Structure, in the younger parts, a central, jointed filament, coated with slen- 
der, interlaced, longitudinal fibres, which emit, to the periphery, dichoto- 
mous, alternate branches, whose apices, united, form the membranous wall 
(or periphery) of the frond; in older parts this latter is much thickened. 
Substance membranous and succulent, filled with juice when recent. In dry- 
ing, the younger parts of the frond adhere to paper. 
OPO eee 
This is apparently a rare plant, which I only know through 
a specimen given me by Dr. Mueller. It is externally so ex- 
tremely like our Rhabdonia verticillata, figured in the following 
Plate, that I may be pardoned for having formerly confounded 
them. Indeed, I can even now scarcely distinguish them but by 
an appeal to the microscope, when the very dissimilar cellular 
structure shows that they cannot be the same, or even placed 
(according to our present views of systematic arrangement) in 
the same genus. The /e/raspores in our present plant, though 
similarly placed to those in Adaéddonia, and of similar structure, 
are of much smaller size. The cystocarps of neither plant are 
known. It was on the present species that Sonder founded his 
genus Lrythroclonium. 
Fig. 1. ErytHroctonium MUELLERI,—the natural size. 2. Branchlets. 3. 
One of the internodes, with ¢e¢raspores. 4. Tetraspores. 5. Cross section 
of the frond. 6. Longitudinal section :—magnified. 
