510 BULLETIN OF THE BUREAU OF FISHERIES. 



aa. Thallus consisting of a monosiphonous central axis partially or entirely surrounded by 



cortical layers \ -c. 



c. Thallus laterally branched, cortex continuous throughout or lacking only on the finer 



divisions 4- Spyridia (p. 512). 



cc. Thallus dichotomously branched, forcipate at apices, cortex continuous or present 



only at the nodes 5- Ceramium (p. 513). 



Genus i. Spermothamnion Areschoug. 



Spermothamnion, Areschoug, 1847, p. 334. 



Thallus composed of erect, naked, monosiphonous filaments arising from creeping 

 filaments attached to the substratum at intervals, erect filaments oppositely or alter- 

 nately branched; tetrasporangia sessile, occurring singly or in groups on short lateral 

 branchlets, triangularly divided; antheridia ovoid-oblong, sessile on short lateral branch- 

 lets, sometimes terminal, composed of minute hyaline cells grouped around a central 

 axis; procarps usually terminal on lateral branchlets, always with two auxiliary cells; 

 cystocarps globose, small, terminal on lateral branchlets, sometimes naked, usually 

 inclosed by short upgrowing, filamentous branchlets, pericarp lacking, containing two 

 gonimoblasts which are small, compressed, and bear numerous single, rounded carpo- 

 spores radiating in all directions. 



About 15 species, in warm and temperate seas. 



Spermothamnion investiens (Crouan) Vickers. PI. XCI, fig. i. 



Cattithamnion investiens, Crouan, in Schramm and Maz, 1865, p. 7. 

 Callitkamnion investiens, Crouan, in Maz and Schramm, 1870, p. 141. 

 Spermothamnion investiens, Vickers, 1905, p. 64. 



Thallus forming dense woolly tufts, closely enveloping the host plant; primary filaments creeping, 

 attached to the substratum at intervals by unicellular, rhizoidal structures flattened at their ends to 

 form attaching disks, secondary filaments erect, numerous, i to 3 mm. tall, 14 to 16 mic. wide, sparingly 

 alternately branched, sometimes simple, branches usually simple, segments 30 to 100 mic. long, usually 

 55 to 70 mic. ; tetrasporangia occurring singly, terminating short (usually one-celled), lateral branchlets, 

 borne oppositely or secundly, ellipsoid or slightly obovate, sometimes almost globose, 30 to 40 mic. 

 wide, 37 to 45 mic. long; antheridia oblong-ovate, borne singly at the apices of more or less prolonged 

 lateral branches or of the main filaments; cystocarps situated like the antheridia; texture velvetyj color 

 rose. 



West Indies. 



Occasionally very abundant on Bogue Beach, Beaufort, N. C., on about half of the specimens of 

 Zonaria flava found on the beach throughout the year, fruiting at all seasons, very abundant on about 

 one-third of specimens of Zonaria flava dredged off coral reef, May, 1907. 



The Beaufort plants are closely similar to Miss Vickers 's specimens from Barbados. This species 

 here forms dense, velvety mats covering in almost pure growths the main stems, branches, and larger 

 ribs of the Zonaria. It has been found only on this host except in one instance when a battered speci- 

 men of Brongniartella mucronata on Bogue Beach had the lower part of its stem densely covered with 

 filaments of this species. It seems very probable that all the plants of Zonaria flava found here have come 

 from the coral reef offshore. 



It has been noted by Farlow (1882, p. 119) and Lewis (1909, pp. 683, 684) that, in S. turneri (Mert.) 

 Aresch, apparent tetraspores may occur on the same individual with procarps, cystocarps, or antheridia. 

 The author has, in the present species, observed cystocarps on the same filaments with what appeared to 

 be undivided tetrasporangia, but has not found cystocarps and mature tetraspores on the same plant. In 

 one instance there was observed a structure (fig. 42) that appeared to be an imperfectly divided tetra- 

 sporangium which had continued its growth as a vegetative filament. At Beaufort the masses of Sper- 

 mothamnion on some specimens of Zonaria seem to be entirely tetrasporic, but on other plants of the 

 host antheridia, cystocarps, and tetraspores occur intermingled. 



