Page:Second Geological Survey of Pennsylvania Report of Progress PPP.djvu/19



The following table gives the distribution of the described species of the genera, and. It is seen that the number of species reached its maximum in the Chemung group, which would naturally be expected from the almost total disappearance of the order Trilobita at the close of the deposition of the Hamilton group.

Besides the species of the list here given, I have seen two undescribed species of, from the Chemung group, of New York; also a large form belonging to the genus , from the Hamilton group of western N. Y.; and another species, probably belonging to the latter genus, from the same horizon in the central part of the State.