er. Chl OROSPEitMEJS. Fara. Valoniacece. 



Plate L. 



MICRODICTYON AGARDHIANUM, Dm. 



Gen. Char. Frond, a sessile, expanded, amorphous, filmy network, formed 

 of distichously branched, anastomosing filaments. Endochrome green, 

 thin and watery. — Microdictyon (Bne.), from fii/cpos, small, and 

 Bttervov, a net. 



Frons retiformis, sessilis, expansa, amorpha, ex Jllis confervoideis articulatis 

 distiche ramosis anastomosantibus conflata. Succus aquosus, viridis. 



Microdictyon AgardUanum ; frond rather rigid, irregularly expanded; 

 filaments trichotomous, the principal branches patent, ramuli irre- 

 gularly anastomosing; articulations about twice as long as broad. 



M. Agardbianum ; fronde rigidiuscula vage expansa ; fills tricholomis, ramis 

 patentibus ramulisque reticulatim confluentibus ; articulis diametro 2—2>-plo 

 longioribus. 



Microdictyon Agardhianum, Due. PI. Arab. p. 115. Endl, Brd Suppl. p. 14 . 

 Kiitz. Sp. Alg.p. 511. Harv. Alg. Austr. Exsic. n. 568. 



Microdictyon Velieyanum, Bne. I. c. 

 Hydrodictyon umbilicatum, Ag. Syst.p. 85. 

 Conferva urnbilicata, Yelley, Linn. Trans, v. 5. p. 169. t. 7. 

 Hab. Abundant throughout Port Jackson, and in the Paramatta River, 

 in June, W. H. H. 



Geogr. Distr. Mediterranean Sea ; Eed Sea ; Trincomalee, Ceylon ! ; Sand- 

 wich Islands ; Friendly Islands. (Canary Islands ?) 



Descr. Frond horn 1-12 inches broad, of no certain outline, lying flat on the 

 surface of rocks or mud, unattached, or fixed to Alga? and Corallines by 

 several points of its lower surface ; wholly composed of confervoid, articu- 

 lated, anastomosing filaments, and comparable either to a network with 

 irregular meshes, or to a skeleton leaf. The filaments composing the net 

 are not all of uniform size. There is evidently a groundwork of closely 

 reticulated, slender fibres, traversed in various directions by trichotomous, 

 patently branched filaments of larger diameter, which may be called ribs 

 and veins, the smaller ones being veinlets. The closeness of the network 

 varies in different specimens, consecmently also the size and length of the 

 component cellules. Usually the cells are about 2-3 times as long as 

 broad, cylindrical or somewhat conical. When the plant is fresh, the celh 

 are filled with a bright-green, watery endochrome, which is dispersed in 

 drying, in which state the frond turns of a dull, clingy or blackish green. 

 The substance, when fresh, is crisp and rigid, and very easily torn. Not- 

 withstanding its delicacy, the plant very imperfectly adheres to paper in 

 drying. 



