ever, were relatively large and had stronger chelae. The specimen of E. scorpionis reproduced on plate 32, retains them in their natural position. Woodward figured them, as pointed out by Laurie, in Eurypterus scorpioides, which is an Eusarcus. In Dolichopterus and Drepanopterus they are not known. In general it may, however, be said that they were extremely similar in the genera of the Eurypterus group, viz, Eurypterus, Eusarcus and Stylonurus.
On the other hand they show extreme variation in the genera of the Pterygotus group, viz, Hughmilleria, Slimonia and Pterygotus. In Slimonia they were discovered by Laurie [1893, p. 511, pl. 1, fig. 3] and found to be very small and with strong curved pincers, but otherwise as in Limulus. Those of Hughmilleria have been fully described by Sarle. They are larger [pl. 61, fig. 6] than in any other genus except Pterygotus, projecting beyond the margin of the carapace when extended and thus forming a transition to their condition in the latter genus. In Pterygotus they have been developed into the gigantic pincers which give that genus its fantastic aspect. Notwithstanding their great size in Pterygotus, there still prevails much doubt as to their structure. The current restoration [Zittel-Eastman's Textbook, fig. 1423] is one that would indicate a structure greatly different from that of the chelicerae of the other eurypterids. Our material fortunately sheds light on this problem and we have for this reason inserted here the following note.
The morphology and formation of the chelicerae in Pterygotus. In several specimens of P. macrophthalmus and P. buffaloensis at our disposal, the chelicerae are so excellently preserved as to remove all doubt regarding their morphology and function. In one [pl. 74, fig. 1] the chelicera of a large individual is perfectly preserved from the distal extremity of the chelae or pincers to the base of attachment. This shows distinctly that the organ consisted only of one unjointed long arm carrying the terminal pincers. In the second specimen the arms of both chelicerae lie side by side, while the pincers of both have swung back, one until it is subparallel with the arm. These latter chel-
