is a possibility that the marginal fold has been destroyed in the posterior portions, but Woodward thinks that the specimen is entire, and that the fold did not pass all the way around the carapace. S. ensiformis is described from a single broken tail spine which, it seems to the author, is hardly sufficient for the founding of a new species, and certainly is of no use in determining the affinities of the fauna. S. powriei, represented by a single individual, has a carapace very similar in form and identical in proportions to S. scoticus, from which species it differs most noticeably in having the last pair of appendages long and tapering, not short and broad. Woodward has suggested that it probably had epimeral prolongations which have not been preserved, because only the internal mold in sandstone has been found, and the epimera would be likely to remain with the actual integuments; for the same reason none of the surface markings are visible. The tail is extremely long and narrow, quite similar to the telson of S. logani from the Ludlow, which form it also resembles in the character of the last pair of appendages. Both species belong to the provisional group of Stylonurus s. st. recognized by Clarke and Ruedemann.
Completing the Old Red sandstone fauna are two species of Eurypterus: E. brewsteri and E. pygmaeus. The first consists of a carapace, a portion of a thoracic segment slightly displaced, and an ovisac containing more than twenty ova (Woodward, 312, 151). Woodward says that "this species agrees most nearly in general form with E. lacustris" from the Bertie, while Clarke and Ruedemann have pointed out a close similarity to E. microphthalmus from the same horizon (39, 195). But since both authors make their comparison on the form, proportions of length or width, and position of eyes, and since the actual figures do not support either statement, I find it impossible to agree with them.
| length of carapace |
width | ratio l:w | |
| mm | |||
| Eurypterus brewsteri | 1.48 | 5.52 | 0.27 |
| E. lacustris | 44.00 | 63.00 | 0.70 |
| E. microphthalmus, type | 15.50 | 22.00 | 0.70 |
| E. microphthalmus, best preserved specimen | 17.5 | 27.40 | 0.64 |
E. pygmaeus is a small form found near Kington, England, and though represented by very young individuals, yet has characters which point to its affinities with E. remipes (Fig. 28).
