NEW MYXOPHYCEAE FROM PORTO RICO 



43 



Growing on rocks with Scijionona about ten kilometers north 

 of Utnado, no. 1565 a, type. 



Phormidium mucosum sp. nov. 



Plate 9, figure 84 



Filaments 7.2-7.8 m diam., long, straight, or arcuate and 

 smooth ; trichome 2.5-3 m diam., not constricted at the dissepi- 

 ments, neitlier uncinate nor capitate; cells 2-2.5 times as long as 

 the diameter, contents homogeneous, walls inconspicuous ; apical 

 cells rounded ; end wall not thickened perceptibly more than the 

 others ; color pale aeruginous ; sheath relatively thick, more or 

 less gelatinous, hyaline, homogeneous. 



Growing in a water basin in a garden in Humacao, no. 641, 

 type. 



The relatively thick and mucous or gelatinous sheath of 

 Phormidiiun mucosum as proposed above, reminds one of cer- 

 tain narrow species of T olypothrix and more particularly of cer- 

 tain species of HypheotJirix. It does not branch, and lacks the 

 closed and acute apices characteristic of many species of the 

 latter genus. It is apparently not abundant. 



Phormidium leptodermum capitatum var. nov. 



Plate 9, figure 85 



Filaments forming a dense caespitose stratum, long and 

 more or less flexuous, 6-6.5 |j diam. ; trichomes pale aeruginous, 

 5-5.4 M diam., slightly constricted at the dissepiments ; apices 

 straight, very slightly attenuated ; cells quadrate to one-half the 

 diameter long, homogeneous ; cross-walls very thin and obscure ; 

 end cell slightly tapering, blunt ; terminal wall thickened ; sheath 

 very thin, smooth, distinct, not diffluent. 



Growing on rocks in a stream of warm water, Coamo Springs, 

 no. 364, type. 



The variety differs from the species chiefly in the possession 

 of a thickened end cell wall. 



Phormidium rubriterricola sp. nov. 



Plate 9, figure 86 



Trichomes 2.2-2.4 m diam., short, not constricted, apices 

 straight; cells quadrate to slightly longer or shorter, contents 



