14 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 26 



43. Thallus minute, ranging from 1-2 mm in height; cells of main 

 axes 40-50 p. in diameter A. breviramosus Dawson 



43. Thallus ranging from 0.5-8 cm in height; cells of main axes 



over 100 fx in diameter 44 



44. Gland cells on the terminal cells of lateral branches .... 



A. terminate Inagaki 2 



44. Gland cells lateral or basal on lateral branches and 



branchlets 45 



45. Basal cells of primary ramuli not giving rise to such fila- 

 ments to long, cylindrical, slightly tapering, variously curved 

 filaments A. similans Gardner 



45. Basal cells of primary ramuli not giving rise to such filaments 

 A. occidentale Kylin 



Antithamnion breviramosus Daws. 

 PI. 5, fig. 3; PI. 15, fig. 1 

 Dawson 1949, p. 14-15, fig. 28, 57; Dawson, 1954, p. 342; Dawson 1957a, p. 7; 

 Dawson 1959, p. 28; Dawson 1960, p. 50. 



Thallus minute, commonly epiphytic, consisting of a branched 

 prostrate axis ca. 3-5 mm in extent attached at frequent intervals by 

 simple, mostly unicellular rhizoids from the basal cell of determinate 

 ramuli, the prostrate axes giving rise to erect axes 2-3 mm high; 

 principal axes producing determinate branches in whorls of 3 from the 

 distal end of the axial cells; axial cells 40-50 fi in diameter, 4-5 

 diameters long; determinate branches sometimes simple, commonly 

 with 1-3 forkings, directed upward and adaxially curved, 10-15 /a in 

 diameter, the cells mosty 2-3 diameters long, the basalmost cell shorter, 

 the tips usually blunt, at least not sharply pointed; gland cells frequent 

 on determinate branchlets, each arising from a single cell; reproduction 

 unknown. 



Type: Dawson 4920, March 24, 1948 in Herb. Allan Hancock 

 Foundation 26521. 



Type locality: Epiphytic on Sargassum palmeri in drift, Pebbly 

 Beach, near Avalon, Santa Catalina Island, Calif. 



Mexican distribution: Pacific Baja Calif. — D. 13301, Isla Mag- 

 dalena, Belcher Pt., 12 m. Gulf of Calif.— D. 681, Puerto Libertad; D. 

 512, 1940, 1983, 3542, vicinity of Guaymas; D. 10964, Bahia Topolo- 

 bampo. Colima — D. 21316, Bahia Santiago, 8 m. 



Costa Rica:— Hancock Exp. 465-35, 2/8/35, D. 10736, Playa 

 Blanca. These are near A. breviramosus var. simplex Dawson (1957a, 

 P- 117). 



2 The reduced nature of one opposite pair of the four verticillate branches from 

 each node suggests that this species could equally well be placed in Platytham- 

 nion. 



