Page:The Eurypterida of New York Volume 1.pdf/328

 oblong scales that rise rapidly behind and suggest raindrops running down a windowpane [pl. 58, figs. 1, 2], with a row of especially large drops at the bottom, on the posterior margin of the segments. This peculiar ornamentation is also best developed in species of Stylonurus, though it also occurs in some of the later, especially the Carbonic, species of Eurypterus.

Both the extreme spinosity of the endognathite and the surface sculpture indicate that Echinognathus, in comparison to Strabops or Eurypterus, was already a highly specialized genus and was either closely related to Stylonurus or had a convergent development to that genus as far as the two characters mentioned are concerned. There are no other characters observable in the fragments that would appear competent to shed light on its generic relations.

The monotype of this genus is

Walcott. American Journal of Science. 1882. 23: 152. figs. 1, 2

Walcott: Idem. p. 213

We reproduce the original description as follows:

The only portion of the body discovered is illustrated by figure 1. It appears to be the left side or half of the ventral surface of the anterior thoracic segment. The reference to the ventral surface is from the presence of a thin membranous extension of the anterior margin, a feature observed on the anterior segment of  Hall. The test appears to have been thin and firm, and the margins are clearly outlined on the dark, smooth slate, while the surface is ornamented with fine scalelike markings on the anterior portion that increase in size toward the posterior margin (cc).

Figure 2 is a sketch, seven tenths of the natural size, of the cephalic appendage as it appears on the surface of the slate and in the matrix. The entire length of the appendage from the point a a to the end of the terminal