230 THE HABITAT OF THE EURYPTERIDA 



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 fol- 

 lowed by another long one. The teeth in the chelae in these speci- 

 mens 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, further- 

 more, 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 



Fig. 21A. Pterygotus monroensis Sarle. Fragment or Free Chela. X \. 

 (After CI. & R. 191 2, pi. LXX, fig. 3) 

 Fig. 21B. Pterygotus cobbi Hall. Free Chela of Chelicera. X A. 

 (After Grote & Pitt. 1878, fig. p. 301) 



Dolichopterus. Clearly, with the exception of E. pittsfordensis which 

 wiU be considered presently, the Pittsford-Shawangunk fauna does 

 not supply the ancestors for the Bertie fauna which is thus left with- 

 out progenitors on the basis of the "lagoon-estuarine" theory usually 

 advanced. There is also another difficulty. Stylonurus has repre- 

 sentatives in North America in the Pittsford and in the Devonic and 

 Carbonic, but none existed in the Bertie waters which should, accord- 

 ing 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-Shawan- 

 gunk fauna was ancestral to the Bertie. How can the many points 

 of similarity between certain Bertie and European species be ac- 

 counted for? It has already been pointed out that Eurypterus remipes 

 from the Herkimer region is so closely related to E. fischeri of the 



