Page:The Eurypterida of New York Volume 1.pdf/421

 adaptation to particular marine conditions. Similar stability of the eurypterids is also suggested by the identity or extremely close relationship of the species in the Shawangunk grit at Otisville and the possibly older beds at the Delaware Water Gap and Swatara Gap [see p. 417] in Pennsylvania; and again in the probably somewhat younger McKenzie formation of Pennsylvania [see p. 88], and finally also by the continuation of the same genera apparently from the Ordovicic, but surely from the Siluric into the Carbonic. The eurypterids are then, as a rule, to be accorded but little value for purposes of correlation.

The following species are quite obviously but a meager part of the eurypterid fauna of the Normanskill stage, and future discoveries, now that the attention of collectors is directed to these interesting fossils, will undoubtedly add much to the list. As in the Schenectady shale the generic determinations are entirely provisional, as but few legs and telsons have been found in connection with the carapaces and fragmentary abdomina.

Carapace semioval to semicircular; lateral and frontal margins forming a uniformly rounded curve; length to width as 2:3; basal margin straight transverse. All margins apparently with a broad flat border. Lateral eyes large, about one fourth the length of the carapace, elliptical in outline, prominent, situated forward, in front of the middle transverse line, less than their length distant from the margin. Length of carapace of type, 11.6 mm; width, 16.2 mm.

Carapace semioval, with a tonguelike process in front; length to width as 4:5. Lateral margins moderately convex; frontal margin produced into a squarish process with rounded anterior angles; one