MARINE ALGM OF BEAUFORT, N. C. 507 



Bostrychia rivularis Harvey. 



Bostrychia rivularis, Harvey, 1853, p. 57, pi. 14 D. 

 Bostrychia rivularis, Farlow, 1882, p. 176. 

 Bostrychia rivularis. De Toni, 1903, p. 1157. 

 A. A. B. Ex. No. 54. 

 P. B.-A. No. 140. 



Fronds forming dense tufts, i to 4 cm. high, arising from creeping filaments attached to the sub- 

 stratum at intervals by basal disks, capillary, slender, rather rigid, branching decompound, pinnate, 

 alternate, usually distichous, lower branches spreading, almost horizontal, upper ones rather erect, 

 somewhat fastigiate, apices incurved, branchlets usually slightly curved, more or less acute or obtuse at 

 the apices, polysiphonous almost to the apex or terminating in a more or less prolonged monosiphonous 

 portion; pericentral cells 6 to 8 in the principal branches, divided once transversely, thus being half as 

 long as the central cells, segments about 0.5 to nearly i diameter long, no cortex; tetrasporangia in 

 stichidiumlike branchlets; cystocarps ovate, terminal on the short, naked, lower branchlets; color dull, 

 brownish purple. 



New England to Florida and West Indies. 



Very abundant in harbor, Southport, N. C., in brackish water, forming dense covering on wall 

 alongshore from high tide to 30 cm. below high-tide line, fairly abundant on shells alongshore, August, 

 1909. 



This species is easily recognized, having a structure superficially resembling that of Polysiphonia, 

 with regularly, alternately, distichously branched portions arising from creeping filaments, and tetra- 

 sporangial branches somewhat resembling the stichidia of Dasya. Its upright branches have a flattened 

 habit, and the main stems have a zigzag appearance, due to their manner of branching. It has not 

 been observed at Beaufort, but may be expected there in brackish water and in similar situations else- 

 where. 



Genus 6. Herposiphonia Naegeli. 



Herposiphonia, Naegeli, 1844, p. 238. 



Frond creeping, delicate, small, attached at intervals by short, rootlike filaments, 

 rarely entirely erect, terete or flattened, branching lateral, alternate, regular, long and 

 short branches sharply distinct, single, long, creeping branches' of unlimited growth 

 arising alternately in two rows from the flanks of the creeping filaments at each fourth 

 segment, single short erect branches of limited growth arising alternately in one or two 

 rows from the dorsal surface of the creeping filaments at all the other segments, creeping 

 filaments dorsiventrally constructed, revolute at the apices, erect filaments dorsiventrally 

 or radially constructed, at first revolute, later becoming straight at the apices and 

 bearing more or less evanescent trichoblasts; structure consisting of a central row of 

 cells surrounded by a circle of numerous (usually 12 to 18) pericentral cells, of the same 

 length, so that the frond has a segmented appearance, no cortex, growth monopodial, 

 " apical cell transversely or somewhat obliquely divided ; tetrasporangia occurring in more 

 or less broken single rows in the lower or middle portions of erect, short branches, covered 

 by special cover cells, triangularly divided; antheridia lanceolate or long elliptical, 

 attached by short, monosiphonous stalks to trichoblasts toward the apices of erect, 

 short branches; procarps borne on the trichoblasts at the apices of erect short branches; 

 cystocarps as in Polysiphonia. 



About 15 species, in warm seas. 

 Herposiphonia tenella (Agardh) Ambronn. PI. CX, fig. i. 



Hutchinsia tenella, Agardh, 1828, p. 103. 



Polysiphonia tenella, J. Agardh, 1842, p. 123. 



Polysiphonia pecten-Tienerisy&i. ft, Harvey, 1853. p. 46, pi. 16 D. 



Herposiphonia tenella, Ambronn, 1880, p. 162. ^ . .' 



Herposiphonia tenella, De Toni, 1903, p. 1051. 



P. B.-A. Nos. 1044, 1943. 



