The Upper Silurian rocks of Lesmahago, Lanarkshire, have long been known to contain Arthropod remains. In the Kelvin-grove Museum, Glasgow, are a number of curious forms from the Logan Water Lesmahago, which Professor McNair was good enough to allow me to examine. In the hope of solving some problems presented by them, I obtained, through the kindness of the Keeper of the Geological Department of the British Museum, the loan of a specimen from the same locality, which forms the subject of this note. Instead, however, of solving any difficulties, the specimen presented a new problem.