Genus ECHINOGNATHUS Walcott
This genus from the Lower Siluric of New York is based on unsatisfactory fragments which indicate relationship to Stylonurus and we associate them provisionally with that genus. Walcott's original diagnosis of Echinognathus follows [1882, p. 213]:
Endognathary limbs (one or more pairs) formed of eight or nine joints, six of which carry long, backward curving spines articulated to their posterior side. Terminal joint slender, elongate, acuminate. Surface of the body and larger joints of the cephalic appendage ornamented with scalelike markings, as in the genus Pterygotus. Type, E. clevelandi.
Two characters are not only the most prominent features of the originals[1] but also of distinct value in determining the taxonomic position of the genus. The first is the great number of paired long, flat spines to each segment of the endognathite. The common genera of eurypterids, as notably Eurypterus and Pterygotus, have but one pair of longer spines to each segment. The greater number of spines occur typically only in the genera Dolichopterus and Stylonurus, and but very exceptionally in other genera—the exceptions being Eurypterus dekayi Hall and probably also Eusarcus scoticus (Laurie).[2] Such continuous series of spines, however, as are exhibited by the endognathite of Echinognathus, are characteristic of the subgenus of Stylonurus here termed Ctenopterus.
It would also seem that the spines of Echinognathus possessed a rather flat, subtriangular section, giving them a bladelike appearance, a character which, coupled with a distinct longitudinal striation, is also repeated in certain species of Ctenopterus.
The second character that we have here in view, is the surface sculpture. This is also of unusual type and consists of very prominent
