NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 81 



tic, stipitate blades 2.0-2.5 mm. broad with strongly developed midribs 

 extending to within 200-600 fx of the tips; branching of new blades 

 from lower stipe parts or occasionally from the midrib of a blade; 

 young blades obovate, becoming vaguely palmate: sometimes eroding 

 early to leave the persistent midrib, with entire margins above except for 

 occasional production of rhizoidal outgrowths from the margins, more 

 or less undulate and with rounded apices; midrib 200-300 /x thick, 

 consisting in transection of a group of subspherical, colorless medullary 

 cells 30-50 [x in diam. and a pigmented cortex of smaller cells more 

 or less like those of the blade, without rhizoidal filaments; growth from 

 a group of terminal initials; blade cells in surface view 6-12 /x in 

 greatest diameter; tetrasporangia borne in sori usually occuring as a 

 single, broadly rounded patch in the middle or upper part of a blade and 

 occupying most of its width. 



Type: E. Y. Dawson 1008, Feb. 22, 1946, in Herb. A. Hancock 

 Foundation (5361). 



Type locality: Intertidal rocks, Isla Partida, Gulf of Calif. 



Mexican distribution: Pacific Baja Calif. — D. 10448, 12 mi. 

 east of Punta Eugenio, Bahia Vizcaino. Gulf of Calif. — D. 853, 861, Isla 

 Jorge; D. 738, 755, Isla Patos; D. 18568, Isla San Pedro Nolasco, on 

 thin sponges at 1-2 m.; D. 18873, El Solitario, Bahia Agua Verde; D. 

 18673, Isla Cholla, off Isla Carmen. 



This species closely resembles Myriogramme subdichotoma Segawa, 

 but seems to differ in its less extensive dichotomy and in its large, 

 usually solitary tetrasporangial sori occupying the greater part of the 

 breadth of a fertile segment. 



Platysiphonia clevelandii (Farlow) Papenfuss 

 PI. 39, fig. 4; PI. 40, fig. 1 

 Papenfuss 1944, p. 206; Silva & Cleary 1954, p. 258-259, fig. 27a. Taenioma 

 clevelandii Farlow 1877, p. 236. 



Thalli epiphytic or entangled, attached by rhizoids, to 2 cm. in 

 extent, consisting of ligulate acuminate blades 90-175 /x broad branched 

 dorsiventrally from the center line of each blade; blades 5 cells broad, 

 composed of a central axial cell row surrounded by four pericentral 

 cells, each lateral pericentral cell flanked by two cells; base of branches 

 with lower two segments lacking flanking cells; tetrasporangia produced 

 in ultimate blades by acropetal succession, in two longitudinal rows, 

 one sporangium by each lateral pericentral cell and bordered 

 by two flanking cells which divide vertically to produce two more ; sexual 

 plants not seen. 



Type: A collection by Daniel Cleveland in the Farlow Herbarium, 

 Harvard University. 



Type locality: San Diego, California. 



