NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 255 



A large number of plants were found growing on a Polysiphonia taken 

 on shore at Turner's Island, D. 737, July. They are 30-50 fi high exclu- 

 sive of the long terminal hairs. 



Rhodochorton arcuatum Drew 



Drew, 1928, p. 165, pi. 37, figs. 1-3. 



Specimens growing on the surface of Sphacelaria are quite identical 

 with the figure given by Drew. The plants are hairless, about 50 p, long, 

 and consist of a few short branches of barrel-shaped cells. The plants may 

 be recognized further by the reclining position of the main branch in re- 

 lation to the host, always ascending at an acute angle (see Drew descrip- 

 tion, p. 165). 



D. 686d, on Sphacelaria jurcigera. Turner's Island, July. 



Rhodochorton Hancockii sp. nov. 

 Plate 41, Figs, 4-6 



Frondes epiph)^icae, per cellulam unicam basalem non-amplificatam affixae; 

 filis erectis 500-1500 n longis, 5-7 \x, latis, leviter attenuatis, cellulis 3-4-plo diam. 

 longioribus; filis sterilibus rare, filis fertilibus frequenter, ramosis; ramellis curtis, 

 secundis, vulgo simplicibus, 2 (-pauci)-cellularibus; monosporis vulgo in ramellis 

 Curtis lateralibusque terminalibus aut sessilibus, ovoideis, 6-7 |x diam., 10-11 Ji 

 longis. 



Plants epiphytic, attached to host by a single, unenlarged basal cell ; 

 erect filaments abundant and very close together, slender, 500-1500 \l 

 long, 5-7 ju, diam., slightly attenuated to apices, with cells 3-4 diameters 

 long, cylindrical; sterile filaments rarely or almost unbranched in some 

 specimens, more frequently in others; fertile filaments more frequently 

 branched, with short, lateral, secund branchlets in series; branchlets 

 mostly simple, 2 (or several) celled, narrowed to 4 ju, diam., the cells 1.5-2 

 diam. long; reproduction known only by monospores; sporangia mostly 

 terminal on the short, lateral branchlets, sometimes sessile, ovoid, 6-7 \l 

 diam., 10-11 /t long. 



Type: D. 218a, growing on Gelidium, from shore of Puerto Re- 

 fugio, Jan. 27, 1940. Herb. AHF no. 16. 



No other species has been described from the Pacific coast which has 

 the very long, simple branches and single unenlarged basal cell of this 

 plant. Many cross sections of the host have been made in endeavoring to 

 find penetrating filaments, but only the simple, epiphytic attachment of 

 the single cell has been seen in the type. The filaments arise, however, 

 densely over the whole surface of the host, innumerable simple strands at- 



