LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 550.5 FI V. 12 z 3 this re- 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 ffi Wt3 TO <-l o 0) . Vi 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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