74 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 12 



the rocky point, no. 39-47, 17 Mar. 1939. Nayarft, dredged from 22 

 meters' depth at sta. 970 near I. Maria Magdalena, Las Tres Marias, 

 no. 39-657, 9 May 1939. 



Halimeda discoidea, forma 



The segments deltoid with the forward margin rounded. 

 Costa Rica: scarce, in rock crevices and lower tide pools, Golfo 

 Dulce, no. 39-96. 26 Mar. 1939. 



Halimeda Tuna (Ellis & Solander) Lamouroux 



Barton 1901, p. 11, pi. 1, figs. 1, 4, 6; Collins 1909, p. 400; Taylor 

 1928, p. 85, pi. 10, fig. 8. 



Mexico: Is. Revilla Gigedo, rather scarce, mixed with but extending 

 lower than the Caulerpa beds. Sulphur Bay, I. Clarion, no. 39-12, 16 

 May 1939. 



Derbesiaceae 



Plants matted or tufted, with a creeping rhizomatous portion bearing 

 attaching holdfasts and generally erect simple or branched assimilative 

 filaments ; sporangia lateral on the erect or upper free filaments, develop- 

 ing several zoospores, each with an anterior circle of fiagella. 



DERBESIASolier, 1847 

 KEY TO SPECIES 



1. Forming mats without particularly distinct erect filaments; fila- 

 ments 75 n diam. or less ; sporangia less than 100 ju, diam . . . 

 D. longifructa 



1. At least part of the plant erect and tufted; filaments generally 

 100 IX diam. or more ; mature sporangia exceeding 100 /x diam. 2 



2. Zoosporangia numerous, seriate, subspherical . . . D. prolifica 

 2. Zoosporangia few on an axis, turbinate . . . . D. Hollenbergii 



Derbesia longifructa n. sp.^^ 

 Plate 1, Figs. 3-6 



Plant matted, without particularly distinct erect filaments, near the 

 free tips often curved, dichotomously and laterally branched, 38-75 /* 

 diam., with crosswalls at the divisions infrequent; zoosporangia scattered 



f>6 Derbesia longifructa n. sp.— Planta implecta, filamentis erectis subdistinctis, 

 prope cacumina saepe curvatis, dichotome lateraliterque ramosis, 38-75 ii diam.; 

 zoosporangiis dispersis aut ad 4 simul, in stipitibus obliquiter positis, 14-17 \i 

 diarn ; sporangiis cylindrico-ovatis, 58-90 n diam., 121-180 ]i long. Planta typica in 

 loco dicto Pta. Santa Elena, Salinas, Guayas, Ecuador, legit W. R. Taylor no. 

 34-464, 8 Feb. 1934. 



