types of E. eriensis came from the hydraulic limestones (Monroe formation) of Beach Point, Put-in-Bay Island, Lake Erie.
Remarks. E. microphthalmus is well characterized by a number of peculiarities, the most notable of which are the round outline of the head, the small size and subcentral position of the lateral eyes and the short compact form of the preabdomen, from which the cylindrical postabdomen is well set off. The slight compression of both the carapace and the abdomen shows that the integument must have been relatively very strong. To this fact may be also due the absence of the scales on the surface.
While the differences between the carapaces of E. microphthalmus and E. eriensis, cited by the author of the latter species, seemed well founded as long as the poorly preserved type of the former species or the not quite successful representation of the same were solely available, the specimens which have lately been collected in the Manlius limestone, leave no doubt of the identity of the Ohio specimens with E. microphthalmus. The proportions of the carapaces are the same, within the small variation due to different compression and to the developmental changes.
E. microphthalmus is, stratigraphically considered, an isolated form, since it is the sole eurypterid hitherto known from the Manlius limestone. It is likewise isolated from the preceding eurypterids by the series of peculiar features cited above as characteristic of this form, and though the form is in general outline near enough to the preceding E. remipes so that its derivation from that common species could be conceived, the fact remains that it is more closely related to later species, like E. brewsteri Woodward, from the British Old Red sandstone, with which it has in common the round outline of the carapace, the small size, forward and approximate position of the eyes—that is, all the features which give it its characteristic aspect. The Old Red species is also without ornamentation of the carapace. A third species exhibiting the same characters, except the lack of ornamentation, is E. approx-
