Page:The Habitat of the Eurypterida.djvu/159

Rh most fully agrees with the suggestion made by Goodchild that all of the rocks above the Upper Ludlow in Scotland be hereafter designated by the term Lanarkian from the locality in which those higher Siluric beds are so well exposed.

The Lanarkian is a series of conglomerates and sandstones with a total thickness of about 2800 feet, which are either unfossiliferous or contain only fish and eurypterid remains with the usual ostracods, and with Dictyocaris and Ceratiocaris. Plant remains, a myriopod and a scorpion are among the local associates of the above fauna. The series in Scotland is a more strongly marked continental one than that in England. Thus there was a gradual retreat of the sea from the north towards the south, beginning in Scotland in Lower Ludlow time, if not earlier, and leaving all of England except Devonshire dry by the end of the Siluric.

. It is only the higher divisions of the Ludlow in England which contain eurypterids: i. e., the Upper Ludlow rock, the Ledbury shales, the Downton Castle sandstone, and the Tilestones, according to the commonly accepted classification. Elles and Slater, who have done a great deal of work in the Ludlow district, have been able to determine smaller subdivisions; and since it is from these horizons that the eurypterids have been obtained, I quote so much of the new classification as is needed to follow the merostome occurrences (61, 198).

A few typical sections summarized from those given by Elles and Slater will serve to bring out the relations between the eurypterid-bearing beds, and the strata containing other groups of organisms. On the right bank of the Teme River near Ludlow Castle a section is exposed showing the beds from the Aymestry Limestone through the Downton Castle sandstone. Just a little south of Dinham Bridge which crosses the Teme, less than half a mile west of Ludlow, the Aymestry limestone is seen. This is characterized by entamerus knighti, Encrinurus punctatus and other typical forms. This