NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 245 



Sargassum MacDougalii sp. nov. 

 Plate 35, Figs, 1-8; Plate 36, Figs. 1-7; Plate 37, Figs. 27-30 



Frondes axi primaria gracili, 1 era. longa, a disco parenchyraatico, affixa; 

 ramis primariis paucis, teretibus, levibus, usque ad 5 dm. continuis; foliis ramorum 

 primariorum ecostatis, asymmetricis, 4-8 mm. longis, 0.6 usque ad quam latis quara 

 longis, acute-denticulatis, cryptostomatibus deuntibus ; foliis superis usque ad 2 cm. 

 longis; vesiculis elHpticis extensionibus foliaceis coronatis. 



Primary stems several, terete, smooth, continuous as main axes to at 

 least 5 dm., from a slender stipe 1 cm. long, attached by a small paren- 

 chymatous disk-holdfast; leaves of lower parts of primary branches ecos- 

 tate, asymmetrical, small, 4-8 mm. long, 0.6 to nearly as broad as long, 

 lower halves of upper sides smooth, concave, the remainder of blade 

 sharply denticulate especially at apices; cryptostomata absent; upper 

 leaves the same but longer and larger, to 2 cm.; vesicles elliptical with 

 dentate foliar extensions about as long as the bladder; mature plants with 

 receptacles unknown. 



Type: MacDougal (U.C. 615657; isotype AHF no. 14), Puerto 

 Libertad, Sonora, December, 1923. 



D. 383, rocky shore, Tepoca Bay, Feb.; D, & R. 3392, in deep rock 

 pools, Punta San Pedro, near Guaymas, Dec. 



D. & R. 3287 and 3311, cast up on shore near Guaymas, December, 

 are very probably of this species, but due to prolonged floating habit have 

 become very lax and all parts attenuated. 



III. The Sinicola Group 



Plates 38, 39 



Leaves expanded, symmetrical, costate, irregularly and more or less 

 strongly dentate or dentate-serrate, usually with abundant cryptostomata ; 

 vesicles mostly spherical, often with cryptostomata. 



The largest and most variable assemblage of Sargassum forms in the 

 Gulf of California is that which falls under the above characterization. 



The spiny receptacles of Sargassum horridum and S. Marchantae 

 were among the first subjects to be investigated in this group. They were 

 soon found to belong to the same entity, S. horridum being a spiny oogoni- 

 al plant, S. Marchantae, a spiny antheridial plant. Since the former name 

 appears first in the 1924 account, according to article 56 of the Inter- 

 national Rules, it is here adopted. Both plants were of the same collec- 

 tion. Eureka, Lower California. 



The macrospecies, Sargassum sinicola, probably the commonest and 

 most widespread in the region, has, on the whole, smooth receptacles, 



