NO. 1 DAWSON: MARINE RED ALGAE OF PACIFIC MEXICO 41 



Descanso; D. 68, D. 5179, D. 6482, D. 6483, Cabo Colnett (intertidal) ; 

 D. 8915, Punta Baja (intertidal); D. 9765 Bahia Blanca (18-30 m.). 



Pleonosporium globuliferum Levr. 

 PI. 15, fig. 2-6 

 Levring 1941, p. 647, fig. 19; Dawson 1960, p. 50 



Thalli 6-7 mm. high (epiphytic, often on C odium) , attached by a 

 group of branched, multicellular, penetrating rhizoids, tufted, consisting 

 of several erect, multifariously branched axes; primary axes uncorti- 

 cated, 70-110 fi in diam. of cells 1.0-1.5 diameters long near the base, 

 longer (to 4 diameters) above; branching multifarious throughout, the 

 determinate lateral branches 1 mm. long or more, ascending and 

 somewhat incurved, about 30 /a in diam. at the base, of cells 3-4 

 diameters long, tapering to about 12 /jl in diam., the tips blunt; 

 polysporangia sessile, subspherical, scattered along lateral branches, 

 mainly adaxial, about 40 ft in diam. ; spermatangial clusters subcylindri- 

 cal, about 80 ll long, 30 p. in diam., sessile along adaxial side of lateral 

 branchlets. 



Type: A collection by Carl Skottsberg, 14 March, 1917, in the 

 Herbarium of the Botanical Garden, Goteborg, Sweden. 



Type locality: "ausserhalb Sanchez, Masafuera" Island, Islas 

 Juan Fernandez, Chile. 



Mexican Distribution: Pacific Baja Calif. — D. 8521 (on Codium, 

 intertidal, D. 8237 (on Sargassum, 6-29 m.), Isla Guadalupe. South- 

 eastern Baja Calif. — D. 3093, Cabo Pulmo, on Sargassum. Oaxaca — 

 D. 21433, Puerto Guatulco. 



Pleonosporium mexicanum sp. nov. 

 PI. 16, fig. 1 



Thalli 2-5 cm. alt., fruticosi, abunde ramosi, constantes ex axibus multis e 

 basi per rhizoidea affixa orientibus; axes ecorticati 120-200 /j. diam., sursum gra- 

 datim reducti, cellulis longitudine variantibus, saepe in partibus infimis aeque 

 longis ac latis, in partibus mediis 2-4 plo longioribus quam latae, supra breviores 

 rursus (c. 1.5 plo longioribus quam latae); alterni distichi, non ex omni 

 cellula orientes; rami primarii plerumque sine ramis in partibus inferioribus 

 mediisque, supra ramulis lateralibus distichis alternis determinatisque ex omni 

 cellula praediti; ramuli determinati laterales plerumque simplices, e 15-30 

 cellulis compositi, valde incurvati satis corymbosi ad basim 40-70 /i diam., e 

 cellulis 1-2 plo longiorbus quam latae compositi, ad cacumen obtusum gradatim 

 reducti, (non, autem, attenuati, cellula basali paulo breviore quam aliae; poly- 

 sporangia seriata sessilia, in ramulis lateralibus determinatis adaxilalia, late 

 ovata, cum involucro crasso c. 90 fi diam., c. 32 sporas habentia; reproductio 

 sexualis non visa. 



Thalli 2-5 cm. tall, bushy, abundantly branched, consisting of num- 

 erous axes from a rhizoidially attached base; axes ecorticate, 120-200 [x 

 in diam., gradually reduced upwards, the cells of variable length, often 1 

 diam. long in lowermost parts and to 2-4 diameters long in mid-parts 



