148 BYNOPSIS of britisii seaweeds. 



llali. Parasitical on the larger Algae, frequently on Lamiumia 

 digitata, Oodium tomentotum^ etc. 

 The character by which C. hrachiatum appears i 

 tially to differ from C. tetiragonum, is to be Found in the 

 ultimate ramuli, which in this are constantly subulate, 

 gradually tapering from the base to the apex ; and in that 

 are suddenly acuminate, or, as it were, mucronate. This 

 is what originally induced me to admit the species, which 

 I found indicated in the unpublished ' Algae Appineo 

 Carmichael. under the name C. fruticuloswm ; and so far 

 as my observations have gone, this character appears to be 

 constant. Minor and less important distinctions may be 

 taken from the length of the joints, and their form, which 

 is cylindrical in the present species and oval in C. tetrago- 

 num. Both plants are equally common, and found in the 

 same situations. 



259. tetricum {The rough CaUithamnion) ; rigid, shrubby; 

 stem and branches robust, densely covered with ramuli, 

 shaggy below, plumulate above ; plumules crowded, quadri- 

 farious, simply pinnate ; pinna? acute, tapering to the base, 

 erecto-patent ; articulations twice or thrice as long as broad ; 

 tetraspores elliptical, minute, sessile on short lateral pro- 

 cesses of the pinnae, -4^. Sp. Alg. v. 2. f. 179. (Atlas, 

 PI. LYI. Fig. 259.) 

 Phlebothamnion tetricum, Ktz. Conferva tetrica, Dillw. 

 Hab. South of England, and south and west of Ireland. On the 

 perpendicular faces of rocks within tide-marks, from half- 

 tide level to low-water mark. Perennial. Summer. 

 This is the coarsest of the British Callitkamnia, resem- 

 bling in its bushy habit, shaggy tufts of Sphacelaria scopa- 

 ria, and is often of a very dark brown colour, with little 

 trace of the purple endochrome characteristic of the genus. 

 At other times, much more shaggy specimens with a 

 brighter colour are found, and some of these resemble 

 large specimens of C. Borreri. Specimens collected at 

 various seasons and from different localities differ much in 

 the abundance and regularity of the plumules, as well as 

 in the greater or less development of the hair-like ramuli. 



260. Hookeri {Hooker's CalUthamnion) ; stem setaceous, inar- 

 ticulate or nearly opaque, with traces of joints, simple, set 

 with one or more series of alternate, spreading, flexuous 

 branches, the smaller of which are articulated, and all 

 densely plumulate ; plumules patent, naked below, pinnate 



