The genotype is not sufficiently known to establish its relationship to any of the three subdivisions here proposed.
Subgenus A is typically represented by S. logani and S. macrophthalmus. Its first three pairs of legs retain the characters of those of Drepanopterus and are like those of Eurypterus, i. e. relatively short and stout and furnished with two curved, strong spines on each segment. S. ornatus Laurie also belongs in this group.
We suspect that also Eurypterus scabrosus, a curious form described by Woodward [1887, p. 481] from the Lower Carbonic shales of Eskdale, belongs here, although the specimen does not retain the fifth pair of legs, whicht are of critical importance in the distinction of Eurypterus from Stylonurus.[1] The great length and slenderness of the preceding legs, however, are a character only found in Stylonurus, but not in any of the species of Eurypterus known to us. Likewise the coarse, roundish, tuberculate sculpture of the posterior margins of the tergites is more suggestive of Stylonurus than of Eurypterus.
Subgenus B. This is typically represented by S. elegans Laurie and S. cestrotus Clarke. Its second and third pairs of legs are relatively much longer and furnished with more than two pairs of long, less curved spines which are vertical on the lower side of the segments. Besides the species mentioned, another form from the Pittsford shale, S. multispinosus, only known from two of its legs, clearly belongs here; and we surmise that S. excelsior also, from the character of its first legs which alone are known, should be brought under this group. In case this structure should not be found in Stylonurus proper, the
- ↑ Woodward refers this form unhesitatingly to Eurypterus, stating in regard to the fifth pair of legs [p. 483]: "The fifth pair of broad spatulate swimming feet answering to the maxillae, or to the maxillipeds of the higher Crustacea, are not preserved in this fossil; but as they have been found with nearly all the species of Eurypterus hitherto described, there is little doubt that this form also possessed them when entire. Certainly the other appendages reproduce with only slight modification in their style of ornamentation those of the Russian, the American and the Lanarkshire Eurypteri already described and figured by Hall, Schmidt and myself."
