NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 243 



of a markedly foliaceous extension 1-3 times as long as the bladder. The 

 upper leaves are large, strongly one-sided on most specimens, and boldly 

 dentate. 



A specimen collected in December by MacDougal at Puerto Libertad 

 is recognized as the same as D. 383 from Tepoca Bay and D. & R. 3392 

 from Guaymas. These three examples, though immature and sterile, have 

 leaves on the lower parts of the primary stems sufficiently different from 

 the other species of this group that it seems well to distinguish the species 

 Sargassum MacDougalii. The proposal is tentative, however, awaiting 

 the collection of more mature material. The nature of the branching, the 

 parenchymatous holdfast, and the short, slender stipe as well as the gen- 

 eral character of the leaves are in perfect congruity with the lapazeanum- 

 complex. 



A comparative study of juvenile specimens of the several species of 

 this group suggests strongly that distinctive characters are evident in the 

 early developmental stages of these plants. 



Sargassum lapazeanum S. & G. 



Plate 34, Figs. 1-34 



Setch. & Gard., 1924, p. 733, pi. 20, f^g. 74. Sargassum Bryantii S. & G., 

 1924, p. 733, pi. 21, fig. 83. Sargassum insulare S. & G., 1924, 

 p. 735, pi. 20, figs. 67, 68, pi. 21, fig. 78. 



Fronds 4.5-6 dm. high, arising from a solid, parenchymatous disk; 

 stipe about 1 cm. long; primary branches terete, smooth, becoming con- 

 fused above in the secondary branches which are equally long ; leaves 0.5- 

 1.25 cm. long, essentially ecostate, asymmetrical, widest above the middle, 

 with very short petioles, the basal half of the upper margin smooth and 

 concave, the remainder of the blade sharply dentate, cryptostomata usu- 

 ally quite abundant and conspicuous; vesicles ellipsoidal, 4-6 mm. long 

 overall, the bladder 1.5-3 mm. crowned or rimmed by foliar remnants 

 which form a crest; receptacles in 2-4 times closely branched, usually 

 more or less heteroclyte inflorescences, the antheridial receptacles some- 

 what more broadly branched and smaller in diameter than oogonial, va- 

 riously and quite abundantly denticulate in both sexes. 



M. 21, 24, cast ashore. Eureka, May; Bryant 5, La Paz; M. -, Guay- 

 mas, Aug.; J. 20, Tortuga Island, June; J. 10, 11, San Marcos Island, 

 June; D. 712, lower littoral rocky reef. Turner's Island, July (all young 

 but seem to have the juvenile characters of this species) ; D. 746 from 

 same locality seems to be very old, dying or mostly disintegrating speci- 

 mens of the same species. 



