154 SYNOPSIS OF BRITISn SEAWEEDS. 



pinnule, 11' r. ;„ Hook. Br. FL v. 2. p. 846. (Atlas, PI. 

 U\. Kg. 275.) 

 Callithamnion thuyoidee, Ag. Conferva thuyoides, E. Bot. 

 Hub. On rocks, near low-water mark ; rare. Annual. Spring 

 and summer. 

 One of the most concinnate of the Callithamnia, eleganl 

 in all its minute parts, and strictly neat in its mode of 

 growth. In essential character it closely approaches C. 

 gracillimum, from which it is more to be distinguished by 

 habit than by any very definite character. C. gracillimwm 

 is a larger and more tufted plant, more irregular in ramifi- 

 cation, with longer and more indefinite plumules, varying 

 much in the composition of its ramuli. The plumules are 

 very generally triply pinnate. Faveilce are much less com- 

 monly found on this species than tetraspores, and gene- 

 rally burst from the sides, and not the apex of a branchlet. 

 Though found in many places, C. thuyoideum must be 

 ranked among the rarer forms of the genus. 

 271. corymbosum (The corymbose Callithamnion) ; frond se- 

 taceous at the base, capillary and byssoid above, flaccid, 

 gelatinous, excessively branched ; secondary branches alter- 

 nate, repeatedly dichotomous, subflabelliform, level-topped ; 

 ramuli many times forked, with patent axils ; apices obtuse ; 

 articulations of the branches from eight to ten times as long 

 as broad ; tetraspores solitary, opposite the axils of the 

 terminal forks, sessile, globose ; favellse binate, on truncated 

 branches, Ag. Sp. Alg. v. 2. p. 165. (Atlas, PL LIX. Fig. 

 276.) 

 Callithamnion versicolor, Ag. Phlebothamnion corymbosum, 

 Ktz. P. versicolor, Ktz. Ceramium corymbosum, Ag. C. 

 versicolor, Ag. Conferva corymbosa, Eng. Bot. 

 Hab. On the leaves of Zostera, the fronds of various Alga?, and 

 attached to rocks and stones, near low-water mark. Annual. 

 Summer. 

 A very variable plant : so much so, that most authors 

 regard as distinct species two forms which I here bring to- 

 gether. Hitherto in British works we have recognized the 

 original Cal. corymbosum of Eng. Bot., and the Cal. 

 color of Agardh, the differences between which are said to 

 be, that the former is much more slender than the latter, 

 with longer joints, a less evident stem, and a less pinnated 

 branching. Some specimens are indeed very slender, and 

 dichotomously divided, and others are robust, with an un- 

 divided stem and lateral branches ; but between the most 



