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Eurypterus approximatus Hall & Clarke. Warren, Warren co., Pennsylvania

Eurypterus (Anthraconectes) mazonensis Meek & Worthen. Mazon creek, Indiana

E. (A.) mansfieldi C. E. Hall. Beaver county, Pennsylvania

E. (A.) pennsylvanicus C. E. Hall. Venango county, Pennsylvania

E. ? potens J. Hall. Pennsylvania

E. (A.) stylus J. Hall. Beaver county, Pennsylvania

It is not necessary for us to discuss here the Algonkian and Cambric occurrences, further than to mention that the Cambric species which is a true eurypterid, conclusively demonstrates the great age of the merostomes and their early existence in truly marine beds.

The earliest appearance of the eurypterids in profusion is in the Lower Siluric Frankfort shale of Schenectady and Schoharie counties, N. Y., lately discovered. Here at least 11 species, at present referred to the genera Eurypterus, Dolichopterus, Stylonurus, Eusarcus, Hughmilleria and Pteryrgotus, have been found to range through the eastern littoral marine development of the formation.

The earliest appearance of the characteristic biologic facies of the Eurypterida in America is that in the waterlime of Kokomo, Indiana which contains four species of the order. Kindle [1904] has distinguished two stratigraphic horizons in the Niagaran of Indiana, which correspond to the Lockport and Guelph formations of New York respectively, and