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" UNIVERSITY OF

3 ILLINOIS LIBRARY

AT URBANA-CHAMPAIGN

GEOLOGY

'SO.b

FIELDIANA
Geology

Published by Field Museum of Natural History

Volume 35, No. 6 April 18, 1977

New Information on the

Holocystites Fauna (Diploporita) of the Middle Silurian

of Wisconsin, Illinois, and Indiana

TERRENCE J. FREST

RESEARCH ASSISTANT, DEPARTMENT OF GEOLOGY

UNIVERSITY OF IOWA

DONALD G. MIKULIC

research assistant, department of geology
Oregon State University

and
CHRISTOPHER R. C. PAUL

LECTURER, DEPARTMENT OF GEOLOGY
UNIVERSITY OF LIVERPOOL

INTRODUCTION

Since publishing a revision of the Holocystites fauna of North
America (Paul, 1971) additional information on specimens, locali-
ties, stratigraphic correlation, etc. has become available which we
feel should be put on record. First, on a visit to the American
Museum of Natural History, New York (AMNH), in September,
1972, Paul relocated the missing holotype of Holocystites ovatus
Hall, thus allowing the taxonomic position of this form to be inter-
preted for the first time. He also discovered 14 specimens of
Trematocystis, Pentacystis, and Triamara among material collected
last century by G. K. Greene (of Indiana) from a previously unre-
corded locality ( Ryker's Ridge) in Jefferson County, Indiana.

Frest presents additional information on localities and the occur-
rence of holocystitids in the Middle Silurian of southern Indiana,
including details of the section exposed along Big Creek within the
Jefferson Proving Grounds, which historically was the richest
source of holocystitids from Indiana. Mikulic presents new facts on

Library of Congress Catalog Card No.: 76-56533

The Library of the

Publication 1255 83

J UN 06 1977

at Urbana -Champaign

84 FIELDIANA: GEOLOGY, VOLUME 35

the occurence of cystoids in, and the correlation of, the Niagaran
dolomites of Wisconsin and Illinois. He has also traced the exact
sources of many specimens in old collections, largely using the
correspondence of T. A. Greene (of Wisconsin). Field work has
helped to establish the preservational history of the cystoids and
their relationship to the well-known Niagaran bioherms.

In addition to fieldwork, extensive use has been made of the large
collections of relevant Silurian material, catalogued and uncata-
logued, reposited in Field Museum to supplement the data pre-
sented in Paul (1971). In particular the sizeable collections of
Osgood cystoid types and Niagaran dolomite fossils from
Wisconsin and Illinois, and lesser amounts of Laurel limestone
(Indiana) material, have been of considerable value in formulating
a paleoecologic framework for the Holocystites fauna. Many of the
fossils accumulated in the course of fieldwork have been donated to
Field Museum. Finally, Dr. Hertha Sieverts-Doreck has kindly
drawn our attention to her interpretation (Sieverts, 1934; Sieverts-
Doreck, 1963) of hemispherical pits in fossil echinoderms as borings
of parasitic gastropods.

ACKNOWLEDGEMENTS

We would like to acknowledge, individually or jointly, the help of
the following people: Dr. R. L. Batten and Dr. N. D. Newell,
American Museum of Natural History, New York (AMNH); Miss
A. Clark, British Museum, Natural History, London (BMNH);
Dr. E. S. Richardson, Jr., Field Museum of Natural History,
Chicago (FMNH); Mr. J. Emielity, Milwaukee Public Museum and
Dr. K. G. Nelson, Greene Museum, University of Wisconsin,
Milwaukee, for access to, or the loan of, material in their care;
K. Oliverson, J. Ripp, and J. Schmidt for access to the Vulcan
Materials quarries in Racine and Franklin, Wisconsin; and R.
McClung, Provost Marshall, and R. Rea, Chief Security Officer,
Jefferson Proving Grounds, Indiana for access to the Big Creek
Section. Mrs. M. Frest, Mrs. J. Mikulic, Mr. J. Shema, and Mr. B.
Witzke helped with fieldwork. Fieldwork and museum visits by
Paul during September, 1972 were financed by a grant from
Reading University. Dr. G. Raasch and W. Bode provided informa-
tion and access to unpublished work on the Silurian of Wisconsin
and J. Mikulic provided information on T. A. Greene's correspon-
dence. Finally, Dr. Raasch, Dr. R. Paul, and Dr. Nelson read and
commented on parts of the manuscript. To all our sincere thanks.

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA

Fig. 1. Holocystites ovatus Hall, 1864. Stereophotos of the holotype, AMNH
2021. a, Lateral view to show thecal outline, b, Oral view. Both X1.3. Both whitened
with ammonium chloride sublimate.

Holocystites ovatus Hall, 1864. Figure 1.
For synonymy see Paul, 1971, p. 149.

Type— Holotype (monotype), AMNH 2021, original of Hall, 1868,
pi. 12, fig. 2.

Horizon and Locality. —"In the limestone of the Niagara Group
at Waukesha, Wisconsin." Hall, 1864, p. 10. See pp. 95-97 for details
of this locality.

Description. —

Theca: ovoid, probably originally pyriform, now slightly crushed
and with the base missing. Internal mold 45 mm. high and 40 mm.
maximum width.

86 FIELDIANA: GEOLOGY, VOLUME 35

Plates: probably two generations but not well preserved.
Arranged in at least 10 poorly defined circlets of more than eight
plates each. Primary plates reach 8-9 mm. in maximum dimension.

Pore-structures: dipores present but on an internal mold it is
impossible to confirm that they were originally humatipores.

Mouth: preserved as a tubercle 5 mm. in diameter at the oral
pole.

Anus: similarly a 5 mm. diameter tubercle close to the mouth.
Hydropore and gonopore: not detectable with certainty.

Internal structures: ill-defined ridges on the internal mold pass
to the right from the positions where the gonopore and hydropore
might be expected by analogy with other holocystitids. These
ridges mark the positions of channels on the inner surface of the
theca which could have housed the gonoduct and stone canal.

Attachment: unknown, base of theca missing.

Remarks. — This specimen is almost certainly conspecific with
H. scutellatus Hall, 1864. Two forms of H. scutellatus were recog-
nized (Paul, 1971, p. 99) and the type of H. ovatus agrees better
with the larger, more globular form which has larger plates.
Evidence is insufficient to determine whether the two forms repre-
sent distinct species or not, and so for the present H. ovatus is
included in the synonymy of H. scutellatus. Although the former
name has page priority, the name//, scutellatus is retained for three
reasons. First, it maintains consistency with the original revision
(Paul, 1971); secondly, there is a possibility that both names may
be validated if the two forms can be shown to represent distinct
species; and finally, the ICZN rules do not demand the recognition
of page priority; the decision is left to the first revisor.

Localities. —INDIANA: 17 (for Indiana localities 1-16 see Paul,
1971, pp. 163-164). Ryker's Ridge, Jefferson County, Indiana
(probably locality 49 of Foerste, 1897, p. 251). In the G. K. Greene
collection (AMNH) are 14 cystoids labelled "Rocker's Ridge,
Jefferson County, Indiana." No locality with precisely this name
occurs on any map of Jefferson County that we have seen. However,
Foerste's map (Foerste, 1897, pi. 15) shows a Riker's Ridge (Sec-
tions 18, 19, 20, and 29, T4N, RUE, on the current Canaan 71/2'
quadrangle where it is spelled "Ryker's Ridge") and "Racket
Ridge" (sections 8 and 9, T3N, R12E, Carrollton 71/2' quadran-
gle). Racket Ridge lies about 4 miles beyond the easternmost

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 87

limit of the Silurian outcrop in southern Jefferson County and
extends into Switzerland County. No Silurian strata remain in this
area of the Cincinnati Arch and Racket Ridge cannot be Greene's
locality. It seems that "Rocker's Ridge" is a misspelling of
"Ryker's Ridge" or alternatively that the name has "evolved"
since Greene's day.

The Brassfield Limestone and Basal Osgood crop out on the south
side of the road 0.2 miles east of Ryker's Ridge Church in the head-
waters of Wolf Run (NW1/4, SW%, section 20, T4N, RUE, V/t
quadrangle). This is Foerste's locality 49. Paul visited this spot
(July 2, 1968) and recorded 2 ft., 2 in. of tan, yellow, and brown
cherty Brassfield underlying 8-9 in. of Basal Osgood, but the rest
of the section was largely overgrown. Foerste (1897, p. 251) re-
corded the following section on the opposite side (i.e., north) of the
stream:

"Upper Osgood Clay" no thickness stated

"Osgood Limestone" 4 ft.

"Lower Osgood Clay" 14 ft.

"Basal Niagara Limestone" 8 in.

"Clinton" ( =Brassfield) 34 in.

Most likely this is the section from which Greene collected his
material. The cystoids include 11 complete or partial thecae of
Trematocystis, two complete thecae of Pentacystis, and the base
of a Triamara ventricosa (Miller). Specific identification of the Tre-
matocystis and Pentacystis will require some cleaning of the speci-
mens; nevertheless, from the known stratigraphic distribution of
these genera a fairly complete section is suggested. Trematocystis
is only known from the Trematocystis bed (Paul, 1971, p. 37) below
the lower limestone band, Pentacystis from the lower limestone
band, and Triamara ventricosa from the Upper Osgood Shales,
above both limestone bands.

Hitherto all known specimens of Pentacystis came from Big
Creek (localities 3-5 of Paul, 1971) or Osgood (locality 11 of Paul,
1971). This locality represents a southern extension of the range
of the genus. Frest has also found a possible Pentacystis from the
road cut at New Marion (locality 10 of Paul, 1971). Even with
these new localities the total known geographic range of Penta-
cystis is remarkably small.

St. Paul, Indiana (locality 16, Paul, 1971, p. 164).
Frest has been actively investigating the biostratigraphy and

88 FIELDIANA: GEOLOGY, VOLUME 35

paleoecology of Middle Silurian sedimentary rocks of southern
Indiana (see Frest, 1975, pp. 81-84). The most probable source
of most of Springer's crinoids from the Laurel Limestone of St.
Paul (Springer, 1926, pp. 6-7) is the old Adams Quarry (SW%,
SW1/4, SE1/4, section 3, TUN, R8E, Adams 71/2' quadrangle). A
summary section is given in Frest (1975, fig. 1). Holocystites
occurs here and in the active quarry of the St. Paul Stone Co.
(NE1/4, section 9, TUN, R8E, Shelby County, Indiana, Waldron
V/t quadrangle). The Holocystites occur only in the lower part of
unit 1, a 52-in. thick pure white, fine-grained partly dolomitized
biomicrite which weathers to give a vuggy surface and exhibits
indistinct bedding. In this unit cylindrical Holocystites alternatus
and Triamara sp. occur in life position: the Holocystites lie on bed-
ding surfaces or mounds of coarser debris with the oral surface
directed upward (cf. Paul, 1971, p. 75, fig. 33, p. 90). Their presenta-
tional history would seem to have been simple. Only loss of the
ambulacral appendages and the oral and anal cover plates plus the
growth of some epifauna intervened between death and burial in
situ.

Big Creek (localities 3-5 of Paul, 1971, p. 163; localities 74-76 of
Foerste, 1897). Figures 2-3.

Foerste's localities 74-76 lie along a 2 mile stretch of Big Creek
entirely within the Jefferson Proving Grounds (fig. 2). Access is
difficult and dangerous due to the large number of unexploded
shells which litter the outcrop. Approximately 1 Vz miles of section
were explored and a composite section measured (fig. 3). This
section differs little from the details published by Foerste ( 1897, p.
257) and the section measured by Paul ( 1971, fig. 12) about 1 V2 miles
further east-northeast.

Just upstream of Foerste's locality 74 the Basal Osgood (unit 7,
fig. 3) is exposed in the creek bed. About 6 in. of white silty,
unfossiliferous limestone are visible. These are followed by the
Lower Osgood Shales (unit 6, fig. 3), about 7 ft. thick with
Trematocystis near the top. Above this lies the lower limestone
band of the Middle Osgood Limestone (unit 5c, fig. 3), which is a
1 ft., 10 in.-thick argillaceous fossil fragmental calcarenite. The
proportion of clastic material increases from bottom to top and is
especially high in the uppermost 4 in., which are hard to distinguish
from the overlying shale beds when deeply weathered. The lower
limestone band is not as resistant as the upper and the bedding is

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA

Fig. 2. Outline map of the area along Big Creek within the Jefferson Proving
Grounds surveyed by Frest, i.e., between the diagonal broken lines across the creek.
X = Foerste's localities 74-76, sites where section (fig. 3) was measured. The Lower
Osgood Shales were measured at a and b, the Upper Osgood Shales at c-g. Cystoid
occurrences as follows: H = Holocystites scutellatus, Hs = Holocystites spangleri,
P = Pustulocystis ornatissimus (found in float), T = Trematocystis spp., Ti = Tria-
mara. 500 ft. contour dotted, diagonal shading indicates restricted areas. The area
of this figure corresponds to the SE corner of the San Jacinto 71/2* quadrangle.

more distinct. The usual sequence of beds is: VA in. (bottom), IV2
in., 4 in., 3 in., 8 in., 4 in. H. spangleri and Triamara tumida occur
on the underside of the lowest two beds.

Between the two limestone bands is a muddy silty bed called the
middle shale (unit 5b, fig. 3). It is about 1 ft. thick and contains
many highly fossiliferous nodules or lenses in the lower 4-6 in. Most
of the fauna of the Osgood occurs in these beds. The upper limestone
band (unit 5a, fig. 3) is approximately 1 ft., 6 in. thick and is a resis-
tant fine-grained unfossiliferous limestone with indistinct bedding.
H. scutellatus occurs on the upper surface.

FIELDIANA: GEOLOGY, VOLUME 35

Fig. 3. Composite section through the Osgood and Laurel Formations as exposed
along Big Creek within the Jefferson Proving Grounds to show the stratigraphic
occurrence of cystoids and some other echinoderms.

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 91

The Upper Osgood Shales (unit 4, fig. 3) are best exposed about
halfway between Foerste's localities 75 and 76 where the contact
with the underlying limestone is sharp but apparently conformable.
The upper shales are 6 ft., 1 in. thick and the lower 2 ft. are highly
fossiliferous with limestone lenses scattered throughout but most
commonly in the basal 1 ft. 7 in. A fairly persistent 1-2 in. limestone
band with H. scutellatus occurs 7 in. above the base. T. ventricosa
occurs in 10 in. of shale and nodular limestone above this. H.
alternatus has also been found in the basal 7 in. Most fossils are
echinoderms but other members of the Osgood fauna occur. This
precise lithology is not now exposed anywhere else, although it may
be inferred to occur below the floor of the old quarry at Osgood
(locality 11 of Paul, 1971).

The transition from the upper shales to the Laurel Dolomite is
sharp. The lowest 3-5 ft. of the Laurel (unit 3, fig. 3) are usually
silty dolomite with indistinct bedding and contain Flexicalymene
celebra and other trilobites and occasional patches of A try pa and
crinoid stems lying on bedding planes. Above this comes 8-10 ft. of
highly cherty unfossiliferous limestone in thin ( 1-3 in.) beds (unit 2,
fig. 3). Capping the hills are 2-3 ft. of dolomitic limestone (unit 1,
fig. 3) which is deeply weathered and eroded. Quite likely this was in
turn originally overlain by more cherty limestone beds.

WISCONSIN.

For more than a century southeastern Wisconsin has been known
as a source of a large variety of Silurian fossils, including a diverse
fauna of pelmatozoans.

Most of these specimens were collected during the late 1800 's
when there were numerous stone pits and small quarries in many
communities throughout the area. Since locality data given with
most of the museum specimens is vague, an attempt has been made
to determine the exact collecting localities and stratigraphic posi-
tions of these specimens, with emphasis on cystoids. At present
very few of the old exposures are accessible or productive and some
reference must be made to earlier descriptions of these localities.
The correspondence and specimens of some of the nineteenth-
century collectors, particularly Thomas A. Greene, were checked
for useful information. Research is also being done on the Silurian
stratigraphy in southeastern Wisconsin since early work was found
to be inaccurate in some of the areas.

92 FIELDIANA: GEOLOGY, VOLUME 35

Four significant Holocystites localities (Grafton, Racine,
Waukesha, and Sussex) will be described in this section of the
paper, and a list is given of major bioherms and other localities in
Wisconsin and Illinois which have produced or may produce
cystoids. A general description of bioherms in the area is included
since cystoids are commonly associated with these structures.

Grafton ( Wisconsin, locality 1 of Paul, 1971).

The quarries at Grafton, Wis. (N1/2, sec. 25, T10N, R21E, Ozaukee
Co., Wis. ) are listed as the type locality for Holocystites cylindricus
by Hall (Paul, 1971, pp. 81, 16b). The rock exposed at the quarries
contains very few, if any, pelmatozoans, and the study of old collec-
tions shows no other cystoids have been found there. It is felt that
the specimen was incorrectly labelled and probably came from
Racine. Edgar Teller ( 1911, p. 202), a prominent collector of the late
nineteenth century, was also of the opinion that the specimen was
not from Grafton.

The Groth's Quarry at Cedarburg (center W1/2, sec. 35, T10N,
R21E, Ozaukee Co., Wis.), 1% miles southwest of Grafton, has pro-
duced rare and poorly preserved specimens of Holocystites and
Gomphocystites. A large bioherm which is thought to be younger
in age than those at Racine is present in the north corner of the
quarry.

Racine (locality 2 of Paul, 1971 ). Figure 4.

Fossiliferous dolomite is exposed in two areas near Racine. The
largest area is the type locality for the Racine Dolomite. It consists
of several small outcrops and quarries which extend for approxi-
mately three-fourths mile south of the rapids on the Root River,
northwest of the city of Racine (SW%, NE1/4, sec. 6, T3N, R23E,
Racine Co., Wis.). Presently there is a large water-filled quarry on
the east side of the river known as Horlick's Quarry which is now a
public park. Adjacent to it, on the west side of the river, is a small
abandoned quarry which was once known as Beswick's Quarry.

One of the best exposures of a bioherm in southeastern Wisconsin
can be found in the Horlick's Quarry. A small exposure of the core is
present in the southeast corner of the quarry with the flank beds
dipping to the north and west. To the southwest small satellite reefs
are partially exposed on both sides of the river.

The second area consists of several quarries on the north side of
Racine (SEy4, sec. 29, T4N, R23E, Racine Co., Wis.), approximately

ft Unit

- 120

-105

-75

-60

-45

-30

Dolomite

Chert

Silt

REEF

t^:

/ ? / p /

JOLI E T

RACIN E Fm

SUGAR RUN ?
Fm

ROMEO Mbr

MARKGRAF
Mbr

BRANDON
BRIDGE Mbr

Fig. 4. Section exposed at the Vulcan Materials quarry, Ives, Wis. 1973 to show
the probable correlation of NE Illinois and Wisconsin stratigraphic units. Illinois
terminology follows that of Willman, 1973.

94 FIELDIANA: GEOLOGY, VOLUME 35

1% mile northeast of the type locality. These quarries are referred to
as the Ives' quarries after the small community at that place which
has since been incorporated into Racine. A large quarry is presently
being run by the Vulcan Materials Company, but the others are
completely water-filled.

The correspondence of T. A. Greene indicates that the vast major-
ity of the nineteenth-century fossils labeled "Racine" came from
the Horlick's and Beswick's quarries, and that the quarries at Ives
were then in somewhat unfossiliferous inter-reef rock. This informa-
tion agrees with T. C. Chamberlin's (1877, pp. 361-362) description
of the area. Greene also indicated that most of the pelmatozoans
came from excavations close to the river at the Horlick's and Bes-
wick's quarries; recent field work has verified this information.
Expansion of the Ives' quarry in the 1940's and 1950's exposed
several bioherms which have the same fauna as the Horlick Bio-
herm.

The Racine Dolomite is Late Wenlock- Ludlow in age (Berry and
Boucot, 1970, pp. 200-201). The exposures around Racine are in the
lower part of the Racine Dolomite, which is Upper Wenlockian in
age as indicated by the presence of the Silurian trilobites Stauro-
cephalus and Trochurus, neither of which is known from younger
rocks.

Since no more than 30 ft. of the Racine Dolomite are now exposed
at the type section, the following section (fig. 4) of the deep quarry
at the Vulcan Materials Company at Ives is given to clarify the
stratigraphy.

Unit 1. The Racine Dolomite is the highest unit exposed in the
quarry. It consists of 50 or more feet of crystalline, porous, thick-
bedded, gray dolomite. Fossiliferous debris consisting of small dis-
articulated pelmatozoans, brachiopods, and rugose corals is com-
mon throughout the unit occasionally forming small lenses. Several
large bioherms are found in this unit. They have a massive struc-
tureless core with stromatoporoids as prominent framebuilders. The
flank beds are highly fossiliferous with disarticulated pelmatozoans
being the most common fossils.

Unit 2. Consists of 26 ft. of thin-bedded, fine-grained, light gray
dolomite. Chert nodules are abundant throughout most of the unit
although they occasionally grade laterally into non-cherty beds.
Fossils are locally common and include small disarticulated cri-
noids, trilobites, bryozoans, and brachiopods. The lower 8 ft. is

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 95

thicker bedded and more uniform. Where chert nodules are abun-
dant the unit is irregular-bedded and highly fractured and very con-
spicuous in the quarry wall.

Unit 3. Twenty feet of thick-bedded, light gray dolomite with
stylolitic bedding planes. It is nearly chert-free and poorly fos-
siliferous.

Unit 4. Seventeen feet of thick-bedded, cherty gray dolomite. The
center 5 ft. of the unit is chert-free. This unit correlates with the
Markgraf Member of the Joliet Dolomite. Specimens of the trilobite
Stenopareia are found in the lower cherty layers which indicates it is
Early Wenlock or Llandovery in age.

Unit 5. Consists of 6 ft. of thin-bedded, argillaceous, red and
brown dolomite. These layers become greenish toward the top. This
unit forms the floor of the quarry and correlates with the Brandon
Bridge Member of the Joliet Dolomite.

The presence of bioherms in the Racine Dolomite has resulted in
much sagging in the underlying units directly beneath the bio-
herms, extending through the Brandon Bridge beds.

Waukesha (locality 3 of Paul, 1971).

The second major source of Silurian cystoids in Wisconsin was
the area around Waukesha. The Silurian stratigraphy in the Wauke-
sha area is still poorly understood although in 1955 Gilbert Raasch
solved many of the problems in an unpublished manuscript. There
were two areas in which the bedrock has been quarried around Wau-
kesha. The first was Cook's Quarry which was located at the present
site of the Carroll College Athletic Field (SE%, sec. 3, T6N, R19E,
Waukesha Co., Wis.). Only a small outcrop of the Waukesha Dolo-
mite remains on the east side.

The second area was a group of quarries, originally Hadfield's, on
both sides of the Fox River in the northern part of Waukesha (center
SY2, sec. 26, T7N, R19E, Waukesha Co., Wis.). There are now two
large quarries of the Waukesha Lime and Stone Company occupying
this site. Many of the cystoids and other echinoderms found in Wau-
kesha were found in a unit which was described as "Racine beds" by
early authors. The most productive exposure of these beds was
Cook's Quarry. Chamberlin (1877, pp. 357-358) gives a general de-
scription of the exposure. These beds do show some lithologic simi-
larities to some of the biostromal beds of the Racine Dolomite, but

FIELDIANA: GEOLOGY, VOLUME 35

-70

-60

-50

-40

■30

c / / / : ±2

s?2

77/

Dolomite

Chert

Cephalopod bed
Holocystites

/**/** /*>/ <*>/^\

Fig. 5. Section exposed in the Halquist Lannon Stone Company quarry, Sussex,
Wis. to show the occurrence of Holocystites.

the faunas of the two units are distinct. The "Racine" unit in Wau-
kesha is equivalent to the Romeo Member of the Joliet Dolomite
(Raasch, personal communication, 1970).

Beneath the "Romeo beds" is the Waukesha Dolomite. The
erroneous identification of the "Racine beds" in the area by many-
authors has resulted in confusion as to the exact stratigraphic posi-
tion of the Waukesha Dolomite and miscorrelation with other areas.
According to Raasch, the true Waukesha Dolomite is equivalent to
the Markgraf Member of the Joliet Dolomite, which would mean it
is far below the true Racine Dolomite (Raasch, personal communica-

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 97

tion, 1969). The Waukesha Dolomite contains mostly poorly pre-
served cephalopods, but rare and poorly preserved Holocystites
have been found.

Sussex. Figure 5.

Approximately 5V« miles north of Waukesha a large quarry has
recently been developed by the Halquist Lannon Stone Company
(EV2, NW1/*, sec. 35, T8N, R19E, Waukesha Co., Wis.).

A few specimens of Holocystites have been collected from a
micritic dolomite layer about 18 in. thick and of almost lithographic
stone quality which forms a prominent layer in the upper part of the
quarry. This layer is referred to as the cephalopod layer because of
the abundance of the cephalopods Dawsonoceras, Kionoceras, and
cyrtocones. Also commonly associated with the cephalopods is the
trilobite Bumastus graftonensis, with rare specimens oilllaenoides,
Dalmanites, Calymene, Scutellum, and Cheirurus. Eucalypto-
crinites is the only other echinoderm found in the layer besides
Holocystites, and they are both rare.

Paul infers the preservational history of Holocystites as follows:
death was followed rapidly (or caused) by detachment from sub-
strata. Build-up of decomposition gases caused the thecae to be-
come buoyant and to drift (together with the nautiloids) perhaps
over considerable distances. During this phase the ambulacral
appendages and cover plates were lost. Escape of gases, possibly
caused by loss of the cover plates, allowed the thecae to sink or they
simply grounded on shallow lime-mud flats. Thecae became partly
or completely filled with sediment and partly buried. It is inferred
the cystoids drifted in because of their association with nautiloids,
which are known to have been buoyant, and the absence of ben-
thonic fauna.

During burial the sediment was contemporaneously dolomitized
and the upper parts of many fossils were lost, possibly by solution.
This is suggested by the cavity-free micritic texture of the dolomite
and the fact that only the lower part of most nautiloids is preserved.
In turn the contemporaneous dolomitization implies very shallow or
emergent conditions, and hence that the drifting shells were strand-
ed on lime-mud flats. Finally the sediments were lithified, by which
time much of the original shell material was lost.

A general section of the quarry is given in Figure 5.

98 FIELDIANA: GEOLOGY, VOLUME 35

Unit 1. Approximately 15 ft. of fine-grained, flaggy dolomite with
stylolitic bedding planes, locally known as "Lannon" stone. Daw-
sonoceras and Phragmoceras are present in these layers.

Unit 2. Twenty feet of massive-bedded, gray dolomite which is
moderately fossiliferous. The lower part contains disarticulated
pelmatozoans (including Caryocrinites), rhynchonellid brachipods,
and other fossils. Toward the middle of the unit the beds become
thinner, brown in color and contain numerous small solution cavi-
ties. Above this there is approximately 3 ft. of fine-grained dolomite
lithologically similar to the cephalopod layer but lacking cephalo-
pods and cystoids. The trilobites Bumastus ioxus and Dalmanites
are preserved along with strophonellid brachiopods. The lower part
of Unit 2 is equivalent to the Romeo Member of the Joliet Dolomite.

Unit 3. The cephalopod layer is considered the top of this unit.
Beneath this are 20 ft. of thick-bedded, coarse-grained, white dolo-
mite with poorly preserved cephalopods.

Unit 4. Consists of approximately 30 ft. of thick-bedded gray
dolomite with several prominent layers of chert nodules. A notice-
able layer or layers of pentamerid brachiopods are found in this
unit. The only other fossils are a few poorly preserved Favosites.

BIOHERMS IN THE RACINE DOLOMITE
There was extensive biohermal development in southeastern Wis-
consin and northeastern Illinois which is primarily confined to the
Racine Dolomite. These bioherms, or reefs, had a prolific fauna of
crinoids, cystoids, rare blastoids, and other invertebrates. They had
a vertical thickness of up to 350 ft., and some have been found with
an area of over 1 sq. mile. All have the same general structure,
although there are some significant faunal differences.

There is a distinct core which consists of fossiliferous, massive,
and cavernous dolomite surrounded by steeply dipping thick beds of
coarse bioclastic flank rock. The dip of the flank rock decreases and
grades into horizontal thin-bedded and fine-grained dolomite at the
boundary of the bioherm.

The framebuilders and binders of the core were predominantly
stromatoporoids with corals, algae, and some bryozoans being
locally important.

The interstices between the framebuilders were filled with bioclas-
tic debris. Large crevices and cavities were occasionally filled with
disarticulated molts of trilobites (Bumastus, Kosovopeltis, Arc-

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 99

tinurus) and small orthoconic and cyrtoconic cephalopods. These
crevice fillings have also been noted in flank beds close to the core.

The flank beds consist of fragments of both core-dwelling organ-
isms and those which lived on the flank itself. It is in this area that
pelmatozoan remains are abundantly found; again they are usually
found in the form of disarticulated skeletal elements, but occasion-
ally large concentrations of crinoid cups and cystoid thecae occur.
These beds are the source of the prolific pelmatozoan fauna of the
Racine Dolomite.

It appears that most of the pelmatozoans lived in the flank area,
since they are only common in small areas of the core. Because of
their fragile nature they probably could survive only in areas shel-
tered by wave-resistant structures, such as the coral and stromato-
poroid ridges in the Thornton Bioherm of Illinois (Ingels, 1963, p.
419). Also, few holdfasts or root systems are found in the core area,
but they are found in the flank beds. The crinoids Eucalyptocrinites,
Lampterocrinus , Ochlerocrinus , and Siphonocrinus are common. Of
the cystoids, only Caryocrinites is common but occasional speci-
mens of Gomphocystites, Hallicystis, and Holocystites are also
present.

Associated with a small satellite reef a fair number of Gompho-
cystites and Holocystites thecae have been found in the old Bes-
wick's Quarry in Racine. This satellite reef is located on the west
side of the larger bioherm. The inter-reef rock contains few fossils
with the exception of large orthoconic cephalopods and fine bioclas-
tic debris from the bioherm.

Most of the echinoderms are preserved as internal and external
molds in the dolomite, the original calcite having been dissolved
away. Despite complete and well preserved, the thecae of Car-
yocrinites are not in situ. Most lie on their sides and are largely
filled with matrix which now forms the dolomitic internal mold.
Paul infers their preservational history to have been as follows:
death was followed (or caused) by separation from the stem. The
detached thecae lost the arms and anal cover plates but were other-
wise deposited intact. Sediment filled most of the thecae but usually
a small part at the top was left unfilled: the resulting cavity may
have been filled with drusy calcite subsequently. The sediment was
then lithified. Post-lithification dolomitization affected the sedi-
ment within and outside the thecae and produced a cavernous
texture. The original organic calcite was dissolved away contempo-

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FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 105

raneously with or prior to dolomitization, thus forming molds which
are frequently covered with small dolomite rhombs. Often the inter-
nal molds are slightly incomplete and the missing portion is always
uppermost in undisturbed thecae. In some holocystids from the
Niagaran of Illinois and Wisconsin the inner parts of the thecal
plates are partly dolomitized (e.g., Paul, 1971, figs. 19b, 37b). This
suggests very early onset of dolomitization, certainly before solu-
tion of the test material. Equally, however, other examples, like the
Caryocrinites from Racine, have both the internal and external
molds covered with small dolomite crystals which must have formed
after solution of the test was complete. Both types of preservation
occur together. The Holocystites from Racine probably had a simi-
lar preservational history to that inferred for Caryocrinites.

Racine Dolomite bioherms have been found in many places in
southeastern Wisconsin and northeastern Illinois and a list of sig-
nificant exposures is given in Table 1 .

It should be noted that in the northern half of Milwaukee County
several prominent bioherms ( Schoonmaker, Moody, Soldier's
Home, Brown Deer) have little or no pelmatozoan remains present
in the core or flank rock. The cores are typical stromatoporoid-coral
mounds with many small branching bryozoans present. The flank
rock is primarily made of fragments of small branching corals, flat
stromatoporoids and tabulate corals, brachiopods, trilobites, and
bryozoans. These bioherms may be slightly younger than those at
Racine, but the absence of pelmatozoans at these localities is prob-
ably due to presently unknown ecological factors.

PARASITES

Many holocystids have hemispherical pits excavated in their sur-
faces which Paul (1971, p. 41), arguing from first principles, inter-
preted as the attacks of parasites. Paul could not positively identify
the nature of the parasites involved. Published accounts of parasites
(Hyman, 1955, pp. 115-119; Clark, 1921, p. 645) do not describe in
sufficient detail injuries caused to the hosts. Dr. Hertha Sieverts-
Doreck kindly drew attention to her earlier interpretation ( Sieverts,
1934; Sieverts-Doreck, 1963) of very similar but smaller pits in the
Devonian crinoid Cupressocrinites Goldfuss as borings of ectopara-
sitic predatory snails. In Cupressocrinites, as in holocystitids, none
of the pits penetrated through the calyx wall into the coelomic cavi-
ty. Many occurred on arm ossicles and even stems were attacked

106

FIELDIANA: GEOLOGY, VOLUME 35

( Sieverts-Doreck, 1963, pi. 1). This morphology does not agree well
with descriptions of the biology and feeding of recent parasitic gas-
tropods found on crinoids and other echinoderms. In an attempt to
settle the matter the spirit collections of recent crinoids in the Brit-
ish Museum, Natural History were searched. A single specimen of
Rhizocrinus lofotensis (Reg. No. 85-3-30 No. 122G, from 400 fath-
oms at lat. 9° 10 S, long. 34°49 W) was located with two pits, one
with the remains of a gastropod attached (fig. 6). The crinoid is
extremely small: the cup is 1.75 mm. high and 1.50 mm. wide. The
two pits are in a radial plate and are surrounded by a raised area of
thickened plate which grew in response to the attack. The exposed
pit (i.e., the one without the remains of the gastropod still attached)
is 0.42 mm. in diameter, penetrates right through the plate (which
is, of course, very thin) and has a small central tubular hole 0.13
mm. in diameter which passes deep into the interior of the crinoid.
The other pit has a soft tissue cover across the surface emerging
from the center of which is the proboscis of the snail (fig. 6).

/I (X III Br

/"W§N

1 1 Br \

p \ \

®v 7

//oJ*

A B /
i i

FlG. 6. Sketch of Rhizocrinus lofo-
tensis parasitized by a snail (BMNH
85-3-30 no. 122G). B = basal plate;
IBr, IIBr, IIIBr, first three brachial
plates of arms ; Op, operculum of snail ;
P, proboscis of snail; R, radial plate.
Scale in mm.

The pits are similar to those of fossils except for one important
detail. The modern example reaches into the interior of the cup and
has a deep tubular hole where the proboscis of the snail penetrated
the soft tissue. This morphology agrees very well with descriptions
of feeding methods of modern parasitic snails ( Fretter and Graham,
1949; Clark, 1921, pp. 645-647).

Nevertheless, the fossil pits are very similar to the recent borings
(except that they do not penetrate the thecal cavity) and are unlike
the galls produced by other parasites such as myzostomid worms
and various copepods. Also it may be unwise to place too much reli-
ance on a single example in a very thin-plated recent crinoid al-

FREST, MIKULIC & PAUL: HOLOCYSTITES FAUNA 107

though Clark ( 1921, pp. 645-647) consistently uses the word "holes"
to describe the injuries to recent crinoids. It seems most likely that
Sieverts-Doreck is correct in- her interpretation. This still leaves the
puzzling fact that the fossil snails apparently never managed to
penetrate into the interior of the cup. Perhaps they received ade-
quate nourishment from tissues within the plates. Clark (1921, pi.
57, fig. 1362) illustrates a Stilifer attached to the arm of Bathymetra
sp.

One final point: although these pits are known in echinoderms
from at least the Middle Ordovician ( Benbolt Formation of Tennes-
see and Virginia) to the Triassic, none is as large as the examples in
holocystitids. Holocystitid pits are usually 4 mm. in diameter as
opposed to 1.4-1.7 mm. in Cupressocrinus (Sieverts-Doreck, 1963, p.
241) and not more than 2 mm. in any other examples. Plausibly the
Osgood snails were also much larger than normal. As far as we are
aware, no snails with suitable shells (see Clark, 1921, pi. 57, figs.
1359-1361) have been found in the Osgood Formation, but they
should certainly be sought.

REFERENCES

Berry, W. B. N. and A. J. Boucot
1970. Correlation of the North American Silurian rocks. Geol. Soc. Amer., Spec.
Pap., 102, 289 pp., 12 figs.

Chamberlin, T. C.

1877. Geology of Eastern Wisconsin, pp. 93-405. In Geology of Wisconsin, Vol. 2.

Clark, A. H.
1921. A monograph of the existing crinoids. Volume I. The comatulids. Part 2.
Bull. U.S. Nat. Mus., 82, 795 pp., 1-57 pis., 949 text figs.

Day, F. H.

1878. On the fauna of the Niagara and Upper Silurian rocks as exhibited in Mil-
waukee County, Wisconsin, and in counties contiguous thereto. Trans. Wis.
Acad. Sci. Arts Let., 4, pp. 113-125.

Foerste, A. F.
1897. A report on the geology of the Middle and Upper Silurian rocks of Clark,
Jefferson, Ripley, Jennings and Southern Decatur counties, Indiana. Indiana
Dept. Geol. Nat. Res., Rept. 21, pp. 213-288, pis. 14-17, illus.

Frest, T.

1975. Caryocrinitidae (Echinodermata: Rhombifera) of the Laurel Limestone of
southeastern Indiana. Fieldiana: Geol., 30(4), pp. 81-106.

108 FIELDIANA: GEOLOGY, VOLUME 35

Fretter, V. and A. Graham
1949. The structure and mode of life of the pyramidellidae, parasitic opistho-
branchs. Jour. Marine Biol. Assn. U.K., 28, pp. 493-533, 12 figs.

Greacen, K. F. and J. R. Ball
1946. Silurian invertebrate fossils from Illinois in the Thomas A. Greene Memorial
Museum at Milwaukee-Downer College. Bull. Milwaukee-Downer Coll., (1946),
61pp.

Hall, J.
1864. Account of some new or little known species of fossils from rocks of the age

of the Niagara Group. Albany, New York. (Advance publication of the 18th

report N.Y. State Cab. Nat. Hist.)
1868. Account of some new or little known species of fossils from rocks of the age

of the Niagara Group. Rept. N.Y. State Cab. Nat. Hist., 20, pp. 305-401, pis.

10-23, 16 figs.

Hyman, L. H.
1955. The invertebrates. 4 Echinodermata. The coelomate Bilateria. VI + 763 pp.,
280 figs. New York, Toronto and London.

Ingels, J. J. C.
1963. Geometry, paleontology and petrography of Thornton reef complex, Silurian
of Northeastern Illinois. Bull. Amer. Assoc. Petrol. Geol., 47, pp. 405-440, 16
figs., 2 pis.

Paul, C. R. C.
1971. Revision of the Holocystites fauna (Diploporita) of North America. Fieldi-
ana: Geol., 24, 166 pp., 70 figs.

Sieverts, H.
1934. Neues iiber Cupressocrinus Goldfuss. Sber. Naturh. Ver. Preuss. Rheinl.
Westf. 26-27, pp. 89-192, 4 text-figs.

SlEVERTS-DORECK, H.

1963. Uber Missbildung bei Cupressocrinus elongatus aus dem Mitteldevon der
Eifel. Decheniana, 115, pp. 239-244, 1 pi.

Springer, F.
1926. American Silurian crinoids. Smithsonian Institution, iv + 239 pp., 33 pis.,
3 figs.

Teller, E.E.
1911. A synopsis of the type specimens of fossils from the Palaeozoic formations
of Wisconsin. Bull. Wise. Nat. Hist. Soc, 9, pp. 170-271.

WlLLMAN, H. B.

1973. Rock stratigraphy of the Silurian system in northeastern and northwestern
Illinois. 111. State Geol. Surv., Circular 479, 55 pp., 10 figs.

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