A new Devonian trilobite from southern Illinois

"L I B RAFLY

OF THE
UN IVLRSITY
OF ILLINOIS

bb05

REMOTE

GEOLOGICAL SERIES

OF
FIELD MUSEUM OF NATURAL HISTORY

Volume yi Chicago, December 11, 1933 Pages 67-82

A NEW DEVONIAN TRILOBITE FROM
SOUTHERN ILLINOIS

By Sharat Kumar Roy
Assistant Curator of Invertebrate Paleontology

INTRODUCTION

The trilobite here described and illustrated was collected by the
late Henry Pratten in 1850 from a chert bed at the Devil's Back
Bone, near Grand Tower, Jackson County, southern Illinois. In
1912, Field Museum acquired it with several other fossils and a
small collection of rocks and minerals, by purchase from Mr. Pratten's
daughter-in-law, Mrs. Josie Pratten of Chicago. The present writer,
however, was not aware of this purchase and it was only recently,
while going through the study collections of Devonian trilobites,
that this remarkable specimen first came to his attention.

Henry Pratten was assistant to David Dale Owen in field work,
the results of which were afterward published in 1852 as "Owen's
Geological Survey of Wisconsin, Iowa and Minnesota." The
library of the Museum has three volumes of Pratten's original field
notes which he took while he was connected with Owen and later
with James G. Norwood. Nowhere in these notes, however, could
any reference to the present specimen be found.

The writer here wishes to express his appreciation to Dr. Carey
Croneis of the University of Chicago for giving helpful suggestions
and reading the entire manuscript, and to Dr. B. F. Howell of
Princeton University and his secretary, Miss Delia A. Mauer, for
providing him with a complete bibliographic index of the Devonian
Dalmanites which has greatly aided in the preparation of this paper.

The reconstructions (Figs. 3, 4a) were made by Mr. Carl F.
Gronemann, Illustrator of Field Museum.

GENERAL REMARKS

The species here described is represented by a single, nearly
complete specimen enrolled in a somewhat unusual fashion. The

No. 327

Natural History Survey

Library

68 Field Museum of Natural History — Geology, Vol. VI

manner of enrollment suggests that the carapace was subjected to a
sudden extraneous force. Posterior to the tenth thoracic segment,
the carapace, including the last or eleventh segment and the
pygidium, has retained its original horizontal position, whereas
anterior to the eleventh thoracic segment the carapace has formed
a semicircular arch overlying nearly two-thirds of the ventral side
of the pygidium. The remaining portion of the pygidium projects
out but is completely obscured ventrally by a mass of adhering
matrix, much of which also forms a mold of the greater part of
the cephalon and conceals it. The pygidium is broken through the
fourteenth segment, and so it is possible to pull apart the broken
portion and with it the adhering cephalic mold. Thus the entire
cephalon may be exposed.

It is pertinent to mention here that it is somewhat difficult to
detect the line of union between thorax and pygidium in the present
specimen. The reasons are: (1) The pygidium is as strongly seg-
mented as the thorax; and (2) the enrolling has taken place anterior
to the eleventh thoracic segment instead of along the line of articula-
tion between the pygidium and the thorax. Consequently, the
eleventh thoracic segment superficially appears to be more a segment
of the pygidium than of the thorax.

The occipital ring and the posterior marginal borders of the
cephalon, a part of the right axial and pleural segments of the thorax,
and portions of the right and left pleural segments of the
pygidium are not preserved in the specimen. The erect caudal
spine, with the exception of its base, is also wanting.

The specific name is in honor of the late Henry Pratten, the
collector of the specimen.

Horizon and locality. — Devonian. Devil's Back Bone, near
Grand Tower, Jackson County, southern Illinois.
No. P 16704 Field Museum.
Holotype.

SPECIFIC DESCRIPTION

Class Crustacea

Subclass Trilobita Walch

Order Proparia Beecher

Family Phacopidae Corda

Subfamily Dalmanitinae Reed

Genus Dalmanites Barrande

A Devonian Trilobite — Roy

H, V

69

IG. 1. Dalmanites pratteni Roy, sp. nov. a, Front view of head. 6, Dorsal view of cephalon
and portion of enrolled thorax, c, Pygidium, including ninth, tenth, and eleventh thoracic segments.
No. P 16704 Field Museum.

70 Field Museum of Natural History — Geology, Vol. VI

Dalmanites pratteni Roy, sp. nov. Figs. 1-4.

General form and proportions. — Body subelliptical in outline,
rounded or slightly produced at the extremities. Surface moderately
convex, distinctly trilobate. Length to width as 2 to 1.

Cephalon more than twice as wide as long, strongly convex,
subcrescentic in outline with a slight median lip-like extension in
front. Surface sloping rapidly to the marginal borders.

Glabella subpentagonal, broadest near the anterior margin of
the frontal lobe, width along the posterior margin one-half the
maximum width, bounded laterally by moderately wide, deep, and
gradually diverging dorsal furrows except at the junction of the
anterior half of the first lateral glabellar lobes with the palpebral
lobes where the furrows become shallow and very much elevated.
Length of glabella about seven-tenths its maximum width.

Frontal lobe subrhomboidal, rounded in front but interrupted
by a slight extension at the middle. Surface of the frontal lobe
moderately convex and characterized by a shallow line of depression
at the middle of the posterior end.

First lateral lobes subtriangular to subrhomboidal, widest and
most elevated at their outer margin, sloping and gradually becoming
narrower within and abruptly depressed close to the median portion
of the glabella. Anterior margins of the first lateral lobes oblique
outwardly and inwardly, posterior margins nearly straight in
transverse direction.

Second lateral lobes similar to the first but smaller, also less
elevated at their outer margins and less depressed near the median
portion of the glabella. They are partially coalescent externally
with the first lateral lobes as a result of the shallowing of the second
lateral furrows.

Third lateral lobes subrectangular, smaller and less elevated at
the outer margins than the second and wholly separated from
them. They slope upward and inwardly with a slight anterior arch
at the median portion which at this point is the most elevated portion
of the glabella.

Occipital ring not preserved.

First lateral furrows the longest, of moderate width, deepb
impressed, a little arched postero-laterally, extending obliquely
inwards and backwards, not joined across the median portion of
the glabella which here is very narrow and rounded, the rounding
caused by the depressed inner ends of the first lateral lobes am
deeply impressed second lateral furrows.

A Devonian Trilobite— Roy

71

Fig. 2. Dalmanites pratteni Roy, sp. nov. a, Enlargement of left eye. Rear view. X4. Field
Museum photograph No. 78079. b, Right eye. Front view, c, Dorsal view, showing height of eye
above glabella and portion of enrolled thorax, d. Enlargement of section of lenses. X5. No. P 16704
Field Museum.

72 Field Museum of Natural History — Geology, Vol. VI

Second lateral furrows much less oblique than the first, joined
across the glabella with deep excavation but not extended to the
dorsal furrows.

Third lateral furrows transversely straight, distinctly defined
but not deeply impressed. They do not join across the glabella
but extend to the dorsal furrows.

Occipital furrow moderately wide, deeply incised and arched
slightly forward in its median portion.

Cheeks subtriangular in outline; large and convex. Postero-
lateral angles not preserved, but the indications are that they were
produced slightly into short, blunt spines. Surface of cheeks dips
abruptly from the deeply undercut furrows at the base of the faceted
surface of the eyes to the marginal borders laterally and anteriorly,
more abruptly anteriorly where the cheeks are also most prominent.
The sloping of the cheeks, however, is interrupted by the cheek
furrows which are moderately deep and wide. Posteriorly the cheeks
are marked by a marginal furrow which arches forward at the middle
and which is continuous with the occipital furrow.

Anterior limbs of the facial suture extend from the anterior
extremities of the eyes and follow the antero-lateral and anterior
margin of the frontal lobe where they unite.

Posterior limbs of the facial sutures directed laterally from the
posterior extremities of the eyes with a slight sigmoidal flexure,
terminating at the lateral marginal borders at or a little below a
line through the occipital furrow.

Marginal border wide laterally, becoming suddenly narrow
anteriorly and constricted at the middle of the front.

Postcephalic marginal border not preserved.

Eyes subconical, of unusual appearance, remarkably large and
of extraordinary height. They are situated close to the dorsal
furrows and cover a large portion of the free cheeks. Their anterior
extremities are opposite the anterior extremities of the first lateral
glabellar lobes and their posterior extremities opposite the middk
or little below the middle of second lateral glabellar lobes. The)
are bounded externally around the base of the faceted surface ty
a deep, moderately wide, undercut furrow. Faceted surface nearh
vertical at the anterior and posterior extremities, becoming mor
and more inclined towards the middle where the inclination is about
seventy degrees. Lenses biconvex, variable in size, the majority
being of the same size (.6 mm.), many with a concave border as well
as with a central pit-like depression suggesting that the membrane

A Devonian Trilobite — Roy 73

has collapsed there. Each lens is enclosed in a socket of its own
and has a separate cornea. Interspace between lenses is free from
pustules. There is a total of forty-two vertical rows of lenses on
each eye, the rows consisting of ten to twenty lenses which are
closely set. The exact number of lenses cannot be determined, as
not all of them are preserved, nor are the areas which they occupied
distinctly outlined. It is, however, certain that there are not less
than 770 lenses on each eye. This is the largest number known to
occur in the family of Phacopidae.

Palpebral lobes large, their lateral and anterior margins forming
a parabolic curve. The lobes slope abruptly upward from the dorsal
furrows and are elevated at the middle.

Thorax strongly trilobate, subquadrate in normal position, a
little wider than long, consisting of eleven segments. The third
thoracic segment (of which the axial ring as well as the anterior
pleural bands are not preserved) appears to have been pushed over
the second segment during enrollment. As a result the line of
demarkation between the second and third thoracic segments cannot
be readily detected.

Axial lobe strongly convex, occupying less than a third of the body.
First axial ring narrower than the second, the width of the second
to the fifth practically uniform, the remaining portion of the axis
tapering very gradually to the pygidium. Axial rings widest
along the dorsal furrow, narrowing gradually and curving upward
at the middle. Articulating half rings prominent, axial furrows
moderately wide and deeply incised.

Pleural lobes somewhat flattened about one-third their width
from the axial furrows, then rising gradually and sloping to the
lateral margins. Pleurae conspicuously grooved longitudinally, the
grooves originating at the axial furrow and becoming obsolete at
the distal extremity. The anterior pleural band is wide proximally,
becoming rapidly narrower distally; the posterior pleural band is
narrow and rounded proximally, becoming gradually wider distally.

Pygidium subtriangular in outline, wider than long, with an erect
caudal spine. The caudal spine is not preserved. Its upturned base,
however, clearly indicates that its position was not only at right
angles or nearly so to the plane of the axis, but also that the spine
was three-sided, the sides being slightly rounded.

Axial lobe convex, sharply separated from the pleural lobes by
deeply incised dorsal furrows, conspicuously narrow, its greatest
width one-fifth of the maximum width of the pygidium. It tapers

74 Field Museum of Natural History — Geology, Vol. VI

gently posteriorly and terminates at the edge of a furrow which
cuts the postaxial region and separates the axis from the caudal
spine. It is divided into twenty-three annulations which are slightly
wider at the dorsal furrows than at the middle.

Pleural lobes gently arched for more than half the width from the
dorsal furrows, sloping rather abruptly at the sides to the lateral
margins. The lobes are divided into twenty-two grooved segments
which curve backward, reaching just within the lateral margins.
The segments are wider and more flattened distally than within.

It is difficult to determine satisfactorily the nature of the margin
or the marginal border of the pygidium from the present state of
its preservation. There are strong indications, however, that the
margin is entire and the marginal border narrow, widening at the
posterior extremity and bending upward to produce into a stout,
erect spine. The structure of the broken caudal spine and the
character of the postaxial region are such as to leave no doubt
that the caudal spine is the posterior, upturned extension of the
marginal border rather than a similar extension of the axis proper.

Surface ornamentation. — The entire surface of the cephalon,
especially the frontal lobe, is heavily studded with rounded and
subrounded tubercles of varying size. In addition to the tubercles,
the frontal lobe bears on its posterior portion a short scar placed
centrally, almost overlapping the median axis. The frontal lobe
also bears two pairs of anterior and posterior pits or impressions
symmetrically situated with reference to the median axis. The
meaning of these impressions and of the median scar has not been
definitely determined. They are, however, believed to be muscle
impressions, although the myology of the trilobite is so imperfectly
known that no definite inference can be made here now. If they
are muscle impressions, the paired ones are probably points of
attachment of hypostomial muscles. There is a remote possibility
that the anterior pair might have been connected with the antennae,
but as the antennae are generally believed to have been attached
to the dorsal furrows at the sides of the hypostoma, such a possibility
can hardly deserve serious consideration. The median scar is
probably the place of insertion of the muscles of the heart or of the
alimentary canal, if the interpretation and position of these organs
as described by previous writers (E. Beyrich, 1846, p. 30; J. Barrande,
1852, p. 229; A. von Volborth, 1863, Plate I, fig. 12; C. D. Walcott,
1881, p. 200; P. E. Raymond, 1920, pp. 81, 85, 93, figs. 24, 26-27,
and 29) are accepted.

A Devonian Trilobite — Roy

75

Fig. 3. Dalmanites pratleni Roy, sp. nov. Reconstruction drawing. Dorsal side. Field Museum
photograph No. 78081. No. P 16704 Field Museum.

76 Field Museum of Natural History — Geology, Vol. VI

It may be of interest to note that another species of Dalmanites,
namely, D. phacoptyx Hall and Clarke, bears on its frontal lobe a
single pair of elevated blunt spinules (J. M. Clarke, 1908, p. 123,
text fig.) almost exactly at the same points as the posterior pair
of impressions of this species are situated . What the true significance
of these spinules might have been could not be ascertained. If they
were points of insertion of muscles as the similarly placed impressions
of the present species were believed to be, it would seem possible
that they were merely evaginated impressions.

The thorax is also tubercled. Scattered among the tubercles
are a few irregularly placed spinules which are all broken, and their
height, therefore, is not determinable. The tubercles on the axial
lobe of the pygidium have no definite arrangement, whereas they
are more or less regularly arranged in two transverse rows along the
anterior and posterior bands of the pleural segments.

Caudal spine. — Mention may be made here of the erect caudal
spine of this species and its probable function. It is generally
accepted that the members of the Phacopidae were both crawlers
and swimmers, and occasionally burrowers. Dalmanites pratteni,
doubtless, was primarily an active swimmer, as shown by the
character of its eyes and the large pygidium. It probably never
was a burrower inasmuch as following such a habit it could not
have developed its extraordinary eyes, nor could it have buried its
head without damaging them. Furthermore, the erectness of the
spine would have been a decided hindrance rather than an advantage
in burrowing. Admittedly, the true significance of the spine cannot
be clearly demonstrated. If it were a defensive weapon, or a balanc-
ing mechanism or even an organ to help cutting water while swim-
ming by the undulatory movement of the pygidium, it might con-
ceivably have been useful but certainly was not indispensable.

Dimensions. — The dimensions are of the enrolled specimen.

mm.

Length of entire specimen 157.5

Width at fourth thoracic segment, which is best preserved 86.0

Length of cephalon excluding occipital ring 32.0

Height of eye 15.0

Length of thorax '. 63.0

Width of axial lobe of thorax at front 24.0

Width of axial lobe of thorax at back 20.0

Length of pygidium 60.0

Width of pygidium at front 75.0

Width of pygidium at postaxial region 18.0

Length of axial lobe of pygidium 53.0

Width of axial lobe of pygidium at front 18.0

Width of axial lobe of pygidium at posterior extremity 3.0

A Devonian Trilobite — Roy 77

It is to be expected that the dimensions given on the preceding
page will somewhat vary from the measurements of Fig. 3, which
has been drawn to show the natural position.

Comparison with other species. — There are no described species
to which the present one can be directly referred. The character
of its eyes and of the caudal spine alone sharply distinguish it from
all other known species of the genus. Of nearly one hundred Devon-
ian Dalmanites known, only three, Dalmanites (Chasmops) anchiops
(Hall), Dalmanites (Coronura) aspectans (Hall), and Dalmanites
phacoptyx Hall and Clarke, may be conveniently mentioned here
as having certain resemblances to the species of this paper. For
comparative purposes the principal specific features of each is here
given.

D. anchiops (Hall).

Cephalon. — Short and wide, crescentic, slightly produced on the frontal margin ;
frontal border crenulated. Glabella subpentagonal, first and second
glabellar lobes coalescent. Facial sutures normal. Eyes lunate, some-
what elevated, with about 180 lenses. Occipital ring bearing a central
spine. Surface pustulose.

Pygidium. — Subtriangular, length and maximum width about equal; axial
annulations 9-14; pleural segments 8-9, faintly grooved distally. Margin
entire, border narrow, posterior extremity produced into an upwardly
curved spine, not elevated axially. Surface tubercled.

Horizon. — Onondaga, Schoharie, Oriskany, Upper Helderberg.

D. phacoptyx Hall and Clarke.

Cephalon. — Only imperfectly known. Border broad and uninterrupted. Frontal
lobe bears a single pair of elevated blunt spinules symmetrically placed
with reference to the median axis. Facial sutures depressed. Eyes
elevated bearing not less than 500 lenses.

Pygidium. — Broadly triangular, length on three sides nearly equal; margin
entire, border narrow. Axial annulations 13-16; pleural segments 12-14,
grooved. Caudal spine bent upward,1 elevated axially. Surface tubercled
and spinose, axial tubercles irregularly arranged, pleural ones on anterior
limbs only.

Horizon.— Onondaga, Oriskany, Upper Helderberg.

D. aspectans2 (Hall).

Cephalon. — Known from detached portions only. Semielliptical, border flat.
Glabellar structure unknown. Facial sutures about normal. Eyes sub-
semicylindrical, remarkably elevated, reaching a height of 9 mm., bearing
not less than 700 lenses, each surrounded by a hexagonal frame.

1 The nature of the caudal spine of D. phacoptyx is somewhat confusing. It
has been variously interpreted as "long, cylindric tail spine," "stout spine, strongly
bent upward," and "caudal spine quite slender, usually absent."

2 A closely allied species is Dalmanites (Coronura) myrmecophorus (Green).

78 Field Museum of Natural History — Geology, Vol. VI

Pygidium.— Subovate-triangular, much wider than long, border fringed with
spines, terminal spines separated by a distance equal to the width of the
anteriormost axial annulation. Axial annulations 16-20; pleural seg-
ments 16-18, faintly grooved. Surface tubercled to smooth.

Horizon.— Onondaga, Schoharie, Upper Helderberg.

D. pratteni Roy.

Cephalon. — Short and wide, crescentic, slightly produced in front, frontal
border smooth. Glabella subpentagonal, frontal lobe bearing two pairs of
impressions symmetrically placed with reference to the median axis and a
single median scar situated posteriorly, first and second glabellar lobes
coalescent. Facial sutures normal. Eyes extraordinarily elevated, having
not less than 770 lenses, each separated by a rounded interspace.

Pygidium. — Subtriangular, wider than long, margin smooth, border narrow.
Axial annulations 23; pleural segments 22, grooved. Caudal spine erect,
not elevated axially. Surface tubercled and sparsely spinose, axial
tubercles irregularly arranged, pleural ones arranged in two transverse
rows along the anterior and posterior bands.

Horizon: Devonian.

It is apparent that none of the species listed above shows, as a
complete individual, close relationship with Dalmanites pratteni Roy.
However, when isolated parts of these species, either the cephalo
or the pygidium (but not both together of any one species) a:
compared with the corresponding parts of D. pratteni, certain definite
similarities may be readily observed. Obviously, D. pratteni reached
its high degree of specialization, as illustrated by the structure of
its glabella, eyes, and pygidium, by branching off from the main
Dalmanites stem early in its history and by pursuing an independent
and probably eccentric course. It is, however, a formidable, if not
an impossible task, to trace its history back to the point where it
might have branched off and to follow the developmental history of
its specific characters in chronological succession. In fact, none of
the species known at present can furnish the necessary data.

STRATIGRAPHICAL NOTES

It has been already mentioned in the Introduction that the
trilobite here described was purchased in 1912. Data that accom-
panied it, however, did not include its stratigraphical position.
Only the name of the collector, the year of collection, and the
locality are available.

Attempts to establish the exact horizon have been made but
no evidence, direct or indirect, which is at hand permits a definit
conclusion. None of the other fossils included in the purchase w£
from the same locality, and none shows similar lithological character

a

A Devonian Trilobite — Roy

79

U. s
E

• 2

o> **

M"S
•1

CO V

"OS

3 *

2"

b"5

*>*^

°E

■w 3

sl

'r be

-C >>

a

&»_

.5 "

'5 c»

o o;

-S'-S,

<« t.n

o-

I8!

<D t- H

Wj

t-. <

— $f

J^ft.

wl

c £ .

? o o)

* S 5:

i- c -

B •

o fc C

p 3 o

• eg

If H

QSf|

a ".3

ii

>.2~

° > c

. *.2

ft 4,-C

■S'B

**£

HI

C»_

» 6«

Izi

Oft-

.J J

«E§

S2

80 Field Museum of Natural History — Geology, Vol. VI

nor does the matrix adhering to the fossil in question contain any
other fossil as a possible clue for the determination of the horizon.

At present, all that is known of- the age of the specimen is that
it is Devonian, as the beds of the locality where it was found are
known to be Devonian. Even if the locality were not known, one
would not, judging from the structure of the cephalon and the
large number of axial rings of the pygidium, long hesitate to refer
it to the Devonian. It should be mentioned, however, that structural
specialization in the members of Dalmanites has not gone on in
chronological succession, and it is not always possible to determine
the stratigraphic position of a Dalmanites on the basis of the degree
of its structural development. Certain Silurian species of Dalmanites
show evident signs of greater advance in development than some
of the Devonian ones. The same irregular developmental relation-
ship is also found among certain species of Ordovician and Silurian
Dalmanites.

The Devil's Back Bone, near Grand Tower, Jackson County,
southern Illinois, where the specimen was found, is a narrow ridge,
about one hundred feet high and one-half mile long. Its detailed
stratigraphy is not known, although this locality has been long
recognized (Norwood and Pratten, 1855, pp. 23-32; James Hall,
1867; Stuart Weller, 1897, pp. 625-635) as a favorable collecting
ground for Devonian fossils. Weller (1897, pp. 626-635) gives the
results of his faunal studies of a section about 167 feet thick of
the Devil's Bake Oven which he considers to be really the northern
end of the Devil's Back Bone although isolated from it by an interval
of several hundred feet. He finds the faunas of the lowest beds
correspond to the Upper Helderberg series and those of the upper-
most beds to the Hamilton. He also sets forth conclusively the fact
that the Devonian faunas of southern Illinois are a western extension
of the faunas of the eastern interior province, namely, the faunas
of New York.

The Devonian geology of the Alto Pass quadrangle (Charles F.
Basset, 1925, pp. 360-368), which includes the Devil's Back Bone
area, is better known and may be considered as typical of the
Devonian of southern Illinois. Comparative generalized sections of
the Devonian of southern Illinois and New York are given on page 81.

It will be seen from the section that the rocks composing the
Devonian formations of southern Illinois are limestone, chert, shale,
and sandstone. Chert is very abundant. Grassy Knob chert is
believed to be 225 feet thick. In addition to the chert formations

A Devonian Trilobite — Roy

81

referred to in the section, numerous interbeds of cherts occur in
practically all other formations. The reason for emphasizing the
occurrence of chert formations and interbeds of chert in the Devonian
sequence is to make more evident the difficulty of determining the
particular chert bed from which the specimen under discussion
might have been collected. Doubtless it would be interesting to
know the exact horizon. Dalmanites pratteni is a highly specialized
form, probably the most highly specialized form known, and it would
be significant to know if the culmination of specialization took place
earlier in its history or just before the genus became extinct.

COMPARATIVE SECTIONS OF DEVONIAN FORMATIONS

Period

New York

Southern Illinois

Series

Formation

Formation

si
B
E
E
P

Chautauquan

Chattanooga
shale

Mountain Glen shale

Senecan

Portage

Alto formation

■
a
5
g

Erian

Hamilton

Lingle shale

<

z

o

>

Ulsterian

Onondaga

Grand Tower limestone
Dutch Creek sandstone
Clear Creek chert

Q

Oriskanian

Oriskany

Backbone limestone
Grassy Knob chert

I

Q

►J

Helderbergian

New Scotland

Bailey limestone

PHYSICAL CHARACTERS AND CHEMICAL

COMPOSITION1 OF THE CHERT MATRIX

ADHERING TO DALMANITES PRATTENI ROY

Chert may often vary in physical characters and chemical com-
position, and, occasionally, stratigraphical correlation is possible
on the basis of lithological similarities. For this reason, the physical
characters and chemical composition of the matrix of the present
specimen are here given as these data may be useful in the future

1 Analysis by H. W. Nichols and Sharat K. Roy.

82 Field Museum of Natural History — Geology, Vol. VI

as corroborative evidence in determining the horizon not known at
present.

Physical Characters

Chemical Composition

Color

Texture

Hardness

Si02

A1203, Fe203

Minor components
not determined

Exposed surface
reddish yellow;
white when
freshly chipped

Fine
grained

Very
hard

97.23

2.32

.45

BIBLIOGRAPHY
Barrande, J.

1852. Systeme silurien du centre de la Boheme, 1.

Bassett, C. F.

1925. Trans. 111. State Acad. Sci., Ann. Rept., 18.

Beyrich, E.

1846. Untersuchungen ueber Trilobiten, 2.

Clarke, J. M.

1908. N. Y. State Mus., Mem. 9, pp. 120-134.

Hall, J.

1859. Nat. Hist. N. Y., Pal., 3, pp. 359-364.

1862. N. Y. State Cab. Nat. Hist., 15th Ann. Rept., pp. 83-92.
1867. Nat. Hist. N. Y., Pal., 4.
1876. N. Y. State Geol. Surv., Adv. 111. Dev. Fossils, Crustacea.

Hall, J. and Clarke, J. M.

1888. Nat. Hist. N. Y., Pal., 7, pp. 28-68.

Lindstroem, G.

1901. Researches on the Visual Organs of the Trilobites. K. svenska Vet.
Akad. Handl., New Ser., 34, pp. 1-86, Plates 1-6.

Meek, F. B. and Worthen, A. H.
1858. Geol. Surv. 111., Chap. 4.

Norwood, J. G. and Pratten, H.

1855. Jour. Acad. Nat. Sci. Phila., Ser. 2, 3, pp. 23-32.

Raymond, P. E.

1920. The Appendages, Anatomy, and Relationships of Trilobites. Mer
Conn. Acad. Arts and Sciences, 7.

Reed, F. R. C.

1905. The Classification of the Phacopidae. Geol. Mag., New Ser., Dec.
2, No. 4, pp. 172-178, 224-228.

VOLBORTH, A. VON

1863. Ueber die mit glatten Rumpfgliedern versehenen russischen Trilobiten,
nebst einem Anhange ueber die Bewegungsorgane und ueber das Herz
derselben. Mem. Acad. Imp. Sci. St. Petersburg, Ser. 7, 6, No. 2.

Walcott, C. D.

1881. The Trilobite: New and Old Evidence Relating to Its Organizatior
Bull. Mus. Comp. Zool., 8.

Weller, S.

1897. Correlation of the Devonian Faunas in Southern Illinois. Jour. Geol.,