NEW MYXOPHYCEAE FROM PORTO RICO 



83 



ture of the sheath at that point in the filament ; sheath very thin, 

 smooth, liomoi>-eneous, fj,()klen yellow; branching- sparse. 



Growing on hark along the road near Coamo Springs, no. 

 1913, type. 



The medium size of the filaments, the thin, close-fitting col- 

 ored sheath, and the pale-colored cells densely congested with 

 granules distinguish this species of Hassalia from others. In 

 size it is between Scytonema Hofmanni and S. javanicum, but 

 the branching is all single under the heterocysts, a typical 

 Hassalia. 



Hassalia heterogenea sp. nov. 



PlATE 19, FIGURE 42 



Filaments very short, much contorted, with smooth, gentle 

 curves, moderately branched, about equally single and geminate 

 branching, soon recurving, 13-16 n diam. ; trichomes 9.5-13 n 

 diam., not constricted at the dissepiments, or only moderately so 

 in part; cells quadrate in the older parts, one-half to one-fourth 

 as long- as the diameter at the apices, pale aeruginous, homo- 

 geneous ; heterocysts of the same shape and size as the contigu- 

 ous cells ; not abundant ; sheath close-fitting, thin, homogeneous, 

 dark brown. 



Gro"wdng on rocks at Hacienda Holm, Mayagiiez, no. 1191, 

 type; on lava rock at Coamo Springs, nos. 1923 a and 1921. 



The above-described species might be almost equally well 

 placed in either Scytonema or Hassalia. On account of its di- 

 minutive size and short branches I have placed it in the latter 

 genus. 



Hassalia discoidea sp. nov. 



Plate 19, figure 43 



Filaments scattered among- other algae, not forming- a defi- 

 nite stratum alone, relatively short, comparatively straight, 

 22-25 n diam. in main filaments, less in the branches ; branch- 

 ing moderately frequent, simple under the heterocysts and ap- 

 pressed ; trichomes much constricted at the dissepiments, 17-20 m 

 diam., uniform throughout the entire length ; cells discoid, 4—6 \i 

 long, or slightly longer in the oldest parts, bright blue-green 

 or methyl green, finely granular ; heterocysts of the same shape 

 and size as the cells, golden yelloAv, numerous ; sheath 2-3 p thick, 

 smooth, homogeneous, hyaline, changing to yellowish. 



