Page:AmJourSci 4 39 233 551-554.djvu/2

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552
E. W. Shuler—New Ordovician Eurypterid.

The posterior margin of the proximal joint is supplied with two prominent spines or flattened bristles, the larger of which occupies the distal corner. This is the largest spine preserved. It has a length of 41mm. The width, 2mm, is fairly uniform along its whole length. In common with the other spines it originates in a projecting alveolar process or ring-like swelling of the integument at the base, which from its unusual development, is a significant characteristic of this species. The smaller

Figs. 1-6.

AmJourSci 4 39 233 552 figures 1-6.jpg

Figs. 1-6. Stylonurus (Ctenopterus) alveolatus sp. n.

Figure 1. A part of the telson spine with the impression of two abdominal segments. Figure 2. Moulds of the tubercles on a fragment of the carapace (× 2). Figure 3. Endognathite probably belonging to the first pair of post-oral appendages. Figure 4. Endognathite belonging to the second or third pair of post-oral appendages. Figure 5. Undetermined fragment of an appendage. Figure 6. A fragment of a joint from the walking leg. All figures except figure 2 natural size. The specimen represented in figure 4 is to be considered the holotype of the species.

spine has a measured length of 14mm. The broken jagged ends indicate that the spines were originally much longer.

The adjacent segment shows four alveolar processes with parts of three spines preserved. Again the distal corner was occupied by the largest spine. All spines have been lost from the third segment but five alveolar processes are seen, the dis-