Page:The Eurypterida of New York Volume 1.pdf/96

 which are there obviously near the climax of their development. It is also the horizon where individual development is greatest.Though we have been discussing the eurypterids of the Bertie waterlime as if they constituted a single congeries, there is actually a very marked geographic distinction in their distribution. At the two productive localities, Erie county and Herkimer county, there are noteworthy distinctions in respect to species. The two faunules are as follows:

The species common to both are  and , both of which are quite rare, while the predominant species in both places are unlike. It is not believed that these differences necessarily express distinct stratigraphic horizons, as both congeries lie near the top of the waterlime succession, but rather indicate original regional separation into distinct lagoons or pools, so that we may without impropriety speak of these regions as the Buffalo pool and the Herkimer pool, which we may assume to have been synchronous. There is, in the face of the differences suggested, a certain degree of approximation in the two expressed by such vicarious species as  and ,   and  , which may well mean distinctions due to geographic isolation. The Herkimer pool is well restricted and its faunule can not be traced very far toward the west; the Buffalo, however, appears alone as far east as Union Springs, Cayuga co., and as far west as Bertie, Ontario. Another difference in these faunas is the preponderating great size of all the species in the Buffalo pool and, by contrast, the small size of and abundant young among the Herkimer county species; a distinction which may be due to differences in depth. That the smaller creatures lived in conditions of shallower water is evinced by the sun-dried and cracked rock surfaces of their matrix, while such evidences are wanting in the Buffalo pool; and indeed it would be quite in accordance with our acquaintance with