term Ctenopterus may be applied to this group. The leg from the Utica shale figured by Walcott as Echinognathus clevelandi, shows a like structure in exaggerated form and may prove to represent the group, in which case the term Echinognathus would take precedence. At present the employment of the latter term would be unwarranted as the body of the Utica form may be entirely different from that of Stylonurus.
Subgenus C. This is represented alone by S. scoticus. Its differential characters are the flat broad last pair of legs, the greatly enlarged winglike epimera of the postabdomen and the emphasized sculpture of the posterior margin of the tergites. The short club-shaped telson is also notable. The carapace and the form of the abdomen are as in Stylonurus. We propose for this group the term Tarsopterus.
Subgenus D. Finally Drepanopterus is, in our opinion, not more differentiated from the typical Stylonurus than S. scoticus, though it stands quite at the other end of the phylogenetic line. Drepanopterus longicaudatus nov. is a form distinctly intermediate between Stylonurus and the type of Drepanopterus. On account of its phylogenetic importance in the development of Stylonurus we have treated this division as a separate genus.
The majority of the species can not at present be definitely referred to any of these groups as only their carapaces are known. The following is a provisional synoptic table of the species:
| Subgenus A. (Stylonurus s. st.) | |
| S. logani H. Woodward | S. powriei Page |
| S. macrophthalmus Laurie | Stylonurus (?) scabrosus (H. Woodward) |
| S. ornatus Laurie | |
| Subgenus B. (Cternopterus) | ||
| S. cestrotus Clarke | S. multispinosus nov. | |
| S. elegans (Laurie) | (?) | S. excelsior Hall |
| Subgenus C. (Tarsopterus) | |
| S. scoticus H. Woodward | |
