I. Introduction. In Southern Sweden occurs a series of shales of Wenlock age, which Tullberg divided into zones by means of their predominant graptolites. 1 During a visit to that country in the early part of 1896, I was enabled, through Dr. Törnquist's kindness, to spend some time in studying the fauna of these zones, and I determined that when I returned to England I would ascertain whether some such zonal classification did not also hold good for the beds of Wenlock age in our own country. During the past four years I have studied in detail the strata and the graptolites of the Wenlock Beds of the Welsh Borderland, and I find that such a classification can certainly be made. Further, as the existence of Tullberg's zones 2 has recently been called in question, and doubt has been thrown upon the validity of several of his species, it seems only fair to the memory of that geologist to bring forward the results that I have obtained, which appear to me to confirm his work completely. A glance at the Geological Survey maps of the Welsh Borderland would seem to indicate that the Wenloek Shales cover a considerable extent of country. This, however, is not really the case: far from being of wide extent, the Wenlock Shales are generally present as a mere fringe below the Ludlow rocks. It is the Ludlows, and particularly the Lower Ludlows, which occupy the greater part of the area. Frequently the so-called ‘Ludlow’ of the Geological