NEW MYXOPHYCEAE FROM PORTO RICO 



55 



sheath. In Hypheothrix and closely related genera, the plants 

 are, as a rule, oriented into a basal and an apical part. In this 

 respect Lynghijopsis is more closely related to such genera as 

 Lyughya and Phormidium, in Avhich the trichonies are not ori- 

 ented into apical and basal portions, the whole trichome being 

 meristematic. The multiplication of trichomes within a sheath 

 is brought about in Lynghyopsis by the formation of hormogonia 

 as in Ly II ghy a and in related genera by the death of certain cells. 

 Upon elongation of the hormogonia in both directions the ends 

 meet, and, instead of the sheath dissolving and liberating the tri- 

 chomes, it remains intact; and, instead of the ends of the tri- 

 chomes, or hormogonia, crawling or pushing each other out of 

 the sheath, the sheath seemingly stretches and encloses them 

 both. Repetition of the process in the same part of the filament 

 results, at times, in several trichomes being enclosed within the 

 same sheaths; sooner or later one or more trichomes break 

 through the sheath, forming a false branch. Either or both ends 

 of a trichome may push through the sheath, so that the branches 

 may arise anywhere along the filament, and extend in opposite 

 directions. The branches, while yet attached to the parent fila- 

 ment, repeat the process, resulting in a tangle of several genera- 

 tions of attached filaments. But a single species appears in 

 Wille's collections and I am dedicating that to him. 



Lyngbyopsis Willei sp. nov. 



Plate 11, figure 1 



Filaments 4-6 mm. long, variable in diameter, forming a 

 flocculent stratum, composed of 1-6 trichomes, branching fairly 

 abundant; trichomes smooth or in part slightly constricted at 

 the cross-walls towards the apices, 5.8-6.2 n diam. ; cells quadrate 

 to one third as long as the diameter, pale aeruginous, homo- 

 geneous ; apical cell blunt, rounded, with slightly thickened ter- 

 minal wall ; sheaths firm, smooth, hvaline, homogeneous, 1-2 n 

 thick. 



Growing on rocks in a brook about five kilometers north of 

 Utuado, no. 1597, type. 



Microcoleus acutissimus sp. nov. 



Plate 11, figure 2 



Filaments small and relatively straight, 400-550 \i long, 20- 

 35 M diam., containing 15-30 trichomes, closed at the conical tips 



