THE EURYPTERIDA OF NEW YORK . 71 
are, as a rule, furnished with serrations, which become more prominent 
in posterior direction. 
The articulation of the telson 1s “quite like that of Limulus, consist- 
ing of a broad transverse lower and a small upper segment and is mainly 
adapted to movement in a vertical plane. 
II 
MODE OF LIFE | 
The mode of life of the eurypterids has thus far been touched upon 
incidentally in the description of the “swimming feet’’; the earlier writers 
have generally assumed that the eurypterids were active swimmers on 
account of the structure of these legs which Hall very properly compared with 
the quite similar swimming organs of the common “lady crab” (Plat- 
yonichus ocellatus) of our eastern Atlantic coast. Woodward 
pointed out that the position of the eyes of Pterygotus, half above and 
half below the margin, indicates that it can not have been a mud grubber 
and he has also said of P. anglicus that its large eyes, its powerful 
natatory appendages and the general form of its body suggest that it 
was a very active animal. Laurie [1893, p. 511; 1893, p. 124], on the 
other hand, has repeatedly advanced the view that the eurypterids were 
bottom crawlers and diggers in the mud. He says of the swimming 
leg of Slimonia [op. cit. p. 511]: 
This appendage is always described as a swimming organ, but I am 
inclined to doubt the correctness of this interpretation of its function. 
The Eurypteridae appear to me, from their general build, more fitted for 
crawling than swimming, and I am inclined to explain this appendage as 
having been used by the animal to get a firm hold on the bottom, and prob- 
ably also for. digging out sand and covering itself, in much the same way 
that Portunus uses its very similar pair ‘of appendages. 
Holm concluded from his study of Eurypterus fischeri 
that the last pair of legs of that species was principally adapted to 
swimming. He says: 
Die Hauptbewegung des achten Gliedes im Verhaltniss zum sicbenten 
scheint von vorn nach hinten gewesen zu sein, indem sich, wie schon von 
Fr. Schmidt hervorgehoben ist, das achte Glied bei der Bewegung uber 
die dreieckige Platte wie ein Scheerenblatt tiber das andere schiebt. Die 
beiden Glieder missen daher beim Schwimmen wie ein einziges Ruder- 
