466 BULLETIN OF THE BUREAU OF FISHERIES. 



Genus 4. Erythrotrichia Areschoug. 

 Erythrotrichia, Areschoug, 1850, p. 209. 



Thallus erect, filiform, attached below by a dilated basal cell or a few-celled disk, 

 above filamentous or more or less thickened and terete or dilated and foliaceous; cells at 

 first arranged in a single row, later sometimes divided longitudinally, or occasionally 

 even forming a one-layered disk; asexual propagation by naked monospores which are 

 passively distributed; monosporangium formed from the upper, smaller, denser of two 

 cells arising from the unequal division of a vegetative cell by an oblique wall; sexual 

 reproduction by apparently nonmotile spermatia and eggs; antheridia formed from 

 portions of vegetative cells in a way analogous to the monosporangia, the contents being 

 divided into numerous minute spermatia; eggs arising singly from the entire contents 

 of vegetative cells; fertilized egg forming a one or few celled fruit. 



About five species, all marine. 

 Erythrotrichia carnea (Dillwyn) J. Agardh. Fig. 24. 



Conferva carnea, Dillwyn, 1809, pi. 84. 

 Conferva ceramicola, Lyngbye, 1819. p. 144. Pi- 48 D. 

 Erythrotrichia ceramicola, Areschoug, 1850, p. aio. 

 Erythrotrichia carnea, J. Agardh, 1881, p. 15, pi. 19. 

 Erythrotrichia ceramicola, Farlow, 1882, p. 113. 

 Erythrotrichia ceramicola, De Toni, 1897, p. 24. 

 P. B.-A. No. 1642 (Erythrotrichia ceramicola). 



Thallus epiphytic, consisting of erect, flaccid filaments i to 30 mm. long, composed of single, 

 unbranched rows of cells, attached by the expanded, colorless basal cell of each filament; cells 12 to 20 

 mic. long, 12 to 18 mic. wide, rose or flesh color; monospores spherical, 15 to 18 mic. in diameter. 



Warm and temperate North Atlantic; Alaska; Adriatic. 



Common in small quantities on Dictyota dichotoma and Padina vickersice, Beaufort, N. C., June to 

 December, and on Dictyota dichotoma at Marshallburg, N. C. On old specimens of these species it 

 becomes very abundant, either mixed with other filamentous epiphytic algae or covering the entire host 

 plant with a pure growth. 



Genus 5. Erythrocladia Rosenvinge. 



Erythrodadia, Rosenvinge, 1909, p. 71. 



Thallus horizontally expanded, growing on or in other algae, composed of branched 

 filaments irregularly or more or less regularly radiating from a common center, separate 

 from each other in the beginning, later fusing more or less to form a thin disk consisting 

 of a single layer, filaments growing at the apices; asexual propagation by naked mono- 

 spores which are passively distributed; monosporangium formed from the denser of two 

 cells arising from the unequal division of a vegetative cell by an oblique wall; sexual 

 reproduction by apparently nonmotile spermatia and eggs; spermatia (at least in some 

 cases) raised slightly above the surface; carpogonium furnished with a short beak or 

 trichogyne projecting slightly beyond the surface; fertilized egg forming a small fruit 

 (sporocarp) bearing one or more carpospores. 



Four species, known only from Denmark, North Carolina, and, with some doubt, 

 from St. Thomas, West Indies. 



KEY TO SPECIES. 



Mature thallus consisting of filaments forming an irregular suborbicular structure, the fila- 

 ments somewhat compact and coalescent at the center and radiating from this toward 

 the edges, cells 8 to 25 mic. long and 3 to 12 mic. broad i. E. recondita (p. 467). 



Mature thallus consisting of straggling or irregularly radiating filaments, not forming a com- 

 pact structure at the center, cells 9 to 40 mic. long and 6.5 to 15 mic. broad. .2. E. vagabunda (p. 467) 



