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230 tooth, then three shorter ones. The chela of P. cobbi from the Bertie shows three long teeth at the end, two short ones, a long one nearly as long as the one at the extremity, then three fairly short ones followed by another long one. The teeth in the chelae in these specimens are similar neither in size nor arrangement, so that no particular relationship is set up between Pterygotus monroensis and P. cobbi (Fig. 21 a and b).

Not only, then, do the species themselves offer no indication that the Bertie fauna was derived from the Pittsford alone, but, furthermore, it seems impossible to believe that the five Pittsford species included in four genera should give rise to the profuse Bertie fauna of fourteen species included in four genera, two of which are different. The four Pittsford genera are: Eurypterus, Pterygotus, Eusarcus, and

Dolichopterus. Clearly, with the exception of E. pittsfordensis which will be considered presently, the Pittsford-Shawangunk fauna does not supply the ancestors for the Bertie fauna which is thus left without progenitors on the basis of the "lagoon-estuarine" theory usually advanced. There is also another difficulty. Stylonurus has representatives in North America in the Pittsford and in the Devonic and Carbonic, but none existed in the Bertie waters which should, according to the generally accepted views, have been the one place for the perpetuation of the race of the eurypterids in the late Siluric.

There is yet one other difficulty arising if the Pittsford-Shawangunk fauna was ancestral to the Bertie. How can the many points of similarity between certain Bertie and European species be accounted for? It has already been pointed out that Eurypterus remipes from the Herkimer region is so closely related to E. fischeri of the