140 i ollins un> bebvei . 



Sound, Jan., cv i , \-.-ar'> [aland, July, Aug., shore of Gibbet [aland, 

 Aug., cave, Ducking Stool, Dec, Colli] isporea in April, Aug, 



and Dec 



Growing on walla and roofs of caves, or in smaller cavities in rock-, 

 usually anion-: other algae with a creeping base, such as Rhodochorton 

 an<l Spermothamnion. We have found this quite a puzzling form, as 

 there are three European species, in different genera, of similar rise 

 and habit, and with tetraspores similarly placed. Two of these, 

 Ptilothamnion pluma Hornet in LeJolis, L863, p. 11 s and Plumaria 

 Schousboei (Hornet 1 Schmitz, 1896, p. 7, while differing in cystocarpa 

 and antheridia, are almost identical otherwise, but a comparison of 

 the plates, Hornet & Thuret, 1876, p. 32, PL X. and Bornel & Thuret, 

 1880, p. 179, PL XLVI, shows that the Plumaria has shorter cells 

 throughout, and that the branches arise at the upper edge of the cells 

 of the axis, while in the Ptilothamnion they are distinctly lower. 

 The Bermuda plant agrees exactly with Plumaria Schousboei in form 

 and proportions of cells, and place of insertion of branches; on that 

 account we have placed it in the genus (J ymnothamnion, recognizing, 

 however, that when the sexual fruit is discovered, a different disposi- 

 tion may he necessary. The uniformly opposite character of the 

 branching is quite noticeable; even in the prostrate filaments any 

 other branching is rare and evidently abnormal, though in most 

 species with opposite branching in the erect parts, the basal part is 

 apt to vary from this. Moreover, every rhizoid that we have observed 

 is opposite to an erect axis. Hornet and Thuret, describing P. S<-hoiis- 

 boeif say " ils adherent par des crampons semblables a ceux des Spermo- 

 thamnion et des Polysiphonia"; hut an examination of HI. X, fi,<:. 1, 

 shows all the rhizoids opposite to erect axes, while this is not the c 

 in Spermothamnion flabellaium shown in PI. VIII, fi<;. 1. We are led 

 to keep the Bermuda plant separate from /'. Schousboei principally 

 from the fact that all well developed fronds heir erect branches of a 

 second order, in luxuriant individuals one such branch from every 

 cell of a 1 (ranch of the first order, always on the upper side of the 

 latter. If these branches were in pairs, the distinction would he less 

 important, and might mean merely a repetition of the normal branch- 

 ing in luxuriant individuals, but we have never seen an outgrowth 

 from the under side of a branch of the first order. ( uriously enough, 

 this mode of branching is identical with that of AntUhamtlion j>trro- 

 ton (Schousb. Bornet, L892, p. 331, HI. III. figs. S 9, in regard to 

 which the author says, "Cette elegante petite Algue ressemble beau- 

 coup aux Callithamnion ]>lum<i et elegans mais elle est plus delicate, 



