MARINE ALGA! OF BEAUFORT, N. C. 517 
numerous minute carpospores somewhat fasciculately radiating from a central point and 
tightly inclosed by gelatinous material. 
About 25 species in warm seas. 
KEY TO SPECIES. 
a. Frond terete or slightly flattened, dichotomously branched................. 1. H. agardhii (p. 517). 
aa. Frond with broad, flattened, central axis and main branches and rather terete or slightly 
flattened secondary branches, laterally branched........................ 2. H. floresia (p. 518). 
aaa. Frond flat, expanded, borne on a short stipe, simple or giving off several lobes from 
near the base, sometimes proliferous from the margins... 1.2.0... 0. ccs e cece eee cee ene eens b. 
b. Frond gelatinous-fleshy, moderately thick, surface appearing roughly papillate under 
microscope, many starlike ganglia plainly visible below surface........ 3. H. gelinaria (p. 518). 
bb. Frond firm membranaceous, thin, surface smooth, few starlike ganglia visible below 
surface; eplor purplish pink «).f4;.. i025 3 bowsthels Shas grigeme Loews 4. H. floridana (p. 519). 
1. Halymenia agardhii De Toni. Pl. CXII, fig. 1. 
Isymenia flabellata, J. Agardh, 1899, p. 66. 
Halymenia agardhii, De Toni, 1905, p. 1542. 
A. A. B. Ex. No. 80 (Halymenia decipiens). 
P. B.-A. No. 647 (Halymenia decipiens). 
Frond terete or flattened, 5 to 20 cm. tall, 2 to ro mm. in diameter, dichotomously decompound, 
often with a few short dichotomous proliferations, gradually tapering toward the apices, branches rather 
erect and spreading above, rounded sinuses, habit usually dense, fan-shaped, apices obtuse, inner fila- 
ments more or less abundant, intermixed with jelly, irregularly branched, anastomosing, segmented, 
forming more or less long, cylindrical, or short, somewhat rounded cells; tetrasporangia scattered over 
the surface among the cortical cells, inconspicuous; cystocarps immersed in the inner cortex, forming 
no swellings on the surface, appearing as small, inconspicuous dots scattered over the frond; texture 
rather gelatinous; color yellowish pink to dark, purplish pink. 
Florida; West Indies; Bermuda. 
Two fruiting plants dredged from coral reef offshore, Beaufort, N. C., August, 1915, occasional on 
Bogue Beach, summer and autumn, sometimes fruiting. 
In typical specimens of this species the dichotomies are frequent, becoming more numerous toward 
the tips, forming a dense habit with the upper branches crowded, the apices are rounded, and the internal 
filaments are fairly numerous and usually of uniform diameter. But apparently there is considerable 
variation among authentic specimens in the size of the plants, the acuteness of the apices, and the 
amount of spreading of the ultimate branches. 
The specimens here referred to this species vary in habit and somewhat in structure. In some the 
branching is profuse, forming the dense habit given as characteristic of the species, but in others this 
is distant, forming an open habit. The apices are sometimes rounded, but are more often acuminate, 
the same specimen sometimes having some branches rounded and others acuminate. The internal 
filaments may be fairly numerous, but are often sparse. While, therefore, some of the plants do not 
have all the characters given as typical for the species, authentic specimens themselves vary in these 
respects. It may be that, in the present case, two species are confused, but it has seemed impossible 
to separate the specimensinto two groups. It has been mentioned that Dictyota dichotoma, growing under 
different conditions, may vary in the acuteness of the apices and may assume habits described for different 
forms and even different species. No study has yet been made of H. agarhdii in this respect, and we do 
not know enough of the influence of the environment on its form to warrant the separation of species on 
slight, variable differences in habit. 
This species may easily be mistaken for members of other genera reported from Florida, and there- 
fore liable to be cast on our coast. It closely resembles Halarachnion ligulatum (Woodw.) Kuetz. The 
latter species has a more generally open habit, more acute apices and fewer internal filaments than 
Halymenia agardhii, but, as has been mentioned, the latter species may itself vary in these respects. 
The essential distinction between these species can be made only by the characters of the genera, in that 
Halarachnion forms its auxiliary cells and cystocarps on the primary filaments, while Halymenia forms 
these on special secondary branches. 
