CERAMIACE^. 235 



Callithamniou tetragonum. The four-angled 

 Callithamnion. 



Fronds from two to five inches long ; stem indistinctly 

 jointed, veined ; branches simple or alternately divided, 

 clothed with short, alternate, spreading, level-topped plu- 

 mules ; branchlets of the plumules incurved, robust, taper- 

 ing suddenly at the point. Favellee in pairs, formed in the 

 centre of the plumules ; tetraspores tripartite, very minute, 

 on the inner side of tbe tips of the branchlets of the 

 plumules. 



This is a handsome plant, and, for the genuSj of large 

 size j it is parasitic on various Algse, and, in a young 

 statCj forms a fringe on the edge of their fronds ; when 

 mature, the form of the plant is pyramidal. In drying, 

 the specimens lose much of their beauty : the plumules 

 become matted together, and do not lay out well, nor 

 adhere to paper. 



Callithamnion tetragonum, var. /3. brachiatum. 



Branchlets of the plumules more slender, and tapering 

 from the base to the tip. 



This variety is figured and described as a separate 

 species [Callithamnion brachiatum) in the ' Phycologia 

 Britannica,' but it would appear that Dr. Harvey adopted 

 this course in deference to Professor Agardh, and as the 

 latter botanist has since altered his opinion, I feel my- 

 self at liberty to insert the plant in what I believe to be 

 its correct position, as a variety. 



Callithamnion tetricum. The rough Calli- 

 thamnion. 



Fronds two to eight inches long, very bushy, much 



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