Philonotis capillaris, described by S. O. Lindberg in 1867, has been variously treated. Some authors considered it to be a small form of P. marchica, but Lindberg himself combined it as P. fontana var. capillaris on the basis of its spreading perigonial leaves, which are erect in P. marchica. P. T. Husnot was confused by Lindberg's solution and described the same taxon as P. arnellii in 1890. Many new related species were soon described, and for a while some authors accepted both P. capillaris and P. arnellii. H. N. Dixon provisionally synonymised P. arnellii with P. capillaris in 1896, while L. Loeske (1906) and M. G. Dismier (1908) did this definitively. Nonetheless, while North American floras and checklists unanimously use the correct name P. capillaris, the name P. arnellii is still used in almost all recent European floras and checklists. The latter name has until now been cited from Husnot's "Muscologia Gallica" (Jun-Jul 1890), but the valid publication by Husnot in Revue Bryologique (Apr-Mai 1890) antedates this. Here we clarify, based on that correct protologue and Husnot's letters to S. O. Lindberg and V. F. Brotherus, why Husnot described P. arnellii.