ON THE GENERA ANADYOMENE AND MICRODICTYON. 49 
Anadyomene Brownii. Its study induces me to propose to divide the 
genus into two subgenera, thus : — 
l. The cells of main stem linear; interspaces between the main 
: filaments and cells close on their sides, filled up with nearly equal- 
sized minute cells.—SrTENOCYsTIS, for A. Wrightii. 
2. The cells of main stem ovate ; interspaces between the main fila- 
ments filled up with large very different-sized cells.—ANADYOMENE, 
for A. stellata and A. Culleria. 
Stenocystis is somewhat intermediate between Anadyomene and Calo- 
mena, but it evidently belongs to the genus to which I have referred it, 
as instead of the main filament being only forked, it is provided with 
radiating cells at the top. 
Genus 3. GRAYEMMA. 
Frond fan- shaped from a central root; the main stem and branches in 
the centre of the frond and lobes formed of three or four parallel 
close series of short cells in transverse bands. 
This genus is very different in its structure from Anad: lyomene.. In 
the latter, the series of cells that form the axis of the frond and its lobes 
is single, one cell on the end of the other like a Conferva, the end cell 
being crowned with a radiating group of cells. 
In Grayemma the frond and its lobes are supported by a broad mid- 
rib, which is formed of several close parallel longitudinal series of cells, 
the cells on the side of the midrib giving off radiating groups of cells. 
The end of the midrib is branched, and is Ais: by the develop- 
ment of a radiating group of cells at the end of the former one, and 
this is how the many series of cells in the midrib are formed, and why 
they look like what they really are, a continued succession of radiating 
groups of cells forming a thick midrib; the parietes of the cells are so 
thin that in the dry specimen the outer surface of the cell is sunk in 
leaving the side-margin elevated ; from the side of the midrib arises a 
group of diverging cells, and on the apex of these are formed another 
series as the frond enlarges: thus the branches on the midrib are 
gradually formed and lengthened. 
The disk of the frond between the midribs is filled up with a very 
numerous series of cells much smaller in size and more numerous than 
in Anadyomene, consequently there is a much greater difference between 
VOL. 1V. [FEBRUARY 1, 1866.] E 
