NEW MYXOPHYCKAE FROM PORTO RICO 



75 



turn outward, as in the group Myoehrotes. Tn cases in which 

 several successive periods of growth have followed each other 

 in rapid succession at the apices, the ocreate condition character- 

 istic of Petalonema appears. Rather unusual variability exists 

 in all of the characters of the species. The same filament may 

 be almost twice as thick in some parts as in others. The cells 

 may be very short, one-fourth the diameter long in the main 

 body of the trichome. They may be perfectly cylindrical or 

 dolioform in the older parts of the trichome. 



Scytonema magnum sp. nov. 



Plate 16, figure 31 



Filaments 400-fiOO p long, 24-32 m diam., densely interwoven, 

 forming a flocculent stratum 1-1.5 mm. thick ; trichoines 15-22 n 

 diam. ; cells cylindrical to dolioform, subquadrate in the meri- 

 stematic region, up to twice as long as the diameter in the older 

 parts, purplish gray, mostly homogeneous ; cross-walls thin but 

 distinct ; heterocysts numerous, of the same size and shape as the 

 cells, yellowish brown; sheath thick at first, hyaline and homo- 

 geneous, becoming yellowish brown and lamellose, the lamellae 

 not divergent, surface smooth. 



Growing on rocks in a brook about five kilometers north of 

 Utuado, no. 160.9, type; on rocks between Utuado and Adjuntas, 

 no. 1661. 



The material in the above-mentioned collections is well ad- 

 vanced in age, and the branching is very sparse, but as far as 

 observed, the branches are geminate. 



Scytonema punctatum sp. nov. 



Plate 16, figure 32 



Filaments loosely entangled into a floccose stratum 2-A mm. 

 thick, moderately tortuous, sparsely branched, 18-26 m diam. ; 

 trichome bright aeruginous, not constricted at the dissepiments, 

 14-18 M diam. throughout ; cells cylindrical, one-half to one-third 

 as long as the diameter at the apices, quadrate to twice as long 

 in the older parts of the trichome, very finely and more or less 

 densely granular ; walls thin and white ; heterocysts of the same 

 shape and size as the cells, slightly yellomsh ; sheath hyaline or 

 in extreme age yellowish, homogeneous, filled with very small 

 refringent granules, 2-3.8 \i thick. 



