NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 149 



Mexican distribution: Oaxaca — ^Taylor 34-555, Tangola-Tan- 

 gola, Feb. 



At least three other collections, including material from La Paz, 

 Baja California and from Acapulco, Guerrero, have enough in common 

 with Taylor's specimen to permit them to be mentioned here. 



Taylor's number 30 from Isia Socorro, Revillagigedo Archipelago, 

 referred by him to this species in 1945, is fragmentary and includes por- 

 tions of other species. Taylor 39-56 from the same locality is probably 

 the same and may represent a form of Amphiroa crosslandii, although 

 the terminal segments tend to be narrow and not much compressed. 



The presumably distinctive features of this small, flattened species 

 appear to be the usually decumbent branches, and the irregularly forked, 

 flattened, usually terminally expanded segments. The limits of the species 

 are, however, not clearly defined and additional material from the type 

 locality will be required for ultimate clarification of its circumscription 

 among the several Pacific American amphiroas. The several varied ex- 

 amples recognized below under A. franciscana show considerable 

 similarity in size and habit. 



Amphiroa franciscana Taylor 



Taylor, 1945, p. 187, pi. 48, fig. 2, pi. 49. Amphiroa fragilissima 

 (L.) Lamx., as interpreted by Setchell & Gardner, 1930, p. 178. 



Thalli 1.5-2.5 cm. high, forming close clumps on shells or nullipores, 

 from an inconspicuous crustose base, abundantly, irregularly dichotom- 

 ously branched, the branches rather erect, or divaricate and somewhat 

 reflexed; segments mostly compressed or flattened, especially in mid- 

 parts, cylindrical or subcylindrical in uppermost parts, 250-350 (400) /£ 

 broad, mostly 1-3 mm. long, sometimes simple, but usually once or some- 

 times twice forked ; apices truncate or blunt ; younger segments distinctly 

 annulate; genicula usually consisting of two tiers of long cells and of a 

 cortical tissue which becomes split ; intergenicular medulla usually show- 

 ing 3-4 tiers of long cells alternating with one short tier; cortex thin, 

 of about two layers of small cells apparently with little or no secondary 

 growth; tetrasporangial and carposporangial conceptacles prominent, 

 hemispherical, superficial, and 250 /a in diameter, more or less confined to 

 the margins of the flattened segments, or irregularly distributed on all 

 sides. 



Type: Holotype is Taylor 34-484, Feb. 11, 1934, in box 3616 and 

 on slide 1470 in HAHF. 



