ON THE GENERA ANADYOMENE AND MICRODICTYON. 43 
tinct groups, perhaps to distinct families, but this cannot be determined 
until the fructification and habits of the two genera have been studied ; 
the chief difference between the two groups being that one has the 
lines of cells united by their sides, so as to form a membranaceous frond, 
and the other the cells isolated from each other, ndi a net with 
open polygonal meshes, as pointed out by M. Monta 
There is a certain amount of resemblance between de fronds of the 
Microdictyonee and those of Síruvea ; but the cells which form the 
frond of Microdictyon and the stem especially from which the frond of 
Phyliodictyon arises, are much more like the cells of the filament of 
a Conferva than of a Dasycladus ; on the other hand, Sfruvea, in its 
structure and mode of growth, is very nearly allied to the unicellular . 
Alga. The stipes and the midrib or axis of the frond isa simple one- 
celled continuous tube, very unlike the slender articulated stem and 
midrib of Microdictyon and PAyllodictyon. Indeed, it appears to me 
that the stem, the midrib, and the cells that form the reticulation of 
these two genera are very similar to the cells which form the filament 
of Oladophora, and it would appear that the tribe is more allied to 
Confervacee than Valoniacee. 
Group I. ANADYOMENEX®.—The frond membranaceous, formed 
of articulated forked or digitate proliferous filaments, the inter- 
spaces between the branches filled with polygonal cells. 
This group consists of three genera: one, the Anadyomene of Lamou- 
roux ; one, very like the former genus in appearance, discovered in Aus- 
tralia by Mr. R. Brown; and the third, founded on a beautiful Alga, 
which the late Mr. Menzies discovered in the Gulf of Mexico, and 
named -Anadyomene Menziesii by Dr. Harvey. 
This A. Menziesii has the interspaces filled up, as in daadyomene, 
but in that genus the main ribs of the frond are formed of a single 
series of articulations like a Conferva, while in the Conferva umbilicata 
of Menzies the main stem is formed of several transverse series of cells 
condensed into a midrib, differing in this respect from all the other 
genera of marine Alge. 
The genus is evidently the plant referred to by Professor Harvey in 
the following terms :—'* The largest specimen I possess was given to 
me by the late Mr. Menzies, as having been dredged in twenty fathoms 
in the Gulf of Mexico. This specimen measures 6 inches, and its 
