Page:The Eurypterida of New York Volume 1.pdf/380

 doubtfully referred to this species a postabdominal segment characterized by rather evenly distributed small triangular scales. In form and surface sculpture this is identical with the segment of the postabdomen of  and quite obviously to be referred to that species. The ramus, however, is distinct from that of the chelae of both  and   in the greater relative width of its base and its more regular tapering in distal direction; and most strikingly by the even rounding of the distal end to form a terminal tooth instead of an angular extremity.

By a strange coincidence, this type which Hall says was the "fifth unequivocal fragment of the genus Pterygotus that came under [his] notice from any American locality," seems to represent the rarest of all forms; for so far as we know only one other representative of this species has been thus far found. This is a ramus about twice as large as Hall's type. Grote and Pitt figured it and referred it to their species, which had been previously described and based upon a coxa. The latter probably belongs to, while the ramus is not referable to that species. These writers cited as distinguishing characters from, the difference in size and the fact that the "apex of the joint is pointed in  , while in   and   it is obtuse." By the "apex of the joint" the point of the terminal tooth is meant. The type of, however, has only obtuse teeth and it is obvious that this is entirely due to weathering. To the same cause and the poor preservation of the type in general may be also attributed the absence of the smaller intercalated teeth in both specimens.

The question suggests itself whether old age could not have produced in  or   a free ramus like that upon which this species is based; or whether it might not be indicative of a slight variation only. The first suggestion is refuted by the presence in our collection of free rami of  of similar size, with typical angular points of the jaws; and perhaps still more by