Page:The Habitat of the Eurypterida.djvu/257

Rh existing between the genera and species of different faunas in order to determine from which continents these were derived, it is evident that a claim of close similarity between a species in the Shawangunk fauna, derived as I believe from Appalachia, and a species in the Old Red sandstone derived from the continent of Atlantica, as I hope to prove, must be carefully investigated. Therefore, I proceed to the points enumerated, always bearing in mind that certain types of similarity are of more value than others. In the beginning I may state that S. myops is known only from immature specimens, most of which are carapaces alone, and that only one entire specimen has been found and this is but 55 mm. in length (see pl. 52, fig. 6, Clarke and Ruedemann). The largest carapace of S. myops observed measured 19 mm. in length by 27 mm. in width; the only carapace of S. scoticus known measured 16 cm. in length and 19 cm. in width; the single, entire individual known measured 3 feet, 4 inches in length. A most profound difficulty arises at once, namely, that of comparing neanic and nepionic specimens of a mid-Siluric species with a gerontic, or perhaps a late ephebic individual of the Lower Devonic. But granting that such comparisons are possible or even allowable, let us turn to the characters which would justify placing these two species in the same subgenus. First, there is the outline of the carapace. It must be admitted even by Clarke and Ruedemann that, with all due allowance for compression, the carapaces of S. myops display a most unusual amount of variation in outline, some, were it not for the position,of the eyes, being easily referable to Eurypterus. The carapaces show a strong tendency to grow narrower posteriorly, showing the greatest width in the anterior third, whence the lateral margins slope gently backwards; the nearly parallel sides shown in the carapace of S. scoticus are usually not present in S. myops, while the frontal