Page:The Eurypterida of New York Volume 1.pdf/210

 would be so abnormal for that very reason as to invite close scrutiny. It is evident that like the type of " ," this supposed 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 presence of crowded small scales along the edge, all indicate that this is the posterior margin of a postabdominal segment. In, 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  is hence unknown and the term undoubtedly a misnomer.

The postlateral extensions of the segments are faintly indicated in  but absent in other members of that genus. Some species of Eurypterus, however, as, have them equally well developed and they also appear to represent an ontogenetic 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