Page:The Eurypterida of New York Volume 1.pdf/253

 The specimen measures 24 inches in length, whereas none of those from which the description of  was compiled exceeded 14. There are also only three cusps on the front edge of the first, third and fourth pairs of gnathopods, and four on the second pair. In  these cusps are sometimes 8 to 12 in number, and apparently in some cases project from the back of that organ, though this must be considered uncertain and against analogy.

There is, moreover, on the large paddles, no trace of the fringed or serrated edges which are so conspicuous in the paddles of. They are perfectly even and smooth.

None of the differences cited seem to us to warrant any specific distinction, the different size being clearly due to age, since no important corresponding discrepancies in the proportional lengths of the parts of the body could be found to corroborate the supposed distinction. The cusps are, to our knowledge, of like number in all these Eusarci, all segments, save the first two and the last, bearing two spines each, the last forming a single spine. Both spines were of nearly equal size, as we have already observed in the generic description, but frequently only those of one side are observable, the others being either broken away, leaving their wartlike bases [ pl. 33, fig. 1], or imbedded in the rock above or below the bedding plane on which the body rests. Of the two specimens of  before us, one [ pl. 37] shows the spines of both sides and would hence correspond to   s. str., the other only those of one side and would hence have in this regard the character of.

The last difference cited is the absence in  of the fringed or serrated edges "so conspicuous in the paddles of  ." Much of the serrated appearance of the edges of the paddles in the eurypterids is due to a cracking of the thickened margin of this thin leaf like organ. For this reason one frequently sees in some specimens of this species an apparently very marked serration, while others have a distinctly smooth edge. The same is true of both  and ,   possessing, in reality but a very weakly developed serration.

The supposed differences between  and   are doubtless due to slight variations in preservation, but even if of actual