Pennsylvanian invertebrates of the Mazon Creek area, Illinois : Eurypterida

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PENNSYLVANIAN INVERTEBRATES

OF THE MAZON CREEK AREA, ILLINOIS

EURYPTERIDA

ERIK N. KJELLESVIG-WAERING

FIELDIANA: GEOLOGY

VOLUME 12, NUMBER 6

Published by

CHICAGO NATURAL HISTORY MUSEUM

SEPTEMBER 17, 1963

OeOLOQY LlBHABtY

PENNSYLVANIAN INVERTEBRATES

OF THE MAZON CREEK AREA, ILLINOIS

EURYPTERIDA

ERIK N. KJELLESVIG-WAERING
Research Associate

FIELDIANA: GEOLOGY

VOLUME 12, NUMBER 6

Published by

CHICAGO NATURAL HISTORY MUSEUM

SEPTEMBER 17, 1963

Library of Congress Catalog Card Number: 63-220^8

PRINTED IN THE UNITED STATES OF AMERICA
BY CHICAGO NATURAL HISTORY MUSEUM PRESS

5" aEOLOG^r

Eurypterida

Eurypterids are rarely encountered in the Mazon Creek area, al-
though the number of known specimens has increased gradually since
the first report of the holotype of Adelophthalmus mazonensis by
Meek and Worthen in 1868. In 1948 (p. 17), Kjellesvig-Waering
reported on seven more specimens. Up to the present, however,
only these eight specimens have been reported in the literature, all
of them representing one species, Adelophthalmus mazonensis (Meek
and Worthen).

The purpose of this notice is to record new morphological and
biometric data on twenty-three hitherto unreported specimens of
A. mazonensis (Meek and Worthen), and to describe two new euryp-
terids previously unknown in the Mazon Creek fauna. One of these,
a very unusual eurypterid of the family Stylonuridae, is described as
a new species of the new genus Mazonipterus, and the other is repre-
sented by fragments of a specimen belonging to Mycterops, a peculiar
genus previously reported in Pennsylvanian beds of Pennsylvania,
Belgium and Holland.

The complete list of Mazon Creek eurypterids is as follows:

Adelophthalmus mazonensis (Meek and Mazonipterus cyclophthalmus, new gen.
Worthen) and sp.

Mycterops, sp. indet.

Acknowledgments. — I am particularly indebted to Dr. Eugene S.
Richardson, Jr., as solely through his co-operation I have been able
to locate the specimens of Mazon Creek eurypterids, which are in
the hands of private collectors residing principally in the Chicago
area. It is mainly through the ceaseless efforts of these avid col-
lectors that the bulk of the Mazon Creek fauna has been revealed
to science. I am also indebted to Dr. Willard P. Leutze, who told
me about the important specimen PE 6263, which was at that time
in the private collection of Mr. Bruce Bell, of Flossmoor, Illinois;
Mr. Bell has since presented it to Chicago Natural History Museum.
Mr. Jerry Herdina, whose remarkable collection of Mazon Creek
eurypterids was kindly lent for description, particularly deserves
acknowledgment. Acknowledgments are also due to Messrs. James

85

86 FIELDIANA; GEOLOGY, VOLUME 12

Konecny, Michael Moore, and Harry C. Witmer for the loan of
their specimens. For the loan of other specimens used in this
study I wish to thank the United States National Museum, through
Dr. G. Arthur Cooper and Dr. Henry B. Roberts; the Museum of
Comparative Zoology, through Dr. Harry B. Whittington and Dr.
Donald Baird; the Princeton University Museum, through Dr. B. F.
Howell; and the Peabody Museum, through Dr. Carl O. Dunbar.
Mr. Matthew Nitecki, of the Walker Museum, University of Chi-
cago, kindly lent the specimen of Adelophthalmus mansfieldi (C. E.
Hall) shown in figure 51. My wife, Virginia Kjellesvig-Waering,
has been of constant and most valued assistance, particularly in
photographing the specimen of Mazonipterus cyclophthalmus.

Class Merostomata Dana, 1852

Subclass Eurypterida Burmeister, 1843

Superfamily Eurypteracea Burmeister, 1845

Family Hughmilleriidae Kjellesvig-Waering, 1951

Genus Adelophthalmus Jordan and Meyer, 1854

Adelophthalmus mazonensis (Meek and Worthen)
Figures 44-50

Eurypterus (Anthraconedes) mazonensis Meek and Worthen, 1868, Amer. Jour.
Sci., 46, pp. 19-22; 1868, Geol. Surv. Illinois, 3, pp. 544-547; Miller, 1877,
Am. Palaeoz. Foss., p. 209; J. Hall, 1884, 2nd Geol. Surv. Pennsylvania,
Rept. Progr., PPP, pp. 24-28, figs. 2, 3; Lesley, 1889, 2nd Geol. Surv.
Pennsylvania, Rept. P4, 1 (A-M), pp. 235-236; Woodward, 1907, Geol.
Mag., Dec. V, 4, p. 278; Clarke and Ruedemann, 1912, New York St.
Mus., Mem., 14, pp. 223-226, pi. 26, fig. 1, text figs. 50-51; O'Connell,
1916, Buffalo Soc. Nat. Sci., Bull., 11, p. 42; Grabau, 1920, Geol. Surv.
China, Bull., 2, p. 65; Diener, 1924, Foss. Cat., I, Animalia, 25, Euryp-
terida, p. 20; Pruvost, 1930, Mus. Roy. Hist. Nat. Belg., Mem., 44, pp.
193-194; Moore, 1936, Geol. Assoc, Proc, 47, p. 364; Shimer and Shrock,
1944, Index Foss. N. Amer., p. 707, pi. 299, figs. 8, 9.

Eurypterus mazonensis (Meek and Worthen) Miller, 1877, Am. Palaeoz. Foss.,
p. 217; Woodward, 1888, Geol. Mag., Dec. Ill, 5, p. 419; Miller, 1889,
N. Amer. Geol. Pal., p. 548; Laurie, 1895, Roy. Soc. Edinburgh, Trans., 37,
p. 520; Weller, 1898, U. S. Geol. Surv., Bull., 153, p. 269; Clarke, 1909,
New York St. Mus., Bull., 133, p. 37; Pruvost, 1911, Soc. Geol. Nord,
Ann., 40, p. 300; Woodward, 1913, Geol. Mag., Dec. V, 10, p. 298;
Stainier, 1915, Geol. Soc. London, Quart. Jour., 71, p. 642; Pruvost, 1919,
Mem. Carte geol. det. France, p. 327.

KJELLESVIG-WAERING: EURYPTERIDA 87

Lepidoderma mazonense (Meek and Worthen) Kjellesvig-Waering, 1948, Illi-
nois St. Mus., Sci. Pap., 2, no. 4, pp. 17-24, pis. 1-5, pi. 6, fig. 1; St0rmer,
1955, Treatise Inv. Paleont., P, Arthropoda 2. p. 30, fig. 21 (36, c).

Adelophthalmus mazonensis (Meek and Worthen) Pfibyl, 1953, Cesk4 Akad.,
Tf., 53, no. 2, p. 7; Caster and Kjellesvig-Waering, 1956, Jour. Paleont.,
30, p. 27; Kjellesvig-Waering, 1958, Jour. Paleont., 32, p. 1140; Waterston,
1960, Palaeontology, 3, p. 245.

Adelophthalmus imhofi (Reuss) Van Oyen, 1956, Med. Geol. Sticht., ser. C-
IVS, no. 7, p. 59, text figs. 5, 6, 27.

This rare eurypterid was previously known from the holotype
and seven specimens (Kjellesvig-Waering, 1948, p. 17). To this
number can be added data from twenty-three specimens. Eighteen
of these specimens were collected during ten years of intensive search
by Jerry Herdina, of Berwyn, Illinois, and form part of his extensive
collection. It includes the largest carapace known (see fig. 44).

Twenty-two of the specimens discussed here are from the spoil
heaps of the abandoned strip mines of the Peabody Coal Company
in Will and Grundy Counties, Illinois (Richardson, 1956). Several
beds of coal have been exploited in these mines, but it is probable that
the concretions bearing the famous Mazon Creek fauna (including
these eurypterids) are derived from the Francis Creek shale member
of the Middle Pennsylvanian (Westphalian C) Carbondale formation
overlying Coal 2. The remaining specimen, from the Chiefton strip
mine a few miles south of Terre Haute, in Vigo County, Indiana, is
slightly younger. Spoil heaps of this mine are at present yielding
large numbers of ironstone concretions to the same industrious col-
lectors who have recovered so many fine specimens from the Illinois
locality. According to Dr. Charles E. Wier, Head of the Coal Sec-
tion of the Indiana Geological Survey, the concretion-bearing bed in
the Chiefton mine lies above Coal VII, and is thus in the Shelburne
formation (also Westphalian C).

The measurements of the holotype given by Clarke and Ruede-
mann (1912, p. 226) are erroneous as to the width of the carapace,
which is given as 53.0 mm. This appears to be a typographical
error, as the correct dimension is 43.0 mm, across the base of the
carapace.

The new morphological data include the structure of the impor-
tant ventral shield of the carapace, definite outlines of the spatulate
plates of the Type A operculum, and the presence of the alimen-
tary canal. Measurements of all carapaces are recorded for bio-
metric comparisons. In this connection it should be noted that
the condition of preservation of the carapace is of great importance

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KJELLESVIG-WAERING: EURYPTERIDA

89

in biometric studies; therefore the state of preservation is given with
each specimen. The dimensions of these carapaces are as follows:

Width

Width

Specimen

at base

behind eyes

Length

number

mm.

mm.

mm.

Ratio

Condition

H-7

11.5

10.3

7.3

6.3:10

C and und.

Vigo Co.,

Ind. 15.5

13.3

10.0

6.4:10

PC and und.

H-11

16.3

broken

11.2

6.8:10

C and und.

H-16

16.5

broken

11.8

7.1:10

C and und.

H-14

19.4

17.7

14.5

7.4:10

C and und.

PE 6263

19.5

14.5

7.4:10

C and und.

H-15

20.3

17.0

8.3:10

unc. and und

H-8

20.3

15.0

7.3:10

PC and und.

H-18

20.4

16.8

14.5

7.1:10

PC and und.

H-3

20.8

18.5

15.3

8.8:10

PC and und.

PE 3969

26.8

22.5

16.7

6.3:10

C and und.

PE 5094

23.0

20.3

16.2

8.8:10

PC and und.

H-12

23.8

20.2

16.6

6.9:10

PC and und.

H-2

24.6

20.8

17.3

7.0:10

PC and und.

H-4

26.1

24.0

18.5

7.0:10

C and P dis.

H-10

26.1

24.0

19.0

7.2:10

und.

Witmer

30.0

26.5

19.5

6.5:10

C and und.

H-5

31.8

28.8

24.5

7.7:10

PC and und.

H-13

34.3

25.4

7.4:10

PC and und.

H-1

broken

29^7

25.6

C and und.

H-9

36.8 est

. 31.4

27.3 est.

7.4:10

C and und.

H-6

51.0

43.8

37.8

7.4:10

PC and und.

C = con]

pressed

dis. = distorted

P= partly

unc. = uncompressed

und. = undistorted

The ventral shield (fig. 46) comprises a broad plate, not unlike
that of Hughmilleria, but without trace of any sutures except a longi-
tudinal one dividing the plate into two halves, longitudinally, along
the anterior. This suture is present in Hughmilleria (St0rmer, 1934,
fig. 2). A very narrow, raised, marginal rim surrounds the carapace.
A small, deep, triangular indentation occurs at the middle of the
anterior of the shield to receive the triangular process at the anterior
of the carapace, thereby forming a locking device for the ventral
shield.

The ventral shield is ornamented with very fine semi-lunar scales
that point away, or radiate, from the position of the mouth (see also
fig. 45). It was almost entirely preserved in specimen PE 6263 and
partly preserved in specimens H-2 in the Herdina collection and
PE 3347.

Specimen PE 5094 (a male. Type A) has the eyes located on the
carapace, 4.9 mm. from the anterior margin, 7.7 mm. from the pos-

Fig. 45. Carapace of Adelophthalmus mazonensis (Meek and Worthen) from
the Herdina collection (H-2), showing the outline of the ventral shield; X 2.8.
The scales on the ventral shield point outward (see fig. 46).

90

KJELLESVIG-WAERING: EURYPTERIDA

91

Fig. 46. Schematic drawing of the ventral shield of Adelophthalmus mazo-
nensis (Meek and Worthen) based on specimens H-2, PE 6263 and PE 3347.

terior margin and 3.8 mm. from the lateral margins. They are
2.8 mm. in length, 1.8 mm. in width, 6.7 mm. apart at the front,
and 8.6 mm. apart at the back. The ocellar mound is located on
the carapace 8.2 mm. from the anterior margin, 6.8 mm. from the
posterior margin, and 9.3 mm. from the lateral margin; diameter,
0.8 mm.

Another well-preserved specimen (H-3) has the eyes located on
the carapace, 4.2 mm. from the anterior margin, 7.3 mm. from the
posterior margin, and 3.7 mm. from the lateral margins. The lat-
eral eyes are 3.7 mm. in length, 2.0 mm. in width, 5.6 mm. apart at
the front, and 7.3 mm, apart at the back. The ocellar mound is
located on the carapace, 8.5 mm. from the anterior margin, 5.5 mm.
from the posterior margin, and 9.0 mm. from the lateral margins.
In an uncrushed condition, the ocellar mound is nearly round and
measures approximately 1.3 mm. in diameter.

The largest carapace (H-6) has eyes that are 6.8 mm. in length
and 4.5 mm. in width.

Although the details of the Type B operculum are known (Kjel-
lesvig-Waering, 1948, p. 23, pi. 1, fig. 6), those of Type A are mainly
known from an inconclusive outline given by Meek and Worthen
(1868a, pp. 19-22), as the holotype is a dorsal impression and the
shape of the operculum could only be surmised by its reflection
through the mesosoma. Little can still be added to Meek and
Worthen's original interpretation except to reveal that the spatu-

92

FIELDIANA: GEOLOGY, VOLUME 12

Fig. 47. Well-preserved specimen (male; Type A) of Adelophthalmus mazo-
nensis (Meek and Worthen), PE 5094; X 1.5. The underlying mesial appendage
was developed to reveal the lateral lobes of the operculum shown on figure 48.

late lobes are large, ear-shaped, and very similar to those of Type B
(see fig. 48). This is an important morphological structure, as the
operculum of Adelophthalmus mansfieldi (C. E. Hall) is quite dif-
ferent with regard to the spatulate lobes. The Type A mesial
appendage of A. mazonensis, although not clearly preserved, is con-
siderably larger than in A. mansfieldi. The operculum of A. mans-
fieldi is given here for comparison (see fig. 51). This is James Hall's
hypotype (1884, fig. 4), which remains the only known well-preserved
Type A operculum of the genus Adelophthalmus.

A very poorly preserved specimen, PE 6174, paradoxically rep-
resents the only specimen in which the alimentary canal is preserved.
This is preserved from the second tergite to about the ninth, and
appears to be thickest in the area occupied by the fourth, fifth, and

KJELLESVIG-WAERING: EURYPTERIDA

93

sixth tergites (see fig. 50). Ruedemann (1919, p. 92) has previously
shown the alimentary canal in Carcinosoma newlini (Claypole), and
Heubusch (1962, p. 222) has shown it in specimens of Eurypterus
remipes lacustris Harlan.

Fig. 48. Central part of operculum of specimen
PE 5094, Adelophthalmus mazonensis (Meek and Worthen).
The spatulate lobes of the male are as well developed
as those in the female.

Specimens examined. — The specimens listed as H-1 to H-18 are in
the private collection of Jerry Herdina. The specimen listed as
"Witmer" is in the private collection of Harry Witmer, of Downers
Grove, Illinois; the Vigo County, Indiana, specimen is in the collec-
tion of Michael Moore, of Tulsa, Oklahoma; and those listed as
PE 3969, PE 5094, and PE 6263 are in the collection of Chicago
Natural History Museum. All except the Indiana specimen were
collected from the strip mines on the Will-Grundy County line,
Illinois. All of the specimens collected by Herdina and the Bell
specimen (PE 6263) are from the vicinity of the Santa Fe and the
Gulf Mobile and Ohio railway tracks, where they cross the strip
mines (see Richardson, 1956, pp. 6, 7). The specimen with the ali-
mentary canal preserved is in the private collection of Francis Tully,
of Lockport, Illinois; the copper cast, PE 6174, is in the collection
of Chicago Natural History Museum.

Remarks. — The mode of preservation of eurypterids, particu-
larly with reference to biometric studies, is of primary importance.
It should be emphasized that the more incompetent the encasing
material, the greater the amount of distortion that is found. To
illustrate this point, the measurements of two carapaces of Slimonia
acuminata (Salter) from the Silurian, Ludlow shales of Lesmahago,
Scotland, are given (specimens in Princeton University) :

Specimen
number

1

2

Length
mm.

103.5
150.0

Width at
base
mm.

96.0
80.0

Width at

midsection

mm.

88.0

77.5

The length /width-at-base ratio of No. 1 is 10.5:10 whereas that
of No. 2 is 18.8:10. The latter carapace has been stretched but it

Fig. 49. A particularly well-preserved and only partly compressed specimen
of Adelophthalmus mazonensis (Meek and Worthen) from the Herdina collection
(H-3); X 1.8. The ocellar mound and the short genal spines of the carapace are
particularly well preserved.

94

KJELLESVIG-WAERING: EURYPTERIDA

95

appears not to be distorted, as there are no breaks on the integu-
ment. Both carapaces are of approximately the same size, as attested
by the nearly similar dimensions of the lateral eyes. The thin chitin
however, is easily distorted when the encasing material is argilla-
ceous. Specimen No, 1 represents the normal dimensions of the
carapace of the eurypterid.

Fig. 50. Schematic drawing of the intesti-
nal tract of Adelophthalmus mazonensis (Meek
and Worthen) in specimen PE 6174 (copper
replica).

For comparison with Adelophthalmus mazonensis, the following
measurements from specimens of A. mansfieldi (C. E. Hall) are
offered. The specimens are all from the Darlington black shale of
the Middle Pennsylvanian Allegheny formation, collected near Can-
nelton, Beaver County, Pennsylvania. All are preserved in black
shale with varying degrees of slight distortion, but overall, the speci-
mens listed here are mainly undistorted, though compressed (all
carapaces are complete unless indicated). I have made the follow-
ing measurements:

96

FIELDIANA: GEOLOGY, VOLUME 12

Width

Width

behind

at base

eyes

Length

Specimen

(a)

(b)

(c)

Ratio

number

mm.

mm.

mm.

a : c

Condition

5323/10

9.2

6.2

6.7:10

C

M848

9.7

8.6

7.7

7.9:10

C

5323/25

11.3

8.3

7.3:10

C and dis.

5323/11

11.8

8.0

6.8:10

C and dis.

M836

12.0 est.

11.0 est.

8.0 est.

6.7:10

C

M844

12.5

11.3

7.8

6.2:10

C

M881

13.0

11.0

7.5

5.8:10

c

M794

13.0

11.1

9.6

7.4:10

c

5323/9

13.2

10.35

7.8-10

C and und.

M809

13.4

12.0

11.6

8.6:10

C and dis.

12306>

13.5

10.0

7.4:10

C and und.

5323/1

14.0 est.

10.0

7.1:10

C

M828

14.5

11.5

11.5

7.9:10

C

M840

14.5

13.0 est.

12.4

8.5:10

C and dis.

M849

15.0

12.5

11.5

7.7:10

C and und.

M856

15.0

13.0

11.5

7.7:10

C

122962

15.3

9.8

6.4:10

C

2569

15.6

10.5

6.7:10

c

5323/13/29

16.0

11.5

7.2:10

C and P. dis

123023

16.8

15.4

9.2:10

C and dis.

M845

17.0

14.8

11.8

6.9:10

C

5323/12

17.0

13.0

7.6:10

C and und.

12298^

18.2

15.6

12.5

6.9:10

C and dis.

5323/28

18.5

13.8

7.4:10

C and dis.

12296^

19.3

16.5

13.0

6.7:10

C and und.

5323/23

19.6

12.7

6.5:10

C and dis.

5323/3

19.6

12.7

6.5:10

C

M863

20.0

16^0

13.5

6.7:10

C and und.

M839

22.0 est.

19.0 est.

15.5

7.0:10

C and und.

M843

22.0 est.

17.4

17.6

8.0:10

C and und.

5323

22.0 est.

13.0

5.9:10

C and P. dis

M874

23 . 5 est.

21.7

16.6

7.1:10

C and und.

12296"

26.0

16.2

6.2:10

C and dis.

M815

29.5

25.5

23.4

7.9:10

C and und.

5323/27

32.0

28.5

8.9:10

C and dis.

12299^

43.5

31.0

7.1:10

C

iHypotype (Hall, 1884, pi. 5, fig. 9).

2 Hypotype (Hall, 1884, pi. 5, fig. 15).

3 Hypotype (Hall, 1884, pi. 4, fig. 3).

4 Holotype (Hall, C. E., 1877, fig.).

5 Hypotype (Hall, 1884, pi. 5, fig. 12).
« Hypotype (Hall, 1884, pi. 5, fig. 13).
■> Hypotype (Hall, 1884, pi. 5, fig. 3).

Specimens M 794-M 881 are in the Geological Museum, Princeton Univer-
sity; specimens 12296-12306 are in the Walker Museum, University of Chicago;
specimens 5323/1-29 are in the Museum of Comparative Zoology; and specimen
2569 is in the Peabody Museum, Yale University.

KJELLESVIG-WAERING: EURYPTERIDA

97

Fig. 51. The only known, well-preserved, and entire male (Type A) mesial
appendage of Adelophthalmus. This occurs in a specimen of A. mansfieldi (C. E.
Hall) from the Pennsylvanian, Allegheny group at Cannelton, Darlington town-
ship, Beaver County, Pennsylvania; previously figured by James Hall (1884).

In Adelophthalmus mansfieldi and A. mazonensis the length/
width-at-base (of the carapace) ratios and the length/width-behind-
eyes ratios show little difference when plotted and when not taking
into consideration the important preservational factor. For in-
stance, all of the carapaces of A. mansfieldi are preserved in black
shale and almost without exception they are completely compressed
into one plane. Most of the carapaces of A. mazonensis, on the other
hand, are only partly compressed and retain, in many cases, consid-
erable relief. Thus A. mansfieldi is a much narrower form than
A. mazonensis, as compressed carapaces of A. mansfieldi have nearly

98 FIELDIANA: GEOLOGY, VOLUME 12

the same dimensions as less compressed carapaces of A. mazonen-
sis. This is in keeping with the overall narrow aspect of the entire
opisthosoma of A. mansfieldi, in contrast to the robust construction
of A. mazonensis. On the basis of the measurements of the cara-
paces above, my conclusions differ entirely from those advanced by
Van Oyen (1956) in regard to these two species. Other morpholog-
ical differences as stated on page 92 leave no doubt as to the validity
of both species.

An examination of the ratios of both length/width-at-base and
length /width-behind-eyes reveals that A. mansfieldi progressively
becomes more narrow in the carapace with age as compared to
A. mazonensis, whose ratios remain constant.

Van Oyen (1956, p. 38) states that his conclusions regarding the
measurements of the eurypterids from the "Veine D" are based on
the measurements of 130 carapaces. Of the length and width-at-
base measurements of the carapace it is important to note that fully
107 (almost 86 per cent) of these carapaces should not have been
measured, as they represented specimens that were either incom-
plete or obviously too distorted to permit a reasonable interpreta-
tion of the individual variation of the species represented by the
prolific "Veine D" eurypterids. Van Oyen, therefore, presents an
interpretation of the possible limits of distortion of 130 carapaces of
the "Veine D" eurypterids rather than a criterion for the identifica-
tion of the species based on actual individual variation. As a result,
his so-called limits of variation lump together (1956, p. 59) nearly
all of the North American species of the genus, giving a stratigraphic
range from the Middle Pennsylvanian to the Middle Permian for a
single species which he identifies as the Bohemian A. imhofi (Reuss).
Nowhere is a highly specialized form such as an eurypterid known to
encompass such a long range. Van Oyen completely disregards ob-
vious morphological differences, as, for example, the under side of
well-known forms such as A. mazonensis and A. mansfieldi, and both
are included under A. imhofi. In order to reveal the fallacy of the
conclusions advocated by Van Oyen, it might be permissible to com-
pare the holotype of A. imhofi, which has a telson barely as long as
the carapace, with an individual of A. mansfieldi of approximately
the same size; the latter has a telson at least twice as long as the
carapace. The latter also is obviously a much more highly spinous
eurypterid, in contrast to the non-spinous character of A. imhofi.
Nevertheless, Van Oyen groups both as the same species. Morpho-
logically, I know of no two eurypterids that can be so different and

KJELLESVIG-WAERING: EURYPTERIDA 99

still be of the same genus. On the other hand, Van Oyen (1956,
pp. 60, 61) recognizes species and subspecies which easily can be
demonstrated to be growth stages ("E. stylus Hall") or caused by
poor preservation ("E. derbiensis Woodward"). Other American
species, such as AdelophthabnusCi) potens (Hall), he also lumps to-
gether under the Bohemian A. imhofi, although the former probably
does not represent the same genus or even the same family as the
Bohemian form. Considerable evidence indicates that A.? potens
(Hall) should be referred to the Hibbertopteridae.

Of the "Veine D" eurypterid carapaces figured and measured by
Van Oyen (1956) the following are considered sufficiently well-pre-
served and complete to use for biometric studies:

Specimen

Width at base

Length

Ratio

number

mm.

mm.

A-1

30.0

24.4

8.1:10

A-13

35.8

27.5

7.7:10

A-20

19.0

14.5

7.6:10

A-21

36.0

29.5

8.2:10

A-32

19.2

14.6

7.6:10

A-34

10.5

8.8

8.4:10

A-35

10.6

8.9

8.4:10

A-37

24.4

17.2

7.0:10

A-46

15.6

11.5

7.4:10

A-57

12.4

8.9

7.2:10

A-66

16.6

12.0

7.2:10

A-88

13.0

9.7

7.5:10

A-123

33.0

23.0

7.0:10

A-1 30

13.7

. 9.9

7.2:10

A-131

23.4

18.0

7.7:10

A-1321

A-1 36

26.5

2o!o

7^5:10

A-1452

34.5(28.5)

21.5

7.5:10

A-1 72

7.8

7.2

9.2:10

A-1 74

13.2

9.0

6.8:10

A-1 753

36.0

24.7

6.9:10

A-259

20.7

15.5

7.5:10

A-295

9.8

8.1

8.3:10

A-296

11.7

9.5

8.1:10

1 Not measured although complete and mainly undistorted.

2 Erroneously measured by Van Oyen (1956): according to his photograph
(fig. 131) and drawing (fig. 125), the correct measurements are 28.5 mm. in width
at base and 21.5 mm. in length.

' Obviously compressed and widened.

It is not the purpose of this paper to evaluate the conclusions
reached by Van Oyen except where they concern the interpretation
of the eurypterid in question or concern the genus. It has been
recognized that many of the species described are much alike, at

100 FIELDIANA: GEOLOGY, VOLUME 12

least dorsally, and that with more material several may be found
to be conspecific, and certainly several must be delegated to sub-
specific rank (Kjellesvig-Waering, 1948, p. 5). It should be noted,
however, that the eurypterids identified by Van Oyen from the
"Veine D" as A. imhofi (Reuss) differ as much from the holotype of
A. imhofi as from A. mansfieldi. The species from the "Veine D,"
in my opinion, is Adelophthalmus camhieri (Pruvost) .

Superfamily Stylonuracea Diener, 1924

Family Stylonuridae Diener, 1924

Genus Mazonipterus, new genus

Diagnosis. — Stylonuridae of medium size; carapace very elon-
gated, with lateral eyes arcuate and placed anteriorly on the cara-
pace. The greatest width of carapace occurs midway. Palpebral
lobe attached to carapace by a narrow bridge on outer-posterior part
of lobe. Marginal rim very narrow, simple, not ornamented. Orna-
mentation smooth. No other parts known.

Occurrence. — Middle Pennsylvanian of Illinois.

Type species. — Mazonipterus cyclophthalmus Kjellesvig-Waering.

Remarks. — This is an easily recognizable and very unusual genus.
The remarkably long, inflated carapace ind the large disc-like, arcu-
ate eyes, well forward of the center of the carapace, recall the Silurian
genus Ctenopterus Clarke and Ruedemann, 1912, and indeed, may
be the Pennsylvanian straggler of that line. We know of no closely
related forms between the Middle Silurian and the Middle Pennsyl-
vanian, however, that might give substance to that supposition.
The two genera differ in many important structures. Mazonipterus
has a longer, more inflated carapace; an unornamented marginal rim;
highly arcuate eyes, which are covered by disc-like palpebral lobes
that join the carapace at the outer posterior part of the eyes; and
no surface ornamentation. Ctenopterus has a much shorter, converg-
ing carapace; an ornamented marginal rim; sub-reniform, lateral eyes
located on mounds; and prominent scale-like ornamentation. The
Silurian Stylonurus dolichopteroides St0rmer also bears some resem-
blance, which, however, might be of more importance when more is
known of each. The shape of the carapace, as well as the shape of
the lateral eyes, will readily distinguish both.

Mazonipterus is a highly unusual form, not only with regard to
morphology but because it is the first definite stylonurid to be found
in the upper Carboniferous. Augusta and Pfibyl (1951, pp. 2-4,

KJELLESVIG-WAERING: EURYPTERIDA 101

pi. 1, figs. 1, 2) recorded a leg from the marine Namurian of Czecho-
slovakia. They named this form Stylonurus? (Ctenopterus?) ostravi-
ensis and indicated its possible affinities to Ctenopterus. It now might

Fig. 52. Holotype of Mazonipterus
cyclophthalmus, new sp. Slightly re-
duced.

be preferable to questionably refer the Czechoslovakian species to
Mazonipterus. It must be admitted, however, that the incongruous
Czechoslovakian form reveals distinct carcinosomatid traits, al-
though very little, if anything, is known of this family after the
Silurian. Nevertheless, the morphology of the leg of M.(?) ostravi-
ensis recalls forms such as Echinognathus and Carcinosoma. The
marine occurrence of the Czechoslovakian form is certainly more
indicative of the Carcinosomatidae than the Stylonuridae, a family
that occupied more brackish-water habitats (see Kjellesvig-Waering,
1961, pp. 793-794).

Mazonipterus cyclophthalmus, new species
Figures 52-54

Holotype. — United States National Museum no. 41169 a and h.

Diagnosis. — Carapace elongated and campanulate; lateral eyes
large, arcuate, with round palpebral lobes and located intramargi-
nally, but forward on the carapace.

Description. — The holotype and only known specimen consists of
part and counterpart of a rather well-preserved, nearly complete

102 FIELDIANA: GEOLOGY, VOLUME 12

carapace, in dorsal aspect in a typical ironstone concretion. The
specimen is partly compressed, although there is no appreciable dis-
tortion. What appears as a transverse joint-line across the middle

Fig. 53. Counterpart of holotype Fig. 54. Schematic drawing

of Mazonipterus cyclophthalmus, new of carapace of Mazonipterus cy-

sp., showing outline of ventral shield. clophthalmus, new sp., restored.
Slightly reduced.

of the carapace is a narrow plant stem that lies on the outside of the
carapace. This stem was excavated satisfactorily, and there is no
doubt that it represents extraneous material and not the junction
of the carapace with a long first tergite, as in the Scottish Wood-
wardopterus scabrosus (Woodward). A similar stem cuts diagonally
across the carapace (see fig. 52).

The carapace is very long, surrounded by a very thin, unorna-
mented, marginal rim, and is swollen at approximately midsection.
It is therefore campanulate but narrowing toward the genal angles.
The large, highly arcuate eyes, with disc-like palpebral lobes, are
located on the anterior of the carapace, close together, and intra-
marginally. There is no trace of any ocelli or ocellar mound and
enough of the carapace is present to assure their preservation if they
were present. The surface is smooth.

At the anterior of the carapace, the ventral shield is faintly pre-
served as an impression reflected through the carapace. The holo-
type previously had been carelessly excavated with a sharp instrument
toward the anterior, but part of the doublure can still be discerned.
It appears to be strongly cordate (see fig. 52) as in Limulus or stylo-
nurids such as Brachyopterus? pentagonalis (St0rmer).

KJELLESVIG-WAERING: EURYPTERIDA

103

Measurements of holotype. — Prosoma width at base, 42.0 mm.
(est.) ; prosoma width behind eyes, 41.0 mm. (est.) ; greatest width
of prosoma, 49.0 mm. (est.); prosoma length, 65.0 mm. (est.).

Fig. 55. Mycterops sp. Por-
tion of characteristic integu-
ment; X 1.8. Specimen PE
6171.

The eyes are located on the carapace: from anterior margin,
12.5 mm.; from posterior margin, 40.0 mm. (est.); from lateral mar-
gin, 8.5 mm. The eyes are arcuate, but including the palpebral lobe
they are 12.0 mm. in length, 8.5 mm. in width, 3.5 mm. apart at the
anterior, and 12.0 mm. in width at the posterior part.

Horizon and locality. — Pennsylvanian, Francis Creek shale, at
Mazon Creek, Grundy County, Illinois. No collector or date of col-
lection is given on the labels but apparently from the faded character
of the label it was made a considerable time ago.

Family Mycteropidae Cope, 1886

Genus Mycterops Cope, 1886

Mycterops, sp. indet.

Figures 55 and 56

Two fragments are recorded here which reveal the presence of
this very unusual eurypterid. One, collected by James Konecny,
consists of part and counterpart of a medium-sized coxa of the sixth
appendage, which measures 42.0 mm. by 34.0 mm. (fig. 56). An-
other fragment, comprising an undiagnostic, irregular piece of the

UNIVER.<;irY D»;

104 FIELDIANA: GEOLOGY, VOLUME 12

r

Fig. 56. Coxa of swimming leg of Mycterops sp. Specimen in Konecny col-
ion: X 2.

lection; X 2.

integument, is also recorded (fig. 55). Other than to call attention
to the presence of this very unusual eurypterid in the Mazon Creek
fauna, little can be discerned from the fragments known. The genus
is represented in the Darlington shales of the Allegheny Group in
Pennsylvania and is also known in Europe (Kjellesvig-Waering,
1959, p. 251).

Specimens. — The coxa is in the collection of James Konecny of
Mokena, Illinois; the fragment of integument is registered as no.
PE 6171 in Chicago Natural History Museum. Both are from the
strip mines on the Will-Grundy County line.

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106 FIELDIANA: GEOLOGY, VOLUME 12

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Publication 973

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