152 Bl NOrSIS OF BBITISH SEAWEEDS. 



i'v tlic shape of its plumules, from the latter, chiefly by the 

 ie of the axillary ramulus. Unlike as. at first Bight, 

 this plant may appear to C, gracillimum, very Luxuriant 

 specimens closely resemble that Bpecies in habit, an J ex- 

 hibit a nearer approach in microscopic character than could 

 l»e supposed. 



267. affine (The allied Callithamnion) ; much branched and 

 bushy; the stem rather opaque, full of veins; secondary 

 branches long, having a roundish outline, alternately plumu- 

 late ; plumules very narrow, simply pinnate ; pinna? short, 

 erect, increasing in length upwards, alternate, crowded at 

 top : articulations of the branches three or four times, of the 

 pinna? once and a half as long as broad ; tetraspores gene- 

 rally solitary, rising from the basal cell of the pinnae, Ilarv. 

 m Hook. Br. Ft. v. 2. p. 344. (Atlas, PL LIX. Fig. 273.) 

 Hab. Parasitical on Fuel, between tide-marks. Annual. Summer. 

 If this plant be really entitled to specific rank, it is well 

 named affine, for it appears to be akin to several other 

 species, and to form an intermediate link between them. 

 To C. Hookeri it is allied in habit, and in the opacity of 

 the main stem, but here the resemblance ends, for the na- 

 ture of the ramification is extremely different. "With C. 

 roseum we may also compare it, but the narrow plumules, 

 with short, erect pinnules, afford a clear mark of distinc- 

 tion. Perhaps, after all, the nearest approach is to C. vo- 

 lyspermum, which has plumules equally narrow, and pin- 

 nules equally short, and which grows in similar places ; 

 but the solitary, basal tetraspores of C. affine seem to 

 point to another species. The only specimen known was 

 collected in 1832, by Dr. Greville, on the shore of Bute. 



26S. tripinnatum (The three-pinnate Callithamnion) ; frond 

 distichously branched, capillary, decomposito-pinnate ; plu- 

 mules elongate, obovate, tripinnate above ; upper pinna? 

 elongate, and pinnulate, lower short or abortiye, each pinna 

 having at its axil a minute pinnule ; pinnules long, setace- 

 ous ; joints of the stem 3-4 times, of the pinna? about twice 

 as long as broad ; tetraspores oval, lateral on the axillary, 

 and occasionally on the other pinnules, Ag. Sp. Alg. v. 2. 

 p. 168. (Atlas, PL LVI. Fig. 261.) 



Mertensia tripinnata, Qrabel. 



Hab. On marine rocks, at extreme low-water mark. Annual. 

 April, May. Very rare. 

 Though the habit of C. tripinnatum is very like that of C. 



