Pterygotus bilobus Salt., together with three varieties of this species, P. raniceps (Woodw.), Slimonia acuminata (Salt.) and Stylonurus logani (Woodw.). The Pterygotus beds are followed by the "Trochus," more properly, Platyschisma beds which correspond to the beds of the same name in England, and which contain fragments of Slimonia acuminata as do the next overlying beds which mark the transition into the sandy Lanarkian series.
The Lanarkian. About 1400 to 1500 feet above the base of this series occurs a fish-band in the carbonaceous shales of which Eurypterus dolichoschelus (Laurie) has been found associated with Ceratiocaris, five species of fishes, and Pachytheca and Parka. At another locality seven species of fishes, Ceratiocaris, Dictyocaris, Pachytheca, a Myriopod and Eurypterus dolichoschelus (Laurie) and Stylonurus ornatus (Laurie) have been found.
Devonic. The Devonic formations of Great Britain have a better representation of eurypterids than have those of North America. The Old Red Sandstone of Forfarshire has yielded Pterygotus anglicus in abundance and in a good state of preservation and one nearly entire specimen of P. minor. From the same region come three species of Stylonurus, S. scoticus, S. powriei, S. ensiformis, and finally the little known Eurypterus brewsteri. In the Old Red Sandstones of England occur Eurypterus pygmaeus and Stylonurus symondsii. Fragments of Pterygotus problematicus have been reported from the Lower Old Red of the Ludlow district. A few fragments of Eurypterus hibernicus Baily have been found in the Upper Old Red of Kiltorcan, Kilkenny County, Ireland. There are thus ten species of eurypterids from the Devonic of Great Britain, all occurring in the Old Red Sandstone facies of deposits associated with fishes, land plants, fluviatile molluscs, myriopods and crustacea, such as the fresh or brackish-water phyllopod, Estheria, the ostracod Beyrichia and certain phyllocarids. With the exception of Pterygotus anglicus none of the eurypterids is either abundant or well preserved, most of the species being represented by a single portion of the exoskeleton or by a number of fragments. Moreover, these fragments are scattered in occurrence geologically and geographically. Six species are found in Forfarshire, Scotland, in the Lower Devonic (Caledonian); three species are sparingly represented in Brecknockshire and Herefordshire, England, at the same horizon; while a few fragments of a single species occur in the Upper Old Red of Ireland.
Mississippic or Calciferous. The Calciferous fresh-water
