RHODOMELACEiE. Ill 



sections of the tubes, from which they may be readily 

 distinguished by their greater breadth. 



Subditisiox 4. — Tubes seven, branches and branchlets beset 

 tvith single-tubed, forked, jointed ramelli or leaves. 



Polysiphonia byssoides. The byssoid Poly- 

 siphonia. 



Fronds from a few inches to a foot or more long ; stem 

 about as thick as a bristle, undivided throughout its entire 

 length, becoming flat when laid out on paper ; branches al- 

 ternate, bearing one or two series of branchlets, all clothed 

 with short, byssoid, jointed, ramelli or leaves ; articulations 

 varying much in length in different specimens: those of the 

 stem and larger branches from twice to six times as long as 

 broad ; those of the smaller branches usually short. Spores 

 in egg-shaped, stalkless conceptacles ; tetraspores formed 

 from the joints of the branchlets. 



This is a large and handsome plant, and is very generally 

 distributed round our coasts. It grows on stones, shells, 

 and sea- weeds, at and beyond low- water mark. Pos- 

 sessing the characters of a Polysiphonia, in combination 

 with the byssoid ramelli of a Dasya, this plant may be 

 said to be the connecting link between the two genera. 

 Dr. Gray has placed it in a separate, new genus, under 

 the name Dasyclonia. 



Genus XLII. DASYA. 



Frond without visible joints, thread-like, or flat, branch- 

 ing, with a many-tubed, jointed axis, surrounded by a layer 

 of cells ; branches clothed with slender, single-tubed, jointed 



