Plate 87, figure 9 represents a fragment of a large tergite with traces of the Pterygotus ornamentation. This can be referred to P. prolificus with some certainty.
Characteristic telsons of Pterygotus [pl. 87, fig. 5, 7] are not infrequent at Schenectady and Duanesburg. A very different type is represented by plate 87, figure 8. It exhibits a peculiar ornamentation, consisting of small groups of tubercles on low nodes arranged in subconcentric lines; the other side was smooth. The serration of the margin is very distinct and shows by its direction that the small incision on the longer side is the middle of the posterior margin of the telson and is a faint beginning of the bilobation characteristic of Erettopterus.
Plate 87, figure 6 illustrates a form of fragments met with repeatedly in the beds at Schenectady, and quite obviously a last postabdominal segment best comparable to that of a Pterygotus.
Finally, these black shales also contain small patches of integument which retain the surface sculpture in a preservation surpassing any hitherto observed in our eurypterid-bearing rocks. Some of these patches [see pl. 86, fig. 11–15] are clearly referable to Pterygotus.[1]
- ↑ Disjecta membra from the Frankfort shale, not referable to any genus.
Besides the few parts of the integument referred in the preceding descriptions to genera known from the Upper Siluric and Devonic, a considerable number of fragments have been found which cannot be placed with any degree of certainty with any of the genera; some are of noncommittal character, while others differ so strikingly from all later forms that they undoubtedly represent new types of greater than specific rank and must await future discoveries of more complete material, for description. We merely figure these here to indicate the richness of this new eurypterid fauna.
Plate 86, figure 18, is a coxa, possibly belonging to Pterygotus; plate 84, figure 17, the greater part of a broad, rapidly contracting abdomen, possibly belonging to Eusarcus, and plate 84, figure 19, a long, extremely slender, distinctly striated spine, suggesting Dolichopterus and Stylonurus.
Most indicative of the great diversity of forms occurring in the Frankfort beds are the well preserved patches of integument found in the black shale. Some of these have been mentioned in connection with the genera Eurypterus and Pterygotus. We figure here several patches bearing the ornamentation described of Eusarcus, Echinognathus and Megalograptus and exhibiting some variations [pl. 84, fig. 13–16]. Another style of ornamentation is represented by figure 8 of plate 83. This consists of extremely fine, very closely and evenly arranged tubercles. The patch of integument, reproduced in plate 85, figure 8, shows a mass of densely set, short, sharp spines and that shown in plate 85, figure 7, a profusion of long slender spines. Plate 85, figure 10, is a part of a supposed leg segment with a strange pattern of parallel raised lines connected by another set of shorter parallel oblique lines.
