366 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



8. MICRODICTYON Decaisne, 1839, p. 115. 

 Frond a sessile, membranaceous net-work, formed of mono- 

 siphonous filaments, densely branching in one plane in a radiate 

 manner, the tip of one branch attaching itself to another branch 

 by a terminal thickening ; irregular, angular open spaces be- 

 tween the cells. Asexual (?) reproduction by zoospores, formed 

 in any cell. Marine. 



KEY TO THE SPECIES OF MICRODICTYON. 



i. Cells rarely equalling 200 n diam. i. M. Agardhianuni. 



i. Cells up to 500 M diam. 2. M. crassum. 



1. M. AGARDHIANUM Decaisne, 1839, p. 115; HI. umbilica- 

 tnm Hauck, 1885, p. 467, fig. 203. Frond delicately membra- 

 naceous, filaments 50-200 p. diam., main veins rather distinct, 

 radiate, branches patent; cells usually 2-4 diam. long. Fig. 

 132. Guadeloupe Island, Cal. Europe. 



Our plant seems to agree with the common form of the Medi- 

 terranean, which is often known as M. umbilicatnm ; but there 

 is a question whether the European plant is the same as Conferva 

 umbilicata Velley, from the Hawaiian Islands ; Decaisne's 

 specific name is here used as the first one fairly certain. 



2. M. CRASSUM J. G. Agardh, 1894, p. 107. Rather coarse 

 in texture, filaments up to 500 /A diam. ; cells seldom longer 

 than broad, somewhat moniliform ; branches of different orders 

 little distinct in size or position. Bahamas. 



A much coarser plant than our other species. 



9. CYSTODICTYON Gray, 1866, p. 72. 



Frond a perforated membrane with a framework of radiating, 

 monosiphonous, articulate filaments, attached as in Microdictyon ; 

 the intervals being partly filled by smaller cells, with open cen- 

 tral spaces ; reproduction unknown. Marine. 



In this genus there is the same network of radiate filaments as 

 in Microdictyon ; but there are also many short, one or few 

 celled branches, issuing from the filaments irregularly, and 

 attaching by thickened tips. 



C. PAVONIUM J. G. Agardh, 1894, p. 109; P. B.-A., No. 

 666. Frond up to 3 cm. diam. ; main filaments radiating from 

 centers in various parts of the frond, stout, tapering, openings 

 rounded, of various sizes. Fig. 127. Fla. 



10. BOODLEA Murray, 1890, p. 243. 

 Frond as in Cladophora, but the branches attaching them- 



