NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 89 



Leptocladia laxa Taylor 



Plate 6, fig. 7 



Taylor, 1945, p. 163, pi. 38, fig. 1. 



Thalli 12-15 mm. tall, almost wiry, blackish-red in color, gregarious 

 from a small, discoid holdfast, irregularly and alternately polystichously 

 branched, 2-5 branches occasionally arising close together, terete or 

 slightly compressed, 0.5-1.5 mm. in diameter below, 300-500 fi above; 

 branches more or less erect, the upper divisions often with short, spine- 

 like branchlets; apices subacute, with an apical cell; internal structure 

 consisting of a large central axial filament of thick-walled elongated cells 

 to 100 ju. or more in diameter surrounded by a dense central medullary 

 core about 200 /a in diameter of cells of variable diameter (7-18 ju.) and 

 length, mostly distinctly elongated and in part somewhat tending to inter- 

 lace, this core surrounded by the bulk of the medulla of isodiametrical, 

 pseudoparenchymatous cells 40-50 fi in diameter and grading into the 

 subcortex of smaller, similarly shaped cells under \5 fx in diameter; cor- 

 tex at first of a single row of more or less quadrate cells 5-6 fx, in dia- 

 meter, later 70-125 fi thick, of a compact tissue of anticlinal rows of 

 7-10 cells 10-12 /x in tangential diameter, 12-15 ju, in radial diameter; 

 reproduction unknown. 



Type: Holotype is Taylor 603-34, Mar. 7, 1934, on sheet 172, 

 including slides 1428-1431, in HAHF. 



Type locality: Dredged off Punta Hughes, Isla Magdalena, 

 Baja California, Mexico. 



The filaments described by Taylor as invading the central axial cell 

 row have not been detected either in young or old parts of the type and 

 may be presumed not to constitute a constant character. 



The peculiarities of structure as well as the terete form and poly- 

 stichous branching indicate that this plant may prove to represent a dis- 

 tinct group in the Dumontiaceae apart from both Leptocladia and Pikea. 



Leptocladia bingharniae J. Agardh 

 Plate 6, fig. 8 ; Plate 23, fig. 2 



J. Agardh, 1892, p. 96; Setchell, 1912, p. 250; Kylin, 1941, p. 8; 

 Dawson, 1945b, p. 60. Pikea nootkana (Esper) Doty, as employed by 

 Dawson, 1949, p. 219, 229. 



Thalli 15-30 cm. high, consisting of one or more deliquescent axes 

 from a simple, discoid holdfast; axis repeatedly, irregularly, alternately 

 or pseudodichotomously, distichously branched in 4-5 orders, 1.5-3.0 



