Hitherto I have been in the habit of referring the Gyracanthus spines commonly occurring in the Borough Lee Ironstone to G. formosus or tuberculatus of Agassiz, being disposed to believe in the specific identity of those two forms, as has already been suggested by Messrs. Hancock and Atthey, and hinted at by Agassiz himself. In fact, the salient point of difference between the two is the greater extent of the tuberculation of the ridges in the latter, while in the former it is principally seen on the proximal parts of the ridges, which, as they converge towards the anterior middle line of the spine, become first simply undulated and then smooth. The original figured specimen of G. tuberculatus is from the Coal-measures of Sunderland; that of G. formosus is from the same formation at Dudley; but though Agassiz refers to it as occurring also at Burdiehouse, in Midlothian, and Burntisland in Fifeshire, it seems to me very doubtful if these Calciferous Sandstone specimens are really the same. And certainly the study of a large quantity of additional material from Borough Lee has convinced me that the species of Gyracanthus characteristic of this Ironstone of Carboniferous Limestone age is specifically different from both formosus and tuberculatus.