# Second Geological Survey of Pennsylvania. Report of Progress/PPP/Note on the Eurypteridae of the Devonian and Carboniferous formations of Pennsylvania

NOTE
ON THE
EURYPTERIDÆ
OF THE
DEVONIAN AND CARBONIFEROUS FORMATIONS
OF PENNSYLVANIA.
By James Hall.
In April, 1877, Mr. Charles E. Hall, of the staff of the Second Geological Survey of Pennsylvania, commnnicated to the American Philosophical Society the description of a species of Eurypterus, (E. Pennsylvanicus,) from the Lower Carboniferous rocks of Venango county, and another one from the coal measures of Cannelton, Pennsylvania, under the name of Eurypterus (Dolichopterus) Mansfieldi, from the collection of Hon. I. F. Mansfield. The length of the latter specimen described, without the terminal joint, was two and three-fourths inches.
In April, 1881, Mr. Mansfield communicated to the Philosophical Society "a drawing of a fine fossil Eurypterus, found by him in the shale immediately beneath the Darlington cannel coal bed, lower productive coal messures." This specimen has an entire length of nine inches, of which the telson constitutes about three inches. At a later period Mr. Mansfield placed his collection of these fossils in the hands of Professor Lesley to be described and illustrated in the publications of the Geological Survey. Mr. C. E. Hall ​having completed his work, and being no longer connected with the Survey, the specimens have been placed in the hands of the writer for study and illustration.
The specimens of shale containing these remains amount to more than twenty in number, some of them containing only fragments of the fossil crustaceans, and nearly all of them containing coal plants. Two of the fossils are very large and fine specimens, being nearly complete. Several other smaller specimens are essentially complete in their parts and well-preserved, though from extreme compression in the black shale it is difficult to see the details of the organs and the surface sculpture. Several of the fragmentary portions and separated organs of the fossils are very interestesting and instructive.
A critical examination shows what are apparently two very distinct forms, which can be clearly characterized, besides other portions of much larger forms, which are at present unknown in their entire condition. All the better preserved specimens, as well as all the separated members or fragmentary portions having any important significance, have been drawn in a very complete and artistic manner by Mr. George B. Simpson, and are reproduced in heliotype.
Although several species of this family have been described from the carboniferous rocks of Europe, we have heretofore known but a single species from rocks of the same age in America. In the American Journal of Science, Vol. 46, p. 21, 1868, Messrs. Meek and Worthen published the description of Eurypterus (Anthraconectes) Mazonensis from the coal measures of Grundy county, Illinois, and the same is illustrated and farther described in the third volume of the reports of the Geological Survey of Illinois, page 544, 1868. The accompanying illustration, with the explanations, is copied from the volume cited:
* Fig. 2.—Eurypterus (Anthraconectes) Mazonensis—nat. size.
* "a, b, c. Crushed and broken legs as they appear in the specimen, the divisions not being all natural articulations.
* h, h, h, h, h. Impressions of angular ends of the dorsal half of body segments.
* m. Hypostoma in place; m², the same enlarged to show the scale-like sculpturing.
* P. One of the paddles or swimming feet in a broken condition. Its division at i seems to be a natural articulation.
* g, g. Basal joints of same; x, enlarged surface-sculpturing of the latter.
* M. Mesial appendage of the operculum ; 1, 2, 3, its apparent articulations; s, s, two little accessory pieces; x, x, t, t, lateral alae of operculum.
* o. Position of mouth."
After describing the fossil and its parts the authors remark: "From some of the characters mentioned above it will be seen that this fossil differs from the typical forms of Eurypterus, particularly in the great length and ​simple extremity of the mesial appendage of its operculum, as well as in the possession of two little spatulate supplementary pieces (ss). Hence we very strongly suspect that other characters will be found, when better specimens can be studied, showing it to belong to a distinct sub-genus, if not indeed to an entirely distinct genus from Eurypterus proper, in which case we have proposed for it the name Anthraconectes."
Whether these differences noted are of sufficient importance to constitute generic or subgeneric distinction may perhaps admit of different opinion, depending upon the interpretation of the relative value of variations of certain parts of the organism.
A specimen from Mazon creek for many years (from 1860) in my own collection and now in the American Museum of Natural History in New York City, appears to be not only identical with this one, but a counterpart or impression of the specimen described by Messrs. Meek and Worthen (see Fig. 3). It is less complete in its appendages, but the form and proportions of the body and the measurement of the parts correspond in all particulars. The mesial appendage of the thoracic plate extends to the sixth segment, as shown by a median ridge extending to that point, but it cannot be determined whether the posterior extremity is simple or bifurcate. The lines indicating the anterior attachment of this plate are visible but obscure. The existence of the two lateral accessory plates shown in the preceding figure cannot be determined, and the apparent jointing of the median appendage of the thoracic plate is produced by the impress of the articulating surfaces of the body segments.
The accompanying figure will illustrate this specimen and is given for the purpose of comparison with the figures upon Plates IV, V and VI of this paper. So far as evidence from this specimen goes there are no means of separating it from Eurypterus proper, the post lateral processes of the articulations, which become spiniform below, being only a greater development of corresponding parts in forms of that genus.
In comparison with the specimens from the coal measures of Pennsylvania, the Illinois species is more robust, the ​joints of the palpi and the entire palpi are longer, and the body is conspicuously shorter and broader.
* Fig. 3.—Eurypterus (Anthraconectes) Mazonensis, Meek and Worthen. A figure of the specimen which forms the matrix or reverse of Fig. 2.
The Cannelton specimens possess the characters of typical Eurypterus in all the more important parts. The carapace is in all respects that of Eurypterus; the form and position of the eyes are the same. The body and telson are entirely identical with species of that genus. The median appendage of the thoracic plate is narrow, elongate, and bifurcate at the posterior extremity as in Eurypterus. The ​metastoma or post-oral plate found both in the same association and attached is of similar form, with a proportionally greater width than in the ordinary forms of Eurypterus, and approaches more nearly to the form of the same appendage in Pterygotus. The single dactylus at the extremity of the palpi corresponds with known forms of Eurypterus described by Mr. Henry Woodward, and may also be compared with the corresponding part of Pterygotus. The spiniform extensions at the post-lateral extremities of the segments of the body and thorax are but a more extreme development of a feature which is common to all true Eurypterides, and can scarcely be considered of generic importance.
In the elongated joints of the swimming foot and their serrated margins the Pennsylvania forms resemble Dolichopterus, and may be referred to that sub-genus with as much propriety as to any other sub-generic form. In this respect the Eurypterus (Anthraconectes) Mazonensis is still more similar to Dolichopterus in its simple elongate median appendage of the thoracic plate. The two small accessory lateral plates of the median appendage of that species have not been detected in E. Mansfieldi, and their presence in the former species may perhaps, if verified, be considered as of sufficient importance for the separation of that form as a sub-genus. Finally, the forms are not as far removed from the typical species of Eurypterus, in any of their characters, as are several of those which Mr. Woodward has described from the Upper Ludlow rocks of England, and which he does not hesitate to place under the genus Eurypterus.
The Pennsylvania forms are quite unlike the European carboniferous species in their general aspect and proportions, as well as in the details of parts of their organization, and in these respects more nearly resemble the typical forms or the genus.
In addition to the two very well-marked forms described, there are, in the collections examined, several fragments of other crustaceans of this family which cannot be satisfactorily referred to genus and species. Two of these are figured on Plate IV, Figs. 9, 10. The specimen, Fig. 9, is an ectognath belonging to a large form of which we have also ​other evidence in a fragment of a large somite which is too imperfect to be usefully illustrated. The specimen, Fig. 10, presents the inner surface of a fragment of some large crustacean, which is broken and incomplete along the upper margin, as shown in the figure. This may, perhaps, have been a portion of a large ectognath of some sp)ecies of this family.
In addition to the above mentioned forms, Mr. C. E. Beecher has placed in my hands for description a well-marked species of Eurypterus from a sandstone of the Chemung group at Warren, Pennsylvania. This species is the first one noted from this horizon and is of considerable interest.
MEROSTOMATA.
Eurypterus, Dekay, 1825.
Eurypterus Beecheri, n. sp. Plate III, Fig. 1.
Carapace unknown. Body elongate, very convex along the dorsum, composed of twelve free segments which gradually increase in breadth from the head backwards to the fifth somite, from whence they rapidly decrease in width and increase in length, until the eleventh segment has a length equal to half its width, while in the fifth segment the breadth is four times its length. Lateral margins of the segments flattened, and slightly extended backwards on the post-lateral angles, forming a mucronate projection. The posterior tergal margin of each somite is ornamented with several triangular scales or nodes, pointing towards the telson. The number of these nodes on each segment decreases from the anterior segment, which has eight or more, to the tenth somite which is furnished with six. The number on the two posterior segments is not known, on account of their imperfect preservation in the specimen described.
Two joints of one of the great swimming feet are preserved, which are remarkable for their great length and for three or more strong longitudinal carinæ ornamenting them. The distal joint of the two has a length of more than three times its breadth, while the other has a length of nearly five times its breadth. These joints are probably the third and fourth from the attachment of the limb and correspond to the basos and ischium of a typical decapod. Telson and other appendages unknown.
The twelve free segments of the body have a total length of 96 mm., and the width of the fifth segment is 41 mm. The body measures 39 mm. across at the first segment and 25 mm. at the tenth. The longer joint of the natatory appendage has a length of 30 mm.
The specimen from which the present description is taken was found in a bed of fine grained sandstone occurring in the Chemung group at Warren. Although lacking many of ​the important members and appendages of the animal, the body is sufficiently well-preserved to distinguish the species, which is also characterized by the ornamentation of the joints of the swimming limbs. The occurrence of crustaceans of this character, in these rocks, is so rare that every specimen is of importance.
E. Pennsylvanicus is a smaller and more fragile form; they cannot be directly compared on account of the imperfection of the material.
Formation and locality. Chemung group; Warren, Pa.
Eurypterus Pennsylvanicus. Plate V, Fig. 18.
Eurypterus Pennsylvanicus, C. E. Hall, Proc. Am. Phil. Soc.; Vol. VII, p. 621, 1877.
Carapace semi-circular; length a little more than half the breadth, post-lateral angles mucronate.
Eyes situated on the anterior half of the carapace, separated by a distance equal to about one-half the breadth of the head. Midway between the eyes is a small flat node or elevation, on each side of which is a larger longitudinal prominence. There are also two similar nodes above the posterior margin. The posterior angles show two oblique short ridges. These elevations of the carapace probably indicate the positions of internal organs and the points of attachment of muscles.
The surface ornaments are not well-preserved, the specimen shows numerous small tubercles, especially over the posterior portion.
The carapace has a length of 8.5 mm. and a breadth of 15 mm.
The shape of the carapace and the arrangement of the nodes is quite different from E. Mansfieldi, and the geological position is considerably higher in the series than E. Beecheri.
Formation and locality. In an arenaceous shale; at Rooker farm, Pithole City, Venango Co., Pa.
Eurypterus Mansfieldi. Plates IV, Figs. 1–8; V, Figs. 1–11; VI, Fig. 1; VII, Fig 1; VIII, Figs. 1–3.
Dolichopterus Mansfieldi, C. E. Hall, Proc. Am. Phil. Soc. Philad. Vol. XVI, p. 621, 1877.
Carapace semi-oval, nearly one fourth broader than long; sides oblique, nearly straight; margin indented, distinctly limited. Eyes reniform, prominent, situated a little forward of the centre of the carapace and about midway between a median line and the lateral margins. Between the eyes are two broad rounded longitudinal elevations and below are two similar oblique diverging prominences.
Abdomen increasing in breadth from the carapace to the fourth segment, then gradually decreasing to the seventh segment, which is a little more than three-fourths the width of the fourth; the body narrows abruptly at the eighth segment which is about one-half the width of the fourth. The last segment is longer than wide and about one-half the width of the eighth. The posterior angles of the six anterior somites are acute and slightly produced, the seventh is considerably extended and the five posterior somites are armed with strong angular retral spines. The first segment is anchylosed to the carapace.
The telson is very narrow and attenuate; its length about one-third of the entire animal; extremity acuminate.
There are four simple palpi, of which the fourth pair project beyond the margin of the carapace for a distance equal to the width of the carapace, and expose five joints exclusive of the terminal spine. The first pair expose only the last two joints. The margins of the joints of the palpi are serrated, and the outer posterior angles are produced into spines. The palpi terminate in a long curved spine or free dactylus.
The large swimming feet near the carapace are composed of short, broad joints. The penultimate joint has a length more than twice its width. The palette is elongate elliptical in form, with the anterior terminal margin serrate. A small acute terminal plate is inserted in the apex.
The median appendage of the thoracic plate is ​comparatively very long, being six times as long as wide; the extremity is divided into four lobes, two of which form the extremity proper, while the other two are just anterior thereto. The lobes are triangular, and the anterior pair are ornamented with five or six strong plications. In the angle between the distal pair is a short process which may be the point of attachment of a small terminal appendage. Other parts of the epistoma unknown. Two of the maxillæ have been observed in position; they do not differ conspicuously from other described forms of the genus.
Metastoma ovate, bilobate at the smaller end.
Surface ornamented with minute imbricating scales. On the posterior tergal portion of each somite the scales are larger and triangular. The lateral processes of the first six segments and lateral margins of the carapace are marked by sharp, oblique striæ. The processes of the posterior segments are nearly free from ornamentation, being sometimes marked by one or two striæ. The telson appears to be free from the characteristic ornamentation of the other portions of the test. On the metastoma the scales are larger and more irregular than on the segments.
A large and nearly entire individual has the following dimensions: Extreme length from the anterior margin of the carapace to the extremity of the telson, 228 mm.; length of carapace, 31 mm.; width of fourth somite, 53 mm.; width of last somite, 15 mm.; length of telson, 80 mm. The smallest specimen observed has a length of 83 mm., of which 30 mm. belongs to the telson.
This species differs from E. stylus, with which it is associated, in its greater size, so far as observed, the more elongate form of the carapace, more approximate eyes, shorter palpi, and comparatively much shorter and more slender telson. The caudal spine of E. Mansfieldi is usually about one-third the length of the entire animal, while in E. stylus it occupies nearly-one half of the entire length.
E. Mazonensis, M. & W. from the coal measures of Illinois, bears a close resemblance to this species in general form and surface ornamentation, but the carapace is shorter and more regularly rounded.
​The specimen represented in Fig. 1 of Plate IV is here given in outline with the metastoma and maxillæ in position. These parts can scarcely be detected on the finished drawing on acconnt of the obscurity of the specimen, and the falsification which would result if these features were brought out conspicuously.
Fig. 4—Eurypterus Mansfieldi. a.—metastoma. b, b.—maxillæ.
Formation and locality.—Found in the shale immediately below the Darlington cannel coal, near Cannelton, Darlington township, Beaver county, Pennsylvania. Horizon, Alleghany river series.
Eurypterus stylus, n. sp. Plate V, Figs. 12–15.
Carapace broadly semi-oval or semi-circular; length more than two-thirds the width; margin distinctly limited. Eyes situated on a line across the middle of the length of the carapace and distant about one-fourth the breadth from the margin.
Abdomen wide to the seventh segment, then abruptly narrowed and gradually decreasing in width to the telson. The first somite is anchylosed to the carapace. The widest ​part of the body is across the fourth segment, which is more than three times the width of the last one.
Telson very long, having a length equal to nearly one-half the length of the entire animal.
The palpi and swimming feet are comparatively longer than in the preceding species.
Test marked by minute imbricating scales. On the posterior tergal position of the carapace and somites the scales are larger than on the other portions of the surface.
A somewhat distorted specimen has a length of 99 mm., of which 49 mm. pertain to the telson; the width of the fourth somite is 22 mm. and of the last one 7 mm.
This species is distinguished from E. Mansfieldi by its shorter carapace, comparatively wider body, longer and stronger telson and the eyes are more oblique and distant.
Formation and locality.—Found in the shale immediately below the Darlington cannel coal, near Cannelton, Darlington township, Beaver county, Pennsylvania. Horizon, Alleghany river series.
EXPLANATIONS OF PLATES.
PLATE III.
Eurypterus Beecheri.
Page 30.
| Fig. | 1. | Dorsal view of the specimen described, showing the form of the body, the number, size, and orna mentation of the segments, and also a portion of the large swimming appendages. Chemung group. Warren., Pa. |
PLATE IV.
Eurypterus Mansfieldi.
Page 32.
| Fig. | 1. | The head and first abdominal segment, with the palpi and other appendages attached. A portion of the segment and lower part of the carapace is removed showing the median appendage of the thoracic plate. |
| Fig. | 2. | A small individual, enlarged to three diameters. The palpi of the right side and telson are restored from other specimens. The lateral processes of the segments are not preserved. |
| Fig. | 3. | A specimen of the natural size, represented on a block of shale and showing the ferns and other plant remains with which it is associated. |
| Fig. | 4. | The fourth palpus of the right side enlarged to two diameters, showing the form and surface ornamentation. |
| Fig. | 5. | The second or third palpus from the right side, enlarged to two diameters. |
| Fig. | 6. | The last two joints of the large swimming foot, enlarged to two diameters. |
| Fig. | 7. | A terminal joint of one of the large swimming feet, showing the serrated margin enlarged to two diameters. The terminal plate is restored in outline. |
| Fig. | 8. | A separated metastoma, showing the form and ornamentation enlarged to two diameters. |
Eurypterus potens, n. sp.
| Fig. | 9. | A portion of a large ectognath. |
| Fig. | 10. | A large fragment of indeterminate relations, possibly a portion of a large ectognath. A colony of Spirorbis is represented on the upper right hand angle attached to some underlying substance, probably of a plant. |
PLATE V.
Eurypterus Mansfieldi.
Page 32.
| Fig. | 1. | An imperfect specimen, preserving the segments of the abdomen, the telson and the large swimming appendages. |
| Fig. | 2. | A smaller individual, nearly entire, showing on the last abdominal segments what appear to be the articulating surfaces of the segments, or folds produced by the pressing together of the upper and under surfaces. |
| Fig. | 3. | A large specimen, showing the entire form. Four of the palpi are preserved, and a portion of the right swimming foot has been uncovered under the abdominal segments. The specimen being too long for the plate, the extremity of the telson is represented as broken and its continuation given above. The spinous processes at the post-lateral angles of the segments are well-preserved, and show a distinctive ornamentation. |
| Fig. | 4. | An enlargement, to six diameters, of the edge of a portion of the left lateral margin of the segments, showing the striated edge and the narrow, triangular scales with minute intermediate scales. |
| Fig. | 5. | An enlargement, to ten diameters, to show the change from the acute scales near the margin to short and more rounded forms. |
| Fig. | 6. | An enlargement from the middle of a segment, showing the minute imbricating scales along the anterior portion and large, triangular scales on the middle and lower portion. The figure represents also the posterior and anterior portions of the adjacent segments. |
| Fig. | 7. | An enlargement of the test where it is ornamented with narrow, triangular scales. |
| Fig. | 8. | Enlargement showing small and large rounded imbricating scales. |
| Fig. | 9. | A small carapace showing the characteristic elongate form of this part of the animal. |
| Fig. | 10. | The caudal spine of a small individual. |
| Fig. | 11. | A fragment of shale preserving two detached lateral processes of the segments, enlarged to two diameters. |
Eurypterus stylus.
Page 34.
| Figs. | 12, | 13. Two carapaces referred to this species, showing their form and ornamentation. |
| Figs. | 14, | 15. Two individuals of this species, showing the broad form of the body and the strong telson. |
Undetermined fragments.
| Fig. | 16. | A fragment of shale preserving several fragments of somites of undetermined specific relations. |
| Fig. | 17. | An obscure fragment, possibly a portion of an ectognath. |
Eurypterus pennsylvanicus.
Page 31.
| Fig. | 18. | A view of the carapace described, showing its broad form, produced posterior angles and the arrangement of the nodes on the surface. |
PLATE VI.
Eurypterus mansfieldi.
Page 32.
A large specimen preserving the carapace, abdomen and telson nearly entire, with three of the palpi of the left side. A portion of the test is removed along the median line exposing the process of the epistoma or median appendage of the thoracic plate. This figure shows very satisfactorily the mode of occurrence and association of these fossils.
PLATE VII.
Eurypterus mansfieldi.
Page 32.
The abdomen and telson of a specimen as it is seen lying in the shale. Heliotyped directly from a plaster cast of the specimen.
PLATE VIII.
Eurypterus mansfieldi.
Page 32.
| Fig. | 1. | A specimen preserving the body and telson, and showing in a very perfect degree the surface sculpturing. This drawing was made from the specimen, Plate VII |
| Fig. | 2. | An imperfect individual as it is seen lying on a block of shale with some fragments of ferns and other plant remains. |
| Fig. | 3. | A separated palpus enlarged to two diameters showing the form and ornamentation of the joints. In this specimen the terminal dactylus and lateral spine are free. |