In the fourth part of my Monograph on the Merostomata, published in last year’s volume of the Palæontographical Society’s annual issue, I drew attention to two very singular fossil remains which had been somewhat doubtfully referred by Mr. J. W. Salter to the genus Eurypterus. A portion, at least, of the remains referred by him to Eurypterus? mammatus are really plant-remains (as shown by Mr. Carruthers, op. cit., p. 168), whilst the remainder must, for the present, be classed with M. Jordan’s Arthropleura armatu, from the Coal-measures of Saarbruck, Rhenish Prussia, a very anomalous Crustacean (if it be a Crustacean at all, which I greatly doubt), but which is certainly not a Eurypterus.