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 surpassed 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. macrophthalmus 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. macrophthalmus 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 remarkable width of the telson, the preceding, ultimate, segment of the postabdomen is also much wider in P. buffaloensis than in P. macrophthalmus, the widening taking place rather abruptly near the middle of the segment.
Pterygotus cobbi Hall[1]
Plate 77, figure 6
Pterygotus cobbi Hall. 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
