NO. 2 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 273 



dense, small-celled cortex and a loose, filamentous medulla; cortex com- 

 posed of branched anticlinal filaments of usually 3 small cells 9-10 /* 

 in diameter, the outermost ones long-ovoid, the inner ± spherical ; sub- 

 cortex not conspicuous, consisting of sparse, arachnoid cells connected 

 by periclinal filaments ; medulla consisting of loosely arranged filaments 

 of elongate cells tending to be arranged for the greater part anticlinally, 

 but obliquely, apparently lacking filaments with highly refractive con- 

 tents; gonimoblast apparently developing from an auxiliary cell in a 

 system separate from that bearing the carpogonial branch, but the latter 

 not positively observed, the carpospore mass remaining pedicellate on the 

 auxiliary cell; cystocarps scattered, embedded, about 150 /a in diameter; 

 carpospores in a loose mass which readily falls apart, large, not con- 

 spicuously angular, 20-30 /i, in greatest diameter; antheridia and tetras- 

 porangia not seen. 



Type: Holotype is Dawson 6740, Mar. 13, 1949, on sheet 59313, 

 including vial 4179 and slide 2214 in HAHF. 



Type locality: Rock and sand bottom in depths of 8-15 m., bay 

 adjoining Punta Frailes, Baja California del Sur, Mexico. 



Additional material: D. 6904a, 6905, 8-18 m., Canal de San 

 Lorenzo, Baja Calif, del Sur. 



This species is distinguished from the superficially similar Halymenia 

 actinophysa by its sessile thalli, 3 tiered outer cortex, and by the large 

 size and loose massing of the carpospores. It occupies the same habitat as 

 H. actinophysa and sometimes is taken with that species in the dredge. 



The plants recognized by Okamura (1921, p. 109, pi. 176) as H. 

 dilatata Zanard, are similar in habit but differ in the mottled coloration 

 of the blades and in internal structure. Authentic Red Sea material of 

 H. dilatata has not been available for comparative study. 



Halymenia actinophysa Howe 

 PI. 4, figs. 29-34; pi. 15, figs. 59-60 ; pi. 16, fig. 61 



Howe 1911, p. 509, pi. 34; Dawson 1944, p. 277; Taylor 1945, p. 

 206. Halymenia? refugiensis Dawson 1944, p. 278, pi. 44, figs. 2-3. 



Thalli membranous, usually gelatinous, bright to dull rose in color; 

 blades ovate to irregularly orbicular or elongate-elliptical, sometimes 

 reniform, commonly 8-12 cm. long and 5-7 cm. wide, but attaining 30 

 cm. or more in length and 20 cm. in width, simple or occasionally lobed, 

 the margins entire or sinuate, cuneate at the base to a small, slender, 

 compressed stipe 1-3 mm. long and 300-500 fi in diameter; stipe attached 



