NEW MYXOPHYCEAE FROM: PORTO RICO 



77 



grannies; cross-walls distinct, thin; lieterocysts of the same 

 shape and size as the cells ; sheath at first homogeneous and hya- 

 line, becoming lamellose and various shades of brown when 

 older, smooth, firm. 



Growing on rocks by a stream, Utuado, no. 1574, type ; on 

 rocks, near Utuado, no. 1494, collected by Elizabeth G. Britton ; 

 on earth, Utuado, no. 1501 a ; among moss, etc., three kilometers 

 north of Utuado, 7io. 1605. 



Scytonema pulchelluni is apparently closely related to S. 

 ocellatum Lyngb. but may be distinguished from it by the thick, 

 smooth, lamellose sheath, resembling that of 8. guyanense 

 (Mont.) Born. & Flah., and by the long cylindrical cells in the 

 older parts often containing ref ringent granules. 



The branches are about equally single or geminate, the single 

 branches arising under the lieterocysts. 



Scytonema catenulum sp. nov. 



Plate 17, figure 3-t 



Filaments densely aggregated into erect fascicles 1.5-2 mm. 

 long, more or less agglutinated liy their gelatinous walls ; 18- 

 26 M diam., sparsely branched; trichomes moniliform Avhen old, 

 8-12 M diam., the greater diameter being at the apices, diminish- 

 ing gradually in the older parts, in some cases entirely vanish- 

 ing, at the same time the sheath increasing in thickness corre- 

 spondingly; cells compressed dolioform at the apices, becoming 

 subspherical in the older parts, yellowish green to bright aeru- 

 ginous, homogeneous ; cross-wall inconspicuous ; lieterocysts 

 compressed spherical to concave when old ; sheath subgelatinous, 

 homogeneous, and hyaline when young, becoming indistinctly 

 lamellose and ocreate at the apices, and yellowish when mature, 

 roughened on the surface; branching mostly single toward the 

 apices, geminate in part below. 



Growing on rocks about ten kilometers north of Utuado, no. 

 1556, type, and on earth, no. 1561. 



This species of Scytonema is well marked by the character of 

 the cells combined with the indistinctly ocreate sheath. The 

 cells in the meristematic region are very short and dolioform. 

 As the growing region moves forward, the successive cells be- 

 come more and more spherical, the sheath thickening and push- 

 ing in between the cells and eventually, in many instances, com- 



