THE EURYPTERIDA OF NEW YORK 69 
tailed E. newlini; and moreover is so twisted that while the first 
caudal segments show the dorsal or ventral side, the last and the telson 
are seen in profile. This fact, together with the presence of an emar- 
gination in the posterior upper margin of the segments and the downward 
curvature, seems to indicate that the tail was capable of bending upward 
and forward as in the scorpion. 
The section of the postabdomen usually was lenticular at the anterior 
end, remaining so throughout in some forms, as some species of Euryp- 
terus, while in many species it became circular toward the other end. Cir- 
cular sections of the caudal segments of species of Eurypterus and Hugh- 
milleria are frequently found [pl. 63, fig. 12]. 
The lateral angles of the posterior margins are nearly always pro- 
duced into pointed lobes. Those of the ultimate segments are usually 
much larger than those of the preceding segments, ase. g.in E. dekayi. 
In some species these lobes, together with the lateral edges of the segments, 
grow out irito prominent flat winglike appendages, representing the ‘‘epi- 
meral pieces’’ of the caudal segments. These are notably developed in 
Dolichopterus macrochirus, in the subgenus Anthra- 
conectes and in some species of Stylonurus. 
The ultimate and penultimate segments of Pterygotus carry on the 
dorsal side a crest or ridge that begins at about the middle and continues 
to the posterior end. It is doubtless caused by the intestinal canal. 
The telson is an appendage of the rath segment, as indicated by the 
position of the anus in relation to it. Strabops and our larval stages 
seem to indicate that the primitive form of this spine was short, thick and 
four-sided with dorsal, ventral and two lateral edges. This view is 
supported by the consideration that from this pyramidal form we can most 
easily derive the two different lines of development of the telson, which 
culminated on one hand in the styliform telson of Stylonurus and on 
the other in the bilobed telson of Erettopterus. The more primitive 
genera, such as Eurypterus and Hughmilleria, retain the general character 
of the primitive telson and at the same time exhibit in an incipient stage 
