204 NEW YORK STATE MUSEUM 
would be so abnormal for that very reason as to invite close scrutiny. It is 
evident that like the type of “P. quadraticaudatus,” this sup- 
posed telson is in reality the ultimate postabdominal segment, which is 
indeed preserved in a very deceptive manner. On the right margin the 
serration ends abruptly at the postlateral corner, where there is a small 
offset in the edge. The same feature is less distinctly shown on the opposite 
side. The posterior margin is smooth. In ‘true telsons of Pterygotus, 
however, the serrations always increase in posterior direction. The offset, 
the smooth posterior margin and the wrinkling of the test, as well as the pres- 
ence of crowded small scales along the edge, all indicate that this is the 
posterior margin of a postabdominal segment. In P. buffaloensis, 
the ultimate postabdominal segment is described as expanded laterally 
and serrated just like the telson, while the posterior margin is smooth. 
Furthermore, the scales are present on the telson only near the anterior 
margin, but here they are distributed in undiminished size and in the 
same arrangement as on the preceding segments. One side of this segment 
has been dragged backward until its posterior edge forms an apparent 
continuous circular outline with the lateral margins. The curvature and 
direction of the wrinkles on the right side show distinctly that this dragging 
took place. 
The telson of globicaudatus is hence unknown and the term 
undoubtedly a misnomer. 
The postlateral extensions of the segments are faintly indicated in 
Pterygotus anglicus but absent in other members of that genus. 
Some species of Eurypterus, however, as E. pittsfordensis, have 
them equally well developed and they also appear to represent an onto- 
genetic feature of the young of other members of this genus. 
‘ 
The third peculiar character of this species is the “scales.” They 
differ indeed from the surface sculpture of most eurypterids and consist 
of relatively large [1 mm], circular disks, many of which are flat-topped 
while in most the center is slightly sunken or the margin raised. Under 
enlargement [pl. 24, fig. 4] most of the scales have the anterior margin less 
