, fig. 15.

Niagaran: Near Lemont, 111.

.TRIMERUS Green, 1832.
Trimerus delphinocephalus Green, see Homalonotus delphinocephalus

(Green.)

GLOSSARY

Anterior — Situated in front.

Anterior limb of the facial suture — That portion of the facial suture
lying in front of the eye. i

Appendage — A jointed process, two of which were borne by each seg-
ment of the trilobite body.

Axial furrows — Furrows or depressions bounding the axial or median
longitudinal lobe of the trilobites; same as dorsal furrows.

Axis — The median longitudinal lobe of the trilobites.

Carapace — The hard shell covering the -dorsal surface of the trilobite.

Cephalon — The head of trilobites

Cheeks — The two lateral portions of the head or cephalon of the trilo-
bites, divided into fixed and free cheeks by the facial suture.

Compound eyes — EyeS commonly present upon- the free cheeks of trilo-
bites; they are made up of a large number of smaller facets.

Cranidium — The portion of the head or cephalon of the trilobite lying
between the facial sutures, comprising the glabella and the fixed
cheeks.

Distal — Away from the center.

Dorsal — Pertaining to the back.

Dorsal furrows — The furrows or depressions bounding the axial or medial
longitudinal lobe of the trilobites; same as the axial furrows.

Doublure — The infolded margin of the trilobite test.

Endopodite — The inner of the two distal divisions of the typical crusta-
cean appendage.

Exopodite — The outer of the two distal divisions of the the typical crus-
tacean appendage.

Eye lines — A pair of raised lines reaching from the sides of the glabella
to the compound eyes or the ocelli of Some trilobites.

Eye lobes — Lobes of the xfixed cheeks within the inner margins of the
eyes. The palpebral lobes.

Facial suture — The suture in the head or cephalon of the trilobite separat-
ing the fixed from the free cheeks.

Fixed cheek — The portion of the cephalon or head of the trilobite lying
between the glabella and the facial suture.

Free cheek — Lateral portion of the cephalon or head of the trilobite,
lying beween the facial suture and the lateral cephalic border.

Furrows — Grooves or narrow depressions.

Genal angles — The postero-lateral angles of the cephalon or head of the
trilobites. *

Genal spines — The posterior prolongation into spines of the genal angles
of trilobites.

Glabella — The central or axial portion of the cephalon or head of trilo-
bites.

Gnathobase — The basal joint of the ventral cephalic appendages of
trilobites, modified to function as mouth parts.

Holochroal eyes^Compound eyes of the trilobites whose visual area is
covered with a continuous horny integument.

Hypostome — The under lip of trilobites.

212 THE CHICAGO ACADEMY OF SCIENCES.

Lateral — Pertaining to or proceeding from the side.

Lateral furrows — The transverse furrows or grooves of the trilobite
glabella, sometimes continuous across the glabella and sometimes
greatly modified.

Limb of pygidium — The lateral areas of the trilobite pygidium exclusive
of the axis.

Marginal border — The thickened or otherwise differentiated external
border of the cephalon and pygidium of the trilobites.

Marginal furrow — The groove or depression lying just within the mar-
ginal border of the cephalon and pygidium of the trilobites.

Neck segment — The occipital segment.

Ocelli — The simple eyes present upon the fixed cheeks of some trilo-
bites.

Occipital furrow — The posterior transverse groove or furrow of the
glabella of trilobites, lying in front of the occipital segment.

Occipital lobes — Small, lateral lobes of the occipital segment present in
some trilobites, which are morphologically different from the lateral
lobes of the glabella.

Occipital segment — The posterior transverse segment of the trilobite
glabella, lying between the posterior margin and the occipital fur-
row.

Ocular ridges — Ridges extending from near the anterior extremity of the
glabella to the eyes in some trilobites.

Ontogeny — The life history of an individual organism.

Palpebral lobes — Lobes of the fixed cheeks within the inner margins of
the eyes. The eye lobes.

Plurae — The two lateral longitudinal lobes of the trilobite, applied
' chiefly to the thoracic region and the pygidium.

Post axial region — The flattened area occupying the median portion of
the pygidium of some trilobites, posterior to the elevated axis.

Post cephalic margin — The posterior margin of the head or cephalon.

Posterior — Situated behind.

Posterior cheek furrow — The marginal furrows or grooves present in
some trilobites, which extend across the cheeks from the extremi-
ties of the occipital furrow of the glabella towards the genal angles.

Posterior limb of facial suture — That portion of the facial suture ex-
tending from the posterior extremity of the eye to the posterior or
lateral margin of the cephalon.

Protaspis — The earliest recognized stage in the development of the trilo-
bite test.

Protopodite — The basal portion of the typical crustacean appendage
whieh^supports distally the exopodite and the endopodite.

Proximal — Towards the center.

Pygidium — The tail or posterior region of the trilobite test.

Schizochroal eyes — Compound eyes of the trilobites in which the visual
area is occupied by small openings for the separate facets.

Test — Thejhard outer covering of the trilobite.

Thorax — The central segmented region of the body of the trilobite.

Ventral — Pertaining to the under surface.

DESCRIPTION OF GENERA AND SPECIES* ,

Order I. HYPOPARIA Beecher.

"Free cheeks forming a continuous marginal ventral plate
of the cephalon, and in some forms also extending over the
dorsal side at the genal angles. Sutures ventral, marginal or
submarginal. Compound paired eyes absent; simple eyes may
occur on each fixed cheek, singly or in pairs." — Beecher, Zittel-
Eastman Text Book of Paleontology, p. 623.

Family 1. HARPEDIDAE Barrande.

"Cephalon large, with a broad marginal expansion or
limb; glabella short and prominent. Free cheeks ventral,
continuous; suture marginal, following the outer edge of the
limb. Paired simple eye-spots or ocelli, single or double, at
the distal ends of wrell-marked eye-lines on the fixed cheeks,
extending outward from the glabella. Thorax of from twenty-
five to twenty-nine segments, with long grooved pleura. Pyg-
idium (in Harpes) very small, composed of but three or four
segments. ' ' Beecher, Zittel- Eastman Text Book of Paleontology ,
p. 625.

Genus i. HARPES Goldfuss, 1839.
Cephafon large, horse-shoe shaped, strongly convex cen-
trally with a broad flattened marginal expansion or limb which
is produced posteriorly into long, flat, pointed genal spines.
Glabella short, prominent, rounded or sub-truncate in front
with a single pair of small lateral lobes posteriorly or a single
transverse segment. Ocelli situated on the cheeks on either
side of the glabella near its anterior end and connected with the
glabella by raised eye-lines. Thorax conspicuously trilobate,
thoracic segments twenty- five to twenty-nine, with long grooved
pleura. Pygidium very small, composed of but three or four
segments.

Harpes telleri, n. sp., pi. xx, fig. 2.

Description. Cephalon horse-shoe-shaped, with a broad,
slightly concave marginal border or limb which passes pos-
teriorly, with its entire width, into the prominent flat genal
spines; the width of the limb at the sides and front of the head
is equal, but the genal processes become gradually narrower

*For bibliography of the species described here, see the bibliographic list in the earlier
portion of the Bulletin.

214 THE CHICAGO ACADEMY OF SCIENCES.

posteriorly. At the inner margin of the limb, a narrow, deeply
impressed furrrow separates it from the median convex portion
of the head, laterally and anteriorly. The median portion rises
vertically or is even slightly overhanging from the bottom of
the bounding furrow to a height a little above the highest por-
tion of the limb, the direction of the surface then changes ab-
ruptly to a gently convex curve nearly to the central elevated,
axial portion or glabella which is surrounded by a slightly
flattened area.' The glabella is narrow and is abruptly elevated;
posteriorly it is produced laterally into a pair of flattened,
rounded lobes but little differentiated from the cheek surfaces.
Upon each cheek a little back from the anterior extremity of
the glabella and nearly half way between it and the furrow at
the margin of the limb, is a small conical point-like ocellus slightly
elevated above the general surface.

Thorax and pygidium unknown.

The dimensions of the type specimen are: width 19.5 mm.,
total length of head to genal extremities, approximately 24 mm.,
length of head along median line 12 mm., width of limb in front
5 mm., length of glabella 5.5 mm., width of glabella in front of
basal lateral lobes 3.3 mm., distance between ocelli 5.5 mm.

Remarks. This species has not yet been observed within
the Chicago area, the type specimens being from Wisconsin.
It may, however, be looked for at Chicago. The species is the
first representative of the genus which has been recognized in
the Silurian faunas of America, although members of the genus
are not uncommon in the European faunas of similar age.
This American species more or less closely resembles several
European forms, but it is characterized by the deep furrow at
the inner margin of the limb.

The species is named in honor of Mr. E. E. Teller, of Mil-
waukee, Wisconsin, in whose collection the type specimen is
preserved.

Locality. Milwaukee, Wis.

Order. II. OPISTHOPARIA Beecher.

"Free cheeks generally separate, always bearing the genal
angles. Facial sutures extending forward from the posterior
part of the cephalon within the genal angles, and cutting the
anterior margin separately, of more rarely uniting in front
of the glabella. Compound paired holochroal eyes on free
cheeks, and well developed in all but the most primitive family."
— Beecher, Zittel-Eastman Text Book of Paleontology, p. 266.

THE NATURAL HISTORY SURVEY. 215

Family 2. AS APHID AE Emmrich.

"Cephalon and pygidium well developed; glabella often
obscurely limited. Free cheeks usually separate. Facial sutures
extending forwards from the posterior edge of the cephalon
within the genal angles, and cutting the lateral or anterior
margins, occasionally uniting in front of the glabella. Eyes-
usually present, smooth, w^ell developed, sometimes of very
considerable size, even occupying the entire surface of the
free cheeks. Thorax generally composed of eight or ten seg-
ments, but varying from five to ten. Pygidium large, often
with wide doublure." — Beecher, Zittel-Eastman Text Book of
Paleontology, p. 629.

Genus 2. ILLAENUS Dalman, 1826.

Complete body sub-elliptical in outline, the trilobation
often nearly obsolete. Cephalon large, strongly convex,
smooth except for the slightly impressed dorsal furrows and
the eyes. Eyes large, situated laterally and posterior to the
mid-length of the head, their surfaces sometimes protruding
beyond the' lateral margins of the head. Anterior limb of the
facial suture describing a gentle, slightly sigmoidal curve from
the anterior margin of the cephalon to the eyej, the posterior
limb curving rather abruptly laterally from the posterior ex-
tremity of the eye to the post-cephalic margin. Free cheeks
usually triangular. Thorax transversely convex, with nine or
ten broad segments. Pygidium similar to the riead in form
and size, but usually less convex, the axis short and inconspicu-
ous, sometimes obsolete.

Illaenus insignis Hall, pi. xvii, figs. 1-5.

Description. Cephalon large, parabolic in outline, strongly
convex, the most prominent point on the median line between
the centers of the eyes; anterior and lateral margins slightly
produced to form a narrow, thin, projecting, lip-like border.
Dorsal furrows moderately impressed, extending from the
posterior margin of the head nearly to the anterior border
where they terminate in shallow, pit-like depressions. 'Eyes-
large, sub-crescentiform, convex both vertically and horizon-
tally, from two and a half to three times as long as high, situated
a little obliquely, the posterior extremities being a little higher
than the anterior, with the center of the eye a little below the
center of the total height of the cephalon and a little nearer to
the posterior than to the lateral border. Eye-lobes sloping.

2l6 THE CHICAGO ACADEMY OF SCIENCES.

downward laterally from the dorsal furrows, the eyes mod-
erately protuberant with a rather broad, shallow, rounded,
ill-defined furrow beneath them upon the free cheeks. Free
cheeks rather large, the posterior limb of the facial suture
curving backward and downward from the posterior extremity
•of the eye, the anterior limb bending downward and forward
with a slight concave curve and intersecting the margin almost
directly in front of the eyes, it then follows the margin for a
short distance towards the front before curving to the ventral
side where it continues around the anterior extremity of the
cephalon parallel with the margin and joins with the furrow
from the opposite side.

Pygidium semi-ellipitical in outline, strongly convex,
greatest convexity near the middle, slightly flattened at the
.antero-lateral angles, with no indication of axial furrows or of
-a differentiated axis, but usually marked by a slight, median,
longitudinal ridge from near the center to the posterior ex-
tremity.

The dimensions of a large and nearly perfect cephalon are:
width 76 mm., length 35.5 mm., convexity 47 mm.; the dimen-
sions of a pygidium are: length 56 mm., width 54 mm., con-
vexity 25 mm.

Remarks. Specimens have been identified as /. insignis, and
their relations discussed by four authors since the species was
originally described by Hall. In the original description the
character of the strongly marked, elongated dorsal furrows ter-
minating in distinct rounded pits is considered as the most char-
acteristic feature of the species, and this character is well shown
in the specimens from Haw.thorn, where the species occurs in
great numbers almost to the exclusion of other members of the
.genus. These Hawthorn specimens, however, are constantly
more pointed at the front of the cephalon than Hall's illustra-
tions would indicate, but none of Hall's figures give a direct
vertical view of his specimens, the cephalon being tipped back-
ward so that the anterior margin would appear less pointed
in the picture than it actually is in the specimen. The pygidia
from Hawthorn which gccur associated with the heads in about
equal numbers, agree fairly well with the pygidia figured by
Hall, but they are usually marked by a longitudinal median
ridge which is not shown- by Hall. The original pygidium used
by Hall, however, is a small one, which may account 'for the
absence of the rib. «

THE NATURAL HISTORY SURVEY. 2T/

In 1873, Meek* identified as /. insignis a species from the
dolomitic Niagaran limestone at Springfield, Ohio. He pointed
put several characters, however, in which the Ohio specimens
failed to agree with Hall's original description an'd illustrations,
and suggested that if -they should prove to be distinct that the
species might be known as /. springfieldensis. The Ohio species
certainly is distinct from the 7. insignis and the name 7. spring-
fieldensis is used to designate it in the bibliographic list in this
Bulletin. The species does possess the elongate dorsal furrows
terminating in pits, and also the lip-like margin of the cephalon
of 7.' insignis, but the head is proportionally shorter and broader,
and the eyes are more protuberant, the species approaching in
these respects more closely to 7. harrisi described in this Bul-
letin. The pygidium of 7. springfieldensis is altogether different
from that of 7. insignis, as has been pointed out by Meek.

In his Wisconsin report Whitfieldf has identified I. insignis,
but the cephalon he illustrates lacks the strong, elongate dorsal
'furrows terminating in pits so characteristic of 7. insignis, and
the pygidium, although possessing the correct outline and the
median ridge of 7. insignis, has a very different profile, the
greatest convexity being much more posterior in position than^
in the Hawthorn specimens. In all probability Whi.tfield's
specimens represent an undestribed species of the genus.

Foerste'sJ identification of the species from the Clinton
of Ohio is undoubtedly incorrect. His description is brief and
without figures it is not possible to determine just what his
species is. His description of the pygidium agrees more closely
with Whit field 'S' Wisconsin form, than with the original 7. in-
signis.

Kindle's§ identification of the species from northern Indiana
is not entirely satisfactory. Neither his illustration nor his
description indicate fully the characters of his specimens; they
possess the elongate dorsal furrows of the species terminating
in pits, and seem to have the lip-like extension of the anterior
margin, but the cephalon is less pointed in front than the Haw-
thorn specimens, and the pygidia are more rounded behind,
and lack the median ridge.

Locality. Hawthorn, Illinois.

*Pal. Ohio, Vol. 1, p. 189.
tGeol. Wis., Vol. 4, p. 305.

£l5th Ann. Rep. Geol. and Nat. Hist. Surv. Minn., p. 481: also Geol. Surv. Ohio
Vol. 7, p. 525.

§28th Ann. Rep. Dep. Geol. and Nat. Res., Indiana, 1903, p. 479.

2l8 THE CHICAGO ACADEMY OF SCIENCES.

Illaenus harrisi, n. sp., pi. xvi, figs. 1-3.

Description. Cephalon short, large, nearly semi-circular
in outline, strongly convex, anterior and lateral margins slightly
recurved to form a narrow, slightly projecting, lip-like border.
Dorsal furrows rather strongly impressed, especially between
the eyes, elongate, extending nearly to the anterior margin
and terminating in pit-like depressions. Eyes large and promi-
nent, sub-crescentiform in outline, about three times as long
as high, convex both longitudinally and vertically, a little
oblique, the posterior extremity '-being a little higher than the
anterior, the centers situated above the middle of the total
height of the cephalon and much nearer the posterior than the
lateral margin ; eye-lobes convex, extending in a nearly hori-
zontal direction from the dorsal furrows ; the eyes strongly
protuberant with a conspicuous, broadly-rounded furrow be-
neath them upon the free cheeks. Free cheeks of moderate
size, posterior limb of the facial suture curving backward and
downward from the posterior extremity of the eye, the anterior
limb extending downward and forwrard with a slightly concave
curve and intersecting the anterior margin of the cephalon
nearly in front of the eye, it then continues around the anterior
border upon the ventral side just back of the margin, the sutures-
from the opposite sides being continuous anteriorly.

The characters of the thorax and pygidium have not been
observed.

The dimensions of a cephalon, the type specimen, are:
length 32 mm., width 54.5 mm., convexity 29.5 mm.

Remarks. This is not a common species and has been ob-
served only from Bridgeport in the Chicago area. In the elongate
dorsal furrows and projecting lip-like margin of the cephalon it
resembles /. insignis, but it differs from that species in its much
shorter cephalon and in its more strongly protuberant eyes
and eye-lobes. In its proportions it more nearly resembles /.
chicagoensis , but it may be distinguished from that species by
its elongate dorsal furrows, its projecting border and its more
prominent eyes. The nearest ally of /. harrisi seems to be 7.
springfieldensis, but the eyes are more prominent than in .that
species.

The name is given in honor of Mr. G. F. Harris, of Chicago,
who collected the type specimen and presented it to the Walker
Museum of the University of Chicago.

Locality. Bridgeport, Illinois.

THE NATURAL HISTORY SURVEY.

Illaenus cuniculus Hall, pi. xix, figs. 1-6.

Description. Cephalon elongate, longitudinally semi-ellip-
tical in outline, depressed convex, anterior and lateral margins
slightly produced to form a narrow, projecting, lip-like, mar-
ginal border. Dorsal furrows slightly impressed, short, not
extending beyond the anterior extremities of the eyes. Eyes
of moderate size, about three times as long as high, subcres-
centiform in outline, convex longitudinally and vertically,
situated nearly horizontally or with the anterior extremity
slightly higher than the posterior, their centers above the middle
of the total height of the cephalon, and much nearer the pos-
terior than the lateral margins. Eye-lobes sloping downward
from the dorsal furrows, the cheeks sloping much more abruptly
from the outer margins of the eyes to the lateral border; just
outside the outer margin of the eyes upon the free cheeks, is a
slightly impressed, rounded furrow which is deeper and more
conspicuous posteriorly. The posterior limb of the facial
suture is very short, the anterior limb describes a slightly con-,
cave curve towards the front and intersects the margin almost
directly in front of the eyes; the sutures from opposite sides
are then continuous around the anterior extremity of the cepha-
lon upon the ventral side just within the margin. Free cheeks
rather large, longer than wide.

The thorax and pygidium to be associated with this cephalon
have not been recognized.

The dimensions of a small but nearly complete cephalon
are: length 20.5 mm., width 25 mm., convexity n mm., width
between the eyes 21.5 mm. The dimensions of a large crani-
dium are: length 42.5 mm., width between the eyes 50 mm.

Remarks. This species may always be distinguished by
its depressed cephalon, by its short dorsal furrows and by the
posterior position of the eyes. In the short projecting lip-like
anterior and lateral border of the cephalon, the species resem-
bles /. insignis and /. harrisi, but the projection is less con-
spicuous upon /. cuniculus than upon either of the others.
The species does not usually grow so large as /. insignis.

Locality. Hawthorn, Illinois.

Illaenus niagarensis Whitfield, pi. xix, figs. 7-11.

Description. Entire body elliptical in outline, trilobation
obsolete. Head and pygidium nearly equal in length, the
thorax shorter than either. Cephalon sub-elliptical in outline,
moderately convex, the dorsal furrows shallow and ill-defined

22O THE CHICAGO ACADEMY OF SCIENCES.

posteriorly, becoming stronger towards the front, they originate
at the posterior margin back of the eyes and describe a curve
above the eyes terminating in rounded pits about half way
between the eyes and the anterior margin of the cephalon;
below the eyes are other curved furrows originating near the
base of the dorsal furrows with their anterior extremities nearly
meeting those of the dorsal furrows, so that each eye is nearly
surrounded by a sub-elliptical depression. The eyes are of
moderate size and are situated back of the middle line of the
head.

Thorax consisting of ten short 'segments with no indication
of dorsal furrows.

Pygidium semi-elliptical in outline, not trilobate, strongly
convex, a little flattened on top, becoming concave near the
margin posteriorly so as to form an ill-defined concave border,
which extends to the middle of the lateral margins and then
disappears.

The dimensions of an imperfect specimen are: length 56
mm., width 32 mm., length of cephalon 20 mm., convexity of
cephalon 13 onm., length of pygidium 21.5 mm.

Remarks. In the original description of this species by
Whitfield, the specific name niagarensis was used, the reason
for changing it to madisonanus in a later publication by the
same author not being apparent, since the first name used had
not been preoccupied. The entire description originally pub-
lished for /. niagarensis was copied without change as the de-
scription of /. madisonanus. If the law of priority be followed
it will be necessary to go back to the original specific designa-
tion of the species, /. niagarensis, as is done in the present Bul-
letin.

The head of this species with its elongate dorsal furrows
terminating in rounded pits, somewhat resembles /. insignis, but
it may always be distinguished from that species by the ab-
sence of the projecting lip-like marginal border in front and by
its less convexity; the outline of the head is also different from
that species, it being more nearly sub-elliptical. The pygidia
of the two species are very different, that of /. niagarensis may
be recognized by the absence of the slight median ridge and
by the concave border.

Localities. Joliet and Lockport, Illinois.
Illaenus chicagoensis, n. sp., pi. xvi, figs. 10-12.

Description. Cranidium of medium size, semi-circular in
outline, strongly convex, the convexity usually a little greater

THE NATURAL HISTORY SURVEY. 221

than the^length. Dorsal furrows well defined to points opposite
the anterior extremities of the eyes, from there describing a
gently sigmoidal curve and becoming much fainter or some-
times even obsolete, terminating in slight pits which are situa-
ted a little nearer the anterior margin than the anterior ex-
tremities of the eyes. Eye-lobes depressed below the median
portion of th,e cephalon, convex, sloping laterally. Eyes ob-
lique, describing less than ' a semi-circle, situated posteriorly,
three or four times as long as high. Posterior limb of the facial
suture directed obliquely outward, cutting the posterior mar-
gin about two-fifths the distance from the posterior extremity
of the dorsal furrow to the genal angle; anterior limb twice as
long as the posterior, describing a gentle outwardly convex
curve, cutting the anterior margin nearly in front of the anterior
extremities of the eyes. Free cheeks sub-triangular, longer
than wide, depressed in a rounded furrow around the outer
margin -of the eyes and then gently convex to the lateral and
posterior margins. Genal angles rounded.

The pygidium is depressed convex becoming slightly con-
cave near the antero-lateral angles, much wider than long, the
antero-lateral angles obtuse; posterior margin broadly and
regularly rounded with a broad doublure; the anterior margin
arcuate, slighly sinuate or notched on each side about half
way between the center and the antero-lateral angles. Just
within the anterior margin between the axial notches is a shal-
low rounded marginal furrow which becomes deeper and stronger
laterally beyond the axial notches and then becomes obsolete
before reaching the lateral margins. A slight median rib is
usually present upon the surface, extending from the posterior
margin towards the front, becoming obsolete before reaching
the anterior margin.

The dimensions of a nearly perfect cephalon .are: length
20.5 mm., width 39 mm., convexity 23 mm., width between
the extremities of the eye-lobes 3 1 mm.

Remarks. This species has usually been confused with
/. ioxus, but it differs from that species in its smaller size, the
greater convexity of its cephalon, the longer dorsal furrows,
in the more regularly rounded anterior margin of the cephalon
and in the median rib of the pygidium. The species much more
closely resembles I. armatus, differing from that species chiefly
in the absence of the short genal spines and in its greater con-
vexity. In general form the cephalon resembles that of /.
harrisi, but the eyes are less protuberant, the dorsal furrows

222 THE CHICAGO ACADEMY OF SCIENCES.

much less deeply impressed in their anterior extremities be-
yond the eyes, and it lacks the lip-like extension of the 'ante-
rior and lateral margins of that species. The cephalon differs
from /. grajtonensis in its greater convexity and in its more
nearly semi-circular outline.

Locality. Bridgeport, Illinois.
Illaenus armatus Hall, pi. xviii, figs. 4-6.

Description. Cephalon small and rather short, rather
strongly convex, semi-circular - in outline, the anterior and
lateral margins rounded and not produced into a marginal
lip-like extension. Dorsal furrows usually short and not
produced beyond the anterior extremities of the eyes, but in
some specimens they are continued anteriorly as faint depres-
sions and terminate in faintly denned pits. Eyes prominent,
their centers about the middle of the total height of the cepha-
lon, situated near the posterior margin. Eye-lobes convex,
extending in a nearly horizontal direction from the dorsal
furrows. Beneath the outer border of each eye, upon the free
cheeks, is a rather strong, rounded, depressed furrow. Free
cheeks convex, longer than wide, the genal angles produced
backward into rather short and blunt genal spines. Posterior
limb of the facial suture very short, anterior limb sloping ab-
ruptly to the antero-lateral margin.

The dimensions" of a complete cephalon are: length 13 mm.,
width 21 mm., convexity 9.5 mm., width of cranidium between
the eyes 17 mm.

Remarks. This species is usually of smaller size than other
members of the genus in -this fauna, although specimens fre-
quently occur with greater dimensions than those of the speci-
men here illustrated. The species may always be recoginzed
by its short genal spines.

Localities. Bridgeport and Lockport, Illinois.

Illaenus ioxus Hall, pi. xviii, figs. 1-3.

Description. Cephalon attaining a large size, sub-semi-
circular in outline, sub-truncate in front between the anterior
extremities of the facial sutures, moderately convex, the smaller
specimens more convex than the larger. Dorsal furrows rather
broad, but not deeply impressed, becoming obsolete beyond
the anterior extremities of the eyes. Eye-lobes depressed be-
low the median portion of the cephalon, sloping with a convex
curve from the dorsal furrows to the inner margins of the eyes.

THE NATURAL HISTORY SURVEY. 223

Eyes situated posteriorly, oblique, the posterior extremity
higher than the anterior, very narrow, the length in some large
individuals being seven times the width, but in smaller speci-
mens the proportionate length is less. Posterior limb of the
facial suture directed obliquely outward and backward; an-
terior limb more than twice as long as the posterior, describ-
ing a slightly sigmoidal curve and cutting the anterior margin
outside of a line drawn tangent to the surface of the eye. Free
cheeks large, longer than wide, the genal angles rounded, the
surface depressed below the outer margin of each eye, the space
between the depressed surface and the lower margin of the eye
being occupied by a conspicuous rounded ridge nearly as con-
spicuous as the eye itself and parallel with it.

The dimensions of a nearly perfect, large cephalon are:
length 6 1 mm., width 105 mm., convexity 46 mm., width of
cranidium between the eyes 83 mm. ( '

Remarks. This species, perhaps, has been more frequently
identified from the American faunas of Niagaran age, than any
other member of the genus, although some of these identifica-
tions are believed to be incorrect. The species was originally
described from specimens occurring in the dolomitic Niagaran
limestones of Wisconsin. The form commonly present in the
Rochester shales of the New York Niagaran, which was origin-
ally referred to the European species /. barriensis, is now usually
identified as /. ioxus, but such an identification is probably in-
correct; besides this several forms in the dolomites of north-
eastern Illinois and south-eastern Wisconsin have usually been
named I. ioxus by collectors, which are really quite distinct
species. The form described in this paper as /. chicagoensis has
been commonly referred to this species, but the true ^oxus is a
much larger and less strongly convex species, with shorter dor-
sal furrows, with the anterior margin of its cephalon sub-trun-
cate and with much narrower eyes beneath which are con-
spicuous ridges. The two most characteristic features of the
species are its large size and the sub-truncate anterior margin.

Localities. Joliet, Illinois; Racine, Wisconsin.
Illaenus graftonensis M. & W., pi. xvi, figs. 4-6.

Description. Cephalon of medium size, short, moderately
convex, transversely sub-elliptical in outline, somewhat con-
tracted posteriorly, the greatest width nearly opposite the
anterior extremities of the eyes, the dorsal surface rounding
into the ventral surface along the lateral and anterior borders-

224 THE CHICAGO ACADEMY OF SCIENCES.

Dorsal furrows short, rather broad and shallow, starting from
pit-like depressions near the posterior margin of the cephalon,
converging anteriorly and terminating nearly opposite the
anterior extremities of the eyes but becoming less sharply de-
fined anteriorly. Eye-lobes sloping gently from the dorsal
furrows; eyes large, nearly horizontal in position, situated pos-
teriorly, describing nearly a semi-circle, from four to six times
as long as high; beneath the eyes the free cheeks are strongly
depressed, the surface extending horizontally for nearly one-
half their width, then curving abruptly downward and continu-
ing to the lateral margin in a gently convex but nearly vertical
curve. Posterior limb of the facial suture very short, anterior
limb describing a sigmoidal curve and intersecting the anterior
margin of the cephalon nearly in front of the eyes.

The thorax and pygidium of this species have not been
recognized.

The dimensions of a nearly perfect cephalon are: length
26.5 mm., width 47 mm., convexity 19.5 mm., width of cranidium
between the eyes 38 mm.

Remarks. This species may always be distinguished from
its associates by the sub-elliptical outline of the cephalon, by
the posterior position of the eyes and by the conspicuous de-
pression of the inner portion of the free cheeks just below the
eyes.

Localities. Near Lemont and at Joliet, Illinois.
Illaenus transversalis, n. sp., pi. xvi, figs. 7-9.

Description^ Cephalon very short and broad, the convexity
nearly equal to the length, and the breadth more than twice
the length; anterior and lateral margins broadly rounded from
the dorsal to the ventral sides. Dorsal furrows moderately
impressed, short, scarcely reaching beyond the anterior margins
of the eyes. Eye-lobes sloping slightly from the dorsal furrows,
with a slightly convex surface. Eyes describing nearly a semi-
circle, nearly horizontal in position, their posterior extremities
approaching nearly to the posterior margin of the cephalon,
their surface convexly curved vertically and about five times
as long -as high. At the outer margins of the eyes, upon the
free cheeks, are slightly depressed, rounded furrows. Posterior
limb of the facial suture short, directed obliquely outward
toward the genal angles; anterior limb describing a slightly
sigrnoidal curve, cutting the anterior margin of the cephalon
almost directly in front of the eyes. Free cheeks broad, their dor-

THE NATURAL HISTORY SURVEY. 225

sal surface nearly horizontally directed near the margin of the
eyes, then curving with a gentle convex curvature which be-
comes much more abrupt toward the anterior and posterior
margins. Genal angles obtusely rounded.

Thorax and pygidium known not.

The dimensions of the most complete cephalon observed
are: length 16 mm., width 40.5 mm., convexity 16 mm.,. width
of cranidium between the eyes 25 mm.

Remarks. This species is easily distinguished from any of
its associates by the very broad and short form of the cephalon,
by its obtusely rounded genal angles, and by the broad rounding
of the anterior and lateral margins which extends even to the
posterior margin of the free cheeks. The species is not a com-
mon one, onjy a few incomplete heads having been observed.

Locality. Bridgeport, Illinois.

IHaenus imperator Hall, pi. xvi, figs. 13-16.

Description. Cranidium strongly convex, wider than long,
sub-elliptical in outline. Glabella broad -and not denned in
front; dorsal furrows strong, straight, slightly c6nvergent an-
teriorly, less than one-half the length of the head. Cheeks con-
vex, their surface depressed below the glabella posteriorly and
becoming confluent with the general convex surface of the
head anteriorly. Eye-lobes small and situated close to the
posterior margin of the head, produced in a nearly horizontal
direction. Form of the free cheeks unknown.

Pygidium sub-elliptical in outline, less convex than the
head, twice as wide as long, trilobate anteriorly; -the axial por-
tion occupying about one-third of the entire width along the
anterior margin, flattened on top, ill-defined posteriorly, the ,
surface becoming confluent with the general convex surface of
the pygidium at about the middle of its length.

• Surface of both head and pygidium smooth. Thorax un-
known.

The dimensions of a small cranidium are: length 20.5 mm.,,
width between the eyes 37 mm., convexity 20 mm. The
dimensions of a small but nearly perfect pygidium are: length
2 7. 5 'mm., width 55 mm., convexity 10.5 mm.

Remarks. The dimensions given above are in both cases
those of small individuals. Larger specimens of heads attain-
ing a length of 80 mm. or more are not infrequently met with,,
as well as pygidia of similar proportions, but these larger speci-
mens are usually less well preserved.

226 THE CHICAGO ACADEMY OF SCIENCES.

This species does not occur in the higher beds of the Nia-
garan limestone of the Chicago area, being most common in
certain beds at Joliet. It can be readily distinguished from all
other species of the genus in the Chicago area by reason of its
short and small eyes which are situated far back near the pos-
terior border, the dorsal furrows of the head are also stronger
than in most of the other species though in some they are much
longer, and the trilobation of the head along the posterior mar-:
gin is more strongly developed than in most of the species. The
pygidium in its broad and short form, with the anterior triloba-
tion, differs greatly from any of the other species. None of the
other Niagaran species from the Chicago area, when perfectly pre-
served, could possibly be mistaken for this one, but the heads
of /. ioxus, I. graftonensis with their short but strong dorsal
furrows, are often difficult to distinguish from /. imperator
when the free cheeks are removed and the eye-lobes injured. The
species much more closely resembles some of the Ordovician
members of the genus. It is really difficult to point out char-
acters whereby it can be readily distinguished from /. taurus
Hall of the Trenton limestone. The portions usually preserved
are also much like but very much larger than the same portions
of the little Thaleops ovatus of the Trenton limestone, but it
is not likely that the Niagaran species possessed the divergent
spine-like free cheeks of that species.

Locality. Joliet, Illinois.

Genus 3. ILLAENOIDES n. gen.

Similar to Illaenus, but with the cephalon more strongly
trilobed, with longer and stronger dorsal furrows. The eyes
are small and situated much farther forward than in Illaenus.
Thorax and pygidium as in Illaenus.

Illaenoides triloba, n. sp., pi. xvii, figs. 6-9; pi. xix, figs. 12-14.

Description. Cephalon small or of medium size', semi-
elliptical in outline, rather strongly convex, anterior margin
sometimes slightly recurved but never extended into a pro-
jecting lip-like border. Dorsal furrows broad and strong, giving
to the head a conspicuous trilobate contour, extending nearly
to the anterior margin where they gradually disappear; glabella.
smooth, convex; fixed cheeks convex, pointed at their pbs-
tero-lateral extremities, the surface exclusive of the compressed
portion forming a pair of rather large, moderately convex,
sub-elliptical lobes; eye-lobes very small and short, scarcely

THE NATURAL HISTORY SURVEY. 227

separated from the general surface of the fixed cheeks, situated
near the middle of the total length of the head; posterior limb
of the facial suture nearly straight, intersecting the posterior
margin near the rounded genal angle; anterior limb shorter
than the posterior, intersecting the anterior margin nearly in
front of the eyes. Free cheeks longer than wide, sub-triangular
in outline, the surface convex except beneath the eyes where
there is a rounded furrow nearly horizontal in direction.

Pygidium sub-elliptical in outline, moderately convex,
with the greatest convexity near the center, axial furrows want-
ing, thedateral borders somewhat depressed.

The dimensions of a rather small but nearly perfect cepha-
lon are: length 18 mm., width 26 mm., convexity II mm.,
width of cranidium between the eyes 18.5 mm. The dimen-
sions of a large pygidium are: length 29 mm., width 36 mm.,
greatest convexity 11 mm.

Remarks. This species is one of the rarer members of the
fauna of the Chicago area, and can always be distinguished from
members of the allied genus Illaenus by its more strongly trilobed
head, and its small eyes which are situated much farther for-
ward than in any of the associated species of that genus.

Localities. Bridgeport, Joliet and Chicago Drainage Canal,

near Lemont.

Family 3. PROETIDAE Barrande.

"Cephalon about one-third of the whole animal; genal
angles generally produced into spines; glabella tumid, with two
lateral basal lobes defined by oblique furrows in front of the
neck segment. Free cheeks large, separate. Sutures extending
from the posterior margin inward to the eyes, and then forward,
cutting the anterior margin separately. Eyes usually prominent,
often large. Thorax of from eight to twenty-two free segments,
with grooved pleura. Pygidium usually of many -segments ; pleural
and axial portions strongly grooved; margin entire or dentate."
— Beecher, Zittel-Eastman Text Book of Paleontology, p. 631.

Genus 4. PROETUS Stein., 1831.

Complete body sub-elliptical irr outline. Cephalon semi-
circular, with a thickened marginal border; glabella well de-
fined by the axial furrows, more or less strongly convex, narrower
and rounded in front and usually extending to the inner side
of the marginal border, lateral furrows obsolescent, basal lobes
often present, occipital furrow well marked; eyes large and promi-
nent, placed near the glabella. Thorax with well defined axis,

228 THE CHICAGO ACADEMY OF SCIENCES.

segments usually ten, with grooved pleura. Pygidium large,
semi-circular, with a thickened marginal border, the axis well
defined by the dorsal furrows, strongly elevated, distinctly
segmented, and extending to the inner side of the marginal
border, the pleural segments grooved.
Proetus channahonensis n. sp., pi. xx, figs. 6-7.

Description. Head moderately convex, semi-circular in
outline, the length of the genal spines not determined. Glabella
semi-elliptical in outline, depressed convex, denned by distinct
but not deep dorsal furrows; first and second lateral furrows
obsolete or faint, nearly transverse in direction and not con-
tinuous across the median portion of the glabella, posterior
furrows not deeply impressed but always present, they originate
at the dorsal furrows opposite the eyes and extend obliquely
inward and backward with a slight convex curve nearly to the
occipital furrow, their posterior extremities dividing the glabella
into three nearly equal parts. Occipital furrow narrow, well-
defined, including a pair of small subovate occipital lobes back
of the postero-lateral angles of the glabella. Occipital segment
rather narrow, its surface somewhat depressed below the glabella.
Surface of the cheeks sloping with an even convex curve from
the dorsal furrows laterally and anteriorly to within about one
millimeter of the margin, outside this convex slope is an even,,
flattened, continuous marginal border which continues around
the anterior margin of the head; along the posterior margin of
each cheek is a strong posterior cheek furrow which is continuous
from the dorsal furrow opposite the occipital furrow to the inner
side of the marginal border. The anterior extremity of the
glabella is separated from the marginal border by a narrow
band which is continuous with the corrvex portion of the cheeks
on either side. The fixed cheeks are narrow with the palpebral
lobes rising directly from the dorsal furrows. Free cheeks
broad, the eyes of moderate size, their surface describing about
a semi-circle, 'their anterior extremities at about the mid-length
of the glabella.

Pygidium semi-elliptical in outline, the axis strongly con-
vex, bordered by the sharp dorsal furrows, occupying nearly
one-third the entire width of the pygidium at the anterior mar-
gin, tapering posteriorly and terminating in a bluntly rounded
extremity lying within the marginal border, divided into ten
or eleven rounded annulations Vhich become faint posteriorly.
Surface of the pleura slightly flattened adjacent to the dorsal

THE NATURAL HISTORY SURVEY. 22Q

V

furrows and then Becoming moderately convex to the lateral
margins, the thickened marginal border narrow and scarcely
differentiated from the general surface, becoming a little wider
posteriorly; each slope is divided into nine segments which be-
come faint posteriorly, the last two being scarcely recognizable,
the anterior-most segments extend entirely 'to the lateral margin,
but the posterior ones terminate within the margin, in some
specimens the broader segments are faintly grooved but in others
no grooves can be detected.

The surface of both head and pygidium are smooth.

The dimensions of a nearly complete head with the excep-
tion of the genal spines and occipital segment are: width 15.5
mm., length along median line 9 mm., width of glabella at
occipital furrow 6.5 mm. The dimensions of a very perfect
pygidium are: width 10 mm., length 6.5 mm., width of axis at
anterior margin 3 mm., length of axis 5.5 mm.

Remarks. This little trilobite has been observed only in a
brown limestone near Channahon, Will County, Illinois, on the
Des Plaines river, which is believed to be the lowest Niagaran
horizon in the Chicago area. This horizon may be the same
as the so-called Clin,ton of Ohio and Indiana. The species
occurs only as detached, more or less fragmentary, heads and
pygidia. This species most closely resembles P . determinatus
Foerste, from the Ohio Clinton formation but it may be distin-
guished from that one by its more prominent glabella, especially
in front, and by the more strongly impressed dorsal furrows in
front of the glabella, and by the more strongly impressed lat-
eral glabellar furrows.

Locality. Channahon, Will County,. Illinois.

Proetus ? handwerki, n. sp., pi. xx, figs. 8-9.

Description. Head crescentiform in outline, its. width
between the extremities of the genal spines nearly three times
its length along the" median line. Glabella longitudinally (semi-
elliptical in outline, bounded by well-defined dorsal furrows*
truncated posteriorly, broadly rounded, strongly convex and
protuberant in front; frontal lobe large and almost hemispher-
ical; two pairs of lateral lobes may be detected but they are
very small ; of the two pairs of lateral furrows the first are very
faint and short, being little more than slight indentations upon
the lateral surfaces of the glabella at about the middle *of its
length, the second or posterior pair are a little more deeply im-
pressed and extend from the dorsal furrow inward and then

230 THE CHICAGO ACADEMY OF SCIENCES.

backward towards the occipital furrow, nearly surrounding the
very small posterior lateral lobes. Occipital furrow deep and
strong, the anterior slope nearly vertical, the posterior slope
less abrupt. Occipital segment narrow. Cheeks broad, their
anterior slope nearly vertical from the eyes, the lateral slopes a
little less abrupt, differentiated laterally and anteriorly into a
well-defined marginal border which is separated from the gla-
bella in front by a deep indentation beneath the protuberant
frontal lobe; posterior margins marked by posterior cheek fur-
rows which extend laterally front the occipital furrow. Fixed
cheeks narrow; anterior limb of the facial suture nearly straight,
the posterior limb curving outward and cutting the posterior
margin of the head at about one-half the distance from the dorsal
furrow to the lateral margin. Eye-lobes strongly and abruptly
elevated from the dorsal furrow, their summits being nearly
as high as the glabella. Fixed cheeks broad, the postero-
lateral angles produced into genal spines' whose entire length
cannot be determined in the type specimen. Eyes rather large
and very prominent, their surface describing nearly a semi-
circle. Thorax and pygidium unknown.

The dimensions of the type specimen are: extreme width
between the extremities of the genal spines 18 mm., length along
median line 6 mm., width of glabella 5 mm.

Remarks. This species differs from all other members of
the genus Proetus in its strongly convex and protuberant gla-
bella. In some respects its characters are as near those of the
genus Cyphaspis as Proetus, but the postero-lateral lobes of the
glabella are less prominent than in that genus and there is a
slight indication of a pair of lateral glabellar furrows in front of
the posterior pair, which are never present in Cyphaspis. It is
quite possible that the species should be considered as the type
of an undescribed genus.

The species is named in honor of Mr. J. H. Handwerk of
Joliet, who collected the specimen used as the type.

Locality. Chicago Drainage Canal near Lemont.

Genus 5. CYPHASPIS Burm., 1843.

Entire body sub-elliptical in outline. Cephalon semi-
circular with a thickened marginal border which is produced
posteriorly into genal spines. Glabella ovoid, strongly convex,
with lateral furrows obsolete except the posterior pair which
are deep and extend obliquely backward, connecting with the

THE NATURAL HISTORY SURVEY. 23!

occipital furrow and bounding on their outer sides a pair of small
ovoid orp yriform basal glabellar lobes. Eyes small, situated near
the glabella. Cheeks broad, connected anteriorly by a broad
area between the anterior extremity of the glabella and the
marginal border. Thorax with well-defined axis, segments
10 to 17 with grooved pleura. Pygidium small with a short
axis and. depressed pleura.

Cyphaspis intermedia, n. sp., pi. xx, figs. 3-5.

Description. Glabella semi-elliptical in outline, about three-
fourths the length of the head, rounded in front and truncate
behind, strongly convex longitudinally and transversely, sur-
rounded laterally and anteriorly by a narrow but well defined
dorsal furrow, the bottom of which is a little impressed below
the inner margin of the cheeks ; at the base of the glabella are a
pair of small but well-defined lateral lobes which extend about
half way up the sides of the glabella, they are separated from
the main portion of the glabella by the posterior glabellar
furrows which originate at the dorsal furrows about two-thirds
the distance from the anterior extremity of the glabella to the
occipital furrow, they describe a slight curve obliquely backward
and inward, meeting the occipital furrow about half way between
its middle point and the dorsal furrows; a second pair of lateral
furrows are slightly impressed in the sides of the glabella just
above the dorsal furrows, just in front of the mid-length of the
glabella. The occipital furrow is narrow and shallow. The
occipital segment is narrow and flat, its surface being consider-
ably depressed below the glabella. The fixed cheeks extend
nearly horizontally from the dorsal furrows into the palpebral
lobes which lie opposite the outer extremities of the posterior
glabellar furrows; in front and back of the palpebral lobes the
surface slopes away rather abruptly from the dorsal furrows
and is continuous around the anterior extremity of the glabella
as a rather broad, slightly convex, sloping area between the
dorsal furrow and the marginal border. Marginal border
sharply defined and rather broad. Free cheeks not preserved
in any of the specimens observed. Thorax and pygidium un-
known. Entire surface of the cranidium covered with fine
papillae which are more crowded upon the cheeks, being nearlv
obsolete upon the marginal border.

The dimensions of the best preserved specimen, a cranidium,
are: length 5 mm., width between the margins of the palpebral"

232 THE CHICAGO ACADEMY OF SCIENCES.

lobes, approximately, 5.7 mm., length of glabella and occipital
segment 4.25 mm., convexity of glabella 1.2 mm.

Remarks. This species is somewhat closely allied to C.
christyi Hall, from Waldron, Indiana, but it may be distinguished
from that species by the proportionately more elongate glabella,
that portion of the head in C. christyi being described as one-
half the length of the head, while in C. intermedia it is usually
a little more than three-fourths of the total length of the head
The species differs from C. clintonensis Foerste, described from
the Clinton formation of Ohio and elsewhere, in its proportion-
ately shorter glabella, the glabella of that species reaching to
the innerside of the marginal border. C. intermedia, therefore,
occupies a position between C. christyi and C. clintonensis in
respect to the proportionate length of the glabella.

Locality. Channahon, Will County, Illinois.
Family 4. BRONTEIDAE Barrande.

"Dorsal shield broadly elliptical. Cephalon less than one-
third the entire length; glabella rapidly expanding in front, with
faint indications of lobes. Free cheeks larger than the fixed-
Facial sutures extending from the posterior margin just behind
the eyes abruptly inward around the palpebral lobes, and then
diverging and cutting the antero-lateral margins separately.
Eyes crescentic. Thorax of ten segments, with ridged pleura.
Pygidium longer than cephalon or thorax; axis" very short,
with radiating furrows extending from it across the broad limb
toward the margin ; doublure very wide ; margin generally entire . ' ;
Beecher, Zittel-Eastman Text Book of Paleontology, p. 631.

Genus 6. BRONTEUS Goldf., 1839.
Entire body brbadly elliptical. Cephalon sub-semicircular;
glabella rapidly expanding anteriorly, lateral furrows and lobes
more or less obsolescent; eyes crescentic, situated back of the
middle of the head, their outer margin usually being about in
line with the lateral margins of the broad anterior portion of the
gjlabella, free cheeks larger than the fixed. Thorax with ten
segments. Pygidium very large, semi-circular or semi-elliptical
in outline with entire margin, usually longer than the cephalon or
thorax; axis very short with radiating furrows extending from
its margin across the broad, flattened pleural surfaces toward
the margin; doublure very wide.

Bronteus acamas Hall, pi. xx, fig. 1.

Description. Cephalon broad, depressed-convex, dorsal
furrows extending a little more than one-third the entire length

THE NATURAL HISTORY SURVEY. 233

of the head from the occipital furrow; frontal lobe of the gla-
bella not differentiated laterally from the cheeks ; a single pair
of lateral glabellar furrows which at their inner extremities
curve backward and join the occipital furrow, cut off a pair
of sub-ovate lateral glabellar lobes; occipital furrow not
continuous across the median portion of the glabella; occipital
segment rather broad, with a pair of small occipital lobes back
of the postero-lateral margins of the glabellar lobes; palpebral
lobes comparatively broad and moderately elevated.

Pygidium sub-semielliptical or parabolic in outline, wider
than long; axis short, sub-semielliptical in outline, with one or
two transverse furrows near the anterior margin; upon each side
the limb is marked by seven slightly elevated ribs which become
obsolete before reaching the margin, the anterior ones usually
have a slight sigmoidal curvature; the median rib or post-axial
region is about twice as wide as the lateral ribs, through the
first half of its length from the posterior margin of the axis it
increases gradually in width, this increase becoming more rapid
posteriorly until at the margin it is four or five times the width
of its point of origin.

The dimensions of a nearly perfect pygidium are: length
33.5 mm., width 41 mm.

Remarks. The heads of this species are rarely preserved,
and the few specimens which have been observed are in a yery
fragmentary condition. The above description of this portion
of the species has been taken from Hall's illustration and defi-
nition. The pygidia also are among the rarer members of the
fauna of the Chicago area, although they are commonly much
better preserved than the heads.

Winchell and Marcy's species B. occasus has been shown
by Hall to be a synonym of B. acamas, although it would be
impossible to determine this from the original description and
illustration of the species. Hall, however, has refigured the
type specimen of B. occasus and this corrected drawing shows it
to be only a small specimen of B. acamas.

Localities. Bridgeport and Romeo.

Family 5. LICHADIDAE Barrande.

"Dorsal shield generally large and flat, with granulated
test. Cephalon small, not more than one-fourth the entire
length; genal angles spiniform. Free cheeks separate; sutures
extending from the posterior margin obliquely inward to the
eyes, and then almost directly forward, cutting the margin

234 THE CHICAGO ACADEMY OF SCIENCES.

separately. Glabella broad, with a large, often tumid .central
lobe, and from one to three side lobes. Eyes not large. Thorax
with nine or ten segments, and grooved and falcate pleura.
Pygidium large, flat, commonly with toothed or notched margin
corresponding to the pleural grooves; doublure very broad."
Beecher, Zittel-Eastman Text Book of Paleontology, p. 632.

In' the subdivision of the family Lichadidce into generic
groups, the work of F. R. Cowper Reed " Notes on the Genus
Lichas" (Quart. Jour. Geol. Soc. London, vol. 58, pp. 59-82, 1902),
has been followed in the main, although his subgeneric divisions
are given generic rank.

Genus 7. CORYDOCEPHALUS Corda, 1847.

Cephalon broadly sub- triangular in outline, studded with
tubercles, spinules or spines. Glabella well denned by the dorsal
furrows, the median lobe protuberant in front and extending
backward to the occipital furrow, second pair of lateral furrows
obsolete, in consequence of which the first and second lateral
glabellar lobes are confluent and form a single pair of large com-
pound lobes, third pair of lateral glabellar lobes well defined,
lying between the large compound anterior lobes and the oc-
cipital furrow, behind these are a pair of basal or occipital lobes ;
cheeks broad, produced into a pair of curved genal spines which
proceed from the sides outward and backward, the post-cephalic
margin curving forward laterally to the bases of the spines.
Pygidium with a thickened marginal border; axis strongly de-
fined, elevated, connected with the marginal -border posteriorly
by a narrow post-axial ridge; the pleura with two segments,
each of which is produced laterally into more or less elongate
backwardly curving spines, the spines being produced across the
surface of the pleura to the axis as strongly raised ridges.
Corydocephalus phlyctainodes (Green), pi. xxu, figs. 1-4.

Description. Cephalon, when viewed from above, semi-
elliptical or obscurely sub-triangular in outline, very convex,
strongly protuberant in front, deeply furrowed and covered
with tubercles and spines. Dorsal furrows deep and strong
anteriorly, becoming shallower behind, describing a convex
curve from the frontal margin to the outer extremities of the
third lateral furrows, then continued in a second convex curve
around the extremities of the third lateral lobes, and a third
slightly convex curve around the occipital lobes to the occipital
furrow. Glabella sub-circular or broadly sub-ovate in outline,

THE NATURAL HISTORY SURVEY. 235

very convex, the anterior and lateral slopes protuberant,
Anterior, lateral furrows broad and deep, sub-parallel from the
frontal margin upward and backward, slightly converging pos-
teriorly where they terminate in a depression between the inner
extremities of the third lateral lobes. Second lateral furrows
obsolete. Third lateral furrows as strong as the anterior pair,
curving from the dorsal furrow slightly upward and backward,
meeting the anterior pair in the depression between the third
lateral lobes. Median lobe sub-ovate of sub-quadra.te in outline,
occupying more than one-third of the entire surface of the gla-
bella, broadest in front of the center where its width is from two-
thirds to three-fourths its length, strongly 'convex and protu-
berant beyond the frontal margin anteriorly, the posterior slope
gently convex and terminating in the depression between the
inner extremities of the third lateral lobes; at its most anterior
extension the median lobe bears "two large spines which are
produced forward in a nearly horizontal direction, slightly di-
verging from the base, on the dorsal surface in front of the
middle are two other similar spines nearly in line with those in
front, one of which is sometimes situated farther forward than
the other, they are directed obliquely upward.. and forward.
The compound anterior lateral lobes large, sub- triangular or
irregularly sub-ovate in outline, acutely angular behind, the
longer axis oblique to the median line of the cephalon, the
surface somewhat depressed between the median lobe and the
third lateral lobes. The third lateral lobes sub-elliptical or sub-
ovate in outline, more than half the size of the anterior lobes,
strongly convex, bearing a large spine on the outer extremity
above the eye-lobe. Occipital lobes small, nearly flat, more or
less indistinctly outlined, one-third or less than one-third the
size of the third lateral lobes. Occipital furrow broad and deep
in its central portion, dividing laterally, one division passing
in front and the other behind the small occipital lobes, the
divisions much narrower than the central portion. In front of
the occipital furrow, between the inner extremities of the third
lateral lobes, is a rather broad depression across which an in-
distinct ridge connects the inner extremities of these lobes.
This ridge is surmounted by three tubercles, one situated me-
dially and one at each end. Occipital segment strongly arched,
broad, elevated along the posterior border which is produced
into three strong spines directed obliquely backward and upward,
its surface sloping toward the front. Fixed cheeks convex,
narrow in front, becoming much broader posteriorly, with small

236 THE CHICAGO ACADEMY OF SCIENCES.

palpebral lobes. Eyes small, situated opposite the outer ex-
tremities of the third lateral lobes of the glabella, beneath the
bases of the spines which surmount these lobes. Surface of the
test thickly set with tubercles or short spines and by a smaller
number of long spines which are themselves covered with tu-
bercles. The most conspicuous of these spines are the two which
extend forward from the anterior surface of the median glabellar
lobe and the two which surmount the outer extremities of the
third lateral lobes of the glabella; two somewhat smaller spines
arise from the dorsal surface of the median glabellar lobe, and
three from the posterior border of the occipital segment; these
spines have usually been broken off but their bases may always
be detected. Free cheeks not known.

Pygidium sub-semicircular in outline, with four long,
marginal, tuberculate spines. The axis large and convex,
narrowly sub-semielliptical in outline, with two annulations
'anteriorly, the first of which extends across the pleural slopes ;
occupying more than one-third the width of the pygidium an-
teriorly, the sides convex and converging posteriorly, the
posterior extremity reaching nearly to the marginal border and
.connected with it by a narrow and short post-axial ridge. The
pleural surfaces divided into two grooved segments, the pos-
terior element of each segment being much elevated in a broadly
rounded ridge extending from the dorsal furrow to the margin,
and then being produced into one of the long, rounded, tapering,
tuberculate spines which are longer than the body of the pygid-
ium itself; the anterior pair of spines have a strong backward
curvature until at their extremities they point in a posterior
direction, the posterior pair are less strongly curved, from the
margin of the pygidium they first diverge slightly, gradually
curving until in their posterior half they slightly converge. The
margin of the pygidium between the bases of the spines is
differentiated as a broad, thickened, convex, marginal border.

The dimensions of a nearly perfect but rather small crani-
dium are: length 23 mm., greatest width 24 mm., convexity
10 mm. The dimensions of a pygidium are length 15 mm.,
width 22.5 mm., approximate length of spines 20 mm.

Remarks. This species is a close ally of the Bohemian C.
palmata Barr., but the cephalon of that species is not provided
with the large spines of the American form, and the shape of the
head is also different. The pygidia of the two species are also
quite different, the four spines of the American species being much
more elongate than the corresponding spines of the Bohemian

THE NATURAL HISTORY SURVEY. 237

form, the two median spines are also lacking which are present
in C. palmata. The specimens referred to a variety of this
species by van Ingen, from the St. Clair limestone of Arkansas,
differ from the typical form in the shape of the median lobe of
the glabella and should doubtless be considered as a distinct
species for which his varietal name depauperata may be used.
Localities. Joliet and Chicago Drainage Canal near Lemont.

Genus 8. DICRANOPELTIS Corda, 1847.

Cephalon tuberculate, sub-triangular in outline. Glabella
well-defined by the dorsal or axial furrows, the median lobe
more or less protuberant in front, extending backward to the
occipital furrow. First lateral furrows extending backward to
the occipital furrow, deep and strong anteriorly, sometimes
becoming shallower and less well defined posteriorly. Second
pair of lateral furrows obsolete so that the first and second
lateral glabellar lobes are combined into a single pair of large
compound lobes. Third pair of lateral lobes well defined, lying
between the compound anterior lobes and the occipital furrow;
behind these are a pair of basal or occipital lobes. Pygidium
rather large, axis elevated with two annulations anteriorly and
continued posteriorly in a flattened post-axial area; lateral
lobes flattened, with three pairs of grooved pleura each with a
free point, the posterior pair sometimes not completely marked
off posteriorly from the post-axial area.
Dicranopeltis decipiens (W. & M.), pi. xxn, figs. 10-11.

Description. Cephalon very convex, sub-triangular in
outline, produced laterally in rather strong, flattened spines
which extend obliquely outward and backward, breadth between
the extremities of the lateral spines more than twice the length.
Glabella sub-pentagonal in outline, flattened on top posteriorly,
the anterior slope strongly convex and slightly protuberant,
lateral slopes gently convex. Dorsal furrows deep and strong
anteriorly, becoming shallower posteriorly; describing a convex
curve from the anterior margin to the junction with the third
lateral glabellar furrows, beyond which they describe a slightly
concave curve past the outer extremities of the third lateral
and the occipital lobes to the occipital furrow. Median lobe of
the glabella widest at the anterior margin where its breadth is
nearly 'equal to that of the glabella at its mid-length, broadly
convex in front, becoming narrower posteriorly where it forms
a little less than the median third of the glabella at the junction

238 THE CHICAGO ACADEMY OF SCIENCES.

of the anterior or first with the third lateral glabellar furrows,
back of which point it is partially coalescent with the third
lateral lobes. Anterior lateral furrows deep and narrow, cle-
scribing a concave curve from their anterior point of origin to.
their junction with the third lateral furrows, beyond which
they are produced posteriorly to the occipital furrow as slight,
ill-defined depressions. Second pair of glabellar furrows obso-
lete. Anterior lateral lobes large, compound, formed by the
coalescence of the first and second pairs of lobes, strongly convex,
irregularly sub-elliptical in outline, the longer axes directed
obliquely forward. Third lateral furrows of the same depth and
size as the anterior ones and continuous with them, being
joined by a sharp curve; from this point to their junction with
the dorsal furrow they are straight and are directed obliquely
forward. Third lateral lobes quadrilateral in outline, length
and breadth nearly equal, not sharply separated from the
posterior portion of the median lobe, less than one-half the
size of the compound anterior lobes. Occipital furrow broad,
deep and straight across the posterior extremity of the median
glabellar lobe, dividing on each side, the two divisions on each
side bounding a pair of small, triangular occipital lobes situated
back of the outer portions of the third lateral glabellar lobes.
Occipital segment gently arched, broad in the center, becoming
narrower laterally. Fixed cheeks convex, sloping both an-
teriorly and posteriorly, the palpebral lobes rather large, -elevated,
semi-circular! Free cheeks convex, sloping rather abruptly
from the eyes, produced laterally from a point nearly opposite
the eyes into flattened spines which are directed obliquely
backward, and whose length is equal to about one-fourth of .the
width of the cephalon exclusive of the spines. The post-cephalic
margin curving forward to the bases of the lateral spines.

Pygidium sub-semielliptical in outline; the axial portion
occupying a little more than, one-fourth of the entire width at
the anterior margin, strongly convex anteriorly with two narrow,
rounded annulations, back of which is a convex bulbous portion
which becomes depressed near the center of the pygidium ; back
of the elevated portion the two axial furrows which bound the
post-axial region converge to the posterior margin; the pleura
are nearly flat and are divided into three, broad, grooved seg-
ments, all of which are produced on the margin into short, free
points. The entire surface finely tuberculate.

The approximate dimensions of a large cephalon are:
length 17 mm., width to ends of lateral spines 37.5 mm., width of

THE NATURAL HISTORY SURVEY. 239

cranidium between the eyes 18 mm. The dimensions of a pygid-
ium are: length 12.5 mm., width 17.5 mm.

Remarks. This species, founded on the pygidium alone,
was briefly described by Winchell and Marcy from Bridgeport.
Their illustration was clearly incorrect, as pointed out by them
in the "errata" of their paper, and really .does not represent the
essential characters of the species at all. The species, however,
is not uncommon in the collections from Bridgeport, it is in fact
the most common lichad which has been observed from that
locality. Hall did not recognize Winchell and Marcy's species at
all, but figured a pygidium (Rep. N. Y. St. Cab. Nat. Hist., pi. 21,
fig. 14) from Bridgeport under the name Lichas breviceps, whicfc
he afterwards made the type of the new species Lichas emargi-
natus, which represents the species far better than Winchell
and Marcy's original illustration. The head figured by Hall in
the same place differs from anything that has been observed
during the preparation of the present Bulletin, and doubtless
belongs to another species. The head which is here associated
with this species occurs about as commonly in the Bridgeport
collections as the pygidia, and while these two portions of the
body have never been found in such a position as to indicate
that they originally belonged to the same individual, yet the
heads and pygidia are not infrequently found closely associated.
Occurring as they do in this manner, in approximately equal
numbers, there seems to be no reasonable doubt as to the cor-
rectness of considering them to be parts of one species. If
they do not belong to the same species, then there is no head for
the common pygidium and no pygidium for the common head.
The cephalon which is illustrated herewith on plate xxii, is not
from Bridgeport, but from near Lemont, it differs from the
Bridgeport specimens in its larger size and in the more sparse
tuberculation of the surface, it has been used for illustration
because it is more complete than any of the Bridgeport speci-
mens in that it preserves one of the free cheeks.

The species which has recently been described as Arges
arkansana • by van Ingen, from the St. Clair limestone of In-
dependence County, Arkansas, is very closely allied to this form
from the Chicago area, and it is possibly not distinct from it.
Both of these species, if they are distinct, are somewhat closely
related to the Bohemian species Lichas scabra Beyr,, the Amer-
ican and the European forms being co-generic.

Localities. Bridgeport, Hawthorn and Chicago Drainage
Canal near Lemont.

24O THE CHICAGO ACADEMY OF SCIENCES.

Dicranopeltis nasuta, n. sp., pi. xxn, figs. 5-7.

Description. Cephalon triangular in outline, strongly con-
vex, extended anteriorly into an acutely pointed projection.
Dorsal furrows each describing a sigmoidal curve, strongly
defined anteriorly, nearly obsolete along the outer margin of
the third glabellar lobes. Glabella sub-pentagonal in outline,
strongly convex, not sharply defined by the dorsal furrows,
the general surface being continuous with that of the cheeks,
anterior and antero-lateral slopes protuberant. Median lobe
elongate, sub-pentagonal in outline, nearly twice as long as wide,
the anterior half sub-conical and slightly compressed laterally,
protuberant far beyond the anterior margin, the dorsal median
line straight and sloping upward from the occipital furrow to
the apex which is consequently elevated; in both specimens
examined the apex is fractured and appears to have been pro-
duced into a slender spine. Anterior lateral lobes large, com-
pound, sub-ovate in outline, completely surrounded by a deep
and well-defined furrow, less than half their entire surface
visible dorsally, their longer axes oblique to the median line
of the cephalon, their length about twice their width, pointed
at their inner extremities and rounded externally, strongly
convex along their median line. Third lateral lobes trapezoidal
in outline, nearly confluent with the median lobe within and
scarcely defined by the dorsal furrow externally, the surface
gently convex, completely visible dorsally, about one-half as
large as the anterior lobes. First and third lateral furrows
of the glabella strongly defined and confluent around the inner
end of the anterior lateral lobes; the second lateral furrows
obsolete. Occipital furrow well-defined, dividing at the pos-
tero-lateral angles of the median glabellar lobe, the two divisions
on each side passing one in front and one behind the small
triangular occipital lobes whose surface is slightly convex and
completely visible in a dorsal view; the posterior branches
of the occipital furrow are narrower and deeper than the median
portion. Occipital segment narrow. Fixed cheeks narrow
and linear from the lateral margins of the cephalon to the eyes,
back of the eyes they are triangular with a gently convex sur-
face which slopes laterally from the dorsal furrows with a width
about equaling the length of the third glabellar lobes, the an-
terior linear portion of the cheeks bends abruptly downward
in front of the eyes to the margin of the cephalon; palpebral
lobes very small. Free cheeks sub-quadrangular in outline,

THE NATURAL HISTORY SURVEY. 24!

nearly vertical in position, the surface gently convex above
and slightly sinuous below, genal angles imperfect. Eyes small
elliptical in outline, the longer axes oblique, the surface convex.
Entire surface of the cephalon, except in the furrows and along
the facial suture, covered uniformly with rounded tubercles
of two sizes. Thorax and pygidium unknown.

The dimensions of the best preserved specimen which has
been observed are: length of cephalon along median line 19
mm., greatest width of cephalon 24 mm., convexity 13.5 mm.

Remarks. This species has not yet been observed in the
Chicago area. The types, which are the only specimens known,
are from Milwaukee, Wisconsin, and were collected by Mr.
E. E. Teller. The species is entirely different from any other
American form.

Locality. Milwaukee, Wisconsin.

Dicranopeltis teller!, n. sp., pi. xxii, figs. 8-9.

Description. Cephalon sub-semielliptical in outline, bluntly
rounded in front and slightly protuberant beyond the anterior
margin. Dorsal furrows well defined along the outer margins
of the anterior lateral glabellar lobes, much less well-defined
adjacent to the third lateral lobes. Glabella sub-pentagonal
in outline, broader than long, dorsal surface gently convex in
front, general surface of the median and lateral lobes continuous,
being indented only by the narrow but sharply defined furrows »
Median lobe broadest at the anterior margin, becoming grad-
ually narrower to the inner extremities of the anterior lateral
lobes, where it becomes abruptly wider and then continues
posteriorly to the occipital furrow with nearly parallel sides,
anterior extremity very slightly protuberant beyond the mar-
gin. Anterior lateral lobes compound because of the obsol-
escence of the second lateral furrows, sub-ovate in outline,
nearly twice as long as wide, nearly the whole of their surface
visible dorsally. Third lateral lobes quadrilateral, rhombic-
ovoid in outline, three-fifths as long as wide, about one-third
as large as the anterior lobes, the longer sides and more acute
extremities directed obliquely outward and forward, their
entire surface visible dorsally. Occipital furrow narrow and
deeply impressed, gently arched toward the front, dividing at
the postero-lateral angles of the median glabellar lobe, the
branches on either side passing one in front and one behind the
small, triangular occipital lobes which are less than one-half a's
large as the third lateral glabellar lobes. Occipital segment

242 THE CHICAGO ACADEMY OF SCIENCES.

rather broad, gently arched between the lateral margins of
the glabella, becoming narrower back of the occipital lobes.
Fixed cheeks sub-triangular in outline, their surface gently
convex and continuous with that of the glabella; palpebral
lobes small, scarcely elevated. Entire dorsal surface, exclusive
of the furrows, thickly set with small, low, rounded papillae,
which are somewhat variable in size. Free cheeks, thorax
and pygidium not preserved.

The dimensions of the type specimen are: length of cepha-
lon along median line 15.5 mm., width of cranidium between
the eyes 20.5 mrn., greatest width of cranidium 23 mm., width
of glabella at base 13.5 mm., width of glabella at middle of
anterior lateral lobes 16.5 mm.

Remarks. This species like the last, has not been observed
in the Chicago area, and is known only from Milwaukee, Wis-
consin. The type specimens were collected by Mr. E. E. Teller,
in whose honor the species is named, and are now in his collection.

Locality. Milwaukee, Wisconsin.

Genus 9. METOPOLICHAS Giirich, 1901.

Cephalon broadly sub-triangular, tuberculate. Glabella
completely marked off by the dorsal or axial furrows ; the second
lateral glabellar furrows obsolete or indicated only by slight
indentations of the first lateral furrows at the sides of the median
glabellar lobe, and the third pair of lateral furrows also exhibiting
a tendency to become obsolete, so that the third pair of lateral
lobes are not sharply defined; basal or occipital lobes present.
Cheeks broad, produced laterally into long, curved, genal spines
which extend outward and backward, the post-cephalic margin
curving forward to the bases of the spines. Pygidium with a
rather short, elevated axis with one or two annulations, and a
broad flattened post-axial area; lateral lobes flattened, with
three pairs of grooved pleural segments, the two anterior pairs
completely defined and with free points, the third pte-ir not
completely marked off from the post-axial area posteriorly and
without free points.

Metopolichas pugnax (W. & M.), pi. xxi, figs. 1-4.

Description. Cephalon broadly sub-triangular in outline,
the margin rounded in front, becoming sinuate on either side
in front of the eyes in th£ anterior portion of the free cheeks,
and then broadly convex to the extremities of the genal spines,
the post-cephalic margin curving forward near the postero-

THE NATURAL HISTORY SURVEY. 243

lateral angles of the cranidium, the posterior margins of the
free cheeks deeply sinuate; anterior and lateral margins de-
pressed in a flat marginal border which is narrowest in front
of the glabella. Glabella bordered by well-defined dorsal or
axial furrows; the median lobe prominent and abruptly elevated
in front, but not protuberant beyond the anterior cephalic
margin, very broad in front, becoming rapidly narrower poste-
riorly; the anterior lateral furrows deeply impressed, continuous
posteriorly with the third lateral furrows which curve outward
toward the eye-lobes and terminate somewhat abruptly, not
joining the occipital furrow; anterior lateral lobes compound,
elliptical in outline, strongly convex, their posterior extremi-
ties higher than the surface of the median lobe between; second
lateral furrows nearly obsolete, represented only by slight in-
dentations in the inner margins of the anterior lateral lobes
at about their mid-length ; third lateral lobes ill-defined, coalescent
with the anterior lobes externally in front, and partially coales-
cent with the median lobe internally. Occipital furrow well-
defined, nearly straight in its central part, broadening laterally
back of the third lateral glabellar lobes and including a pair of
small, depressed, sub-triangular, ill-defined occipital lobes.
Occipital segment convex, rather broad, becoming a little nar-
rower laterally. Fixed cheeks prominent in the region opposite
the eye-lobes, sloping abruptly to the front and somewhat less
abruptly, with a convex surface, postero-laterally back of the
eyes. Free cheeks large, depressed except near the eyes where
the surface is rather abruptly elevated to the outer margins
of the eyes, produced laterally opposite the eyes, into broad,
flat spines which curve outward and backward, the post-cephalic
margin curving forward to the bases of the spines.

Pygidium sub-elliptical in outline, its surface depressed-
convex. Axis occupying more than one-third of the entire
width of the pygidium at its anterior margin, with a single dis-
tinct annulation anteriorly, bordered by distinct dorsal or axial
furrows which continue posteriorly and bound a broad post-
axial region which- is strongly contracted near the middle of
the pygidium and which is coalescent posteriorly with thepleural
segments on either side. The limb is divided into three pairs
of broad, deeply grooved segments, the general surface is gently
convex from the dorsal furrows through about one-half the
width to the lateral margins, beyond this becoming slightly
concave. The postero-lateral extremities of the two anterior
pairs of plemral segments are produced somewhat into back-

244 THE CHICAGO ACADEMY OF SCIENCES.

wardly directed rounded free points, the posterior margin of the
pygidium back of the second pleural segments is entire and
describes nearly an arc of a circle. The surface of both head and
pygidium are covered with scattered, rounded tubercles, some-
what variable in size.

The approximate dimensions of an incomplete cephalon
are: length 44 mm., estimated width 118 mm., convexity 18
mm. The approximate dimensions of an incomplete pygidium
are: length 80 mm., width 123 mm., width of axis at anterior
margin 44 mm.

Remarks. This is perhaps the largest trilobite in the en-
tire Niagaran fauna of the Chicago area. It is known only
from incomplete heads and pygidia, although the more recent
collections have afforded far better material for study than the
original type specimens of Winchell and Marcy. In no case
have specimens of the head and pygidium been observed in
such position as to show that they belonged to the same indi-
vidual, but the two portions of the body have frequently been
found associated, and no other large heads or pygidia occur
in the same beds. That the two portions of the body here de-
scribed are really parts of one species can be assumed to be
established beyond reasonable doubt. The large free cheek
also which has been identified as a part of this species is
an isolated specimen, but it occurs in the same beds with the
heads and pygidia and can belong to no other known species.
In the illustration of the cephalon of the species the free cheeks
have been restored from the single specimen of that part of the
head which has been observed.

Locality. Bridgeport.

Metopolichas ferrisi, n. sp., pi. xxii, figs. 12-13.

Description. Entire body sub-elliptical in outline. Crani-
dium sub-triangular in outline, broadly rounded or sub-trun-
cate in front. Glabella depressed-convex, about as wide as
long, bordered laterally by shallow but well-defined dorsal
furrows, narrowest a little back of a line joining the eyes, a little
broader at the occipital segment than in front; median lobe
occupying the entire width of the glabella in front, rapidly be-
coming narrower posteriorly until in line with the eyes it oc-
cupies only one-third the width of the glabella, posteriorly
it is nearly confluent with the third lateral lobes externally;,
first lateral furrows strong and well-defined, curving from
just back of the antero-lateral extremities of the median lobe,

THE NATURAL HISTORY SURVEY. 245

backward and inward, nearly parallel with the dorsal furrows
to a point just back of the line joining the eyes, where they
are continuous with the third lateral furrows, making a sharp
turn outward and forward around the posterior extremities
of the anterior lateral lobes, this inner well-defined portion of
the third lateral furrows is short, being continued obliquely
forward to the dorsal furrows as slight depressions which are
sometimes almost obsolete; second lateral furrows represented
by slight indentations of the anterior furrows into the inner
sides of the anterior lateral lobes at about the middle of their
length; anterior lateral lobes compound, sub-elliptical in out-
line, the longer axis a little more than twice the shorter, directed
outward and forward, confluent posteriorly towards the dorsal
furrow with the third lateral lobes; third lateral lobes much
smaller than the anterior ones, ill-defined, separated from the
median lobe by slight depressions only, which may sometimes
be almost obsolete, from the anterior lateral lobes they are
sharply separated within but laterally towards the dorsal fur-
rows they are almost wholly confluent. Occipital furrow shal-
low, rather broad and ill-defined in the center, becoming more
strongly defined laterally where it divides, the two divisions
on each side surrounding a small, sub-ovate or slightly sub-
rhombic occipital lobe. Occipital segment rather broad and
flattened in the middle, a little narrower and more convex
laterally. Fixed cheeks very narrow in front of the eyes, con-
nected anteriorly around the front of the glabella by a narrow,
flat, marginal border, back of the eyes they are much broader
and are produced laterally,* they are crossed near the posterior
margin by the well-defined posterior cheek furrows, between the
eyes and the posterior cheek furrows the surface is gently con-
vex and slopes laterally and posteriorly. Palpebral lobes small,
free cheeks unknown.

The thorax is represented in the specimens studied only
by detached and broken segments. The axis is apparently
broad and depressed-convex.

Pygidium depressed-convex, semi-elliptical in outline;
the axis depressed, but little elevated above the surface of the
pleura, occupying more than, one-third of the entire width
of the pygidium anteriorly, crossed anteriorly by two trans-
verse furrows, the first of which is much better defined and
continuous across the entire width of the axis, the second one
is less sharply defined, and is not continuous across the median
portion of the axis, each of the two lateral portions curving

246 THE CHICAGO ACADEMY OF SCIENCES.

backward toward their inner extremities; posteriorly the axis
is produced into a depressed post-axial region, the dorsal fur-
rows converge posteriorly to about the middle of the pygidium
where the axial region is about one-half its width at the ante-
rior margin, from here the dorsal furrows diverge posteriorly,
the axial region again becoming broader, the furrows do not
reach the posterior margin of the pygidium so that the axial
region is coalescent posteriorly with the pleural segments on
either side. The pleura are divided into three pairs of broad
grooved segments, the posterior-lateral angles of the two an-
terior pairs project slightly beyond the border of the pygidium
as posteriorly pointing free points, between the free points of
the second pleural segments the border is continuous.

The entire surface of the head, pygidium and thoracic
segments is covered with small, more or less irregular, rounded
papillae.

The dimensions of the best preserved cranidium observed
are: length 17.5 mm., approximate width between the eyes
18.5 mm., width at posterior margin 30 mm., width of median
lobe of glabella in front 13 mm. The best preserved pygidium
has the following dimensions: length 16 mm., width 24 mm.,
width of axis at anterior margin 9 mm., width of axial region
at narrowest point 4 mm.

Remarks. In general form this species resembles M. brevi-
ceps (Hall), from the Waldron shale of Indiana, but it differs
from that species in several important characters. In the loba-
tion of the glabella M. ferrisi is much more primitive than M.
broyiceps, the rudimentary, secern}, lateral, glabellar furrows
being still discernible as slight indentations of the inner border
of the compound anterior lateral lobes, while in M. breviceps
these furrows have entirely disappeared; M. ferrisi also pos-
sesses a pair of third lateral glabellar lobes of .some size, while in
M. breviceps these have been nearly crowded out, the glabella
assuming in this respect nearly the condition of the genus
Arctinurus. These differences wouldv suggest at once that M.
ferrisi is the earlier species of the two, and this is the case, it
having been observed only in the lowest Niagaran beds recog-
nized in the Chicago area, while M. breviceps occurs in the Wal-
dron shale, well up towards the summit of the Niagaran.

The species is named in honor of Mr. J. H. Ferris of Joliet,
Illinois, who accompanied the writer at the time the type
specimens were collected.

Locality. Near Channahon, W ill Ccimty, Illircis.

THE NATURAL HISTORY SURVEY. 247

Genus 10. - ARCTINURUS Castelnau, 1843.

Glabella completely ' marked off by the dorsal furrows,
the median lobe extending to the occipital furrow, the first
and second lateral lobes combined and extending to the occipital
furrow, the third lateral lobes squeezed out so as to be entirely
absent; the second furrows obsolete or indicated by mere in-
dentations of the first furrows; occipital lobes absent. Pygidium
with one or two axial segments, the axis reaching about half
way to the posterior border, the broad post-axial region with
a sinuate or emarginate posterior margin ; three pairs of grooved
pleural segments, the two anterior pairs complete and with
free points, the posterior pair complete or nearly complete.

Arctinurus occidentalis (Hall), pi. xx, figs. 10-12.

Description. Pygidium somewhat pentagonal or hexagonal
in general outline, broader than long, the two lateral margins
sub-parallel, the anterior margin nearly straight or sloping
away laterally on each side of the axis. ' Axis strongly convex
in the anterior third of its length, with one distinct annulation
anteriorly and a second one a little less distinct and broader;
the greatest elevation is at the anterior margin from which
point the slope is abrupt laterally and more gentle posteriorly;
back of the elevated portion is a depressed post-axial region;
at the anterior margin the axis occupies about one-fourth the
total width of the pygidium, the axial furrows converge rapidly
posteriorly to a point just back of the elevated portion where
the width of the axial region is about one-third its width in
front, from here the axial furrows are slightly divergent pos-
teriorly to the posterior margin which is deeply sinuate between
the posterior extremities of the axial furrows which terminate
near the ends of. a pair of strong, acute, backwardly pointing
extensions of the pygidium. Pleura nearly flat throughout the
greater portion of their width, becoming slightly convex in
proximity to the anterior elevated portion of the axis, divided
into three pairs of deeply grooved segments which are strongly
bent backward, their terminations being acutely angular free
points, between which are deep emarginations, the terminations
of the six angular pygidial extensions are directed posteriorly,
the median pair, at either side of the posterior margin of the
axial regipn, extend the farthest back, the terminations of the-
second pair are a little farther forward, and the outer pair a
little in front of the second.. The surface of the pygidium is

248 THE CHICAGO ACADEMY OF SCIENCES.

studded with small, crowded, depressed, rounded tubercles.
The cephalon and thorax are unknown.

The approximate dimensions of an average sized pygidium
are: length 58 mm., width 68 mm., width of axis at anterior mar-
gin 17 mm.

Remarks. These pygidia are essentially like those which
occur in the fauna of the Waldron shale of Indiana, which have
always been considered as a variety of A . boltoni of the New York
Niagaran fauna. The characters of all these western pygidia
seem to be quite constant and to differ from the typical A.
boltoni in having the pleural segments more elongate and di-
rected more nearly in a posterior direction. Because of the
constancy of these characters the form is' here recognized as
having full specific rank. Wherever it occurs the species is
known almost wholly from the pygidium, and no heads cer-
tainly belonging to it have been observed in -the Chicago area.
However, one incomplete lichad glabella showing parts of a
broad, moderately convex median lobe and a single pair of
smaller lateral lobes, with the marginal border produced in
front in a flat lip-like extension, perhaps represents the cephalic
portion of this species.

The species Lichas boltoni, with which M. occidentalis is
certainly co-generic, has been used at different times as the type
for three different genera or sub-genera of the Lichadidce. Cas-
telnau first used the name Arctinurus in 1843*, Conrad, however,
had used the name Platynotus in 1838!, but this name had
been preoccupied for a genus of insects, and so cannot be re-
tained. In 1885 Schmidt proposed the name OncholichasJ.,
with L. boltoni as the type, associating with it certain Baltic
Ordovician species which probably are not co-generic. In the
present paper Castelnau's name is retained for the generic group.

Locality. Joliet and Bonfield, Illinois.

Arctinurus chicagoensis, n. sp., pi. xxm, figs. 7-8; pi. xxii, fig. 14.

Description. The entire head not known. Glabella sub-
pentagonal in outline, strongly convex, bounded laterally by
strongly defined dorsal furrows; the median lobe extending
from the anterior margin of the head to the occipital furrow,
broadest in front where it occupies more than one-third the

*Ess. Syst. Sil. 1'Amer. Sept., p. 21.
tRep. N. Y. State Geol. Surv. for 1838, p. 118.

JRev. Ost, Bait. Sil. Tril., pt. 2, Mem. Acad. Imp. Sci. St. Petersburg. Vol. xxxiii.
No. 1, p. 3.

THE NATURAL HISTORY SURVEY. 249

entire width of the glabella, becoming regularly narrower back-
ward to about the position of the line joining the eyes, where
its width is less than half that at its anterior margin, and then
slightly expanding again to the occipital furrow; first lateral
furrows strongly defined and continuing backward on either
side of the median lobe to the occipital furrow; lateral lobes
not divided but consisting of a single pair which are compound,
being formed by the coalescence of the first and second lateral
lobes, they are large, each one being about two-thirds the size
of the median lobe, convex, sub-elliptical in outline, their
anterior extremities not as far forward as the median lobe,
extending backward to the occipital furrow; second and third
lateral furrows and the third lateral lobes obsolete. Occipital
furrow broad, shallow and ill-defined back of the median glab-
ellar lobe, becoming narrower and more sharply impressed
laterally, not enclosing a pair of occipital lobes, apparently
contiguous laterally with the posterior cheek furrows. Occi-
pital segment rather broad with parallel margins. The cheeks
imperfectly preserved.

Pygidium sub-pentagonal in outline. The axis strongly
convex from the anterior margin to near the middle where it is
rather abruptly depressed and continues to the posterior mar-
gin as a depressed post-axial region in the same general plane
with the pleural lobes, it is well defined by the dorsal furrows,
and at its anterior extremity occupies about one-third the
entire width of the pygidium; the dorsal furrows converge
posteriorly to a little back of the elevated portion of the axis,
the axial region at this point being less than one-half its width
anteriorly, from here the dorsal furrows continue posteriorly
sub-parallel with each other becoming slightly divergent again
toward their posterior extremities; anteriorly the axis has two
distinct annulations with a third less distinct one, the third
transverse furrow not being continuous across the median por-
tion; the posterior margin of the axial region is broadly sinuate.
The pleura nearly flat, divided into three pairs of broad, deeply
grooved segments, the lateral extremities of the two anterior
segments on each side are produced into bluntly rounded,
backwardly directed free points, and between the angular
extremities of the third pair of segments lies the sinuous pos-
terior margin of the axial region. The entire surface of the
head and pygidium are covered with depressed, rounded and
crowded papillse of rather large size. Thorax unknown.

25O THE CHICAGO ACADEMY OF SCIENCES.

The dimensions of the most complete head that has been
studied are approximately: length 28.5 mm., width between
the eyes 44 mm., greatest width of median glabellar lobe 20
mm., greatest width of glabella 34 mm. The approximate
dimensions of an incomplete pygidium are: length 120 mm.,
width 76 mm., width of axis at anterior margin 26 mm.

Remarks. This species is best known from the pygidium,
several examples of which, from the Van Home Collection, have
been under observation. The heads are less numerous than
the pygidia and are even less perfectly preserved, only two
examples have been seen , both upon a single specimen of lime-
stone about 12x15 cm. in size where they are associated with
two fairly well preserved pygidia, so that the correlation of the
head and pygidium of the species is satisfactorily established.
The large hypostome illustrated on plate xxn., figure 14, is as-
sociated with the parts of this species and is believed to belong
here.

Locality. Hawthorn.

Family 6. ACIDASPIDAE Barrande.

"Dorsal shield spinose. Cephalon transversely semi-
elliptical, quadrate or trapezoidal; genal angles spiniform.
Glabella with one large median axial lobe and two or three
lateral lobes. Free cheeks large, separate. Sutures extending
from just within the genal angles abruptly inward to the eyes,
and then forward, cutting the anterior margin each side of the
glabella. Eyes small, often prominent. Thorax of eight to
ten segments, with ridged pleura extended into hollow ^spines.
Pygidium usually small, with spinous margin." — Beecher,
Zittel-Eastman Text Book of Paleontology, p. 633.

Genus n. ACIDASPIS Murch., 1839.

Entire body sub-elliptical in outline, strongly trilobate,
the margin of the head, thorax and pygidium bordered with
spines. Cephalon usually sub-crescentiform in outline, some-
times sub-truncate in front, the genal angles produced into
spines. Median lobe of the glabella elongate, extending from
near the anterior margin to the occipital furrow, with two or
three pairs of lateral lobes which are successively larger from
the anterior to the posterior, the occipital segment bearing a
single median spine directed posteriorly. Thorax with nine or
ten segments. Pygidium with two or three annulations.

THE NATURAL HISTORY SURVEY. 25!

Acidaspis vanhornei, n. sp., pi. xxin, figs. 3-4.

Description. Cephalon, exclusive of the genal and median
spines, sub-quadrangular in outline, the breadth nearly twice
the length, the surface finely granular throughout. Glabella
sub-cordate in outline, depressed-convex, a little wider than
long, its greatest width at the middle of the posterior lateral
lobes, the. lateral lobes but little depressed below the median
lobe. Median lobe elongate sub-ovate in outline, narrowly
rounded in front, truncate behind, its greatest width about
one-half its length, its anterior lateral expansions scarcely
separated from the lateral lobes and coalescing with the ocular
ridges. Anterior lateral lobes minute, scarcely separated from
the anterior lateral expansions of the median lobe; the second
lateral lobes much larger, their axes directed obliquely outward
and forward; posterior lateral lobes about three times as large
as the second pair, sub-ovate in outline, their longer axes nearly
parallel with the median line of the cephalon; all the lobes
coalescing with the median lobe internally. Anterior pair of
lateral glabellar furrows scarcely distinguishable, second pair
deeply impressed, slightly curved and directed obliquely for-
ward and outward, extending to the dorsal furrow; third pair
less strongly impressed than the second, the innermost strongly
impressed portion directed nearly straight towards the front,
the outer portion bent obliquely outward. Dorsal furrows de-
scribing a gentle curve, strongest at their junction with the
occipital furrow, becoming faint anteriorly and scarcely recog-
nizable in front of the second pair of glabellar furrows. Occipital
furrow rather shallow back of the median glabellar lobe, be-
coming much more deeply impressed back of the lateral lobes.
Occipital segment sublunate in outline, broadest in the middle,
its lateral extremities becoming mere points just outside the
posterior ends of the dorsal furrows, it bears a single, long,
slender, median spine, which is directed backward with a slightly
convex curve. Cheeks sub-rhomboidal in outline, moderately
convex, their, postero-lateral angles extended into slender,
divergent, slightly curved genal spines, facial sutures not dis-
tinguishable. Eyes small, situated nearer the inner and pos-
terior margins than the lateral and anterior, connected ante-
riorly by narrow but well-defined ocular ridges with the an-
terior lateral expansions of the median glabellar lobe; the inner
area between the ocular ridge and the dorsal furrow is nar-
row, acutely pointed in front and strongly convex longitudin-

252 THE CHICAGO ACADEMY OF SCIENCES.

ally, especially opposite the eyes; the outer area of the cheeks is
moderately convex, with a raised marginal border, which ex-
tends from the bases of the genal spines entirely around the
lateral and anterior margins of the cephalon and which bears
a fringe-like row of^ spines directed almost vertically down-
ward from the margin; these spines are about twelve in num-
ber on each side, the longest ones being directly in front of the
bases of the genal spines, the succeeding ones becoming regu-
larly smaller until the most anterior ones in front of the anterior
extremities of the ocular ridges are minute. Thorax and py-
gidium not known.

The dimensions of a nearly perfect cephalon are: length
exclusive of the posterior median spine 10 mm,, length, in-
cluding the spine, 16.5 mm., width at base of genal spines 21
mm., width at extremities of genal spines 28 mm., width of
glabella 10.5 mm., distance between the eyes 15 mm., con-
vexity 8 mm.

Remarks. The specimen upon which the description of
this species is based is included in the Van Home Collection in
the Walker Museum. In the illustration of the species on plate
23, the occipital and genal spines are drawn in outline, but in the
specimen, 'while the casts of the spines themselves are broken
off as shown in the drawing, their impressions in the matrix
are fully preserved so that the outlines shown represent the
exact form of the spines. The species is quite distinct from any
other American member of the genus, but approaches most
closely to the form identified by Van Ingen as A . quinquespinosa
Salter-Lake, from the St. Clair limestone of Arkansas. The
glabella of A. vanhornei is much like that of the Arkansas
specimen, but the occipital spine is much more elongate and
more slender and it lacks the four additional protuberances
upon the posterior margin of the occipital segment. The mar-
ginal fringe of short spines in A. vanhornei is peculiar, in that
the spines are directed ventrally in such a manner as to be
wholly invisible in a dorsal view of the cephalon, only being
seen in a lateral or anterior view of the head; other species
with a similar marginal fringe of spines usually have them
directed more or less laterally so that they may be clearly seen
in a direct dorsal view of the cephalon.

Locality. Bridgeport.
Genus 12. ODONTOPLEURA Emmrich, 1839.

The members of this genus are essentially like those ,of
Addas pis, except in the ornamentation of the occipital segment

THE NATURAL HISTORY SURVEY. 253

of the head, which is entirely smooth or is marked only with
a small central tubercle, no median spine ever being present.
The lateral lobes of the glabella are always distinct.

Odontopleura illinoiensis, n. sp., pi. xxm, figs. 5-6.

Description. Cranidium sub-quadrangular exclusive of
the posterior portions of the fixed cheeks which are produced
laterally. Glabella sub-cordate in outline, prominent, the
lateral lobes but slightly depressed below the median lobe, a
little wider than long, the greatest width at the middle of the
posterior lateral lobes. Dorsal furrows well-defined, becom-
ing deeper posteriorly where they join the occipital furrow.
Median lobe of the glabella elongate, sub-quadrangular in out-
line, broadest in front, extending to the occipital furrow. An-
terior lateral lobes obsolete; second lateral lobes strongly con-
vex, sub-ovate in outline; posterior lateral lobes more than
twice as large as the second pair, strongly convex, sub-elliptical
in outline, their longer axes directed antero-laterally. Anterior
glabellar furrows obsolete; second pair deeply impressed at
their antero-lateral extremities, shallower within, curving
posteriorly and joining the third pair of furrows; third pair
of furrows more deeply impressed in their anterior half than
the second, shallower behind where they curve posteriorly and
join the occipital furrows as shallow rounded furrows. Oc-
cipital furrow broadly rounded and rather shallow in the mid-
dle, becoming deeply impressed back of the posterior glabellar
lobes. Occipital segment without median tubercle or spine,
the posterior margin nearly parallel with the occipital furrow,
including a pair of small rather ill-defined occipital lobes lying
behind the posterior glabellar lobes. Fixed cheeks in front of
the eye-lobes divided into two, regions by the ocular ridges
which are prominent and describe a backward curve from
opposite the antero-lateral angles of the median glabellar lobe
to the eyes ; the inner region of the fixed cheek is narrowly sub-
crescentic in outline, lying opposite the lateral glabellar lobes,
and rather strongly convex; the outer region is strongly de-
pressed, extending in a nearly horizontal direction, sub-triangu-
lar in outline, becoming narrow posteriorly and also towards
the median point of the anterior cephalic margin, being widest
opposite the anterior lateral angles of the -cranidium. Eye-
lobes small, not well preserved. The posterior portion of the
fixed cheeks are produced laterally in elongate, slender points.

254 THE CHICAGO ACADEMY OF SCIENCES.

Free cheeks not known. Entire surface of the glabella and pro-
tuberant portions of the fixed cheeks finely tuberculate.

Pygidium, aside, from its spines, more than twice as wide
as long, with eight marginal spines directed posteriorly, the
bases of the spines joined by the thickened marginal border
of the pygidium. The outer spine on each side is small and
short, the second ones are much larger and longer than any
of the others, between these two large spines are four small
ones along the posterior margin. The axis is prominent in front
and depressed posteriorly where it is confluent with the thick-
ened marginal border of the pygidium, it is marked by two
strong annulations, the anterior one of which is continued across
the limb as an elevated, rounded ridge which curves backward
on each side and becomes continuous with the two larger mar-
ginal spines. Each pleural lobe is depressed between the axis
and the thickened marginal border, the depressed regions on
each side being divided into two sub-triangular areas by the
elevated ridge which joins the anterior annulation of the axis
with the larger marginal spines. Surface of the pygidium
smooth.

The approximate dimensions of an imperfect cranidium
are: length 4.5 mm., width along the posterior margin 10 mm.,
greatest width in front of the eyes 5 mm., width of glabella 4
mm. The dimensions of a pygidium are: length, exclusive of
the spines, 3 mm., width 8 mm., width of axis at anterior margin
2 mm. , approximate length of larger spines 3 or 4 mm.

Remarks. The head and pygidium here associated under
the name Odontopleura illinoiensis have not been observed in
actual position in such a manner a*s to show certainly that
they are parts of the same species, but they are associated in
same bed, and being the only acidaspids there present they are
considered as belonging together. The genus Odontopleura is
represented in American Silurian faunas by only two species
aside from the one here described. Both of these species are
imperfectly known, but 0. illinoiensis differs so markedly from
either of them that no comparisons are necessary.

Locality. Near Joliet.

Genus 13. CERATOCEPHALA Warder, 1838.
In the characters of the glabella and cheeks the members
of this genus closely resemble Addas pis and Odontopleura, but
the occipital segment bears two divergent spines which are
separate at their bases.

THE NATURAL HISTORY SURVEY. 255

Ceratocephala goniata Warder, pi. xxm, figs. 1-2.

Description. Cephalon short and strongly convex, trans-
versely sub-elliptical in outline, the whole surface strongly
tuberculate. Glabella broadly sub-ovate, moderately convex,
scarcely defined by the dorsal furrows which follow a convex
curve and become most strongly impressed at their junction
with the occipital furrow, a little wider than long, the greatest
width at about one-third its length from the occipital furrow,
about three-fifths the entire width of the cephalon, its pos-
terior margin nearly straight; median. lobe well defined, elongate
sub-ovate in outline, its length being equal to the total length
of the glabella, slightly protuberant in front, its greatest width
nearly two-thirds its length, its width in front three-fourths
its width behind, a little more than one-half the width of the
entire glabella, anterior lateral expansions slight and depressed,
coalescing with the ocular ridges; lateral lobes depressed below
the median lobe, the anterior pair almost obsolete and scarcely
separated from the anterior lateral expansions of the median
lobe; second lobes trapezoidal orv sub-rhomboidal in outline,
their longer axes directed obliquely outward and forward,
coalescing laterally with the cheeks; third lateral lobes nearly
twice the size of the second pair, sub-ovate in general outline,
their apices directed obliquely outward and forward, sharply
defined posteriorly by the occipital furrow, coalescing laterally
with the cheeks. Anterior pair of lateral furrows scarcely dis-
tinguishable, second and -third pairs deeply impressed at their
inner extremities, directed obliquely outward and forward.
Cheeks sub-quadrangular in outline, facial sutures not recog-
nizable. Eyes small, situated near the center of the cheeks,
connected anteriorly by a sharply defined, raised, rounded
ocular ridge, with the anterior lateral expansions of the median
glabellar lobe; posteriorly from the eyes a furrow faint at first
but becoming strongly impressed posteriorly, follows a back-
ward, upward and then inward curve to its junction with the
occipital furrow. The inner portion of the cheeks, bounded
anteriorly by the ocular ridge and posteriorly by the furrow, is
convex, its surface being essentially a continuation of the sur-
face of the lateral glabellar lobes, it is sub-ovate in outline,
acutely pointed in front, and is divided longitudinally by
a slight furrow which originates opposite the median glabellar
furrow and extends backward with a slightly convex curve to a
point nearly opposite the posterior glabellar furrow and then

256 THE CHICAGO ACADEMY OF SCIENCES.

curves rather abruptly inward, to meet the occipital furrow;
this furrow is most strongly impressed posteriorly, but is fainter
even than the dorsal furrow. The outer portion of the cheek'
is sub-lunate in outline and descends abruptly to the lateral
margin, anteriorly it is concave below the ocular ridge, posteriorly
its upper margin is elevated into a depressed ridge which is
broader but less sharply denned than the ocular ridge, becom-
ing more elevated as it approaches the base Of the cheek spine;
below this ridge the surface is concave, the lateral and pos-
terior margins are raised into an elevated, rounded border, the
posterior extremity is produced into the slender cheek spines
which extend obliquely -Upward and outward. Occipital fur-
row broad and shallow across the median lobe of the glabella,
becoming narrow and deeply impressed back of the posterior
lateral lobes of the glabella. Median portion of the occipital
segment broad and convex, bearing two slender, nearly erect
and slightly diverging spines whose bases are widely separated ;
on the median line between the spine bases and situated a
little in front of them is a strong rounded tubercle ; the occipital
lobes are strongly convex and rather sharply separated from
the median portion, they are sub-oval in outline, with their
longer axes directed obliquely backward and outward. Thorax
and pygidium unknown.

The dimensions of a nearly perfect cephalon are: width
47 mm., length 17 mm., convexity 22.5 mm., width of glabella
26.5 mm., distance between eyes 35 mm., distance between
bases of cheek spines 42.5 mm.

Remarks. The specimen of this species here illustrated
is from the Van Home Collection in the Walker Museum, and
is the most complete cephalon which has been observed. The
species has no nea^ relative in other Silurian faunas of America,
except C. depauperata van Ing., which is a much smaller form;
it is somewhat closely allied to the Bohemian species C.'ver-
neuili (Barr.), but among other characters it lacks the mar-
ginal spines upon the cephalon which are present in that species.
The name originally applied to the species by Warder was long
overlooked and it was redescribed by Hall as Acidaspis dance,
and by Winchell and Marcy as Acidaspis ida, the type speci-
mens of both these authors being from Bridgeport, Illinois, while
Warder's specimens were from near Springfield, Ohio. Dr.
J. M. Clarke has shown that both these latter names are synony-
mous with Warder's earlier name.

Localities. Bridgeport and Hawthorn.

OrTHI

f UNIVERSITY

V or /

THE NATURAL HISTOR^'S^gjfRJ^.^K/ 257

Order III. PROPARIA Beecher.

'Tree cheeks not bearing the genal angles. Facial sutures,
extending from the lateral margins of the cephalon in front of
the genal angles, inward and forward, cutting the anterior
margin separately or uniting in front of the glabella. Com-
pound paired eyes scarcely developed or sometimes absent in
the most primitive family; well developed and schizochroal in
the highest family." — Beecher, Zittel- Eastman Text Book of
Paleontology, p. 633.

Family 7. ENCRINURIDAE Linnarsson.

"Cephalon narrow, transverse.' Fixed cheeks very large.
Free cheeks long, narrow, separate, sometimes with a free
rostral plate between the anterior extremities. Sutures ex-
tending from in front of the genal angles obliquely forward,
and cutting the anterior margin in front of the glabella. Eyes
very small or absent. Thorax of from nine to twelve segments,
with ridged pleura. Pygidium generally composed of many
segments; limb with strong ribs usually less in number than
the annulations of the axis." — Beecher, Zittel-Eastman Text
Book of Paleontology, p. 634.

Genus 14. ENCRINURUS Emmrich7i845.

Cephalon tuberculated, semi-elliptical in outline, the
genal angles produced into spines or not; glabella prominent,
pyriform, with three pairs of lateral furrows; free cheeks nar-
row, separated in front of the glabella by a small rostral plate;
posterior limb of the facial sutures cutting the lateral margins
just in front of the genal angles; eyes small, more or less elevated
on conical prominences or slender stalks. Thorax with eleven
segments. Pygidium sub-triangular, the axis long with many
more segments than are present upon the pleura.

Encrinurus egani S. A. M., pi. xxiv, figs. 8-11.

Description. Cephalon crescentiform with spreading genal
spines. Glabella clavate, strongly convex, two and one-half
times as broad in front as at the occipital furrow, produced an-
teriorly beyond the frontal margin of the head, the lateral mar-
gins concave, bounded laterally by deep, abrupt and rather
broad dorsal furrows, covered with rather coarse rounded tuber-
cles which are more or less regularly arranged in seven or eight
transverse rows, the two posterior rows containing three or
four tubercles each, while the anterior row may contain as many

258 THE CHICAGO ACADEMY OF SCIENCES.

as eight or more; lateral furrows nearly obsolete, represented
by depressions which are scarcely distinguishable from the de-
pressions between the rows of tubercles. Cheeks with a nar-
row, rounded, more or less indistinct marginal border which
bears about three or four tubercles anteriorly on each side of
the glabella, arranged in a row; produced posteriorly into genal
spines of moderate length; the surface elevated just outside the
dorsal furrow into sub-conical -bases for the support of the
long, slender, Spreading peduncles which support the eyes,
around the base of each eyestalk is a more or less irregular circle
of tubercles similar to those upon thje glabella with a few ad-
ditional irregularly scattered tubercles upon the inner slopes
of the cheeks toward the glabella, the remaining surface of the
cheeks and the eye-stalks smooth.

Thorax with well defined axial furrows, the axis strongly
convex, its width a little less than that of the pleural lobes,
segments eleven in number, the next to the last one bearing a
long slender spine which rises from the median line of the axis
with a moderate backward curve.

Pygidium sub-triangular in outline, produced posteriorly
into a long, slender, upwardly curving spine; axis strongly
defined, the elevated portion extending into the posterior spine,
it is divided into twenty or more short segments which in the
casts are not continuous across the median region, and bears
six tubercles along the median line, which lie between the
inner extremities of the pleural ribs except the most anterior
ones. Pleural lobes slightly flattened adjacent to the axial
furrows, and then curving abruptly downward to the lateral
margins, marked by seven pleural ribs which are stronger ante-
riorly, the last one or two often becoming nearly obsolete, each
rib bears a well-defined tubercle just outside the dorsal furrow,
and two or three of the median ribs often bear a second tubercle
a short distance outside these first ones. A pair of tubercles
is also present at the base of the caudal spine, with two or three
additional indistinct ones along the lateral margins in front of
the base of the posterior spine.

The dimensions of a small, more or less imperfect, but
nearly complete specimen are : total length exclusive of the caudal
spine 29 mm., length of cephalon 8 mm., length of thorax 12
mm., length of pygidium, exclusive of spine 9 mm. The dimen-
sions of a nearly perfect cephalon are: length along median
line 10 mm., distance between tips of genal spines 30 mm.,
greatest width of glabella 10.5 mm., width of axis at occipital

THE NATURAL HISTORY SURVEY. 259

segment 6 mm., length of eye-stalks 7.5 mm. The dimensions
of a large pygidium are: length, exclusive of caudal spine 29
mm,, length of spine 10.5 mm., width at anterior margin 18
mm., width of axis anteriorly 7 mm.

Remarks. This species is remarkable by reason of its elon-
gate eye-pedicles. These eye-stalks are difficult to preserve,
and are usually broken off either before the creatures were
fossilized or by the collectors of the specimens, this being the
condition of the type specimen used by Miller in his description
of the species. The thoracic and caudal spines are also usually
broken. The species is so different from any of the other species
of the genus that no comparison with any of them is necessary.

Localities. Joliet, and Chicago Drainage Canal near Le-
mont.

Encrinurus tuberculifrons, n. sp., pi. xxiv, figs. 12-13.

Description. Cranidium sub-triangular in outline. The
glabella prominent, sub-pyriform, not produced in front be-
yond the anterior margin, bounded by deep dorsal furrows;
lateral furrows three on each side, not continuous across the
median portion of the glabella, but the posterior pair more elon-
gate than the others; occipital furrow well defined entirely
across the posterior margin of the glabella, the occipital seg-
ment narrow; in front the glabella is bordered by a narrow flat-
tened marginal border. Fixed .cheeks strongly convex, with
deep posterior cheek furrows originating at the dorsal furrows
opposite the lateral extremities of the occipital furrow and ex-
tending nearly to the genal angles; genal angles apparently
rounded and not produced into genal spines; eye-lobes small,
elevated. Free cheeks not known. The entire surface of the
glabella and fixed cheeks, except the occipital segment and the
posterior marginal border of the cheeks, covered with small
rounded tubercles, the anterior marginal border in front of the
glabella bears a single continuous, symmetrically arranged row
of tubercles similar to those upon the convex portion of the
glabella.

Pygidium sub- triangular, wider than long, not produced
posteriorly into a caudal spine. The axis prominent, bor-
dered by well defined axial furrows, extending nearly to the
posterior margin, its width in front about one-third the total
width of the pygidium, marked by about fifteen annulations
which become finer and less distinct posteriorly. Pleural lobes
a little flattened adjacent to the axial furrows, the surface curv-

2OO THE CHICAGO ACADEMY OF SCIENCES.

ing abruptly downward laterally to the margins, with six strong
pleural ribs whose extremities are slightly produced, giving to
the pygidium slightly serrate lateral margins.

The dimensions of the best preserved cranidium which has
been observed are: length along median line 6 mm., width be-
tween eyes 9.5 mm., width at posterior margin 13 mm. The
dimensions of a pygidium are: length 5 mm., width 6 mm.

Remarks. This is a small species and is known only from
more or less fragmentary cranidia and pygidia. These two
portions of the body occur together at the only locality where
the species has been observed, and since they are associated
with no other members of the genus, it seems safe to consider
them as portions of a single species. The species is 'especially
characterized by the narrow, flattened anterior marginal border
with its symmetrically arranged row of tubercles. The pygidium
may be distinguished by reason of its proportionately greater
width than is usual in the genus. The condition of preservation
of all the specimens examined leaves it uncertain as to the pres-
ence of genal spines ; these seem to be absent from the specimens
studied but additional material may show that they were pres-
ent.

Locality. Near Joliet.

Family 8. CALYMENIDAE Brongniart.

"Cephalon somewhat wider than long. Fixed cheeks large;
genal angles rounded or produced into spines. Glabella narrow-
ing anteriorly. Free cheeks long, separate, usually with a free
plate between the anterior extremities. Sutures extending from
just in front of the genal angles, converging anteriorly, and
cutting the margins separately. Eyes small, facets numerous,
visual surface seldom preserved. Thorax of thirteen segments,
with grooved pleura. Pygidium of from six to fourteen seg-
ments; axis tapering." Beecher, Zittel-Eastman Text Book of
Paleontology, p. 634.

Genus 15. CALYMENE Brongniart, 1822.

Complete body sub-oval in outline, possessing the power
of complete enrollment; cephalon sub-crescentiform with thick-
ened margin, genal angles usually rounded; glabella strongly
convex, narrowed in front, with three pairs of deep lateral fur-
rows; the occipital segment well defined; posterior limbs of the
facial sutures originating just in front of the genal angles; free
cheeks elongate, separate, usually with a free plate between

THE NATURAL HISTORY SURVEY. 26 1

their anterior extremities in front of the glabella; eyes small;
hypostome sub-quadrate, notched. Thorax with thirteen seg-
ments, the axis strongly convex and bounded by deep axial
furrows; pleural lobes wider than the axis, bent down laterally.
Pygidium distinctly marked off from the thorax, with six to
eleven segments, the axis prominent and the margin entire.
Calymene niagarensis Hall, pi. xxm, figs. 9-10.

Description. Body strongly trilobate, sub-ovate in outline,
greatest breadth at the posterior margin of the cephalon, becom-
ing gradually narrower to the junction of the thorax with the
pygidium, then narrowing much more rapidly to the posterior
extremity of the pygidium. When enrolled the body is sub-
globular.

Cephalon short and broad, from two to two and one-half
times as wide as long, anterior margin most sharply rounded in
front, then sloping away to the genal angles with a gently convex
curve. Glabella strongly convex, elevated above the cheeks,
sharply defined by the deep dorsal furrows, broadest across the
posterior lobes where it is as wide as long, broadly rounded or
almost truncated in front ; frontal lobe occupying less than one-
third the length, transversely sub-semielliptical in outline;
first lateral lobes very small, scarcely separatedTTrom the frontal
lobe; second lateral lobes larger and node-like; posterior lobes
much larger, forming a pair of conspicuous sub-globular nodes
at the base of the glabella. Lateral furrows not extending
across the median portion of the glabella; anterior pair scarcely
recognizable, occupying only the lateral slopes of the glabella;
second pair more conspicuous, rounded in the bottom, nearly
confined to the lateral slopes of the glabella; posterior pain
much broader and deeper, broadened or slightly bifurcate at
their inner extremities, the stronger branch turning backward
toward the occipital furrow, the smaller branch turning slightly
forward, between these two divisions of the furrow is a slight
node upon the side of the glabella. Occipital furrow arching
.forward in the center, rather broad and rounded in the bottom
in the middle, becoming narrower and more deeply impressed
back of the posterior glabellar lobes, extended as a broad pos-
terior cheek, furrow across the posterior portion of the cheeks.
Occipital segment broadest in the middle, becoming narrower
back of the posterior glabellar lobes. Cheeks strongly convex
with rounded, lateral, marginal borders, and sharp, posterior,
marginal borders. Just within the raised marginal borders

262 THE CHICAGO ACADEMY OF SCIENCES.

laterally and posteriorly, are shallow, rounded, concave furrows.
Eyes small, situated opposite the second lateral glabellar lobes.

Thorax consisting of thirteen segments, the length two to
two and one-half times that of the cephalon, strongly trilobed,
the axis about two-fifths the entire width, the pleural lobes
flattened on top for about one-third their width, then curving
abruptly to the lateral margins. The segments arched forward
on the axis, each one bearing a distinct, rounded node on either
side just within the dorsal furrows. The pleura of each segment
marked by a broad, deep, rounded furrow which originates at
the axial furrow and extends two-thirds or more of their length,
becoming shallower and' narrower dis tally and terminating on
the flattened distal portion of the segment as a slender groove
with a slight forward curvature.

Pygidium irregularly sub-pentagonal in outline, strongly
trilobed. The axis tapering posteriorly with an obtusely rounded
extremity and terminating within the marginal border, marked
by six or seven annulations. Pleural lobes with a flattened
area in front, adjacent to the dorsal furrows, which tapers pos-
teriorly and becomes obsolete before reaching the end of the
axial lobe, outside this flattened area the surface slopes ab-
ruptly to the lateral margins ; marked by four or five segments
with no longitudinal depressions, which reach half way or less
than half way from the dorsal furrows to the margins; anterior
lateral angles abruptly flattened, lateral margins raised in a
rounded marginal border which becomes narrower posteriorly.

The dimensions of a small, complete individual are: length
36 mm., greatest width across the posterior margin of the head
23 mm., length of head 10 mm., length of thorax 27 mm.,
'length of pygidium 12.5 mm., width of pygidium 12.5 mm.

Remarks. The discrepancy between the sums of the
lengths of the three regions of the specimen whose dimensions
are given above and the total length of the body, is due to the
fact that in the total dimension no account is taken of the cur-
vature of the dorsal surface of the body, while in taking the
three separate dimensions the measurements were made along
their median dorsal lines.

This species is by far the commonest trilobite in the Niagaran
fauna of the Chicago area, and seems to be present in all horizons.
It is very commonly found with all portions of the body, head,
thorax and pygidium together, a condition of preservation which
is extremely rare in all other species of the fauna.

THE NATURAL HISTORY SURVEY. 263

Localities. Bridgeport, Hawthorn, Joliet, near Lemont,
etc., etc.

Family 9. CHEIRURIDAE Salter.

"Glabella well defined. Free cheeks small, sometimes
much reduced. Sutures extending from in front of the genal
angles inward to the eyes, and then obliquely forward, cutting
the anterior margin in front and on each side of the glabella.
Eyes usually small. Thorax of from nine to eighteen segments,
generally eleven; pleura often extended into hollow spines.
Pygidium. small, with from three to five segments; pleural
elements commonly produced into spines." Beecher, Zittel-
Eastman Text Book of Paleontology, p. 635.

Genus 16. CERAURUS Green, 1832.

Entire body sub-ovate in outline. Cephalon sub-semi-
circular or sub-semielliptical in outline, the genal angles pro-
duced into spines; glabella strongly convex, broadest in front,
with three pairs of deep, lateral furrows; posterior limbs of the
facial sutures cutting the lateral margins well in front of the
genal angles; eyes small. Thorax usually with eleven segments,
rarely nine to thirteen; axis prominent, narrower than the
pleura, bounded by strong axial furrows. Pygidium small, the
pleural segments produced into points or spines.

Ceraurus niagarensis Hall, pi. xx'V. figs. 20-21.

Description. Head sub-circular in outline with slender
genal spines projecting straight backward. Glabella mod-
erately convex, broadest in front, limited by well-defined, im-
pressed dorsal furrows, its posterior margin occupying one-third
of the total width of the head; frontal lobe transversely sub-
elliptical, occupying less than one-half of the entire glabella,
first lateral lobes small, sub-quadrangular; second lateral lobes
larger than the first, narrowest at the dorsal furrow; third lateral
lobes sub-triangular, entirely isolated; first lateral furrows
strong and deep, rounded in the bottom, directed a little back-
ward at their inner extremities, extending less than half way
from the dorsal furrow to the median line of the glabella ; second
lateral furrows similar to the first but a little shorter, their di-
rection nearly transverse; third lateral furrows strong and deep,
continuous across the glabella, shallower in the median portion
and arching backward to become confluent with the -occipital
furrow; occipital furrow about equaling in strength the lateral
furrows of the glabella, its median portion shallower and arching

264 THE CHICAGO ACADEMY OF SCIENCES.

forward to become confluent with the third lateral furrows;
occipital segment broadest in the middle, its surface slightly
higher than that of the glabella on the median line. Cheeks
convex, depressed below the glabella, marked laterally by con-
spicuous marginal furrows continuous with the posterior cheek
furrows which extend to the dorsal furrows, their terminations
being opposite the extremities of the occipital furrows; the con-
vex lateral and posterior marginal borders are produced back-
ward, where they become confluent, into the slender genal spines;
palpebral lobes small, eyes and free cheeks not observed. The
surface of the cheeks lying between the bounding furrows is
pitted, the pits being more or less rounded in shape and crowded
together.

Pygidium broad and short, the axis wedge-shaped with three
annulations and' a narrow, posterior, 'median extension which is
produced a little beyond the posterior margin; pleura flat and
broad with three segments which are produced laterally in
flattened spines directed obliquely outward and backward with
a slight curve, the posterior pair of spines are much shorter than
the others, and the anterior pleural segments are grooved
proximally.

The dimensions of a nearly perfect cranidium are: width
55 mm., length along median line 24.5 mm., length of genal
spines about n mm. The dimensions of a nearly perfect pyg-
idium are: extreme width 26 rnm., width between the bases of
the anterior pleural spines 17 mm., length along median line
7 mm.

Remarks. The geographic distribution of this species is
widespread in the Niagaran formations of the Mississippi valley
region, although it never seems to be a common species. It is
a close ally of the European species C. insignis, and in earlier
years w^as frequently so identified.

Localities. Hawthorn, Chicago Drainage Canal near Le-
mont, etc.

Ceraurus hydei, n. sp., pi. xxiv. fig. 22.

Description. A small species. Cephalon semi-circular in
outline with rather slender genal spines whose extremities are
opposite the posterior margins of the third thoracic segment.
Glabella moderately convex, broadest in front, bounded by well
defined dorsal furrows, its anterior margin not reaching the fron-
tal margin of the head, its posterior margin occupying two-
sevenths of the entire width of the head; frontal lobe sub-

THE NATURAL HISTORY SURVEY. 265

elliptical in outline, occupying nearly one-half of the entire gla-
bella; first and second lateral furrows directed at right angles to
the axis and reaching less than one-fourth of the distance across
the glabella; first and second lateral lobes of equal width at the
margin of the glabella; third lateral furrows stronger and deeper
than the others, directed obliquely backward, continuing
across the glabella and becoming confluent with the occipital
furrow in the middle so that the third lateral lobes are isolated
as sub-triangular nodes. Occipital furrow about equaling in
strength the third lateral glabellar furrows, directed forward
from the lateral margins of the glabella and becoming confluent
with the third lateral furrows in its median portion. Occipital
segment flat, broadest in the middle. Cheeks moderately con-
vex with a flattened marginal border which is produced into the
genal spines and which is continued around the anterior extrem-
ity of the glabella. The lateral marginal furrows make a sharp
turn near the genal angles and extend to the dorsal furrow par-
allel with the posterior margin of the head, leaving a narrow
posterior marginal border. Palpebral lobes of moderate size,
scarcely elevated above the general surface of the cheeks, sit-
uated opposite the anterior lateral furrows of the glabella.
Free cheeks small, triangular. The posterior limbs of the facial
sutures extend directly outward to the margins of the head, the
anterior limbs describe a convex curve nearly parallel with the
margin of the frontal lobe of the glabella to the anterior margin
of the head.

Thorax with eleven segments; the axis moderately convex,
occupying about one-third of the entire width, its sides nearly
parallel, bounded by well-defined axial furrows. The pleura
slightly convex. On each side of the axis a slight furrow nearly
parallel with the axial furrow and lying about one-third the dis-
tance between it and the lateral margin, extends the entire
length of the thorax. Between the axial furrows and these
lateral furrows, each segment of the thorax is grooved, the grooves
starting at the axial furrow from near the anterior margins of
the segments and directed obliquely backward nearly to .their
posterior margins.

Pygidium very short with two conspicuous backwardly
pointing spines; the axis sub-triangular with four segments,
reaching nearly to the posterior margin; pleura indistinctly
divided into three segments, the anterior ones being much the
largest and slightly grooved near the axial furrows, they are
produced posteriorly into the strong spines which are directed

266 THE CHICAGO ACADEMY OF SCIENCES.

obliquely outward and backward, the second segments are much
smaller and are not grooved, their distal extremities make slight
projections upon the posterior margin of the pygidium, third
segments minute.

The dimensions of a nearly complete individual are: total
length 24 mm., length of head 7.5 mm., length of thorax 14 mm.,
length of pygidium 2.5 mm., width of head at posterior margin
15 mm., width of pygidium at anterior margin 7.5 mm.

Remarks. This species is founded upon two nearly com-
plete individuals both of which were collected by Mr. L. H. Hyde
in whose honor the species is named. Some of the characters
mentioned in the description are best shown in one of the speci-
mens and some in the other one. The head of the species is
much like that of a small individual of C. niagarensis, but it
lacks the pitted surface of the cheeks and has the marginal
border continuing around the front of the glabella, the most
conspicuous difference between the two species is found in the
pygidium, C. niagarensis having all the pleural segments pro-
duced into spines, while C. hydei has only the anterior pair of
segments so produced. In the form of its pygidium the species
resembles C. pleurexanthemus of the Trenton limestone faunas,
but the cephalon is not tuberculate as in that species. The
specimen here figured is preserved in the collections of the Walker
Museum, the second specimen -being still retained in the
collection of Mr. Hyde. The greater portion of the outlines
restored in the illustration have be'en drawn in from Mr. Hyde's
specimen.

Locality. Chicago Drainage Canal, near Lemont.

Genus 17. SPHAEREXOCHUS Beyrich, 1845.

Complete body elongate sub-ovate in outline. Cephalon
sub-globular, the cheeks much reduced ; glabella nearly spherical
with the two anterior pairs of lateral furrows nearly or quite
obsolete, the posterior pair deeply impressed, curving backward
to the occipital furrow and cutting off the sub-circular basal
lobes from the glabella; eyes small. Thorax with ten
segments, the axis prominent and bordered by strong axial
furrows; the pleural segments smooth, convex. Pygidium
smaller than the cephalon, the axis comparatively large, pleural
segments three with free points.
Sphaerexochus romingeri Hall, pi. xxiv, figs. 16-19.

Description. Cephalon spheroidal, dorsal furrows strong
and deep, sloping downward from the posterior margin to points

THE NATURAL HISTORY SURVEY. 267

opposite the posterior lateral glabellar furrows where they
bend much more abruptly downward to the frontal margin and
continue across the front as a marginal furrow. The glabella
smooth, sub-globular, comprising nearly the entire head, strongly
protuberant anteriorly beyond the frontal margin; the two
anterior pairs of lateral furrows and lobes often entirely ob-
solete, although the furrows are sometimes represented by
slight undulations at the sides of the glabella; posterior furrows
strong and deep, describing nearly a half circle and extending
from the dorsal furrows in front to the occipital furrows behind,
isolating the posterior, lateral lobes which appear as two nearly
circular nodes at the base of the glabella; occipital furrow
deep and rather broad in its meglian portion, becoming narrower
tback of the posterior glabellar lobes, the occipital segment
narrower, its surface elevated nearly as high as the surface of
the glabella in front of the occipital furrow. Cheeks reduced in
size, sub- triangular in form; anterior limbs of facial sutures
extending upward from the anterior margin parallel with and
close to the outer margin of the dorsal furrows to the eyes,
the posterior limbs directed at nearly right angles to the an-
terior limbs and cutting what appears to be the posterior margin
of the head; eyes small, situated opposite the outer extremities
of the posterior lateral glabellar furrows; fixed cheeks in front
of the eyes occupied entirely by the dorsal furrows, back of the
eyes they are broader, sub-triangular in outline with a deep
post-marginal cheek furrow extending from the lateral ter-
minations of the occipital furrow; free cheeks sub-quadrangular
in form, flattened in their outer half, elevated within to the
margin of the eyes, they are produced posteriorly to such an'
extent that the posterior limbs of the facial sutures seem to cut
the posterior margin of the head as in the order Opisthoparia.

Thorax with ten segments, strongly trilobed, the axis oc-
cupying more than one- third the total width, the inner half of
the pleural lobes flattened, the outer half bent abruptly down-
ward to the lateral margins.

Pygidium small, sub-semicircular in outline; the axis
broad and strongly convex with three segments and a terminal
flattened region; the pleural lobes much reduced in size, divided
into three segments all of which are produced distally as free
points.

The dimensions of a small but nearly perfect cephalon are:
maximum width 14 mm., maximum length 10 mm., height
from frontal margin to occipital segment 1 1 mm.

268 THE CHICAGO ACADEMY OF SCIENCES.

Remarks. This species, next to Calymene niagarensis ,
probably has the widest distribution of any of the trilobites of the
Niagaran fauna of the Chicago area. The glabella is the por-
tion of the species most commonly preserved, and the specimens
are usually larger than the dimensions given above, a width of
18 mm. being a not unusual size. Specimens with the cheeks
well preserved, and especially with the free cheeks are rarely
met with. No specimen with the thorax and pygidium pre-
served has been observed from the Chicago area, but a specimen
in that condition from Madison, Indiana, is preserved in the
collections of the Walker Museum. Isolated pygidia are
sometimes met with, but not often.

The species is somewhat closely allied to the European
5. mirus Beyrich, but the body of the European species is broader
throughout, the head of the American species is much more
globular in form with the glabella much more protuberant
beyond the frontal margin. The pygidium also of the American
species has the pleural lobes much more reduced in size and
with the free points of the pleural segments more produced'.

Localities. Bridgeport, Lemont, Romeo, Joliet, etc.

Genus 1 8. DEIPHON Barrande.

Cheeks of the head reduced to elongate, recurved, spine-
like processes; glabella sub-globular, comprised largely of the
frontal lobe which is greatly produced anteriorly, the lateral
furrows nearly or quite obsolete; free cheeks minute, eyes small,
occupying the angle between the spine-like fixed cheeks and the
glabella. Thorax with nine segments with free spiniform
pleura. Pygidium short, with two pairs of lateral, curved,
spiniform processes.
Deiphon americanus, n. sp., pi. xxiv, fig. 14.

Description. Glabella produced anteriorly, the nearly
globular frontal lobe being larger than all the remaining portion
of the cephalon and being extended in its entirety beyond the
frontal margin. Back of the frontal lobe is a broad, rounded,
occipital furrow marked at either extremity in the casts, by a
conspicuous, circular, pit-like depression, these pits probably
representing a nearly obsolete pair of lateral furrows; occipital
segment narrow, arched transversely. Cheeks reduced to mere
spine-like processes which extend obliquely outward and back-
ward with a slight convex curve, their bases opposite the pit-
like depressions at the extremities . of the occipital furrow.

THE NATURAL HISTORY SURVEY. 269

Eyes small, placed just in front of the bases of the cheek spines,
in the rounded angle between the bases of the spines and the
base of the globular frontal lobe of the glabella, they are raised
on slight prominences which extend obliquely forward. Neither
the pygidium nor the thorax have been observed from the
Niagaran fauna of the Chicago area.

The dimensions of a nearly complete cephalon are: length
along median line 8 mm., width of frontal lobe of the glabella
7.5 mm., width between extremities of cheek spines 19 mm.

Remarks. The presence of the genus Deiphon in the Ni-
agaran fauna from near Batesville, Arkansas, has been noted by
van Ingen*, the Arkansas specimens being identified by that
author with the European D. forbesi Barr. A species of the
genus has also been described and illustrated as Sph&rexochus
pisum by Foerstef, from beds of Clinton age in Ohio, the cheek
spines not being preserved in the specimen figured, and the
presence of the same species in the Niagaran beds of New York
is mentioned. These occurrences, with the presence of the
same genus in the Chicago area, show that this highly specialized
genus had a wide geographic distribution in the North American
epicontinental seas of Silurian age. In Europe the species
D. forbesi Barr., is reported from England and Bohemia.

The species which is here described as D. americana differs '
from the European D. forbesi in its broader' occipital furrow
with the pit-like depressions at either end, and in the more
posterior position of the cheek spines, the bases of these spines
being nearly opposite the middle of the globular frontal lobe
of the glabella in Bohemian examples as illustrated by BarrandeJ.
The Arkansas specimens are probably identical with the Chicago
species, while the Ohio specimens described by Fcerste more
closely resemble the European D. forbesi.

Localities. Joliet, Romeo, Chicago Drainage Canal near
Lemont.

Genus 19. STAUROCEPHALUS Barrande, 1846.

Complete body sub-ovate in outline. Cephalon with a
conspicuous globular anterior glabellar lobe produced entirely
beyond the frontal margin of the head, the lateral glabellar
lobes reduced in size; cheeks of moderate size, convex, with
short genal spines; eyes small. Thorax strongly trilobed,

*School of Mines Quart., Vol. 23, p. 35.

tGeol. Surv. Ohio, Vol. 7, p. 528, pi. 37A, figs. 14 a-b.

SSyst. Sil. Boheme, Vol. 1, Supp., pi. 2, fig. 19.

27O THE CHICAGO ACADEMY OF SCIENCES.

with ten segments. Pygidium small, with three pairs of pleural
segments which are produced distally in backwardly pointing
free points.

Staurocephalus obsoleta, n. sp.. pi. xxiv, fig. 15.

Description. Cephalon, exclusive of the anterior extension
of the glabella, sub-semicircular in outline, the postero-lateral
angles produced into rather short but slender genal spines.
Glabella narrow in its posterior portion, sharply arched trans-
versely, bounded by deep and strong dorsal furrows, tapering
gently from the occipital furrow to a point nearly above the
frontal margin of the cephalon, from this point the frontal
lobe of the glabella expands abruptly into a large globular
extension beyond the frontal margin of the cephalon, the
diameter of the globular frontal lobe being equal to one-half
the total length of the cephalon; lateral glabellar furrows and
lobes obsolete; occipital furrow shallow, rounded in the bottom;
occipital segment narrow, strongly arched transversely. Cheeks
sub-triangular in outline with an ill-defined, rather broad,
marginal border, the eyes elevated nearly to the level of the
glabella, facial sutures not distinguishable; in front of the
eyes the surface of the cheek drops away nearly perpendicularly
to the frontal margin, laterally the slope is very abrupt but
not quite perpendicular, posteriorly and towards the dorsal
furrows the slope is gentle ; the outer margin of the cheeks is
bordered by a row of fine, fringe-like spines, there being about
twelve on each side between the genal angle and the base of
the globular frontal lobe of the glabella. Thorax and pygidium
not recognized.

The dimensions of the type specimen are: total length of
head along median line 6 mm., length of globular frontal lobe
of the glabella 4 mm., maximum width of head 9 mm.

Remarks. This species is one of the rarest trilobites in the
Chicago fauna, a single specimen only having been observed.
The species is a close ally of the European S. murchisoni Barr.,
but it may be distinguished from that species by the obsolete
lateral glabellar furrows.

Locality. Chicago Drainage Canal, near Lemont.

Family 10. PHACOPIDAE Salter.

"Glabella tumid, widest in front. Free cheeks continuous,
united anteriorly. Suture extending from in front of the genal
angles inward to the eyes, and thence forward around the

THE NATURAL HISTORY SURVEY. 271

glabella. Eyes generally large, always with distinct facets,
schizochroal. Thorax of eleven segments, with grooved pleura.
Pygidium usually large and of many segments; limb ribbed;
margin entire or dentate." Beecher, Zittel-Eastman Text
Book of Paleontology, p. 636.

Genus 20. PHACOPS Emmrich, 1839.

Entire body sub-ovate or sub-elliptical in outline. Cephalon
sub-semicircular, the genal angles usually rounded; glabella
strongly convex, very broad and expanded in front, the two
anterior pairs of lateral furrows inconspicuous or obsolete;
free cheeks more or less completely anchylosed with the fixed
cheeks so that the facial sutures are frequently obscure; eyes
large and prominent, with distinct, large facets. Thorax twith
strong axial furrows, segments eleven or twelve in number.
Pygidium semi-circular with entire margin.

Phacops handwerki, n. sp., pi. xxiv, figs. 6-7.

Description. Entire body sub-elliptical in outline, tapering
posteriorly. Cephalon semi-circular with rounded genal angles;
glabella gently convex, sub-quadrangular, the anterior margin
arcuate, reaching to the anterior marginal border of the cephalon,
narrowest at its posterior extremity where it occupies about one-
third of the entire width of the cephalon ; lateral furrows of the
glabella obsolete except the posterior ones which are narrow
and deeply impressed and extend across the entire width of
the glabella; the posterior lobe of the glabella very narrow
with a small rounded node at each end, depressed between the
large frontal lobe and the occipital segment. Occipital furrow
narrow but rather deeply impressed. Occipital segment strongly
arched transversely, the surface sloping with a convex curve
into the occipital furrow. Cheeks sub-triangular, the facial
sutures indistinguishable, the palpebral lobes large, their outer
margins elevated to the height of the glabella; eyes very large,
their length equaling one-half the length of the cephalon, the
height of the faceted portion two-thirds their length; the outer
portion of the cheeks sloping away from the eyes rather abruptly
with a slightly convex curve.

Thorax strongly trilobate with eleven grooved segments;
the axis arched transversely, occupying one-third the width of
the body, tapering slightly to the posterior extremity; the
inner half of the pleural lobes flattened with the surface nearly
horizontal, the outer portion bent abruptly^downward.

272 THE CHICAGO ACADEMY OF SCIENCES.

Pygidium sub-semicircular, twice as wide as long; the axis
sharply defined, occupying one-third the width of the pygidium
at its anterior extremity, tapering posteriorly to the narrowly
rounded extremity which does not reach the posterior margin,
marked anteriorly by two faint annulations; the pleura slightly
flattened adjacent to the axis, sloping laterally with a gently
convex curve to the margins, anteriorly they bear two faint
annulations, but posteriorly they are smooth.

Remarks. The genus Phacops is not a common member of
the Silurian faunas of America, Hall's P. trisulcatus from the
Clinton beds of New York .and Fcerste's P. pidchellus from the
Clinton of Ohio and Tennessee being the only species which
have previously been described. Kindle* has illustrated several
specimens of heads from the Niagaran limestone of northern
Indiana which he compares with P. pulchellus, but they much
more closely resemble the species here described as P. handwerki,
though two of his figures show the genal angles to be sharper
than in the Chicago specimens; the pygidium illustrated by the
same author is much more strongly segmented than P. hand-
werki. Fcerste's original illustrations of P. pulchellus show a
form with the base of the glabella much more contracted than
the Chicago species, and with the pygidium much more strongly
segmented on both axis and pleura.

The nearly perfect specimen illustrated on plate xxiv was
collected by Mr. J. H. Handwerk of Joliet, after vwhom the
species is named.

Locality. Chicago Drainage Canal, near Lemont.

Genus 21. DALMANITES Emmrich, 1845.

Entire body sub-oval in outline, generally angular poster-
iorly. Cephalon sub-crescentiform, the genal angles usually
produced into spines; glabella prominent, broadest in front,
with three pairs of well-marked lateral furrows; cheeks large
with clearly defined facial sutures; eyes large and prominent,
coarsely faceted. Thorax with eleven segments, axial furrows
well-defined, axis strongly convex and narrower than the pleural
lobes. Pygidium large, usually sub-triangular, the posterior
extremity frequently pointed or mucronate ; axis prominent
with numerous segments.
Dalmanites plat \caudatus, n. sp., pi. xxv, figs. 3—5.

Description. Entire body sub-ovate in outline, with a long
caudal spine. Cephalon depressed-convex, semi-elliptical in

*28th Ann. Rep. Dep. Geol. and Nat. Res., Indiana, p. 484, pi. 24, figs. 9-12.

THE NATURAL HISTORY SURVEY. 273

outline to the ends of the genal spines, with a flat, rounded,
median lip-like extension in front, the genal spines about two-
thirds the length of the head along its median line. Glabella
depressed-convex, occupying less than one-third the entire sur-
face of the head, limited. laterally by well-defined nearly straight
dorsal furrows, key-stone shaped in outline, widest in front,
the width at the occipital furrow being about three-fifths
that across the frontal lobe ; frontal lobe transversely sub-ellip-
tical in outline, a little elevated above the surface of the lateral
lobes, its length five-eighths its width, occupying nearly one-
half the entire glabella; first lateral lobes wedge-shaped in out-
line, twice as wide at the dorsal furrow as at their inner ex-
tremities; second lateral lobes quadrangular, smaller than the
first; third lateral lobes similar to the. second but slightly smaller;
externally all three lateral lobes on each side are confluent along
the dorsal furrows, but in the internal casts the lateral furrows
continue to the dorsal furrows ; the inner extremities of the first
lateral furrows are nearly opposite the anterior extremities
of the eyes, from their origin they are directed obliquely outward
and forward, they are most deeply impressed toward their
inner extremities; second lateral furrows nearly transverse
in direction, not continuous across the median portion of the
glabella and not confluent with the dorsal furrows; third pair
of lateral furrows similar in all respects to the second except
that they may be a little longer. Occipital furrow continuous
across the posterior margin of the glabella, joining the dorsal
furrows on either side, it is most strongly impressed at the
lateral extremities, becoming fainter across the median portion
of the glabella. Occipital segment with nearly parallel anterior
and posterior margins, its length a little greater than that of
either the second or third lateral glabellar lobes, and its width
a little greater than the glabella at its posterior margin. Cheeks
sub-triangular in outline with a broad flattened marginal border
which is continuous around the anterior margin of the glabella
with a flat rounded median extension in front. Anterior
limbs of the facial sutures parallel with the margin of the gla-
bella from the anterior extremities of the eyes towards the
anterior margin of the head, then continuing parallel with its
frontal margin completely around the anterior extremity of
the glabella, the sutures from the two sides being continuous;
the posterior limbs directed laterally from the posterior ex-
tremities of the eyes, describing a slightly sigmoidal curve

274 THE CHICAGO ACADEMY OF SCIENCES.

and cutting the lateral margins a little back of a line through
the centers of the eyes. Inner surface of the palpebral lobes
sloping gently upward from the dorsal furrows, the outer margins
bent abruptly upward^ to the facial sutures at the inner borders
of the eyes. Eyes large, sub-crescentiform, their length a little
more" than, half the length of the glabella along its median line,
the height of the faceted portion a little less than one-half
their length ; the' faceted portion nearly vertical posteriorly but
gradually sloping inward more and more to the anterior extrem-
ity where the slope is nearly forty-five degrees. Laterally
from the eyes the surface of the cheeks is gently convex to the
marginal furrows, the marginal border is rather broad and
flattened anteriorly, becoming obsolete back of a line passing
through the posterior extremities of the eyes in the extension
of the cheeks into the genal spines. The posterior cheek furrows
are continuous from the dorsal furrows nearly to the lateral
margins, laterally they curve backward but are not confluent
with the lateral cheek furrows.

Thorax with eleven segments; the axis strongly defined,
moderately convex, occupying less than one-third the entire
width; pleural lobes flattened on top for more than one-half
their width and then curving rather abruptly downward to the
lateral margins ; the pleura conspicuously grooved longitudinally,
the grooves nearly bisecting each segment from the dorsal
furrow .to the point where they bend downward, then curving
backward and becoming obsolete before reaching the extrem-
ities of the segments.

Pygidium sub-triangular in outline, with a long, slender,
flattened caudal spine whose length is more than one-half the
total length of, the pygidium. Axis well defined, depressed-
convex, occupying less than one-third the width of the pygidium
anteriorly, tapering posteriorly and terminating within the
proximal extremity of the caudal spine, divided into twelve
segments by transverse furrows which are deeply impressed
laterally in the internal casts but are much fainter across the
median portion of the axis. The pleural lobes are flattened
for more than half their width from the furrows, and then
slope rather abruptly to the lateral margins, they are divided
into eight grooved segments which -curve backward distally
and become obsolete just within the lateral margin, posteriorly
the segments become much fainter, the last one or two sometimes
being scarcely distinguishable.

THE NATURAL HISTORY SURVEY. 275

The dimensions of a small, nearly complete individual
are: total length 41.5 mm., greatest width between extremities
of genal spines 21.5 mm., length of head along median line n
mm., length of thorax 14 mm., length of pygidium 16.5 mm.,
The dimensions of a nearly perfect head are: total length to
extremities of genal spines 43.5 mm., greatest width 44 mm.,
length along median line 26 mm. The dimensions of a nearly
perfect pygidium are: length 42 mm., length of axis 17.5 mm.,
length of caudal spine 24.5 mm., total width 30.5 mm.

Remarks. This species is one of the commonest members
of the genus Dalmanites in the Chicago fauna. It is allied to
the British D. longicaudatus Murch., but differs from that
species in its flat caudal spine and in the less produced and
less mucronate anterior extension of the cephalon. The species
also resembles D, limnlurus (Green) from the New York Niagaran
faunas but has the caudal spine flattened and much more
elongate.

The smaller, nearly complete specimen and the nearly
perfect pygidium illustrated on plate xxv, were collected by
Mr. L. H. Hyde.

Locality. Chicago Drainage Canal near Lemont.

Dalmanites illinoiensis, n. sp., pi. xxv, figs. 1—2.

Description. Pygidium large, sub-triangular in outline,
wider than long, with a short caudal spine which is broad and
flat at its base becoming rapidly narrower and terminating in
a very acute point. The axis together with the segmented
portion of the pleural lobes, form a semi-elliptical, depressed
convex area surrounded laterally and posteriorly by a broad,
smooth, flattened marginal border which is produced pos-
teriorly into the caudal spine. The axis is depressed-con-
vex, sharply defined by dorsal furrows, its width at the anterior
margin of the pygidium is about two-ninths of the greatest,
width of the pygidium, it tapers posteriorly and terminates
in a bluntly rounded extremity at the edge of the flattened
marginal border, it is divided into fifteen segments by trans-
verse furrows which are deeply and sharply impressed laterally
but across the median portion they are shallower and less strongly
defined. The surface of the pleural lobes is flattened for about
one-half their width from the dorsal furrows and then gently
convex to the inner edge of the marginal border, they are di-
vided into eleven deeply grooved segments, the grooves ex-

276 THE CHICAGO ACADEMY OF SCIENCES.

tending from the dorsal furrows to the inner edge of the mar-
ginal border. Head and thorax not known.

The dimensions of a very perfect pygidium are: total
length to end of caudal spine 57 mm., length of axis 36 mm.,
total width 67 mm., width of axis at anterior margin of pygidium
15 mm.

Remarks. This pygidium has been observed from several
different localities and always attains about the same size, but
no heads have been seen which can be associated with it. In
general form the pygidium resembles that of D. verrucosus
Hall, more closely than any other species, but it does not have
the tubercles of that species and the marginal border is broader
and more conspicuous.

Localities. Joliet, Bonfield, Chicago Drainage Canal near
Lemont.

Dalmanites vigilans Hall, pi. xxiv, figs. 1-4.

. Description. Cephalon moderately convex, semi-elliptical
in outline to the ends of the genal spines, with an anterior,
median, upwardly curving, spine-like extension, the entire
length of which has in no case been observed. Surface of the
glabella flattened back of the first pair of lateral furrows and
convexly curved to the front, wedge-shaped in outline, widest
in front, limited laterally by the dorsal furrows which are well
defined except opposite the posterior half of the first lateral
glabellar lobes, the entire glabella occupying about one-third of
the cephalon; frontal lobe transversely sub-elliptical in outline,
most strongly elevated at its posterior border, sloping to its
anterior border with a gently convex curve, occupying about
one-half of the entire glabella, its length about five-sevenths
its width; first lateral lobes wedge-shaped in outline, twice as
wide at their outer margin as within, their posterior halves
confluent with the cheeks across the dorsal furrows; second
lateral lobes quadrangular, smaller than the first and some-
what confluent with them externally; third lateral lobes similar
to the second but slightly smaller and wholly separate from
them; first lateral furrows directed obliquely outward and
forward, not continuous across the median portion of the
glabella, their inner extremities in front of the anterior margins
of the eyes, most deeply impressed internally, becoming nearly
obsolete at the dorsal furrows; second lateral furrows nearly
transverse in their direction, not continuous across the median
portion of the glabella, deeply impressed 'within, becoming

THE NATURAL HISTORY SURVEY. 277

obsolete externally or connected with the dorsal furrows with
faint depressions; third lateral furrows similar to the second
except that they are continuous to the dorsal furrows with their
full depth. Occipital furrow continuous across the posterior
margin of the glabella, most deeply impressed toward its lateral
extremities. Occipital segment with nearly parallel anterior
and posterior margins, its width a little greater than the glabella
at its posterior margin. Cheeks sub-triangular in outline with
a marginal border of moderate width which is continuous around
the anterior extremity of the glabella, and from which the
anterior median spine-like extension is produced. Anterior
limbs of the facial sutures passing forward from the anterior
extremities of the eyes close along the outer margins of the
dorsal furrows, then crossing the dorsal furrows opposite the
lateral extremities of the frontal lobe of the glabella and con-
tinuing around the anterior margin of the glabella close to the
anterior edge of the frontal lobe; posterior limbs of the facial
sutures not well shown in the specimens. Surface of the
palpebral lobes sloping abruptly upward from the dorsal furrows
with the outer border bent still more abruptly upward, so bring-
ing the inner margin of the eye far above the level of the glabella.
Eyes large, their outer margins describing a little more than a
semi-circle, the faceted surface nearly vertical, separated ex-
teriorly from the cheeks by an undercut furrow, the entire surface
elevated above the surface of the glabella. The surface of the
cheeks is most prominent anteriorly from the eyes, they slope
away from the base of the eyes, laterally and anteriorly, rather
abruptly to the lateral cheek furrows which are well denned,
then after this interruption they continue their abrupt slope to
the margin, becoming less abrupt anteriorly; posteriorly each
cheek is marked by a marginal furrow which is continuous
behind the eyes with the occipital furrow, and joins the lateral
cheek furrows at their outer extremities; the genal angles are
produced posteriorly into spines of moderate length.

Pygidium sub-triangular in outline, rather strongly convex,
mucronate posteriorly but not produced into an elongate caudal
spine; the axis well denned, about one-third the width of the
pygidium anteriorly, divided into eleven segments by trans-
verse furrows which, in the casts, are deeply impressed laterally
becoming much shallower across the median portion of the
axis; pleural lobes flattened within, sloping rather abruptly
at the sides to the lateral margins, without a flattened marginal
border, divided into about nine grooved segments which d^

278 THE CHICAGO ACADEMY OF SCIENCES.

not quite reach the lateral margins and which become obsolescent
posteriorly. Thorax unknown.

The dimensions of an imperfect cephalon with the anterior
median projection only partially preserved are: total length
along the median line 24.5 mm., length of glabella from posterior
margin of head 15 mm., length of anterior spine so far as pre-
served, measured from the anterior margin of the glabella, 9.5
mm., total width 33 mm., height of eyes above surface of glabella
4.5 mm. The dimensions of a nearly complete pygidium are:
length 17 mm., width 20 mm., length of axis 13 mm., width of
axis anteriorly 7 mm.

Remarks. This species was originally described by Hall
from specimens collected in the dolomitic Niagaran limestone
at Waukesha, Wisconsin. The type specimens, judging from
the illustrations, agree in all respects with the Chicago specimens,
but the anterior spine-like prolongation of the head is drawn
as a short, acuminate process. More than the broken base of
this process is rarely seen, and in no individual has its full extent
been observed. In Hall's type specimen the process was prob-
ably incomplete and doubtless appeared to be as his figure
shows, but in reality the figure is probably erroneous in this
particular.

At a later date a trilobite occurring commonly in the
Waldron fauna of Indiana was identified with this v Wisconsin
species; the pygidia of the two forms are much alike, but the
cephalon of the Waldron form does not possess the elongate
anterior process, and the eyes are not nearly so highly elevated
above the surface of the glabella. The two forms are clearly
distinct, and the name D. halli has been applied to the Waldron
species in the bibliographic list of species in the earlier portion
of this Bulletin (p. 195).

Localities. Joliet, Chicago Drainage Canal near Lemont.

Dalmanites arkansanus van Ingen, pi. xxiv, fig. 5.

Description. Cephalon sub-triangular in outline, bluntly
rounded in front, moderately convex, flattened on the axial
portion between the eyes, the surface sloping abruptly to the
lateral margins. Glabella sub-pentagonal in .outline, the an-
terior margin coincident with the anterior margin of the head,
broadest through the middle of the frontal lobe, width along
the posterior margin one-half the maximum width, bounded
laterally by shallow dorsal furrows which are somewhat deepened
as they approach the occipital furrow; frontal lobe large, sub-

THE NATURAL HISTORY SURVEY. 279

rhomboidal or sub-triangular in outline; first and second lateral
lobes confluent at their outer margins, the first lobes sub-
triangular in outline, the second sub-circular or sub-elliptical,
but little more than half the size of the first ; third lateral lobes
much smaller than the second, wider at their outer extremities
than within; first lateral furrows the longest, broad and of
moderate depth, straight, extending obliquely inwards and
backwards from just in front of the anterior margins of the
eyes, not joined across the median portion of the glabella, the
width of the unfurrowed median region being one-half the width
of the glabella along its posterior margin ; second lateral furrows
nearly transverse in direction, situated opposite the posterior
third of the eyes, not joined across the glabella, their inner
extremities lying directly behind the inner extremities of the
anterior furrows, they are deeply impressed within and, in the
casts, are joined with the dorsal furrows externally by very
slight depressions; third lateral furrows deeply impressed, their
inner extremities curving slightly forward and terminating
directly behind the inner extremities of the two anterior pairs
of furrows. Occipital furrow narrow, most deeply impressed
laterally, arched forward in its median portion. Occipital
segment broadest in the middle. Cheeks rather large, sub-
triangular in outline, genal angles produced into short spines,
the lateral and posterior margins with a raised marginal border
which is rounded laterally but becomes sharply elevated poster-
iorly as it approaches the axial portion of the cephalon; the
marginal furrows within the raised marginal borders are deepest
and most sharply defined posteriorly behind the eyes, they are
shallower and broader as they round the genal angles and then
become a little deeper in the middle portion of the lateral mar-
gins; within the marginal furrows the surface of the cheeks is
moderately convex. The palpebral lobes elevated at their
outer margins to the height of the surface of the glabella; the
eyes are large and prominent, their length being about five-
twelfths the length of the cephalon along its median line, and
the height of the faceted portion three-fifths their length.
Thorax and pygidium not recognized.

The dimensions of a nearly complete head are : length along
median line 24 mm., width at extremities of genal spines 31.5
mm., maximum width of glabella 16 mm., width of glabella
posteriorly 9.5 mm.

Remarks. This species is readily distinguished from any
other members of the genus in the Chicago fauna by reason of

28O THE CHICAGO ACADEMY OF SCIENCES.

the anterior position of the front margin of the glabella, the
cheeks in this species not being connected around the front of
the glabella by a flattened border. It is an unusual type of
Dalmanites in the American Silurian faunas, the only other
known occurrence being in the St. Clair limestone of Inde-
pendence County, Arkansas, the species in the two regions
apparently being identical.

Locality. Chicago Drainage Canal, near Romeo and near
Lemont.

Dalmanites verrucosus Hall. pi. xxv, figs. 6-7.

Description. Head with genal spines attached, sub-
crescentiform in outline, the outer margin describing a semi-
ellipse, the surface depressed-convex. Glabella depressed-con-
vex, key-stone shaped, broadest in front, limited by well-defined
dorsal furrows; frontal lobe transversely sub-elliptical in outline,
occupying about one-half the entire glabella, its length nearly
two-thirds its width; first lateral lobes wedge-shaped in outline,
nearly twice as wide at the dorsal furrows as at the inner ex-
tremities of the lateral furrows ;. second lateral lobes quadrangu-
lar, smaller than the first; third lateral lobes similar to the
second but a little smaller; lateral furrows deeply impressed,
not continuous across the median third of the glabella, the
anterior pair extend obliquely inward and backward from
their points of origin on the dorsal furrows and are a little less
sharply defined than the two posterior pairs which are trans-
verse in their direction, the posterior pair are connected across
the median portion of the glabella by a slight depression. Oc-
cipital furrow deeply impressed laterally, shallower in the middle
and arched a little forward. Occipital segment about equal
in width to the posterior glabellar lobes, its surface level with
the glabella. Cheeks convex, sub-triangular in outline; the
marginal border rather broad and flattened, continuous around
the anterior extremity of the glabella, abruptly separated from
the convex portion of the cheeks by the marginal furrows, and
produced posteriorly into rather broad genal spines ; the posterior
cheek furrows are strong and deep, originating at. the dorsal
furrows and continuing to the marginal furrows with which
they coalesce in front of the bases of the genal spines; eyes
prominent, their summits a little higher than the surface of the
glabella, their faceted surface describing a sub-semicircle.

Pygidium sub-triangular or sub-elliptical in outline, ab-
ruptly produced posteriorly into a sharp spine of moderate

THE NATURAL HISTORY SURVEY. 28 1

length; the axis about two-sevenths of the entire width at the
anterior margin, limited laterally by strong lateral furrows,
tapering posteriorly to the base of the caudal spine, with eleven
or twelve annulations, the transverse furrows being deeply
impressed laterally, becoming broader and shallower and
arched forward over the median half of the axis; the pleura
moderately convex with a slight flattening upon the lateral
margins which can scarcely be designated as a marginal border,
marked by eight or nine strongly defined segments, all but the
posterior two or three of which are deeply grooved.

The surface of the head, except in the furrows on the mar-
ginal and posterior borders and palpebral lobes, is covered with
rather coarse, scattered, rounded tubercles. The pygidium
is also tuberculate, each annulation o'f the axis bearing a strong
median tubercle with two or three upon each lateral slope;
upon the pleural segments each division bears a line of low
tubercles along its summit which are much less conspicuous
than those of the axis.

The dimensions of an imperfect head are: width 37 mm.,
approximate length along median line 22 mm., approximate
length to tips of genal spines 36 mm. The dimensions of an
imperfect pygidium are: approximate length 40 mm., width
46 mm.

Remarks. This species has not been actually observed in
the Chicago area, but it occurs rarely in the dolomitic limestone
at Bonfield and elsewhere in Illinois, and may yet be found in
our area. Its tuberculate surface markings will, always serve
to distinguish it from other similar species of the genus.

Localities Bonfield 111., and Jersey County, 111.

EXPLANATION OF PLATE XVI.

Figures 1-3 ILLAENUS HARRISI n. sp p. 218

Anterior, dorsal and lateral views of the type specimen, from
Bridgeport. (Pal. Coll. Walker Museum, No. 8,613. Collect-
ed by G. F. Harris).

Figures 4-6 ILLAENUS GRAFTONENSIS M. & W p. 223

Dorsal, anterior and lateral views of a nearly perfect cephalon
from Joliet. (Pal. Coll. Walker Museum, No. 6.855, Gurley

Collection.)

»

Figures 7-9 ILLAENUS TRANSVERSALIS n. sp p. 224

Anterior, dorsal and lateral views of the type specimen, the
lateral and anterior views restored in part, from Bridgeport.
(Pal. Coll. Walker Museum, No. 8,614. Collected by G. F.
Harris.)

Figures 10-12 ILLAENUS CHICAGOENSIS n. sp p. 220

Anterior, dorsal and lateral views of the type specimen, from
Hawthorn. (Pal. Coll. Walker Museum, No. 9,910, Van
Home Collection.)

Figures 13-16 ILLAENUS IMPERATOR Hall p. 225

13-15, Dorsal, anterior and lateral views of an incomplete small
cranidium. 16, Dorsal view of a pygidium. Both spec-
imens from Joliet. (Pal. Coll. Walker Museum, No. 10,728,
Van Home Collection.)

PLATE XVI.

EXPLANATION OF PLATE XVII.

Figures 1-5 ILLAENUS INSIGNIS Hall p. 215>

1-3, Dorsal, anterior and lateral views of a nearly complete
cephalon. 4-5, Lateral and dorsal views of a nearly com-
plete pygidium. Both specimens from Hawthorn. (Pal.
Coll. Walker Museum, No. 9,902, Van Home Collection.)

Figures 6-9 ILLAENOIDES TRILOBA n. sp p. 22(>

(See also Plate XIX., Figs. 12-14.)

6, Dorsal view of an incomplete specimen preserving the head,
thorax and pygidium from nearLemont. (Pal. Coll., Walker
Museum, No. 9,871, collected by L. H. Hyde). 7-9, Anterior,
dorsal and lateral views of a nearly complete cephalon, from
Bridgeport. (Pal. Coll. Walker Museum, No. 10,732. Van
Home Collection.)

PLATE XVII,

EXPLANATION OF PLATE XVIII.

Figures 1-3 ILLAENUS icxus Hall p. 222

Dorsal, anterior and lateral views of a complete cephalon, from
Joliet. (Pal. Coll. Walker Museum, No. 10, 729, Van Home Col-
lection).

Figures 4-6 ILLAENUS ARMATUS Hall p. 222

Lateral, anterior and dorsal views of a complete cephalon, from
Lockport. (Pal. Coll. Walker Museum, No. 9,896, Van Home
Collection).

PLATE XVIII.

6

OF THE

UNIVERSITY

Or

EXPLANATION OF PLATE XIX.

Figures 1-6 ILLAENUS CUNICULUS Hall p. 219»

1—3, Dorsal, anterior and lateral views of a nearly complete
cranidium, from Wauwatosa, Wis. (Pal. Coll. Walker Museum
No. 10,730.) 4-6, Dorsal, lateral and anterior views of a
small but nearly complete cephalon, from Bridgeport. (Pal.
Coll. Walker Museum, No. 6,853, Gurley Collection.)

Figures 7-11 ILLAENUS NIAGARENSIS Whitfield p. 219'

7—8, Dorsal and lateral views of an incomplete specimen pre-
serving the head, thorax and pygidium. 9, Anterior view of
the same specimen, from Joliet. (Egan Collection, Chicago
Academy of Sciences.) 10—11, Lateral and dorsal views of a
nearly complete pygidium, from Lockp'ort. (Pal. Coll. Walker
Museum, No. 10,731, Van Home Collection.)

Figures 12-14 ILLAENOIDES TRILOBA n. sp p. 226»

(See also Plate XVII, Figs. 6-9.)

12-13, Lateral and dorsal views of a large cranidium. (Pal.
Coll. Walker Museum. No. 9,897). 14, Dorsal view of a large
pygidium. Both specimens from near Lemont. (Pal. Coll.
Walker Museum, No. 9,872. Collected by L.H. Hyde.)

PLATE XIX

EXPLANATION OF PLATE XX.

^Figure 1 BRONTEUS ACAMAS Hall p. 232

Dorsal view of a nearly complete pygidium, from Romeo. (Pal.
Coll. Walker Museum, No. 10,733. Collected by J. H. Ferris.)

Figure 2 HARPES TELLERI n. sp p. 213

Dorsal view of the type specimen, a nearly complete cranidium,
from Milwaukee, Wis. (Collection of Mr. E. E. Teller plasto-
type, Pal. Coll. Walker Museum, No. 10,734.)

Figures 3-5 CYPHASPIS INTERMEDIA n. sp p. 231

3, Dorsal view of an incomplete cranidium with the free cheeks
restored in outline. 4—5, Dorsal view of another cranidium
with the profile in outline. Both specimens from near
Channahon, Will Co., 111. (Pal. Coll. Walker Museum, No.
10,735.)

Pigures 6-7. PROETUS CHANNAHONENSIS n. sp p. 228

6, Dorsal view of a nearly complete cephalon. 7, Dorsal view
of a pygidium. Both specimens from near Channahon,
Will Co., 111. (Pal. Coll. Walker Museum, No. 10,736.)

Figures 8-9 PROETUS? HANDWERKI n. sp p. 229

Dorsal -and lateral views of the type specimen from near
Lemont. (Pal. Coll. Walker Museum, No. 9,911. Collected
by J. H. Handwerk.)

Pigures 10-12 ARCTINURUS OCCIDENTALIS Hall .....p. 247

10, Dorsal view of an incomplete pygidium, from Bonfield,
111. (Pal. Coll. Walker Museum, No. 6,867, Gurley Col-
lection.) 11, Dorsal view of another incomplete pygidium,
from Joliet. (Pal. Coll. Walker Museum, No. 10,738, Van
Home Collection.) 12, Fragment of the anterior portion of
a cephalon which may belong to this species, from near
Lemont. (Pal. Coll. Walker Museum, No. 10,739.)

Pl.ATK XX

^ Of THg

UNIVERSITY

,.OF

EXPLANATION OF PLATE XXI.

Figures I-^METOPOLICHAS PUGNAX W. & M p.

1—2, Dorsal and lateral views of an incomplete cranidium with
the cheeks restored in outline. 3, Dorsal view of a free cheek.
Both specimens from Bridgeport. (Egan Collection, Chi-
cago Academy of Sciences.) 4, Dorsal view of an incom-
plete pygidium, restored in outline. (Pal. Coll. Walker
Museum, No. 9,861, Van Home

PLATE XXI

^EXPLANATION OF PLATE XXII.

Figures 1-4 CORYDOCEPHALUS PHLYCTAINODES Greene... p. 234

. 1, Dorsal view of a slightly distorted cranidium preserving
some of the spines, from near Lemont. (Pal. Coll. Walker
Museum, No. 10,741, Collected by J. H. Handwerk.) 2, Dor-
sal view of a nearly complete pygidium, from near Lemont.
(Pal. Coll. Walker Museum, No. 10,743.) v3-4, Dorsal and
lateral views of a nearly complete cranidium, from near ,
Lemont. (Pal. Coll. Walker Museum, No. 10,742.)

Figures 5-7 DICRANOPELTIS NASUTA n. sp p. 240

5-6, Lateral and dorsal views of an incomplete cranidium. 7,
Ventral view of the anterior portion of another incomplete
cranidium. Both specimens from Milwaukee, Wis. (Col-
lection of Mr. E. E. Teller.)

Figures 8-9 -DICRANOPELTIS TELLERI n. sp p. 241

Dorsal and lateral views of the type specimen, a nearly com-
plete cranidium, from Milwaukee, Wis. (Collection of Mr.
E. E. Teller.)

Figures 10—11 DICRANOPELTIS DECIPIENS W. & M p. 237

10, Dorsal view of an incomplete cephalon, restored in out-
line, from near Lemont. (Pal. Coll. Walker Museum, No.
9,876. Collected by L. H. Hyde.) 11, Dorsal view of a
nearly complete pygidium, from Hawthorn. (Pal. Coll.
Walker Museum, No. 8,610. Collected by G. H. Harris.)

Figures 12—13 METOPOLICHAS FERRISI n. sp p. 244

12, Dorsal view of an incomplete cranidium. 13, Dorsal
view of a nearly complete pygidium. Both specimens from
near Channahon, Will Co., 111. (Pal. Coll. Walker Museum,
No. 10,737.)

Figure 14. ARCTINURUS CHICAGOENSIS n. sp p. 248

(See also Plate XXIII., Figs. 7-8.)

A nearly complete hypostome believed to belong to this species,-
from Hawthorn. (Pal. Coll. Walker Museum, No. 10,744,
Van Home Collection.)

PLATE XXII.

OF THE

I UNIVERSITY )

OF

EXPLANATION OF PLATE XXIII.

Figures 1-2 CERATOCEPHALA GONIATA Warder p. 255

Anterior and lateral views of a nearly complete cephalon,from
Hawthorn (Pal. Coll. Walker Museum, No. 9,885, Van
Home Collection.)

Figures 3-4 ACIDASPIS VANHORNEI n. sp p. 251

Dorsal and lateral views of the type specimen, from Bridge-
port. (Pal. Coll. Walker Museum, No. 9,886, Van Home Col-
lection.)

Figures 5-6 ODONTOPLEURA ILLINOIENSIS n. sp p. 253

5, Dorsal view of an incomplete cranidium. 6, Dorsal view of
a nearly complete pygidium. Both specimens from near
Joliet. (Pal. Coll. Walker Museum, No. 10,745.)

Figures 7-8 ARCTINURUS CHICAGOENSIS n. sp p. 248

7, Dorsal view of an incomplete cranidium. 8, Dorsal view of
an incomplete pygidmm restored in outline. Both speci-
mens from Hawthorn. (Pal. Coll. Walker Museum, No.
9,860, Van Home Collection.)

Figures 9-10 GALYMENE NIAGARENSIS Hall p. 261

Lateral and dorsal views of a nearly complete individual, from
near Lemont. (Pal. Coll. Walker Museum, No. 10,746.)

PLATE XX I II.

10

OF THE

UNIVERSITY

OF

EXPLANATION OF PLATE -XXIV.

Figures 1-4 DALMANITES VIGILANS Hall p. 276

1-2, Dorsal and lateral views of an incomplete cephalon, from
near Lemont. (Pal. Coll. Walker Museum, No. 9,879. Col-
lected by L. H. Hyde.) 3, Dorsal view of an incomplete
cephalon, from Joliet. (Pal. Coll. Walker Museum, No.
9,909, Van Home Collection.) 4, Dorsal view of a nearlv
complete pygidium,from near Lemont. (Pal. Coll. Walker
Museum, No. 10,747.)

Figure 5 DALMANITES ARKANSANA v. Ing p. 278-

Dorsal view of a nearly complete cephalon, from Romeo. (Pal.
Coll. Walker Museum, No. 10,748. Collected by J. H.
Handwerk.)

Figures 6-7 PHACOPS HANDWERKI n. sp p. 271

6. Dorsal view of a nearly complete cephalon. 7, Dorsal view
of a nearly complete individual. Both specimens from near
Lemont. (Pal. Coll. Walker Museum, No. 10,749. Collected
by J. H. Handwerk.)

Figures 8-11 ENCRINURUS EGANI S. A. M . .p. 257

8, Dorsal view of a nearly complete cephalon, preserving the
elongate eye-stalks, from near Lemont. (Pal. Coll. Walker
Museum, No. 9,901. Collected by J. E. Webb.) 9, Doisal
view of a nearly complete individual, from near Lemont.
(Pal, Coll. Walker Museum, No. 9,905, Van Home Collec-
tion.) 10-11, Dorsal and lateral views of a nearly com-
plete pygidium. (Pal. Coll. Walker Museum, No. 10,750,
Van Home Collection.)

Figures 12-13 ENCRINURUS TUBERCULIFRONS n. sp p. 259

12, Dorsal view of an incomplete cranidium. 13, Dorsal view
of a pygidium. Both specimens from near Joliet. (Pal.
Coll. Walker Museum, No. 10,751.)

Figure 14 DEIPHON AMERICANUS n. sp p. 268.

Dorsal view of a nearly complete cephalon, from near Lemont.
(Pal. Coll, Walker Museum. No. 9,899.)

Figure 15 STAUROCEPHALUS OBSOLETUS n. sp. . , p. 270

Dorsal view of the type specimen, a nearly complete cephalon,
from near Lemont. (Pal. Coll. Walker Museum, No. 9,870.
Collected by L. H. Hyde.)

Figures 16-19 SPHAEREXOCHUS ROMINGERI Hall p. 266

16, Dorsal view of a complete cranidium. 17-18, Ventral and
lateral views of a complete cephalon. Both specimens from
near Lemont. (Pal. Coll. Walker Museum, No, 5,270.) 19,
Dorsal view of a pygidium. (After Hall.)

Figures 20-21 CERAURUS NIAGARENSIS Hall p. 263

20, Dorsal view of a nearly complete cranidium. 21, Dor-
sal view of a nearly complete pygidium. Both specimens
from near Lemont. (Pal. Coll. Walker Museum, Nos. 9,874
and 9,875. Collected by L. H. Hyde.).

Figure 22 CERAURUS HYDEI n. sp p. 264

Dorsal view of a nearly complete individual, from near Le-
v mont. (Pal. Coll. Walker Museum, No. 9,873. Collected by
L. H. Hyde.)

PLATE XXIV.

EXPLANATION OF PLATE XXV.

Figures 1-2 DALMANITES ILLINOIENSIS n. sp p. 275

1, Dorsal view of a nearly complete pygidium, from Bonfield,
111. (Pal. Coll. Walker Museum, No. 6,835, Gurley Collection.)
2, Dorsal view of another less complete pygidium, from near
Lemont. (Pal. Coll. Walker Museum, No. 9,913.)

Figures 3-5 DALMANITES PLATYCAUDATUS n. sp p. 272

3, Dorsal view of a nearly complete cephalon, a plaster cast
from a natural mould, from near Lemont. (Pal. Coll. Wal-
ker Museum, No. 10,752.) 4, Dorsal view of a nearly com-
plete pygidium, from near Lemont. (Pal. Coll. Walker Mu-
seum, No. 9,878. Collected by X. H. Hyde.) 5, Dorsal
view of a nearly complete individual, from near Lemont.
(Pal. Coll. Walker Museum, No. 9,877. Collected by L. H.
Hyde.)

Figures 6—7 DALMANITES VERRUQOSUS Hall p. 280

. 6, Dorsal view of an incomplete cephalon, from Bonfield,
111. (Pal.'Coll. Walker Museum, No. 6,834, Gurley Collec-
tion.) 7, Dorsal view of an incomplete pygidium, from
Jersey County, 111. (Pal. Coll. Walker Museum, No. 6,833,
Gurley Collection.)

PLATE XXV.

14 DAY USE

RETURN TO DESK FROM WHICH BORROWED
LOAN DEPT.

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