THE EURYPTERIDA OF NEW YORK 371 
the other parts of the body are approximately uniform in the other species, 
we infer from their size (13 cm) that it also attained 5 feet in length. 
Pterygotus buffaloensis and P. cobbi vastly sur- 
passed all other arachnids or any organisms of our Upper Siluric era in size 
and armed with their powerful prehensile pincers, and being evidently active 
swimmers, as shown by their large swimming legs and telson, they must 
have been the terrors of the waterlime sea. 
Remarks. The principal differences in P. buffaloensis and 
the closely related P. macrophthalm us are in the form of the 
carapace, which is less rounded, but more trapezoidal in outline, the 
frontal margin being less evenly convex; and in the form of the ultimate 
segment and telson. The telson of the former is not elongate obovate as 
in P. macrophthalmus, but broadly ovate [pl. 72, fig. 1; pl. 73, 
fig. 2]. While that of P. macro phthalmus is about one sixth 
longer than wide, that of P. buffaloensis is as wide as long or 
sometimes even wider [pl. 72, fig. 3]. Corresponding to this remark- 
able width of the telson, the preceding, ultimate, segment of the postabdo- 
men is also much wider in P. buffaloensis than in P. mac- 
rophthalmus, the widening taking place rather abruptly near the 
middle of the segment. 
Pterygotus cobbi Hall: 
. Plate 77, figure 6 
Pterygotus cobbiHall. Palaeontology of New York. 1859. 3:417*, pl. 83B, 
fig. 4; pl. 84, fig. 8 ? 
Pterygotus cummingsi Grote & Pitt. Am. Ass’n Adv. Sci. Proc. 1878. 26: 
300, 301, fig. 1 
Pterygotus cobbi (P. cummingsi) Semper. Beitr. z. Pal. u. Geol. 
Oestr.-Ung. u. d. Orients. 1898. 11: 80 
This species is based on the “free ramus of the chelate appendage.” 
The type, a rather poorly preserved specimen, is from the waterlime 
at Buffalo and now in the American Museum of Natural History. Hall also 
1 See Appendix. 
