268 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 17 



4. Cortical cells 5 jx or less in greatest surface diameter; a thick 



surface jelly present H. abyssicola 



4. Cortical cells 7 /x or more in greatest surface diameter; a 



thick surface jelly absent 5 



5. Thalli nearly sessile; carpospores loosely massed, 20-30 /u, in 



greatest diameter H. megaspora 



5. Thalli short-stipitate ; carpospores compactly massed, 9-12 /a in 

 greatest diameter H. actinophysa 



Halymenia agardhii De Toni 

 PI. 11, fig. 54 



DeToni 1905, p. 1542; Taylor 1945, p. 205. Isymenia flabellata 

 nom. nud. in J. Agardh 1899, p. 66. Chrysymenia dichotomo-flabellata 

 nom. nud. in Maze and Schramn 1870-77, p. 162. 



Thallus to 11 cm. high or more, light rose in color, soft in texture, 

 dichotomously branched at intervals of 10-15 (25) mm., the branches 

 subterete, 4-6 (9) mm. in diameter, the apices blunt; structurally con- 

 sisting in younger parts of a single pigmented cortical layer of small, 

 ovate to angular cells mostly less than 5 /* in greatest diameter, these 

 surrounding a colorless, gelatinous, medullary area through w^hich run 

 sparse, slender, ramified filaments with frequent ganglia-like junction 

 points ; older parts with a subcortex present of about 2 layers of rotund, 

 colorless cells to 25 /x in diameter, the adjacent 100 /i of the outer me- 

 dulla composed of densely intertwined, mainly longitudinal, thick-walled 

 filaments about 11 /x in diameter, the inner medulla of relatively sparse 

 filaments crossing irregularly from one side to the other, some of them 

 stellate-ganglioid and to 10 /x in diameter; tetrasporangia cruciate, 

 scattered through the unmodified cortex, but much larger than the 

 cortical cells, 25-30 ju, long, 13-16 /x wide; sexual plants not present in 

 the Mexican material. 



Type: Holotype not designated. The syntypes represented by the 

 original collections cited by Maze and Schramn, no. 20, 1015, and 1334 

 are in the Thuret-Bornet Herbarium, Natural History Museum, Paris, 

 France. 



Type locality: Sublittoral, He de la Guadaloupe, West Indies. 



Mexican distribution: Nayarit — Taylor 39-646A, dredged 

 from coralline bottom at 21.5 m., near Isla Maria Magdalena, Las Tres 

 Marias, May. 



This species has been reported from the sublittoral in widely scattered 

 localities of the world. Suitably preserved sexual reproductive material 



