2 A 



As the special characteristics of the Pterygoti are unknown, 

 and not desiring to multiply species, I refer the specimen to P. 

 Buffaloensis, Pohlm. (B. B. S. N. S., Vol. iv, p. 17), because its 

 corresponding parts seem to be identical with it. 



PTERYGOTUS BUFFALOENSIS. Pohlm. 



The carapace is smooth and semi-elliptical, with a proportion 

 between length and width of about seven to ten. The eyes are 

 marginal, project beyond the outline of the carapace, and have 

 the appearance of the eyes of insects. A small tubercle situated 

 centrally is visible, but not very distinct. The carapace is three 

 and three-quarters inches wide and two and five-eighth inches 

 long. 



The body segments are somewhat imbricating and all of the 

 same length, about one and one-half inches in this specimen. As 

 in the Eurypteri the segments increase in length posteriorly, this 

 is a good mark of distinction between the two. The thoracic 

 portion of the body is almost as wide again as the base of the 

 carapace, and measures in the maximum seven and one-half 

 inches. From here the body gradually narrows toward the head 

 and toward the tail, where the eleventh segment has a width of 

 two and one-half inches. The anterior and posterior lateral 

 angles of the five anterior segments are rounded; those of the 

 remaining segments are more pointed. 



The specimen has been subjected to a heavy lateral pressure, 

 which has caused a displacement of the appendages and a com- 

 pression of one side of the thoracic portion of the body, which 

 gives to the dorsal side the appearance of being much narrower 

 than it really is; but the exact dimensions were obtained, when 

 after careful manipulation the anterior half of the fossil was 

 removed from the stone, and a fine exposure of the ventral side 

 of the animal became visible. (Fig. 1, Plate 3.) The compression 

 has affected only the one lateral half, and left the other side in its 

 natural state. In addition to this four anterior feet and one 

 swimming foot were exposed. 



The views expressed by Prof. Hall, Palaeontology of New 

 York, Vol. iii, p. 401, that the number of the body segments of 



