42 Allan Hancock Pacific Expeditions vol. 26 



shorter again (about 1.5 diameters) above; branching alternate, distich- 

 ous, not from every cell ; primary branches commonly barren of branches 

 in lower and mid-parts, provided with distichous, alternate determinate 

 lateral branchlets from each cell above; determinate lateral branchlets 

 usually simple, of 15-30 cells, strongly incurved, somewhat corymbose, 

 40-70 ix in diam. at the base, of cells 1-2 diameters long, gradually 

 reduced (but not attenuated) to a blunt tip, the basal cell only a little 

 shorter than the others; polysporangia seriate, sessile, adaxial on the 

 determinate laterals, broadly ovoid, about 90 [x in diam. including the 

 thick envelope, with about 32 spores; sexual reproduction not seen. 



Type: Hollotype is E. Y. Dawson 3610, Dec. 8, 1946, in Herb. 

 Beaudette Foundation. 



Type locality: Lowermost intertidal on small reef 3 km. north 

 of Belmar Hotel (Playa de Olas Atlas), Mazatlan, Sinaloa, Mexico. 



Additional material: Pacific Baja Calif. — D. 8450, Isla 

 Guadalupe (not corymbose and the branchlets little incurved, but other- 

 wise similar). Gulf of Calif. — D. 851a, Isla Jorge; D. 789, Isla Patos; 

 D. 1004, Isla Partida; D. 680, Puerto Libertad; D. 21691, 21705, Bahia 

 Bocochibampo, near Guaymas. Sinaloa — D. 3591, D. 3657, D. 3666, D. 

 3632, D. 10834, Mazatlan. Nayarit— D. 10860, 10861, 10875, Mira Mar. 



The long, usually simple, strongly incurved and =fc corymbose 

 determinate branchlets are distinctive in this species as is also the barren 

 condition of the lower parts of the primary branches from the principal 

 axes. 



Pleonosporium pygmaeum Gard. 

 Gardner 1927a, p. 379, pi. 79, fig. 2, pi. 80. 



This appears to be a dwarfish, little-corticated variant of Pleono- 

 sporium dasyoides and may ultimately be reduced. It is recognized by 

 its smaller stature (6-20 mm.) and the restriction of corticating filaments 

 to the very base. A single collection available to me (D. 8010 from 30-38 

 m. at Cortes Bank) agrees with Gardner's description but does not lend 

 credence to specific recognition. 



Pleonosporium rhizoideum sp. nov. 

 PI. 14, fig. 1-3; Pi. 17, fig. 7 

 Thalli penicillatim ramosi, ad 2.5 cm. alt., constantes ex axibus multis 

 ramosis erectis, e massa conferta coacta rhizoiderorum adhaerentium formantium, 

 orientibus; axes erecti ad basim 125-170 /i diam., in partibus inferioribus per 

 rhizoidea implicata plus minusve laxe vestiti, e cellulis (1) 1.5-2.0 plo longiori- 

 bus quam latae, admodum distiche ramosis compositi, rami magna ex parte sim- 

 plices longissimi, primum valde incurvati deinde irregulariter curvati recurva- 

 tive, paululum imbricati (interdum extrema in parte uncinati) 60-70 fi diam., 

 paulum attenuati, cacuminibus acutius reductis sed obtusis, ad formandum 

 rhizoideum interdum productis; polysporangia in partibus thalli propriis 

 dense ramosis nata, ramis brevibus irregularibus, polysporangia aggregata 

 alterna sessilia spherica, c. 60 /j. diam., 32 sporas continentia, ferentibus; 



