NO. 10 DAWSON : MARINE ALGAE, GULF OF CALIFORNIA 329 



ing no main axis ; ultimate branchlets longest in lower parts, to 2.5 mm., 

 shorter toward ends of main branches, these often curved toward their 

 ends and the branchlets most abundant on the convex side, about 300 jn 

 thick ; cross section without a palisade cortex, with all cells of about equal 

 diameter; radius of about 4 series; ultimate ramuli slightly constricted 

 at base, simple, slightly clavate, their cells isodiametrical, not protruding; 

 color black upon drying. 



Type : D. 543a, lower littoral rock pockets, Agua Verde Bay, Feb. 

 12, 1940. Herb. AHF no. 60. 



The very small size of this species distinguishes it readily from all 

 others of our region and from the outer coasts as well. 



Genus POLYSIPHONIA Greville 

 Polysiphonia Marchantae S. & G. 



Setch. & Gard., 1924, p. 768, pi. 49a. 



M. 52, 83, 84, Eureka, May; M. 66, La Paz, May; Brand. 12, La 

 Paz; M. 50, Guaymas?, May. Specimens corresponding to these ex- 

 amples have not appeared in any recent collections. It seems likely that 

 the Guaymas record is erroneous. 



Polysiphonia Johnstonii S. & G. 



Setch. & Gard., 1924, p. 767. Polysiphonia sinicola, S. & G., 1924, p. 

 769. 



The following revised description has been drawn up by G. J. Hol- 

 lenberg after re-examination of the types and other Gulf specimens. 



Fronds relatively rigid, 5-10 cm. high, up to 1 mm. diam. toward the 

 base, attached by numerous rhizoids cut off from the pericentral cells of 

 a limited prostrate base; segments in the main branches 1.5 diam. long 

 or less, with 5 or 6 pericentral cells, totally ecorticate ; primary branches 

 several and distinct, repeatedly branched, the branches alternate, arising 

 at a moderately narrow angle ; ultimate branchlets usually relatively close 

 and dense; trichoblasts once or twice forked, numerous, arising one per 

 segment in a left-hand spiral with one-fifth or one-sixth divergence, soon 

 deciduous, leaving persistent scar-cells; branches replacing trichoblasts 

 at irregular intervals; tetrasporangia 1- (2) per segment, 70-90 fi diam.; 

 cystocarps numerous, globular, 450-500 jx diam., nearly sessile; anthe- 

 ridial branches arising as a primary branch of a trichoblast, 30-40 by 100- 

 140 /a; plants dull red to dark reddish brown, usually epiphytic. 



