THE GREEN AI.GAE OF NORTH AMERICA 397 



broad, often connate; color dark green to blackish, easily fad- 

 ing to yellowish ; filaments of medulla of stipe cylindrical to 

 slightly tornlose, 30-75 //. diam. ; filaments of cortex cylindrical, 

 diminishing in ultimate branches to 6-n p diam. In quiet 

 pools. Bahama. 



Borgeseu suggests that this may be a battered state of the fol- 

 lowing species, but an examination of a large number of speci- 

 mens of all sizes and ages shows no indication of such a 

 relation. 



2. C. LUTEO-FUSCUS (Crouan) Borgeseu, 1908, p. 40, figs. 7 

 and 8; Udotca luteo-fusca Howe, 1907, p. 513. Fronds to 10 

 cm. high, brownish ; stipe simple or 1-3 times dichotomous, 

 terete or flattened ; flabellurn cuneate to irregularly orbicular, 

 little or not at all zonate, surface smooth or slightly rugulose ; 

 filaments of medulla of stipe 50-80 p diam., the repeatedly 

 dichotomous branches forming the cortex diminishing in the 

 ultimate divisions to 4-10 p. diam. ; structure of the flabellum 

 similar. Fig. 151. W. I. 



7. HALIMEDA L,amouroux, 1812, p. 186. 

 Frond much calcified, consisting of more or less flattened 

 segments in branching series ; with a more or less distinct 

 stem and a mass of basal rhizoids. A central strand of inarticu- 

 late filaments passes through each segment, giving out lateral 

 branches whose terminations form the surface of the segment, 

 and superficially appear like hexagonal cells. At the apex of 

 each segment the central filaments come into connection with 

 each other, but separate when forming the next segment. 

 Fructification by globose or obovoid sporangia, borne on the 

 margin or on the face of a segment, on branches from the cen- 

 tral filaments, producing biciliate spores, whose development is 

 unknown. 



The species of Halimeda are all tropical or subtropical ; they 

 are conspicuous plants, and the Mediterranean species was de- 

 scribed over 300 years ago, though it was only in the last cen- 

 tury that it was recognized as a plant. About 20 species have 

 been described, based on the external form of the frond, but 

 this is so variable, characters of several supposed species being 

 sometimes found on one individual, that there has been much 

 confusion. By using chiefly Characters derived from the 

 central filaments, and from the size and shape of the ulti- 

 mate segments of their branches, "peripheral utricles," ten 



