Confusion has reigned in the works of British authors as to the relationship between Plumularia catharina, Johns., and a more simple form, with unbranched stem, found, like the former, on many parts of the coast. Johnston and Hincks, and the majority of their successors, have recorded the simple form, where it was thought worthy of mention, as a “stemless variety” of the former; but examination of the type specimens of P. catharina in the British Museum has proved that a fundamental distinction exists between the two forms. P. catharina is a branched species and bears on each side of a hydrotheca a pair of lateral sarcothecce; the other is a branchless, bristle-like form, bears on each side of a hydrotheca a single lateral sarcotheca, and has been long known as Antenella (or Plumularia) secundaria (Gmelin).