68 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



rhizoids, 3-6 mm. high, the segments 100-300 /x in diam., dichotomously 

 branched, corticated only at the nodes; corticating bands composed of 

 approximately 5 horizontal rows of cells, although these are quite angular 

 and irregularly placed, truncate on the lower side and the cells somewhat 

 elongated and irregular on the upper side of the band, the band not 

 swollen and the branches, thus, smooth on the margins; cells of axial 

 filament subspherical, slightly longer than broad; tetrasporangia pro- 

 truding on both adaxial and abaxial sides of the branches, sometimes in 

 whorls of 3-4 at a node, not bracteate; spermatangia in low, pulvinate, 

 adaxial patches at the nodes on upper segments; cystocarps lateral on 

 upper branches, surrounded by involucral branchlets. 



Type: J. T. Howell 757, August 14, 1932, in Herb. California 

 Academy of Sciences (236529). 



Type locality: Growing on Codium fragile, Bahia San 

 Bartolome (Tortuga), Baja California, Mexico. 



Mexican distribution: Pacific Baja Calif. — Hubbs 8/2/46, Isla 

 Cedros; D. 20164 (Neushul), Punta Abreojos, 13 m.; D. 16154 (Lim- 

 baugh), Rocas Alijos. Gulf of Calif. — D. 18837, Bahia Agua Verde. 



Centroceras clavulatum (C. Ag.) Mont. 

 PI. 26, fig. 7; PL 27, fig. 3 

 Montagne, in Durieu 1846, p. 140; Howe 1922, p. 509; Setchell & Gardner 

 1924, p. 779; Dawson 1944, p. 321; Dawson 1945, p. 62, 67; Dawson 1949, 

 p. 224, 235; Dawson 1951, p. 53; Taylor 1945, p. 272. Ceramium clavulatum C. 

 A. Agardh, in Kunth 1822, p. 2. 



Thalli 2-3 cm. high or more, densely tufted, epiphytic or saxicolous, 

 dull reddish, dichotomously branched with the two arms of each 

 dichotomy equal in length and diverging 10-15° ; axes 150-200 /a in 

 diam., segmented, the internodes 300-600 /x long, corticated by small cells 

 in regular longitudinal rows; nodes with a whorl of 1-2-celled spines; 

 apices forcipate or circinate; tetrasporangia about 50 /x in diam., 

 whorled at the nodes, emergent; sexual plants not seen. 



Types A Humbolt & Bonpland specimen, in the Agardh Herbar- 

 ium at Lund, Sweden (according to Howe). 



Type locality: Callao, Peru. 



Mexican distribution: This species is present throughout the 

 entire Mexican coast from northwestern Baja California and the upper 

 Gulf of California to Oaxaca. The following are a few representative 

 collections: Pacific Baja Calif. — D. 8183, Isla Guadalupe; D. 8786, 

 Bahia San Quintin; D. 8703, Punta Baja; D. 10398, Punta San 

 Eugenio; D. 6623, Bahia Magdalena. Gulf of Calif. — Johnson 144, Isla 

 Tortuga; D. 7069, Isla Carmen; D. 11040, near Guaymas; Marchant 

 87, Eureka. Islas Tres Marias— Taylor 39-634, Isla Maria Magdalena. 

 Sinaloa—D. 10956, Bahia Topolobampo; D. 10925, Mazatlan. Nayarit — 



