only by the consideration of former land and sea connections or barriers, it is necessary in discussing the Bertie faunule to take into account the palæogeography of preceding periods and the distribution of earlier faunas.
It has seldom been our good fortune to find two succeeding eurypterid faunas in the same locality, so that not many opportunities have been available to trace direct descent; but New York State has been favored in this respect and too much importance can not be attached to the relational values of the Pittsford, Shawangunk, and Bertie faunas.
Comparison of the Pittsford, Shawangunk, and Bertie faunas. As a matter of fact, the Bertie fauna in neither "pool" shows any very marked affinities with the Shawangunk fauna or with the Pittsford, with one exception, already noted, and more fully discussed, below. Of the fourteen species known from the Bertie, there are only four in which even a slight resemblance can be seen to the upper Niagaran forms, and this resemblance in each case (with the one exception noted) is so very small that it cannot be said to constitute a proof of genetic relationship. For instance, Dolichopterus (?) testudineus from the Herkimer "pool" is represented by a single uncompressed carapace which in outline, general proportions, and the position of the eyes is quite similar to one of the specimens of D. otisius in the Shawangunk. But while this general resemblance to one carapace of the Shawangunk form has been pointed out by Clarke and Ruedemann, attention should also be called to the fact that it is very different from one of the best preserved, most typical Shawangunk carapaces of the same species. The sub-elliptical shape of D. testudineus is quite distinct from the sub-quadrate one of D. otisius, and it does not seem to the author that any genetic relation is indicated between these two forms. To overcome this difficulty of lack of relationship between the Shawangunk and Bertie faunas, it might be argued that the latter was derived from the Pittsford alone. But the only species in the latter which is supposed to have even a semblance of relationship to a Bertie species is Pterygotus monroensis which has been compared with P. cobbi. The former species was founded on a single carapace, and two other fragments are now known. One of these is the fragment of a free pincer of the chelicera which is thought to belong to P. monroensis. This shows one long, rounded tooth at the extremity, then a short tooth, another long tooth but not so long as the first, four short teeth alternating in size, followed by a long
