NEW MYXOrHYCEAE FROM PORTO RICO 



45 



Phormidium autumnale minus var. nov. 



Tricliomes 3.6-4 [\ diam., sliglitly tapering- at the apices and 

 slightly uncinate ; cells quadrate to twice as long as broad ; apical 

 cell blunt-conical. 



Growing among other algae in a water reservoir at the Ex- 

 periment Station, Rio Piedras, no. 203, type. 



This form marks the lowest limit of the species in diameter 

 of the trichome. The cells average longer than in the species, 

 and the apical cell is conical instead of rounded-capitate. 



Growing in a waterfall between Arecibo and Utuado, no. 

 1460, type. 



Phormidium purpurascens homogeneum var. nov. 



Filaments forming a thin, compact, pale-purplish stratum; 

 tricliomes 1.2-1.5 m diam., pale purplish, not constricted ; cells 

 quadrate to one-half as long as the diameter, homogeneous; 

 cross-walls distinct ; apical cell blunt. 



Growing on rocks in warm water flowing from Coamo 

 Springs, no. 367; type. 



The above-described form differs from the species in lacking 

 granules at the cross-walls, in having the trichome smaller in 

 diameter, and the cells shorter. 



Phormidium durum sp. nov. 



Plate 9, figure 88 



Filaments aggregated into a loose, floccose stratum, long, 

 flexuous, rigid ; trichomes 12-14 p diam., neither constricted at 

 the dissepiments nor attenuated at the apices ; cells quadrate to 

 2 times as long as the diameter, homogeneous to finely granular 

 when old, pale purplish-gray ; cross-walls thin but very distinct ; 

 apical cell rounded, not capitate; sheath hyaline, changing to 

 reddish brown when old, homogeneous, smooth, rigid, 2-3 n 

 diam. 



Growing in flocculent masses among moss on shaded rock 

 near the Hacienda Catalina, near Palmer, no. 746, type; on 

 weathered rock near Humacao, no. 649. This latter collection 

 seems to belong to the same species as «o, 746 but is older and 

 the sheath thicker. 



