In my fourth Eeport to the British Association, I described, among other Crustacea, two species belonging to the genus Cyclus, one of which still remains unique. Since that date, I have, by the kindness of Professor T. Rupert Jones, F.G.S., received a number of specimens of this genus, collected by Prof. Harkness, F.R.S.; Mr, Joseph Wright, of Belfast; and Mr. J. H. Burrow, of Settle, Yorkshire; from the Carboniferous Limestone, which I now propose to describe.