Abstract
Synopsis: New material of Mixopterus dolichoschelus, a large eurypterid from the Upper Silurian inliers in Lanarkshire and Ayrshire, Scotland has made possible the first full description of the form, with dorsal and ventral reconstructions. In many features (shape of prosoma, nature of the large ‘walking’ legs (III)) M. dolichoschelus differs significantly from the Norwegian Mixopterus kiaeri Størmer and it is proposed that the Scottish species be placed in a new genus for which the name Lanarkopterus is proposed. A comparison of the enlarged, spinose legs (III) in Megalograptus, Lanarkopterus and Mixopterus suggests a new interpretation of joint numeration in the last two genera.