Page:The Habitat of the Eurypterida.djvu/233

Rh slight knowledge of the various faunas we are unable to perceive relationships which very possibly exist. Two species, however, do show kinship with known forms. Hughmilleria magna has characters in common with H. socialis and H. shawangunk from the Pittsford and Shawangunk, respectively, while Dolichopterus latifrons agrees "closely with D. otisius from the Shawangunk in the posterior contraction of the carapace." Thus, whatever relationship is indicated between the species of the Schenectady fauna and those of later faunas, is to species in the Pittsford and Shawangunk, all three of which formations have elsewhwere been shown to have had their origin in the sediments from Appalachia. Once again, it appears that rivers coming from the same continent have successive faunas more closely related than those from diverse continents.

Comparison of Pittsford and Shawangunk Faunas. The study of the lithogenesis of these two formations has shown that the Pittsford shale is of the same age as the shales in the upper part of the Shawangunk (p. 101 above), for which reason it is fitting to consider the faunas of the two formations at the same time, especially since the sediments are known to have come from Appalachia in both cases. A comparison of the Pittsford and Shawangunk faunas shows that the two most common species, Hughmilleria socialis from the former and H. shawangunk from the latter are almost identical. In the shape of the body and form of the head the two species closely resemble each other, while the telsons of the two are identical. As one reads through the description of the Shawangunk form he is struck with the constant similarities in the anatomy between this and the Pittsford species. For instance, Clarke and Ruedemann say in regard to H. shawangunk: "The metastoma has not been seen well preserved in position, but we refer several metastomas to this species because they possess on the one hand, the form of that in H. socialis, and on the other, exhibit a peculiar, striated ornamentation apparently characteristic of H. shawangunk" (39, 345). Again, "The crawling legs appear to have been both short and slender as in H. socialis" (39, 344). Because of these similarities, it seems not improbable that H. socialis might represent a mature H. shawangunk, especially since no specimen longer than 8 cm. is known from the Shawangunk, and no specimen so short as that from the Pittsford, where the individuals are up to 15 cm. in length.

Of the other five species in the Pittsford, Pterygotus monroensis is of small importance for it is represented by a single carapace and