CERAMIACE.E. 215 



Halurus equisetifolius. The Equisetum-leaved 

 Halurus. 



Frond from four to eight inches long, irregularly branched ; 

 the branches alternate, set with one or more series of side 

 branchlets ; stem and branches thickly clothed with short, 

 forked, jointed, incurved ramelli, which on the younger 

 parts of the frond are regularly whorled round the nodes. 

 Spore-clusters at the tips of shortened branches; tetra- 

 spores inside the involucral branchlets. 



When young and freshly gathered, this is a handsome 

 plant, but it loses its colour, and becomes coarse and 

 shaggy with age. AYith the exception of the difference 

 of colour, it bears a strong resemblance to Cladostephus 

 spongiosum. It grows abundantly on our southern 

 shores, but is much less luxuriant towards the north. 

 It adheres firmly to paper, but, like all the species of 

 Griffithsia, it must be laid out in salt water, or it will 

 stain the paper. 



Halurus equisetifolius, var. simplicifilum. 



'* Stems slender, irregularly branched, whorled with im- 

 bricated, straight, once-forked ramelli." 



In the ' Phycologia Britannica/ this form is hesi- 

 tatingly described as a distinct species. Agardh treats 

 it only as a variety, and I have done the same, as I 

 have never been able to find any distinct specific cha- 

 racters in the specimens I have examined. 



Genus C. G-RIFFITHSIA. 



Frond single-tubed, jointed, forked. Spore-clusters (fa- 

 vellce) surrounded by numerous, regular, involucral branch- 

 lets, containing many angular spores enclosed in a gela- 



