THE GREEN ALGAE OP NORTH AMERICA 369 



A northern species, distinguished by the great difference in 

 size between the base and summit of filament ; the lower cells 

 cylindrical, several times longer than broad ; the upper cells 

 ovoid or globular. 



3. H. Hartzii (Rosenv.) nov. comb. ; Urospora Hartzii Ros- 

 envinge, 1893, p. 922, fig. 38. Filaments 75-90 /w, thick, of 

 nearly uniform diam., cells ^-3 diam. long, usually 1-2, cylin- 

 drical or very slightly swollen, fertile similar to vegetative ; cell 

 wall thin ; chromatophore an open network. Greenland. 



This species has only been found unattached ; the manner of 

 attachment, if known, would indicate whether it was allied in 

 this respect with H. pcnicilliformis or with H. Wormskjoldii. 'In 

 the uniform diameter of the filaments it agrees with the former, 

 but has larger and usually longer cells, with thinner walls ; in 

 the arrangement of the chromatophore it agrees with the latter. 



4. H. crassa (Rosenv.) nov. comb. ; Urospora crassa Rosen- 

 vinge, 1898, p. 106, fig. 23. Filaments tapering to the base and 

 somewhat to the apex ; lower cells up to 70 p., middle part 120- 

 150, summit 105 ^ diam. ; cells in smaller portion }-< diam. long, 

 nearly cylindrical; in larger portion y^- l /i diam. long, swollen ; 

 cell wall thick, chromatophore a network with relatively small 

 openings. Greenland. 



An imperfectly known species, neither the base of the fila- 

 ment nor the fertile cells having been observed ; its best charac- 

 ter would seem to be the short and stout cells. 



5. H. incrassata (Kjellm.) nov. comb. ; Urospora incrassata 

 Kjellman, 18973, p. 7, figs. 6-13; P. B.-A., No. 1125. Fila- 

 ments attached by fibrils from the cell wall at the base, about 

 45 /A diam. at the base, increasing to 135 //., somewhat diminish- 

 ing in the few cells at the apex ; lower cells cylindrical. 1-4 

 diam. long; upper cells i-i l /> diam. long, swollen; cell wall 

 rather thin, chromatophore an open network. Alaska to Cal. 



Europe. 



Nearly related to H. Wormskjoldii and H. crassa ; the former 

 has a greater difference in size between base and apex, arid both 

 have thicker cell wall and shorter cells. 



6. H. COLLABENS (Ag.) Rabenhorst, 1868, p. 364; Conferva 

 coUabcns Harvey, 1846-51, PI. CCCXXVII ; Ulothrix collabens 

 Farlow, 1881, p. 45 ; P. B.-A., No. 970. Filaments very soft 

 and lubricous, bright green, attached by growths from within 

 the lower cells, cylindrical or increasing slightly upwards, vary- 

 ing much in diameter, 50-170^; cells 1-3 diam. long, usually 



