NO. 1 DAWSON : MARINE RED ALGAE OF PACIFIC MEXICO 133 



Distribution: This plant is of very wide distribution on the 

 Pacific Coast from British Columbia to Baja California. In the Mexi- 

 can collections it has been found at virtually every intertidal station 

 along Pacific Baja California to as far south as Isla Magdalena. Un- 

 like Corallina gracilis it tends to occur more abundantly and to grow 

 more luxuriantly in areas of cooler rather than warmer waters along this 

 coast. 



A comparison of our common Pacific Coast plant with South Ameri- 

 can specimens and with examples of Corallina officinalis from various 

 parts of the world, has seemed to the writer to show such general con- 

 formity throughout all the collections as hardly to warrant recognizing 

 the Pacific American form as a distinct species. From the classical C. 

 officinalis L. of the North Atlantic, our plants differ only in a general 

 tendency to compound rather than simple pinnate branching and to 

 more pronounced, acute, upper intergenicular margins. Some variants 

 among our specimens are in fact quite indistinguishable from the typical 

 form of the species. 



Our specimens are coarser and less densely branched than either 

 Corallina vancouveriensis or C. gracilis. 



Lithothrix aspergillum J. E. Gray 



J. E. Gray, 1867, p. 33, figs, a-b; Manza, 1940, p. 296, pi. 10; 

 Smith, 1944, p. 231, pi. 53, fig. 3; Taylor, 1945, p. 184; Dawson, 

 1945b, p. 65. 



Thalli 3-10 cm. high, saxicolous, caespitose, tufted or bushy, consis- 

 ting of numerous erect branches from a basal horizontal stratum; erect 

 parts cylindrical or compressed above, abundantly branched, the primary 

 branching dichotomous, the secondary and subsequent orders in part 

 subpinnate, opposite or irregular and in part polystichous ; main axes 

 mostly 0.6-0.9 mm. in diameter, the ultimate branches 300-400 jx in dia- 

 meter; intergenicula mostly shorter than broad, shaped so as to produce 

 slight constrictions over the genicula which are completely hidden ; geni- 

 cula unizonal, very short, of cells only 12-15 //, long; intergenicular 

 medulla unizonal, of linear, straight cells; cortical cells subspherical, 

 arranged in longitudinal rows; tetrasporangial conceptacles hemispheri- 

 cal, 350-450 /A in diameter, projecting irregularly from the surface of 

 the intergenicula, with a single ostiole; tetrasporangia elongated, 80- 

 120 yu, long; sexual plants unknown. 



