THE EURYPTERIDA OF NEW YORK | 22] 
Genus ECHINOGNATHUS Walcott 
This genus from the Lower Siluric of New York is based on unsatis- 
factory fragments which indicate relationship to Stylonurus and we asso- 
ciate 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. Sur- 
face of the body and larger joints of the cephalic appendage ornamented 
with scalelike markings, as in the genus Pterygotus. Type, E. cleve- 
landi. 
Two characters are not only the most prominent features of the 
originals’ 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 exception- 
ally in other genera—the exceptions being Eurypterus dekayi 
Hall and probably also Eusarcus scoticus (Laurie).? Such con- 
tinuous 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 re- 
peated in certain species of Ctenopterus. 
The second character that we have here in view, is the surface sculp- 
ture. This is also of unusual type and consists of very prominent 
‘These are now in the National Museum, and have been kindly loaned by 
secretary Walcott. 
? Laurie, 1899, pl. 4, fig. 23, pl. 5, fig. 26. 
