66 ON THE GENERA ANADYOMENE AND MICRODICTYON. 
slender branched articulated filament; the main filament simple or 
forked. 
Genus 1. MicropicrTyon. 
The frond broad, expanded, concave, umbilicate ; affixed by a central 
disk, often proliferous, supported by slender articulated filaments, 
which give off branches radiating from one centre to another, form- 
ing a large network, the intermediate spaces between the filaments 
being filled up with a network of anastomosing cells, each side of the 
mesh being formed by a single cell. 
Microdictyon, Decaisne, Arch. du Mus. ii. 115; Kützing, Syst. Alg. 
511 
This genus has an extensive geographical distribution; specimens 
have been described from the Canary Islands in the Atlantic, the Red 
Sea, the coast of Natal, and various parts of the Australian seas. 
** Microdictyon is generally a deep-water production, lying at the 
bottom in 5-10 fathoms, but it sometimes occurs at low-water mark. 
The species of it are all very similar to each other, and have been found 
in the tropics of both hemispheres and in the Mediterranean ; one is very 
abundant in Port Jackson, Australia.”—Harvey, Nereis Bor. Amer. 
iii. 402. 
Dr. Harvey, in his generie character, describes * the endochrome as 
green, thin and watery.” Probably he is the only algologist who has 
observed them growing. 
Montagne, in his text to Webb and Berthelot's Hist. Nat. des 
lles Canaries, vol. v. 180, describes two cies of Anadyomene 
under the name of 4. stellata and A. Calodictyon, and in his specific 
characters of these species gives the generic distinction of the genera 
Anadyomene, Lamouroux, and Microdictyon, Decaisne, viz. ** Venis 
membrana tenuissima connexis," and * Venis membrana nulla con- 
nexis." 
M. Decaisne proposed the genus Microdictyon in a paper on the 
specimens collected by M. P. E. Botta in Arabia Petrea, in the ‘ Ar- 
chives du Muséum, vol. ii. 115, 1841, for a species which he calls M. 
Agardhianum found in the Red Sea near Djedda. He observes, “ C'est 
à ce genre et peut-être à la méme espèce qu'il faudra, ce me semble, 
rapporter PAnadyomene Calodictyon, Montagne. S'il n'en était pas. 
pe ainsi, le om. Microdictyon se composerait de trois espèces, l'une 
