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a more or less regular dicliotomous manner three or four times into 

 obcuneate or sub-flabelliform fronds, the dichotomies rather distant ; 

 axils wide, rounded ; branches erect or erecto-patent, obcuneate or linear 

 obcuneate, rarely acute, generally channeled by the curving upwards 

 of the edges of the frond, especially when tubercles are confined to 

 one side, very variable in breadth ; the more linear forms from two to 

 six lines, the more obcuneate varieties nearly an inch, the apices 

 emarginate or forked, with acute segments. Sometimes the segments 

 are lanceolate or spathulate, entire or bifid, with obtuse or spathulate 

 segments. Tubercles more or less thickly scattered over the surface of 

 the frond, sometimes confined to one side, which is then generally chan- 

 neled, sometimes partly on one side and partly on the other, and 

 occasionally both sides are equally covered ; but generally, when they are 

 abundant on one side of the frond they are wanting on that part of the 

 opposite side. They at first appear in the form of minute papillae, then 

 become elongated and cylindrical, and at length spherical tubercles are 

 formed near the exti'emities, and are extremely common. Tetraspores 

 we have not seen. Stmcture : the central portion composed of longi- 

 tudinal anastomosing jointed filaments, consisting of cylindrical cells, 

 from which arise vertical dicliotomous filaments formed of obovate 

 cells ; their apices simple, of moniliform, deeply coloured cells, closely 

 packed, forming the surface stratum. Substance very tough and rigid, 

 not at all adhering to paper. Colour, a dark reddish brown, almost black 

 towards the base, paler ujDwards and in the younger part of the frond. 



This is one of our most common plants, being found on all our coasts, 

 in many places in greater abundance even than Chondrus crispus, and 

 generally with tubercles. In some places we have seen it on tlie rocks 

 near low-water mark, with a close carpet, prettily dotted with the 

 pale yellowish gi-een fronds of Chondrus crispus. Under such circum- 

 stances there is no difiicxdty in distinguishing the species ; such however 

 is not always the case, for it not unfreqiiently happens that varieties 

 occur whose identity is so difficult to decide that an appeal to the 

 microscope alone can settle the question, and that even with difficulty. 



It is a cm-ious circumstance, if found invariably correct, that tetra- 

 spores are so rare in this species, and so common on Chondrics crispics, 

 while on the other hand tubercles are so rare on the latter, and 

 tetraspores so common. 



The best prhnd facie character perhaps is the channeled frond, but we 

 have seen fronds of this with the segments quite jDlane. Indeed, when 

 there are tubercles equally on both sides of the segments they are 

 generally plane, but if fruited only on one side they are almost invariably 

 channeled, that is, have the margins inciu'ved upon the fruit. Sometimes 



