Erik Norman Kjellesvig-Waering

“ In 1951 Størmer, in an important paper, established the family Rhenopteridae on the significant basis of the ventral shield of the carapace and the form of the metastoma. In all outward appearance—that is, dorsally—the Rhenopteridae could well have been mistaken for Stylonuridae were it not for the very different underside. As in scorpions, considerable and increasing evidence is being accumulated, indicating that the major morphological differences of taxonomic importance are to be found on the ventral surface. ”

“ The large, highly arcuate eyes, with disc-like palpebral lobes, are located on the anterior of the carapace, close together, and intramarginally. 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 preserved as an impression reflected through the carapace. The holotype previously had been carelessly excavated with a sharp instrument toward the anterior, but part of the doublure can still be discerned. ”

“ Diagnosis.—Ventral shield and metastoma unknown; eyes located in posterior half of carapace, opisthosoma undifferentiated, trilobation present; last two legs very long.
The above family diagnosis is based on the type species of Stylonurus as restricted here. However, if genera such as Stylonuroides, Stylonurella, Parastylonurus, Brachyopterus and Brachyopterella are used in the diagnosis, then a much better and more complete diagnosis can be made. I suspect, however, that some of these genera will be found eventually to have no significant affinities with the type genus. ”

“ Family Stylonuridae Diener, 1924
Genus Syntomopterus, new genus
The prosoma is paraboloidal, very wide, straight along the base, and bordered with a wide marginal rim. The ventral shield is very narrow and band-like, and without sutures. The compound eyes, located slightly behind midsection, are crescentic, small, and close-set. The ocellar mound is located opposite the anterior part of the compound eyes. Ornamentation comprises large wart-like pustules, elongated and pointed at the margins.
Type species: Syntomopterus richardsoni, new species. ”

“ Nevertheless, Van Oyen groups both as the same species. Morphologically, I know of no two eurypterids that can be so different and 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") . ”

“ Remarks.—Parastylonurus includes more forms previously included in the genus Stylonurus than do the other genera described here. However, in my opinion, the development of distinct trilobation in the genus Stylonurus sets that genus irrevocably apart from the species that are here referred to Parastylonurus. The position of the eyes is also a major generic difference. ”

“ This marginal rim is composed of a single row of flat, oblong, elevated structures (see fig. 44, a) ; it is narrow at the genal angles and is not developed on the posterior edge. Apart from this ornamented rim, the prosoma is smooth.
The compound eyes are not preserved except for the barely perceptible anterior margin of the left eye and a slight elevation that
may represent the eye node. The node is probably arcuate, and the palpebral lobe covers most of the eye. The prosoma measures 69 mm. in length, 79 mm. in width behind the compound eyes, and 99 mm. ”

“ If the genus Stylonurus is to date from 1856 when Page first proposed it with S. powriensis as obvious type species by monotypy, then the original name of the species must be used, since the genus could not have been proposed without a type species. The nearly whole specimen came from the Lower Devonian Old Red Sandstone of Scotland, and revealed long, slender legs without the characteristic paddles which characterized the hitherto known eurypterids. ”

“ In contrast to these active swimmers, the associated eurypterids, namely, Dolichopterus asperatus and Syntomopterus richardsoni, had simple, small chelicerae not serviceable as weapons of either defense or predation; both were probably benthonic forms, crawling on the mud but perhaps capable of swimming to a limited extent. These could well have been prey to the fishes and, indeed, to the large pterygotids. However, in this shale the fishes are the only animals with a covering rigid and hard enough to abrade the tough pincer-teeth of the pterygotids. ”

“ 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. ”

“ Remarks.—The Pageidae differ from the other families that retain an epistoma, namely the Stylonuridae and Laurieipteridae, in the coffin-shaped metastoma, as against the long, deeply-notched metastoma of the Stylonuridae, and the broadly subrectangular one in the Laurieipteridae. The trilobation, although considered here a generic character, may well be of higher taxonomic importance. The family is monotypic at present. ”

“ However, part of the general stout aspect is inherent. The majority of the teeth are small, with several large, thick teeth interspersed. The central, or principal, tooth of the free ramus (no. 1 in figs. 35–38) is the largest, and is represented by a curved, thick structure. Nearly opposite this tooth is a similar but smaller tooth (no. 3) . In front of this tooth is another one, half as large (no. 4) . This combination is present on all chelicerae of this species. ”

“ The most interesting feature is the shape of the metastoma, which is roughly oval, with a narrow notch at the anterior and a broad base which is slightly cordate or emarginate (see fig. 98) . It measures 8.1 mm. in length and 7.2 mm. in greatest width (see fig. 95) . The female, or Type B (see fig. 97) , operculum is well preserved, showing even such details as the setae. The appendage is small, about one-third the length of the operculum, and consists of an undivided, rather broad lanceolate joint, with two triangular joints at the distal end. ”

“ Other American species, such as Adelophthalmus (?) potens (Hall) , he also lumps together 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-preserved and complete to use for biometric studies:
1 Not measured although complete and mainly undistorted. ”

“ In particular, there is no basis for comparison with the eurypterids of the Lower Devonian Beartooth Butte (listed above as "Wyoming") , as each species is quite different. The same is true of a comparison with the Lower Devonian of the Rhineland, Germany (Størmer, 1936) . The Ohio Lower Devonian eurypterid fauna retains such Silurian elements as Erettopterus and Dolichopterus, two genera previously unknown above the Silurian. Pterygotus (Pterygotus) carmani likewise shows closer relationship to Silurian than to Devonian forms. ”

“ Remarks.—This genus of gigantic eurypterids is composed of two famous species, Hallipterus excelsior (Hall) of New York and H. lacoanus (Claypole) of Pennsylvania, and is well known through the famous restorations of Beecher, and later of Clarke and Ruedemann. Unfortunately, these well known restorations, except for the carapace and first legs, were based mainly on the opisthosoma and appendages of other Stylonuracea. Differences between this genus and Laurieipterus or Ctenopterus have been discussed under the Remarks on those genera. ”

“ Genus Parastylonurus, new genus
Diagnosis.—Stylonuridae of small to medium size; prosoma rounded-quadrate; wider than long, with lateral eyes, arcuate and located on anterior half of the carapace; metastoma very long, with deep triangular notch or deeply cordate and with base truncated; first three walking legs very short with single opposable spines on each joint; last two walking legs very long, reaching to the last tergite; podomere-count: ?–?–7?–8–9–9; ornamentation consists of scales; opisthosoma narrow, undifferentiated ”

“ Specimen No, 1 represents the normal dimensions of the carapace of the eurypterid.
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 Cannelton, Beaver County, Pennsylvania. All are preserved in black shale with varying degrees of slight distortion, but overall, the specimens listed here are mainly undistorted, though compressed (all carapaces are complete unless indicated) . ”

“ The inner margin, armed with teeth, is inclined with respect to the almost straight outer margin, resulting in an overall tapering form. The teeth are short and stout, in keeping with the overall robust aspect of the stem. These teeth are mostly of fairly uniform size, mainly lanceolate to rhomboidal, but some are truncated, giving a nearly quadrate appearance. The two distal teeth are badly worn but apparently were the largest. Wear is also apparent on the succeeding three teeth. No longitudinal ridges ("striations") occur on any of the teeth. ”

“ It is, as the species name of the genotype indicates, and as Størmer (1934, p. 103) has pointed out, another link between the Dolichopteridae and the Stylonuridae, a further step in the transition from species such as Ruedemannipterus stylonuroides (Clarke and Ruedemann) . However, the long carapace and reniform eyes, a considerable departure from the usual greatly arcuate eyes of the stylonurids, may well reveal some affinities with the family Rhenopteridae. ”

“ Descriptions of all families and genera of the Stylonuracea are included here, as well as lists of the species referred to each genus. The families included are: Dolichopteridae, Stylonuridae, Pageidae, Drepanopteridae, Kokomopteridae, Rhenopteridae, Laurieipteridae, Woodwardopteridae, and Hibbertopteridae. ”

“ The species is based on a single well-preserved, complete, free ramus of the chelicera. Inward bowing at the distal end indicates that it is the free ramus of the left chelicera. The specimen is broken through the midsection into two parts. ”

“ The specimen with the alimentary 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, particularly 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. ”

“ Nevertheless, the flattened podomeres indicate that if Tarsopterella is a stylonuracean, it should probably be referred to the Dolichopteridae. This is done here with considerable misgivings until the ventral side is known or some more prosomal appendages are found of this highly spectacular eurypterid. It is not precluded that Tarsopterella may not belong among the Eurypteracea. ”

“ The following species are recognized for this genus:
Genus Strobilopterus Ruedemann, 1935
Diagnosis.—Dolichopteridae of medium size; test covered with pustules and semi-lunar scales; prosoma semiovate; compound eyes submarginal; ocelli unknown; ventral doublure unknown; sixth appendages with movable, supplementary flat lobes on distal joints, ultimate joint forming large, flat lobe; distal joints and lobes forming paddle with strongly serrate margin; metastoma very narrow, cordate at anterior end; base unknown; male median appendage very long, consisting of one undivided joint ”