V. CERAMIACE^. 223 



the tetraspores in conical, pedicellate glomeruli, alternating with the serrated pin- 

 nulte ; favellfe similarly placed, involucrate, the branches of the involucre entire or 

 coarsely toothed, cellular. KUtz. Bot. Zeit. 1847, p. 36. J. Ag. Sp. Alg. 2, p. 9(j. 

 Ptilota plumosa 13 asplenioides, Lyngh. t. 9, / 2. (Excl. Sgn.) 



Hab. Pacific Coast at Sitcha, Ruprecht. Greenland and Newfoundland, /. Agardh. 

 Arctic Coast, Sir John Richardson. Halifax, W. H. H. Boston Bay, Dr. Asa Grag, 

 Mrs. Mudge, Mr. Emerson, W. H. H.., &c. (v. v.) 



Frond four to six inches long, the stem piano-compressed, half a line in breadth, 

 disticliously much branched, the branches decompound-pinnate, all divisions of the 

 frond very patent, almost issuing at right angles. Pinnce and pinnute of every series 

 exactly opposite, except by accidental suppression, but of different size and aspect : 

 one of each pair a line long, horizontal, broadly subulate, sharply serrated especially 

 on tlie outer edge, acute, seldom lengthening and never much lengthened, in the 

 older parts of the frond generally broken, or worn : the other pinna elongate, pin- 

 nated and lengthening out into a branch which becomes again compounded by its 

 pinnae also lengthening in a similar manner. In this way the frond finally consists 

 of several series of short-serrated, and of longer-pinnated opposing pinna?. The 

 favell(je are formed in the apices of the pinnated (or compound) ramuli, which are 

 then abbreviated to a line or two in length ; the branches of their involucre are 

 subulate, either entire or with three or four coarse teeth. Tetraspores in dense 

 conical heads, also formed from suppressed branches, alternating with the serrated 

 pinnte. Substance., cartilaginous. Colour, a deep, full red, becoming brighter in 

 fresh water. In drying, it does not adhere to paper. 



This has the colour, size, and general aspect of Pt. plumosa, with which I have 

 been hitherto accustomed to unite it, nor am I very certain that the characters here 

 pointed out as distinguishing it are to be relied upon as sufficient. The strongest 

 character will perhaps be found in the tetrasporic fruit : that in the ramification is, 

 I fear, less constant. The elder Agardh at one time, and Lyngbye both referred it 

 to Pt asplenioides, from which it is readily distinguished. Agardh afterwards made 

 it a variety of Pt. plumosa. Kiitzing in 1847 first gave it a specific name, but sub- 

 sequently, in 1849, reduced it again as a variety, under Pt. plumosa. Professor J. 

 Agardli, however, restores the species, and points out with his usual acumen the 

 characters by which it may be known from Pt. plumosa. 



These characters, so far as they depend on ramification, are not perfectly satisfac- 

 tory to me, for I find the serrated ramuli of Pt. serrata showing an occasional dis- 

 position to lengthen into branches ; and again, on Pt. plumosa one of the opposing 

 ramuli is, in the younger branches, frequently abortive, in which case the ramuli 

 are alternately unequal, as in Pt. serrata. If tlie ramulus which is formed were 

 always clearly pinnated as it ought to be in Pt. plumosa, there would be no doubt 

 of the validity of Pt. serrata ; but though this is commonly the case, yet I have 

 specimens of the former species in which slightly serrated, or nearly entire ramuli 

 alternate with pinnated ones in some parts of the frond. Both species occur toge- 

 ther in Norway, but Pt. serrata has not yet been found in Britain. Almost all the 



